Exotic Ground States and Excitations in Quantum Magnets
Author: Samuel Patrick Michael Curley
Publisher:
Published: 2021
Total Pages: 0
ISBN-13:
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Author: Samuel Patrick Michael Curley
Publisher:
Published: 2021
Total Pages: 0
ISBN-13:
DOWNLOAD EBOOKAuthor: Charuni Dissanayake
Publisher:
Published: 2023
Total Pages: 0
ISBN-13:
DOWNLOAD EBOOKQuantum mechanical frustration (QMF) in magnetic materials has become a pivotal ingredient in discovering intriguing properties of materials. The quantum spin liquid (QSL) state is a prime consequence of frustration in which spin fluctuations persist to absolute zero temperature. This orderless state is not characterized by symmetry breaking and guarantees an infinite degeneracy in its ground state. The quest to realize such nontrivial ground states in view of spin correlation, elementary excitation, topology, and geometry requires convincing experimental evidence. QMF is often manifested in unique lattice systems, such as spin-1/2 hyper-honeycomb lattices with strong spin-orbit coupling and geometrically frustrated Kagome lattices. Metal-organic frameworks (MOFs) that comprise metal ions with organic linkers via coordinate bonds have recently been proposed to realize the QSL ground state. Owing to the vast versatility of constituent's, the copper-oxalate MOF, [(C2H5)3NH]2Cu2(C2O4)3, unfolds a new avenue for us to realize unusual magnetic phases. To investigate the exotic ground state, we synthesized single crystals of [(C2H5)3NH]2Cu2(C2O4)3 and measured their thermodynamic properties. Our low-temperature and high-magnetic-field heat-capacity (Cp) measurements corroborate an exotic but rich ground state in [(C2H5)3NH]2Cu2(C2O4)3. A finite linear-in temperature Cp term with no indication of any thermal anomaly was observed at low temperature in zero field, indicating the absence of magnetic order and the presence of gapless spinon excitations despite the Mott insulating phase. Applied magnetic fields suppress the low-temperature Cp and drive the system into a gapped phase. The field-induced gap is described by the sine-Gorden model for quasi-one-dimensional antiferromagnetic Heisenberg chains, originating from anisotropic magnetic exchange interactions due to the Jahn-Teller distortion. Kagome lattices are archetypes of potential QSL, superconducting, Chern insulating states due to flat energy bands, Dirac fermions, and van Hove singularities in its electronic band structure. Sc3Mn3Al7Si5 is a transition metal compound with a hexagonal structure in which magnetic Mn atoms form kagome nets and does not show magnetic order down to 2 K, suggestive of a possible itinerant QSL. In this dissertation, to elucidate its exotic ground state, we synthesized single crystals of Sc3Mn3Al7Si5 and measured magnetoresistance, Cp, soft point contact spectroscopy, and torque magnetometry at low temperatures and high magnetic fields. Our experimental results suggest that the unusual ground state is induced by dispersionless energy bands induced by strong electron correlations. Our findings through distinct states of matter spanning from Mott insulators to itinerant metals will provide new insights to characterize the ground state in novel quantum magnets.
Author: Hyejin Ju
Publisher:
Published: 2013
Total Pages: 196
ISBN-13: 9781303052262
DOWNLOAD EBOOKThe study of frustration in quantum magnetism has been the focus of extensive research in the past couple of decades. The class of materials in this category is typically strongly correlated, due to strong electron-electron repulsion. In one- and two-dimensions, quantum fluctuations dominate these systems, and often, semi-classical approximations become an oversimplification. This thesis is concerned with exploring exotic physics that can emerge in low-dimensional quantum magnets. First, we use a T = 0 projected Monte Carlo algorithm in the valence bond basis to study the entanglement scaling of two-dimensional (2d) gapless systems. In particular, we focus on the resonating-valence-bond wavefunction as well as the gapless Goldstone mode in the Heisenberg model on the square lattice. We find that, in addition to the area law, there is a subleading, shape-dependent piece to the entanglement entropy, which is reminiscent of one dimensional (1d) gapless systems. We then explore the Heisenberg model under an applied magnetic field on the quasi-1d problem of a three-leg triangular spin tube (TST), using extensive density-matrix-renormalization group calculations coupled with analytical arguments to describe the results. We find that the physics describing this model differs from some of the well-known results on the two dimensional lattice, especially near low magnetic fields and at 1/3 magnetization. Finally, further research and possibilities in numerical techniques are discussed.
Author: Stephen J. Blundell
Publisher: OUP Oxford
Published: 2012-06-28
Total Pages: 160
ISBN-13: 0191633720
DOWNLOAD EBOOKMagnetism is a strange force, mysteriously attracting one object to another apparently through empty space. It has been claimed as a great healer, with magnetic therapies being proposed over the centuries and still popular today. Why are its mysterious important to solve? In this Very Short Introduction, Stephen J. Blundell explains why. For centuries magnetism has been used for various exploits; through compasses it gave us navigation and through motors, generators, and turbines it has given us power. Blundell explores our understanding of electricity and magnetism, from the work of Galvani, Ampere, Faraday, and Tesla, and goes on to explore how Maxwell and Faraday's work led to the unification of electricity and magnetism, thought of as one of the most imaginative developments in theoretical physics. With a discussion of the relationship between magnetism and relativity, quantum magnetism, and its impact on computers and information storage, Blundell shows how magnetism has changed our fundamental understanding of the Universe. ABOUT THE SERIES: The Very Short Introductions series from Oxford University Press contains hundreds of titles in almost every subject area. These pocket-sized books are the perfect way to get ahead in a new subject quickly. Our expert authors combine facts, analysis, perspective, new ideas, and enthusiasm to make interesting and challenging topics highly readable.
Author: Sarben Sarkar
Publisher: Springer Science & Business Media
Published: 2013-11-11
Total Pages: 320
ISBN-13: 9401599742
DOWNLOAD EBOOKMesoscopic physics has made great strides in the last few years. It is an area of research that is attractive to many graduate students of theoretical condensed matter physics. The techniques that are needed to understand it go beyond the conventional perturbative approaches that still form the bulk of the graduate lectures that are given to students. Even when the non-perturbative techniques are presented, they often are presented within an abstract context. It is important to have lectures given by experts in the field, which present both theory and experiment in an illuminating and inspiring way, so that the impact of new methodology on novel physics is clear. It is an apt time to have such a volume since the field has reached a level of maturity. The pedagogical nature of the articles and the variety of topics makes it an important resource for newcomers to the field. The topics range from the newly emerging area of quantum computers and quantum information using Josephson junctions to the formal mathematical methods of conformal field theory which are applied to the understanding of Luttinger liquids. Electrons which interact strongly can give rise to non-trivial ground states such as superconductivity, quantum Hall states and magnetism. Both their theory and application are discussed in a pedagogical way for quantum information in mesoscopic superconducting devices, skyrmions and magnetism in two dimensional electron gases, transport in quantum wires, metal-insulator transitions and spin electronics.
Author: Sarben Sarkar
Publisher: Springer Science & Business Media
Published: 2002
Total Pages: 328
ISBN-13: 9781402010309
DOWNLOAD EBOOKMesoscopic physics has made great strides in the last few years. It is an area of research that is attractive to many graduate students of theoretical condensed matter physics. The techniques that are needed to understand it go beyond the conventional perturbative approaches that still form the bulk of the graduate lectures that are given to students. Even when the non-perturbative techniques are presented, they often are presented within an abstract context. It is important to have lectures given by experts in the field, which present both theory and experiment in an illuminating and inspiring way, so that the impact of new methodology on novel physics is clear. It is an apt time to have such a volume since the field has reached a level of maturity. The pedagogical nature of the articles and the variety of topics makes it an important resource for newcomers to the field. The topics range from the newly emerging area of quantum computers and quantum information using Josephson junctions to the formal mathematical methods of conformal field theory which are applied to the understanding of Luttinger liquids. Electrons which interact strongly can give rise to non-trivial ground states such as superconductivity, quantum Hall states and magnetism. Both their theory and application are discussed in a pedagogical way for quantum information in mesoscopic superconducting devices, skyrmions and magnetism in two dimensional electron gases, transport in quantum wires, metal-insulator transitions and spin electronics.
Author: Jason Alicea
Publisher: ProQuest
Published: 2007
Total Pages: 284
ISBN-13: 9780549152729
DOWNLOAD EBOOKQuite remarkably, the low-energy behavior of most metals is well captured by effectively ignoring the Coulomb repulsion between the constituent electrons. Yet over the past several decades many examples of "strongly correlated systems" have been discovered for which a strong interplay between interactions and quantum mechanics leads rather to spectacular deviations from an independent-electron picture, as exemplified by quantum Hall systems, high-Tc superconductors, heavy fermion compounds, etc. This thesis is concerned with exploring exotic physics that can emerge in a class of correlated systems known as quantum magnets, where electrons "self-localize" around crystal lattice sites due to interactions, leaving residual spin couplings at low energies. Typically the ground states of such systems exhibit spontaneous symmetry breaking, commonly in the form of magnetic order. But sufficiently strong quantum fluctuations can suppress symmetry-breaking order even down to zero temperature, generating exotic "spin liquid" phases that exhibit novel features such as electron fractionalization, topological order, emergent symmetries, etc.
Author: Hsiang-Hsuan Hung
Publisher:
Published: 2011
Total Pages: 179
ISBN-13: 9781124841243
DOWNLOAD EBOOKThe progress of ultracold atoms renders numerous possibilities to investigate exotic magnetism and superfluidity, which are rarely observed in solid state systems. In this thesis, we will introduce two novel physical descriptions: "frustrated Cooper pairing" and "large-hyperfine spin physics". Geometric frustration in quantum magnetism refers to which magnetic interactions on different bonds cannot be simultaneously minimized, and usually Cooper pairing favors uniform phases among different lattice sites. Here, we introduce "frustration" in Cooper pairing in a fermionic p-orbital model. By mean-field calculations, we show that the system exhibits behavior analogous to frustrated magnetism, and an unconventional supersolid state with the f-wave symmetry. Next, we introduce large-spin physics. In usual condensed matter systems, large spin is not intriguing because large values of spin suppress quantum fluctuations. In contrast, in ultracold fermion systems, large-hyperfine spin enhances quantum fluctuations and brings exotic quantum magnetism. Here the simplest large-spin fermionic system, a spin-3/2 exchange system is proposed, which can be characterized by an Sp(4)/SO(5) symmetry. In one dimension, the ground states exhibit either a dimerized state with a finite spin gap or a gapless spin liquid state by means of the density matrix renormalization group method. In the latter case, the spin-spin correlation functions are identified to have 4-site periodicities, which behaves similarly to the SU(4) chain. In two dimension, we infer that there exist three competing phases: Neel ordering, columnar dimerization and 2 x 2 plaquette formation, in the thermodynamic limit by exact diagonalization calculation on small sizes. Finally we perform the projector Quantum Monte Carlo method to study another large-spin system: the half-filled SU(N) Hubbard model. We show that at half-filling there is no sign problem such that our simulations are accurate. By finite size scaling, it is clearly found that the magnetic Neel ordering can exist not only for N = 2 but also in the N = 4 case at strong interactions. For N>̲ 6 or N = 4 at small U, the numerical results do not have any prominent signal that the long-range ordering exists in the thermodynamic limit. Due to strong finite size effects and finite numerical accuracy, however, we are unable to make any conclusion to identify the physics in the regimes.
Author: Claudine Lacroix
Publisher: Springer Science & Business Media
Published: 2011-01-12
Total Pages: 682
ISBN-13: 3642105890
DOWNLOAD EBOOKThe field of highly frustrated magnetism has developed considerably and expanded over the last 15 years. Issuing from canonical geometric frustration of interactions, it now extends over other aspects with many degrees of freedom such as magneto-elastic couplings, orbital degrees of freedom, dilution effects, and electron doping. Its is thus shown here that the concept of frustration impacts on many other fields in physics than magnetism. This book represents a state-of-the-art review aimed at a broad audience with tutorial chapters and more topical ones, encompassing solid-state chemistry, experimental and theoretical physics.
Author: Tyler Dodds
Publisher:
Published: 2013
Total Pages: 171
ISBN-13:
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