Studies of Quantum Spin Ladders at T=0 and at High Temperatures by Series Expansions
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量子纠缠的数学原理Quantum entanglement is one of the most fascinating phenomena in quantum mechanics. It refers to the strong correlation that exists between particles even when they are separated by large distances. This phenomenon was famously described by Albert Einstein as "spooky action at a distance," highlighting its counterintuitive nature.量子纠缠是量子力学中最令人着迷的现象之一。
它指的是即使粒子相距很远,它们之间仍存在强烈的相关性。
爱因斯坦曾将这一现象形象地描述为“鬼魅般的遥远作用”,突显其反直觉的本质。
One of the key mathematical principles that underpin quantum entanglement is superposition. In simple terms, superposition allows a quantum system to exist in multiple states simultaneously until it is measured or observed. This property is crucial for understandinghow entangled particles can be in a state of flux, with their properties being intrinsically linked regardless of the distance between them.支撑量子纠缠的关键数学原理之一是叠加原理。
关于量子波动速读的作文素材英文回答:Quantum speed reading is a controversial technique that claims to allow individuals to read at speeds far exceeding traditional reading methods. Proponents of quantum speed reading argue that it harnesses the power of the subconscious mind and quantum physics to accelerate the rate at which the brain processes information. However, there is no scientific evidence to support the claims made by quantum speed reading programs.In fact, several studies have found that quantum speed reading does not improve reading comprehension or speed. One study, published in the journal "Reading and Writing," found that participants who underwent a quantum speed reading program showed no significant improvement in their reading speed or comprehension compared to a control group. Another study, published in the journal "Behavior Research Methods," found that quantum speed reading did not improvereading speed or comprehension in children.Critics of quantum speed reading argue that it is a pseudoscience that lacks a solid scientific foundation.They point to the lack of scientific evidence to supportthe claims made by quantum speed reading programs, and they argue that the techniques used in quantum speed reading are not based on established principles of cognitive psychology.中文回答:量子速读是一种有争议的技术,声称可以让人以远超传统阅读方式的速度阅读。
有关量子力学的英语作文Quantum mechanics, a fundamental theory in physics, has been a subject of fascination and debate since its inception in the early 20th century. It describes the behavior of matter and energy at the smallest scales, where the classical laws of physics no longer apply. This essay aims to explore the key principles of quantum mechanics, its implications for our understanding of the universe, and the ongoing challenges it presents to scientists and philosophers alike.Firstly, the concept of wave-particle duality is central to quantum mechanics. This principle posits that all particles, such as electrons, can exhibit both wave-like and particle-like properties. This duality is demonstrated in the famous double-slit experiment, where particles create aninterference pattern when not observed, but act as discrete entities when measured. The act of observation, therefore, plays a critical role in determining the state of a quantum system.Secondly, the superposition principle is another cornerstone of quantum mechanics. It states that a quantum system can exist in multiple states simultaneously until it is measured. This is exemplified by the thought experiment known asSchrödinger's cat, where a cat in a sealed box is considered to be both alive and dead until the box is opened and thecat's state is observed.Entanglement, a phenomenon where particles become interconnected and the state of one instantaneously influences the state of another, regardless of the distance between them, is another intriguing aspect of quantum mechanics. This has led to the development of quantum computing, which promises to revolutionize information processing by performing calculations at speeds unattainable by classical computers.However, quantum mechanics also presents significant challenges. The interpretation of quantum theory is a subject of ongoing debate. The Copenhagen interpretation suggeststhat the act of measurement collapses the wave function, determining the outcome, while the many-worlds interpretation proposes that all possible outcomes of a quantum event exist in separate, non-interacting parallel universes.Moreover, the reconciliation of quantum mechanics with general relativity, the theory of gravity, remains an unsolved problem in physics. The two theories operate under fundamentally different principles, and finding a unified theory that encompasses both has been a holy grail for physicists.In conclusion, quantum mechanics has reshaped our understanding of the microscopic world and has profound implications for technology, philosophy, and the very fabric of reality. As research continues, it is likely that the mysteries of quantum mechanics will continue to inspire awe and provoke thought about the nature of existence itself.。
关于量子的英文作文英文:Quantum physics is a fascinating and complex field that has revolutionized our understanding of the universe. Atits core, quantum mechanics is the study of the behavior of matter and energy at the atomic and subatomic level. The principles of quantum mechanics are fundamentally different from those of classical physics, and they have led to some truly mind-bending discoveries.One of the most famous examples of quantum mechanics is the concept of superposition. This refers to the idea that a particle can exist in multiple states simultaneouslyuntil it is observed, at which point it collapses into a single state. This can be difficult to wrap your head around, but it has been experimentally verified time and time again.Another important concept in quantum mechanics isentanglement. This occurs when two particles become linkedin such a way that the state of one particle affects the state of the other, regardless of the distance between them. This has led to the development of technologies like quantum cryptography, which uses the principles of entanglement to create secure communication channels.Despite its many successes, quantum mechanics is still not fully understood. There are many mysteries and paradoxes that continue to baffle scientists, such as the famous Schrödinger's cat thought experiment. However, researchers are making progress every day, and thepotential applications of quantum mechanics are truly exciting.中文:量子物理学是一个令人着迷而复杂的领域,它彻底改变了我们对宇宙的理解。
第1篇Introduction:Quantum entanglement, one of the most intriguing and challenging concepts in quantum mechanics, has puzzled scientists for over a century. This phenomenon, where particles become interconnected regardless of the distance separating them, has far-reaching implications for our understanding of the universe and potential technological advancements. In this interview question, we will delve into the scientific principles of quantum entanglement, its experimental validations, and the potential applications it may offer in the future.Section 1: Introduction to Quantum Entanglement1.1 Definition of Quantum Entanglement:Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles become linked in such a way that the quantum stateof each particle cannot be described independently of the state of the others, even when the particles are separated by large distances.1.2 Historical Background:The concept of quantum entanglement was first introduced by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935 in their famous paper titled "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?" This paper, often referred to as the EPR paradox, sparked a debate on the completeness and interpretation of quantum mechanics.1.3 Quantum Mechanics and Classical Mechanics:Quantum entanglement is a quintessential feature of quantum mechanics, which fundamentally differs from classical mechanics. In classical mechanics, the state of a system is determined by the positions and velocities of its particles, while in quantum mechanics, particles exist in a probabilistic state until measured.Section 2: The Principles of Quantum Entanglement2.1 Superposition:Superposition is a fundamental principle of quantum mechanics, which states that a quantum system can exist in multiple states simultaneously. This principle allows particles to be entangled, as their combined state cannot be described by the state of each particle individually.2.2 Non-locality:Non-locality is the idea that quantum entangled particles can instantaneously affect each other's states, regardless of the distance separating them. This concept challenges the principle of locality in classical physics, which dictates that no physical influence can travel faster than the speed of light.2.3 Bell's Inequality:John Bell proposed an inequality in 1964 that sets a limit on the amount of non-local correlations that can exist between particles in classical physics. Quantum entanglement violates Bell's inequality, providing experimental evidence for the non-local nature of quantum mechanics.Section 3: Experimental Validations of Quantum Entanglement3.1 Alain Aspect's Experiment:In 1982, Alain Aspect conducted a groundbreaking experiment that confirmed the violation of Bell's inequality, providing strong evidence for quantum entanglement and non-locality. His experiment involved measuring the polarizations of photons emitted from a source and showed that the correlations between the photons exceeded the limits set byBell's inequality.3.2 Quantum Key Distribution (QKD):Quantum key distribution is a secure communication protocol that leverages the principles of quantum entanglement. It allows two parties to share a secret key with the guarantee that any eavesdropping can be detected. QKD has been experimentally demonstrated over long distances, such as satellite-based communication links.3.3 Quantum Computing:Quantum entanglement is a crucial resource for quantum computing, which aims to solve complex problems much faster than classical computers. Quantum computers use qubits, which are entangled particles, to perform calculations by exploiting superposition and interference.Section 4: Implications for Future Technologies4.1 Quantum Communication:Quantum entanglement has the potential to revolutionize communication by enabling secure, long-distance communication using QKD. This technology could be crucial for establishing secure networks and protecting sensitive information.4.2 Quantum Computing:Quantum entanglement is essential for the development of quantum computers, which have the potential to solve complex problems in cryptography, material science, and optimization. Quantum computers could also simulate quantum systems, leading to new discoveries in chemistry, physics, and biology.4.3 Quantum Sensing:Quantum entanglement can be used to enhance the sensitivity of quantum sensors, which have applications in various fields, including gravitational wave detection, quantum metrology, and precision measurement.Conclusion:Quantum entanglement, with its fascinating principles and experimental validations, has the potential to reshape our understanding of the universe and enable groundbreaking technological advancements. From secure communication to powerful quantum computers, the implications of quantum entanglement are vast and far-reaching. As scientists continue to explore this intriguing phenomenon, we can expect even more exciting developments in the field of quantum physics and its applications.第2篇Introduction:Quantum entanglement, one of the most fascinating and enigmatic phenomena in the realm of physics, has intrigued scientists and philosophers alike for decades. This interview delves into the depths of quantum entanglement, exploring its origins, implications, and potential applications. Dr. Emily Newton, a renowned quantum physicist, shares her insights and experiences in this field.Part 1: The Basics of Quantum EntanglementQuestion 1: Can you explain what quantum entanglement is and how it differs from classical entanglement?Dr. Newton:Quantum entanglement is a phenomenon in which two or more particles become interconnected, such that the quantum state of one particle instantaneously correlates with the state of another, regardless of the distance separating them. This correlation persists even when the particles are separated by vast distances, which defies the principles of classical physics.In classical entanglement, such as the entanglement of a pair of dice, the outcome of one die is independent of the other. If you roll a six on one die, it does not affect the outcome of the other die. However, in quantum entanglement, the particles are not independent; their quantum states are correlated in such a way that measuring one particle's state instantly determines the state of the other particle, regardless of the distance between them.Question 2: How was quantum entanglement discovered, and what were the early reactions to this phenomenon?Dr. Newton:Quantum entanglement was first predicted by Albert Einstein, Boris Podolsky, and Nathan Rosen in their famous EPR paradox paper in 1935.They proposed a thought experiment involving two entangled particlesthat seemed to violate the principle of locality, which states that no information can travel faster than the speed of light.The initial reaction to the EPR paradox was skepticism, with Einstein famously dismissing quantum entanglement as "spooky action at a distance." However, subsequent experiments, such as those conducted by John Bell in the 1960s, provided strong evidence in favor of quantum entanglement, leading to a paradigm shift in our understanding of the quantum world.Part 2: The Mechanics of Quantum EntanglementQuestion 3: What are the key factors that contribute to the formation of entangled particles?Dr. Newton:The formation of entangled particles is a result of their interaction during the process of measurement or preparation. For example, when two particles are created together in an entangled state, their quantum states become correlated due to their shared history. This correlationis a fundamental aspect of quantum mechanics and cannot be explained by classical physics.Another way to create entangled particles is through a process called entanglement swapping, where two particles are initially entangled with a third particle, and then the third particle is separated from thefirst two. This results in the first two particles becoming entangled with each other, even though they have never interacted directly.Question 4: Can you explain the concept of quantum superposition and how it relates to entanglement?Dr. Newton:Quantum superposition is the principle that a quantum system can existin multiple states simultaneously until it is measured. This is analogous to a coin spinning in the air, which can be either heads or tails until it lands on one side.In the context of entanglement, superposition plays a crucial role. When two particles are entangled, their combined quantum state is a superposition of the individual states of each particle. This means that the particles can exhibit non-local correlations that are not determined until a measurement is made.Part 3: The Implications of Quantum EntanglementQuestion 5: How does quantum entanglement challenge our understanding of the universe?Dr. Newton:Quantum entanglement challenges our classical understanding of the universe in several ways. Firstly, it defies the principle of locality, which has been a cornerstone of physics for centuries. The idea that particles can instantaneously influence each other across vast distances suggests that the fabric of space-time may not be as fixed as we once thought.Secondly, quantum entanglement raises questions about the nature of reality itself. If particles can be correlated in such a way that their states are instantaneously connected, it challenges the idea that objects have definite properties independent of observation.Question 6: Are there any practical applications of quantum entanglement?Dr. Newton:Yes, there are several potential applications of quantum entanglement. One of the most promising is in quantum computing, where entangled particles can be used to perform complex calculations at speeds unattainable by classical computers. Quantum entanglement is also essential for quantum cryptography, which can be used to create unbreakable encryption methods.Moreover, entanglement has been used in quantum teleportation, where the state of a particle can be transmitted instantaneously from one location to another, potentially leading to new communication technologies.Conclusion:Quantum entanglement remains one of the most intriguing and challenging phenomena in physics. Dr. Emily Newton's insights into the mechanics and implications of this phenomenon provide a deeper understanding of the quantum world and its potential applications. As we continue to explore the mysteries of quantum entanglement, we may uncover new ways to harness its power and reshape our understanding of the universe.第3篇IntroductionQuantum entanglement, one of the most intriguing and mysterious phenomena in the field of quantum mechanics, has captured the imagination of scientists and the public alike. This question invites candidates to delve into the concept of quantum entanglement, its underlying principles, experimental demonstrations, and the potential implications it holds for future technology.Part 1: Introduction to Quantum Entanglement1.1 Definition and Basic PrinciplesQuantum entanglement refers to a phenomenon where two or more particles become interconnected in such a way that the quantum state of each particle cannot be described independently of the state of the others, even when they are separated by large distances. This correlation persists regardless of the distance between the particles, which challenges our classical understanding of locality and separability.1.2 Historical ContextThe concept of quantum entanglement was first introduced by Albert Einstein, Boris Podolsky, and Nathan Rosen in their famous EPR paradox paper in 1935. They described entanglement as "spooky action at a distance," suggesting that it defied the principles of local realism. However, subsequent experiments and theoretical developments have confirmed the reality of entanglement.Part 2: Theoretical Underpinnings of Quantum Entanglement2.1 Quantum SuperpositionQuantum superposition is a fundamental principle of quantum mechanics that allows particles to exist in multiple states simultaneously. This principle is crucial for understanding entanglement, as it enables particles to become correlated in a way that is not possible inclassical physics.2.2 Quantum Correlation and EntanglementQuantum entanglement arises from the non-classical correlations between particles. When particles become entangled, their quantum states become linked, and the state of one particle instantaneously influences the state of the other, regardless of the distance separating them.2.3 Bell's TheoremJohn Bell formulated a theorem in 1964 that demonstrated the incompatibility of quantum mechanics with local realism. Experimentsthat violate Bell's inequalities have confirmed the existence of quantum entanglement and its non-local nature.Part 3: Experimental Demonstrations of Quantum Entanglement3.1 Bell Test ExperimentsBell test experiments have been conducted to test the predictions of quantum mechanics and to demonstrate the non-local nature of entanglement. These experiments involve measuring the properties of entangled particles and analyzing the correlations between them.3.2 Quantum Key Distribution (QKD)Quantum Key Distribution is a protocol that uses quantum entanglement to securely transmit cryptographic keys. It takes advantage of theprinciple that any attempt to intercept the entangled particles will disturb their quantum state, alerting the communicating parties to the presence of an eavesdropper.3.3 Quantum TeleportationQuantum teleportation is the process of transmitting the quantum state of a particle from one location to another, without the particle itself traveling through the space between them. This phenomenon has been experimentally demonstrated and has implications for quantum computing and communication.Part 4: Implications for Future Technology4.1 Quantum ComputingQuantum computing, which relies on the principles of quantum mechanics, has the potential to revolutionize computing by solving certain problems much faster than classical computers. Quantum entanglement plays a crucial role in quantum computing, as it allows for the creation of qubits that can exist in multiple states simultaneously, enabling parallel processing.4.2 Quantum CommunicationQuantum communication utilizes the principles of quantum entanglement and superposition to achieve secure communication and distributed computing. Technologies like QKD and quantum teleportation are expected to transform the field of secure communication and enable new forms of data transmission.4.3 Quantum Sensors and MetrologyQuantum sensors and metrology techniques leverage the precision and sensitivity of quantum entanglement to measure physical quantities with unprecedented accuracy. This has applications in fields such as precision navigation, gravitational wave detection, and quantum simulation.ConclusionQuantum entanglement, with its counterintuitive nature and profound implications, remains a captivating and challenging subject in the field of quantum mechanics. As scientists continue to explore and harness thepower of entanglement, we can expect to see significant advancements in technology, leading to new possibilities in computing, communication, and metrology. This question has provided an opportunity to delve into the fascinating world of quantum entanglement and its potential future impact on society.。
高三英语科学前沿动态引人关注单选题30题1.Scientists are studying a new kind of particle which is called a(n)_____.A.electronB.protonC.neutronD.quark答案:D。
本题主要考查科学前沿动态中的专业术语。
electron 是电子;proton 是质子;neutron 是中子;quark 是夸克。
题干中提到一种新的粒子,夸克在科学前沿动态中相对更可能是新研究的对象。
2.The latest research in astronomy focuses on a distant_____.A.starB.planetC.galaxyD.universe答案:C。
题干中提到天文学最新研究,通常会聚焦在遥远的星系上。
star 是恒星;planet 是行星;galaxy 是星系;universe 是宇宙。
宇宙范围太大,一般不是直接聚焦对象,恒星和行星相对较常见,而星系在科学前沿动态中更有研究价值。
3.In the field of quantum physics, scientists study the behavior of_____.A.atomsB.moleculesC.electronsD.quanta答案:D。
在量子物理学领域,研究的是量子的行为。
atoms 是原子;molecules 是分子;electrons 是电子;quanta 是量子。
前三个选项比较基础,量子是量子物理中的专业术语。
4.The breakthrough in biotechnology is related to a new kind of_____.A.enzymeB.geneC.cellD.virus答案:B。
生物技术的突破通常与新的基因有关。
enzyme 是酶;gene 是基因;cell 是细胞;virus 是病毒。
山西省长治二中等五校2024学年全国卷Ⅲ英语试题高考模拟题注意事项1.考生要认真填写考场号和座位序号。
2.试题所有答案必须填涂或书写在答题卡上,在试卷上作答无效。
第一部分必须用2B 铅笔作答;第二部分必须用黑色字迹的签字笔作答。
3.考试结束后,考生须将试卷和答题卡放在桌面上,待监考员收回。
第一部分(共20小题,每小题1.5分,满分30分)1.Teachers in primary schools ______ influence the kids fall under should be role models.A.whose B.whoC.where D.which2.My friend warned me ______ going to the East Coast because it was crowded with tourists.A.by B.against C.on D.for3.I ________ my cellphone last night. Now the battery is running out.A.could have charged B.might chargeC.should have charged D.would charge4.In contrast with the liberal social climate of the present, traditions in the past were relatively ______. A.competitive B.comprehensiveC.creative D.conservative5.I had been betrayed by those who I trusted several times, ______ in a suspicious attitude towards everything and everyone.A.resulted B.having resulted C.resulting D.to result6.The educational reform is now under way throughout the country, ________ the students more opportunities to develop to their greatest potential.A.to grant B.having grantedC.granting D.granted7.When the admission letter from Harvard University arrived, Ben's parents were and threw a big party.A.in the red B.tickled pinkC.as white as a sheet D.in a blue mood8.Only when _________hard __________ make your dream come true.A.do you work; you can B.you work; you canC.do you work; can you D.you work; can you9.Join us and you will discover an environment ______ you can make the most of your skills and talents.A.that B.whereC.how D.what10.Instead of making choices for their children, liberal parents usually say, “Go where you ________ .”A.will B.shouldC.can D.must11.he newly-discovered star was named _____ a Chinese astronomer ________his contributions to astronomy. A.for; in favor of B.after; in honor ofC.by; in memory of D.as; in praise of12.Much to my ______, my vocabulary has expanded a great deal.A.delighting B.delighted C.delight13.— I want to learn tennis. Would you like to help me?—. But learning tennis is no walk in the park.A.No kidding B.No wonder C.No problem D.No way14.I really don’t know _________ she gets by on such a modest salary.A.what B.whyC.how D.that15.My mom once worked in a very small village school, which is__________only on foot.A.acceptable B.adequate C.accessible D.appropriate16.Don’t leave the water ______while you brush your teeth.A.racing B.rushingC.running D.rolling17.Eggs, meat, vegetables and other foods can easily be poisoned by microorganisms such as ______. A.phenomena B.dilemma C.diploma D.bacteria18.Mankind must first of all eat, drink, have shelter and clothing ________ it can pursue politics, science, art and religion.A.until B.unlessC.before D.since19.Mark has lived in China for many years, yet he still can't ________ himself to the Chinese customs. A.observe B.adaptC.lead D.devote20.—What did you say you were reluctant to risk just now?—_________ to high levels of radiation.A.Being exposed B.Having been exposedC.To be exposed D.Exposed第二部分阅读理解(满分40分)阅读下列短文,从每题所给的A、B、C、D四个选项中,选出最佳选项。
英文原版量子论科普If you're interested in reading about quantum theory in English, here are some recommendations:1. "Quantum Mechanics: The Theoretical Minimum" by Leonard Susskind and Art Friedman. This textbook provides a thorough and accessible introduction to quantum mechanics, starting from the basics and building up to more advanced concepts. It's written in a lively and engaging style, making it suitable for self-study or as a classroom textbook.2. "Quantum Physics: A First Encounter" by John Taylor. This book is aimed at undergraduates and covers the key ideas of quantum theory, including wavefunctions, operators, measurement, and entanglement. It provides plenty of examples and exercises to help readers understand and apply the theory.3. "Quantum Computation and Quantum Information" by Michael Nielsen and Isaac Chuang. This textbook provides a comprehensive introduction to the field of quantum information science, covering quantum computing, quantum algorithms, quantum error correction, and quantum cryptography. It's suitable for graduate students and researchers in the field.4. "The Quantum World" by Christopher French and Carlo Michelli. This book provides a broad overview of modern quantum theory and its applications, including quantum computing, quantum cryptography, and quantum metrology. It's written in a clear and accessible style, making it suitable for non-experts who want to understand the basics of quantum theory.Remember that reading about quantum theory can be challenging because it involves concepts that are counterintuitive and打破常识。
a r X iv:c ond-ma t/962055v19Fe b1996STUDIES OF QUANTUM SPIN LADDERSAT T =0AND AT HIGH TEMPERATURESBY SERIES EXPANSIONSJ.Oitmaa 1∗,Rajiv R.P Singh 2†,and Zheng Weihong 1‡1School of Physics,The University of New South Wales,Sydney,NSW 2052,Australia.2Department of Physics,University of California,Davis,CA 95616,USA.(Feb.7,1996)Abstract We have carried out extensive series studies,at T =0and at high tempera-tures,of 2-chain and 3-chain spin-half ladder systems with antiferromagnetic intrachain and both antiferromagnetic and ferromagnetic interchain couplings.Our results confirm the existence of a gap in the 2-chain Heisenberg ladders for all non-zero values of the interchain plete dispersion rela-tions for the spin-wave excitations are computed.For 3-chain systems,our results are consistent with a gapless spectrum.We also calculate the uniform magnetic susceptibility and specific heat as a function of temperature.We find that as T →0,for the 2-chain system the uniform susceptibility goes rapidly to zero,whereas for the 3-chain system it approaches a finite value.These results are compared in detail with previous studies of finite systems.PACS Indices:75.10.-b.,75.10J.,75.40.GbTypeset using REVT E XI.INTRODUCTIONThe magnetic properties of low dimensional systems have been the subject of intense theoretical and experimental research in recent years.It is by now well established that one-dimensional Heisenberg antiferromagnets with integer spin have a gap in the excitationspectrum,whereas those with half-integer spin have gapless excitations.The former have afinite correlation length,while for the latter it is infinite with the spin-spin correlation function decaying to zero as a power law.In2-dimensions,the unfrustrated square-latticeHeisenberg model has long range N´e el order in the ground state.It has gapless Goldstone modes as expected.In recent years much interest has focussed on systems with intermediatedimensionality and on questions of crossovers between d=1and d=2.One approach to this problem has been to study a two-dimensional system where the coupling for the spins separated along the x-axis is different from those separated along the y-axis[1].Ithas been suggested that an alternative way to explore this issue is through the Heisenberg spin ladders consisting of afinite number of chains coupled together,with a coupling J// along the chains and J⊥between them.These systems have been the subject of considerablerecent theoretical and experimental interest.Experimentally,2-chain S=12ladders are realizedin the strontium cuprate SrCu3O5[3].Theoretically,a number of striking predictions have been made for such systems.These have been recently reviewed by Dagotto and Rice[4].Barnes et al.[5,6]were thefirst to carry out extensive Monte Carlo studies of the excitation spectrum and the magnetic susceptibility for2-chain ladders with antiferromagnetic interchain coupling.White[7]et al.and Hida[8] have used the density matrix renormalization method to study the spin gap.Watanabe[9] has applied the numerical diagonalization method tofinite systems of2-chain ladders with ferromagnetic interchain coupling.Azzouz[10]et al.developed a mean-field theory and used the density-matrix renormalization group method to study2-chain ladders.Gopalan,Rice and Sirgrist[11]presented a variational wavefunction for the ground state of the2-leg ladder. Rojo[12]has shown that spin ladders with odd number of legs have gapless excitations. Troyer et al.[13]have used improved versions of the quantum transfer-matrix algorithm to study the temperature dependence of the susceptibility,specific heat,correlation length etc of2-chain ladders.Finite-size scaling was used by Hatano[14]for multi-leg ladders,and recently Frischmuth et al.[15]and Sandvik et al.[16]have applied Quantum Monte Carlo simulation to compute the temperature dependence of uniform susceptibility and internal energy for spin ladders with up to6legs.One clear result from all these studies is that ladders with an even number of legs have an energy gap,short range correlations and a “spin liquid”ground state.On the other hand,ladders with odd number of legs have gapless excitations,quasi long range order,and a power-law falloffof spin-spin correlations, similar to single chains.Experiments also confirm these features.We have carried out extensive series studies of2-chain and3-chain ladder systems with both antiferromagnetic and ferromagnetic interchain coupling J⊥,via Ising expansions and dimer expansions at T=0,and also by high temperature series expansions.Our results confirm the existence of a gap in the2-chain system and delineate the phase diagram in the parameter space of Ising anisotropy and the parameter ratio J⊥/J//.The complete spin-wave excitation spectra are computed.For the 3-chain system we are unable to exclude the possibility of a small gap,although our results are consistent with a gapless spectrum.In addition,we develop a high-temperature series expansion for the uniform magnetic suscepti-bility and the specific heat for 2-chain and 3-chain systems with J //=J ⊥;the susceptibility of 2-chain ladders is as expected for a system with a spin-gap while that of 3-chain ladders appear to remain finite in the zero-temperature limit suggesting an absence of a spin-gap.We compare our results in detail with previous calculations.II.SERIES EXPANSIONSThe Hamiltonian of a spin ladder with n l legs is given by,H =J //l =n li,l =1S l,i ·S l,i +1+J ⊥l =n l −1 i,l =1S l,i ·S l +1,i (1)where S l,i denotes the S=1/2spin at the i th site of the l th chain.J //is the interaction between nearest neighbor spins along the chain and J ⊥is the interactions between nearest neighbor spins along the rungs.We denote the ratio of couplings as y ,that is,y ≡J ⊥/J //.In the present paper the intrachain coupling is taken to be antiferromagnetic (that is,J //>0)whereas the interchain coupling J ⊥can be either antiferromagnetic or ferromagnetic.This includes the values of interest in the experimental systems discussed earlier where J ⊥∼J //.Without loss of generality,we can set J //=1hereafter.We have carried out three different expansions for the system,The first is the expansion about the Ising limit at zero temperature for both two and three-chain ladders.We have computed the ground state properties as well as the spin-wave excitation spectra by this expansion.The second is the dimer expansion,again at T =0.This expansion can be done for the 2-chain system with antiferromagnetic interchain coupling only.The third is the high-temperature series expansion for the uniform susceptibility of the 2-chain and 3-chain ladders with y =1.A.Ising expansionsTo perform an expansion about the Ising limit for this system,we introduce an anisotropy parameter x ,and write the Hamiltonian in Eq.(1)as:H =H 0+xV(2)whereH 0=l =n l i,l =1S z l,i S z l,i +1+y l =n l −1 i,l =1S z l,i S z l +1,i V =l =n l i,l =1(S x l,i S x l,i +1+S y l,i S y l,i +1)+y l =n l −1i,l =1(S x l,i S x l +1,i +S x l,i S x l +1,i )(3)The limits x=0and x=1correspond to the Ising model and the Heisenberg model re-spectively.The operator H0is taken as the unperturbed Hamiltonian,with the unperturbed ground state being the usual N´e el state for antiferromagnetic interchain coupling,and a fully ordered collinear state for ferromagnetic interchain coupling.The operator V is treated as a perturbation.Itflips a pair of spins on neighbouring sites.The Ising expansion method has been previously reviewed in several articles[17,18],and will not be repeated here.The calculations involved a list of9184linked clusters of up to16sites for the2-chain ladder, and14082linked clusters of up to12sites for the3-chain ladder,together with their lattice constants and embedding constants.Series have been calculated for the ground state energy per site E0/N,the staggered magnetization M for y>0(or collinear magnetization M for y<0),the parallel stag-gered/colinear susceptibilityχ//,and the uniform perpendicular susceptibilityχper site for several ratio of couplings y=±0.1,±0.25,±0.5,±0.75,±1,±1.5,±2,±4,±8up to order x16 for2-chain ladders,and x12for3-chain ladders(the series for uniform perpendicular suscep-tibilityχis one order less in each case).The resulting series for y=±1for the2-chain and 3-chain systems are listed in Tables I and II,the series for other value of y are available on request.To analyze these series,wefirst performed a standard Dlog Pad´e analysis of the mag-netization M and parallel susceptibilityχ//series.We found that for2-chain ladders,theseries lead to a simple power-law singularity at x<1:M∼(1−x/x c)βχ//∼(1−x/x c)−γ(4) with the indicesβandγclose to1/8and7/4respectively.This transition at x<1,with criticality in the universality class of the2D-Ising model,is strong evidence that in the Heisenberg limit the system has a disordered ground state with a spin-gap,as is the case for the spin-one chain[19].In contrast for the3-chain ladders,the series analysis showed poor convergence and suggested a singularity at x≥1.This implies that for the3-chain ladders,the system is analogous to the spin-half chain,with gapless spectra and power-law correlations in the Heisenberg limit.Fig.1shows the phase boundary for2-chain ladders as function of y.It is interesting to note the different behaviour for y>0and for y<0:for antiferromagnetically coupled 2-chain ladders(y>0),x c decreases as y increases,and in the limit of y→∞,x c will approach0.But for ferromagnetically coupled2-chain ladders(y<0),x cfirst decreases as the absolute value of y increase from zero,but then the trend reverses and it,once again, approaches1as y→−∞.To understand this behavior,we can map the system for large negative y to a spin-one chain with on-site(single-ion)anisotropy:H=12i[S z i,tot S z i+1,tot−c(S z i,tot)2+x′(S x i,tot S x i+1,tot+S y i,tot S y i+1,tot)](6)For this model,we have carried out series expansions in x′to order x′14(i.e.14sites) for staggered magnetization M for several different value of c:c=0.275,0.29,0.3,0.325, and performed a standard Dlog Pad´e analysis tofind the critical value c′which gives the singularity of M at x′=1.We get c′=0.29(1).Hence,the asymptotic behaviour of the phase boundary in the limit y→−∞is given byx c=1+0.29/y(7) which is also shown in Fig.1as a bold line near y/(1+|y|)=−1.Fig.2gives the results of the ground-state energy per site E0/N versus y for both2-chain and3-chain ladders at the Heisenberg point x=1.Our results for the ground state energy agree extremely well with the recent quantum Monte Carlo simulation[15].In Fig.3,we present the uniform perpendicular susceptibility at T=0.We also performed the Ising expansion for the triplet spin-wave excitation spectrum of 2-chain and3-chain ladders using Gelfand’s method[20].To overcome a possible singularity at x<1in the2-chain ladders,and to get a better convergent series in the Heisenberg limit, we add the following staggeredfield term to the Hamiltonian in Eq.(2):(−1)i S z i(8)∆H=t(1−x)i∆H vanishes at x=1.We adjust the coefficient t to get the most smooth terms in the series,with a typical value being t=2.We computed the Ising expansion for the triplet spin-wave excitation spectrumǫ(k)up to order x15for2-chain ladders,and up to order x11 for3-chain ladders.These series are too long to be listed here,but are available on request.These series have been analyzed by using integratedfirst-order inhomogeneous differential approximants[21].For the2-chain ladder,there are2bands of excitations,Fig.4shows the dispersionǫ(k),with k y=π,for antiferromagnetic interchain coupling.The other band with k y=0is related to this byǫ(k x,0)=ǫ(π−k x,π).This is simply due to the staggered field,which doubles the spectrum.As a comparison,the dispersion relation of a single chain (that is the case of y=0)is also shown.It can be seen from the graph that in the limit y→0,the dispersion relation has a simple cosine function with a period of2π,and in the limit y→∞,the dispersion relation also has a simple cosine form with a period of4π,and a gap in the spectrum.Barnes and Riera[6]argued that the dispersion,for all y,can be fitted by combining these two functions into the following form:ǫ(k x,π)2=ǫ(0,π)2cos2(k x/2)+ǫ(π,π)2sin2(k x/2)+c0sin2(k x)(9) For y=1,the Ising expansions give an energy gap ofǫ(π,π)=0.44(7).A more precise estimate is obtained by the dimer expansions,which giveǫ(π,π)=0.504(7).We will discuss the dimer expansions later.For ferromagnetic interchain coupling,the two bands of spectra are independent,but each band is a simple cosine function with a gap at the minimum and symmetric about k x=π/2,as shown in Figs.5-6.As noted in Figs.4,it is clear that the spin-gap decreases smoothly as y is reduced,and vanishes at y=0.These results agree well with previous calculations[6].For the3-chain system,there are three bands.In the Ising limit,2bands have initial excitations located in the side rows,and the third band has it in the middle row.Figs.7-12show the spectrum of the three bands for ferromagnetic and antiferromagnetic interchain couplings.From these graphs,we can see that all of the dispersion relations have a simple cosine function(except for middle row band with large y)with a minumum located at k x=0 (or k x=πby symmetry),where two of these three bands have a definite gap,the third(the k y=0band)is consistent with a gapless spectra.The estimate for the gap in the third band for all y values is0.2(3)(except for the case of y=0where we got0.08(10)).Hence, we cannot exclude the possibility of a small gap here.But our results are consistent with a gapless spectrum,and given our earlier results on the phase boundary with Ising anisotropy, we believe the spectra are gapless.B.Dimer expansionsFor2-chain ladders,with antiferromagnetic coupling between the chains,there is an alternative T=0expansion that can be developed.In the limit that the exchange couplingalong the rungs J⊥is much larger than the coupling J//along the chains,that is y≫1,the rungs interact only weakly with each other,and the dominant configuration in the ground state is the product state with the spin on each rung forming a spin singlet,so the Hamiltonian in Eq.(1)can be rewritten as,H/J⊥=H0+(1/y)V(10) whereH0=l=n l−1i,l=1S l,i·S l+1,i(11)V=l=n li,l=1S l,i·S l,i+1We can treat the operator H0as the unperturbed Hamiltonian.The eigenstates of a single pair of spins,or dimers,consists of one singlet state with total S=0and eigen energy E s=−3/4:|Ψ s=12(|↑↓ −|↓↑ )(12) and three triplet states with total S=1and eigenenergy E t=1/4:|Ψ t=[12(|↑↓ +|↓↑ ),|↑↑ ,|↓↓ ](13) The operator V is treated as a perturbation.It can cause excitations on a pair of neigh-bouring dimers.Details of the dimer expansions and the matrix elements of V are given in Ref.[18],and will not be repeated here.We have carried out the dimer expansion for the ground state energy to order(1/y)9 and for the lowest lying triplet excitations to order(1/y)8.The series for the ground state energy per site E0/N is:E0/N=J⊥[−3/8−3/(16y2)−3/(32y3)+3/(256y4)+45/(512y5)+159/(2048y6)−879/(32768y7)−4527/(32768y8)−248391/(2097152y9)](14) and the series for the excitation spectrum are listed in Table III.Again,we use the integrated first-order inhomogeneous differential approximants[21]to extrapolate the series.For y>1, the dimer expansions give much better results than the Ising expansions.For y∼1also the dimer expansions appear to converge better.The overall spectra determined from the combined study of dimer and Ising expansions are shown in Fig.4.C.High temperature series expansionsWe now turn to the thermodynamic properties of the ladder system atfinite temper-atures.We have developed high-temperature series expansions for the uniform magnetic susceptibilityχ(T)and the specific heat C(T),for2-chain and3-chain system with J⊥=J//,χ(T)=βTr e−βH(15)C(T)=∂UTr e−βH(16)The series were computed to orderβ14.The number of contributing graphs,with upto14 bonds was4545for the2-chain ladders and5580for the3-chain ladders.The series are listed in Table IV.We use integratedfirst-order inhomogeneous differential approximants[21]to extrapolate the series.The resulting estimates are shown in Fig.13-14.For the susceptibil-ity,as a comparison,the recent Quantum Monte Carlo(QMC)results of Frischmuth et al [15]and the results from our T=0Ising expansion for3-chain are also shown.It can be seen that our results agree very well with the QMC results except for the3-chain system at very low temperatures.Given the recentfindings that for the spin-half chain,the T=0value is reached fromfinite temperatures with infinite slope[22],one might expect the T→0 behavior for these3-chain systems to be equally complex,making it very difficult to explore numerically.For the specific heat,our results showed good convergence upto the peak,but poor convergence below it.The results for2-chain ladder are consistent with recent quantum transfer-matrix calculations by Troyer[13]et al.III.CONCLUSIONSWe have studied the2and3chain Heisenberg-Ising ladders by a variety of different series expansions.Our results confirm the existence of a gap in the excitation spectrum of2-chain systems,with either ferromagnetic or antiferromagnetic interchain interactions.For3-chainsystems,our results are consistent with a gapless spectrum.The T=0phase diagram as well as the temperature dependence of the uniform susceptibility and the specific heat are also calculated.Overall,our results agree very well with previous numerical studies of these systems.ACKNOWLEDGMENTSThis work forms part of a research project supported by a grant from the Australian Research Council.R.R.P.S.is supported in part by the National Science Foundation through grant number DMR-9318537and would like to thank the University of New South Wales for hospitality and the Gordon Godfrey Foundation for support,while the work was being done.We would also like to thank Dr.Troyer for providing us with the Monte Carlo data for comparison.REFERENCES∗e-mail address:otja@.au†e-mail address:singh@‡e-mail address:w.zheng@.au[1]I.Affleck,M.P.Gelfand and R.R.P.Singh,J.Phys.A27,7313(1994).[2]R.S.Eccleston,T.Barnes,J.Brody and J.W.Johnson,preprint(cond-mat/9406016).[3]M.Takano,Z.Hiroi,M.Azuma and Y.Takeda,Jpn.J.Appl.Phys.Ser7,3(1992);Z.Hiroi et al.,J.Solid State Chem.95,230(1991);T.M.Rice,S.Gopalan and M.Sigrist, Europhys.Lett.23,445(1993).[4]E.Dagotto and T.M.Rice,preprint(cond-mat/9509181).[5]T.Barnes and E.Dagotto,J.Riera,and E.Swanson,Phys.Rev.B47,3196(1993).[6]T.Barnes and J.Riera,Phys.Rev.B50,6817(1994).[7]S.R.White and R.M.Noack,Phys.Rev.Lett.73,886(1994).[8]K.Hida,preprint(cond-mat/9510071)[9]H.Watanabe,Phys.Rev.B50,13442(1994).[10]M.Azzouz,Liang Chen,and S.Moukouri,Phys.Rev.B5,6233(1994).[11]S.Gopalan,T.M.Rice,and M.Sigrist,Phys.Rev.B49,8901(1994).[12]A.G.Rojo,preprint(cond-mat/9512118).[13]M.Troyer,H.Tsunetsugu and D.W¨u rtz,Phys.Rev.B50,13515(1994).[14]N.Hatano and Y.Nishiyama,preprint(cond-mat/9506052).[15]B.Frischmuth,B.Ammon and M.Troyer,preprint(cond-mat/9601025).[16]A.W.Sandvik,E.Dagotto,and D.J.Scalapino,preprint(cond-mat/9512026).[17]H.X.He,C.J.Hamer and J.Oitmaa,J.Phys.A23,1775(1990).[18]M.P.Gelfand,R.R.P.Singh,and D.A,Huse,J.of Stat.Phys.59,1093(1990).[19]R.R.P.Singh and M.P.Gelfand,Phys.Rev.Lett.61,2133(1988).[20]M.P.Gelfand,preprint;R.R.P.Singh and M.P.Gelfand,Phys.Rev.B52,15695(1995).[21]A.J.Guttmann,in Phase Transitions and Critical Phenomena,edited by C.Domb andM.S.Green(Academic,New York,1989),Vol.13.[22]S.Eggert,I.Affleck and M.Takahashi,Phys.Rev.Lett.73,332(1994).FIGURESFIG.1.The phase boundary for2-chain ladder.The asymptotic behaviour as y→−∞predicted by a spin-one single chain system with one-site anisotropy is also shown by the bold line.FIG.2.The ground-state energy per site E0/N as function of y for2-chain and3-chain ladders. The error bars are much smaller than the symbols.FIG.3.The uniform susceptibilityχat T=0as function of y for the3-chain ladder.FIG.4.The dispersions of the spin-triplet excitated states of the2-chain ladder with antifer-romagnetic interchain coupling y=2,1.5,1,0.75,0.5,0.25,0.1,0(shown in thefigure from the top to the bottom respectively),for k y=π.FIG.5.The dispersions of the spin-triplet excitated states of the2-chain ladder with ferromag-netic interchain coupling y=0,-0.25,-0.5,-0.75,-1,-1.5,-2,-4,for k y=0.FIG.6.The dispersions of the spin-triplet excitated states of the2-chain ladder with ferromag-netic interchain coupling y=-2,-1.5,-1,-0.75,-0.5,-0.25,-0.1,0,for k y=π.FIG.7.The dispersions of the spin-triplet excitated states of the3-chain ladder with antifer-romagnetic interchain coupling y=1.5,1,0.75,0.5,0.25,0,for k y=0.FIG.8.The dispersions of the spin-triplet excitated states of the3-chain ladder with antifer-romagnetic interchain coupling y=2,1.5,1,0.75,0.5,0.25,0.1,0,for k y=π/2.FIG.9.The dispersions of the spin-triplet excitated states of the3-chain ladder with anti-ferromagnetic interchain coupling y=2,1.5,1,0.75,0.5,0.25,0.1,0,for the middle excitation band.FIG.10.The dispersions of the spin-triplet excitated states of the3-chain ladder with ferro-magnetic interchain coupling y=0,-0.1,-0.25,-0.5,-0.75,-1,-1.5,-2for k y=0.FIG.11.The dispersions of the spin-triplet excitated states of the3-chain ladder with ferro-magnetic interchain coupling y=-2,-1.5,-1,-0.75,-0.5,-0.25,-0.1,0,for k y=π/2.FIG.12.The dispersions of the spin-triplet excitated states of the3-chain ladder with ferro-magnetic interchain coupling y=-2,-1.5,-1,-0.75,-0.5,-0.25,-0.1,0,for the middle excitation band.FIG.13.Susceptibility as a function of temperature for2-chain and3-chain ladders from the high temperature series expansion,and the Ising expansion at T=0(for3-chain only),also shown are the QMC results of Frischmuth[15]et al as the open symbols(for2-chain)andfilled symbols (for3-chain)for comparison,FIG.14.The specific heat as a function of temperature for2-chain and3-chain ladders from the high temperature series expansion.TABLESTABLE I.Series coefficients for the ground-state energy per site E0/N,the staggered/colinear magnetization M,and staggered parallel susceptibilityχ//.Coefficients of x n are listed for both the spin-12-chain ladders with y=−10−3/81/202−1.250000000000×10−1−1.250000000000×10−1 2.500000000000×10−14−1.562500000000×10−2−6.944444444444×10−2 4.131944444444×10−16 2.443214699074×10−3 1.398473668981×10−39.964453526878×10−28−3.391054004308×10−3−4.293584111636×10−2 6.561704135203×10−1 10−3.0839********×10−4−9.459983497527×10−3 2.592402875212×10−1 12−5.758725813964×10−4−2.517788286146×10−28.633367551243×10−1 14−3.508609329659×10−4−1.290819523741×10−2 5.194241039530×10−1 16−3.658331257827×10−4−2.220489673071×10−2 1.1975912749202-chain ladders with y=10−3/81/202−1.875000000000×10−1−1.875000000000×10−1 3.750000000000×10−14−9.114583333333×10−3−1.176215277778×10−19.751157407407×10−16−6.564670138889×10−3−1.298255449460×10−1 2.2250745482908−1.011191788034×10−2−2.567768064481×10−1 6.46647061429310−4.438918908655×10−3−3.308567310261×10−1 1.436049594755×10112−1.149045736404×10−2−6.754838729347×10−1 3.661634831290×10114−9.014538657677×10−3−1.0596787484818.236161272382×10116−1.860424772341×10−2−2.0874******** 1.962459013257×1023-chain ladders with y=−10−5/121/202−1.111111111111×10−1−1.018518518519×10−1 1.913580246914×10−14−9.126984126984×10−3−2.765516082976×10−2 1.235451495119×10−16−3.430007743753×10−3−2.229002861112×10−2 1.702591936321×10−18−4.479840217373×10−4−6.778016397592×10−39.228960192872×10−2 10−1.150888174205×10−3−1.348552579039×10−2 1.814452046940×10−1 12−5.493987828590×10−4−9.549725222639×10−3 1.785680892107×10−13-chain ladders with y=10−5/121/202−1.777777777778×10−1−1.551851851852×10−1 2.766913580247×10−14 2.0993********×10−3−3.010*********×10−2 2.520792079948×10−16−5.486291040711×10−3−4.567138485811×10−2 4.781602664625×10−18−9.770232257758×10−4−2.676534614009×10−2 5.289125611753×10−1 10−8.540222317364×10−4−2.413110830174×10−2 6.371032432384×10−1 12−7.963887426932×10−4−3.026105625065×10−2 1.024*********TABLE II.Series coefficients for the perpendicular susceptibilityχ⊥.Coefficients of x n are listed for2-chain and3-chain ladders with y=±1.n2-chain y=−12-chain y=13-chain y=−13-chain y=1(n,m)a n,m(n,m)a n,m(0,0) 1.000000000(3,3) 1.250000000×10−1(6,1)9.375000000×10−2(6,5)7.812500000×10−2 (3,0) 3.750000000×10−1(5,3)−9.375000000×10−2(8,1) 2.555847168×10−1(8,5)−2.657165527×10−1 (5,0)−6.250000000×10−1(7,3)−2.222900391×10−1(3,2)−2.500000000×10−1(7,6)−6.835937500×10−2 (7,0) 2.966308594×10−1(4,4)−7.812500000×10−2(5,2) 2.031250000×10−1(7,7) 3.222656250×10−2 (1,1) 1.000000000(6,4)7.128906250×10−2(7,2)−1.728515625×10−1(8,8)−2.618408203×10−2 (4,1)−3.125000000×10−1(8,4) 1.690521240×10−108123660 1−12−2072120 21228−270−522 36−20−2640−5040 4−204903270 5−162−160141876318780 6−630−10525807971075767 7999117298−10663200−28792032 88822880468−118074186−291518730 9−779322−14672009466690203061122900 10−13957358−127928222607816040576820424879 1155717397165603440−42521155560−195632449272 1228279575942955180058−6789937647207−22502126499801 134867299659−2452669132614−687967034169−924449102836。