Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y3: Quantum Spin Liquids |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Douglas Scalapino, University of California-Santa Barbara Room: LACC 515B |
Friday, March 25, 2005 11:15AM - 11:51AM |
Y3.00001: Numerical studies of Spin Liquid Phases Invited Speaker: After discussing the early 90' classification of the different phases of Quantum Antiferromagnets, I will explain why exact diagonalizations have been a useful tool in the quest of Quantum Spin Liquids. Contrary to superficial thinking, signatures of symmetry breakings appear very clearly in exact spectra of small samples of quantum spins. Spin Liquids are states which do not break any simple symmetry: neither spin-rotational symmetry nor lattice symmetry. They are characterized by topological degeneracies (which may be helpful for the realization of quantum bits, with very low rates of decoherence), and generically gapful excitations. The first supposed-to be Quantum Spin Liquid has been discovered in 1998 by Misguich and coll. in the frustrated 4-spin ring exchange model on the triangular lattice. Following this first break-through, simpler models exhibiting well defined Quantum Spin Liquids have been produced. After a rapid review of these cases, I will show some results that may be characteristic of new Quantum Critical Phase Transitions between non colinear N\'eel magnets [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:27PM |
Y3.00002: Two Spin Liquid phases in the anisotropic triangular Heisenberg model Invited Speaker: Recently there have been rather clean experimental realizations of the quantum spin 1/2 Heisenberg Hamiltonian on a 2D triangular lattice geometry in systems like $Cs_2 Cu Cl_4$ and organic compounds like $k-(ET)_2 Cu_2 (CN)_3$. These materials are nearly two dimensional and are characterized by an anisotropic antiferromagnetic superexchange. The strength of the spatial anisotropy can increase quantum fluctuations and can destabilize the magnetically ordered state leading to non conventional spin liquid phases. In order to understand these interesting phenomena we have studied, by Quantum Monte Carlo methods, the triangular lattice Heisenberg model as a function of the strength of this anisotropy, represented by the ratio $r$ between the intra-chain nearest neighbor coupling $J'$ and the inter-chain one $J$. We have found evidence of two spin liquid regions, well represented by projected BCS wave functions[1,2] of the type proposed by P. W. Anderson at the early stages of High temperature superconductivity [3]. The first spin liquid phase is stable for small values of the coupling $r \alt 0.6$ and appears gapless and fractionalized, whereas the second one is a more conventional spin liquid, very similar to the one realized in the quantum dimer model in the triangular lattice[4]. It is characterized by a spin gap and a finite correlation length, and appears energetically favored in the region $0.6 \alt r \alt 0.9$. The various phases are in good agreement with the experimental findings and supports the existence of spin liquid phases in 2D quantum spin-half systems. %%%%%%%%%%%%%%%%%% \vspace{1cm} \begin{description} \item{[1]} L. Capriotti F. Becca A. Parola and S. Sorella , Phys. Rev. Letters {\bf 87}, 097201 (2001). \item{[2]} S. Yunoki and S. Sorella Phys. Rev. Letters {\bf 92}, 15003 (2004). \item{[3]} P. W. Anderson, Science {\bf 235}, 1186 (1987). \item{[4]} P. Fendley, R. Moessner, and S. L. Sondhi Phys. Rev. B {\bf 66}, 214513 (2002). \end{description} [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 1:03PM |
Y3.00003: Quantum Spin Liquids in XY models with Ring Exchange Invited Speaker: Many promising candidate Hamiltonians have been proposed recently as harboring emergent quantum spin liquid states. Regardless, convincing examples of the state are still lacking in large-scale quantum Monte Carlo simulations of microscopic spin models, due in part to the negative sign problem which inhibits studies of antiferromagnetic spins on frustrating lattices. However, recently several unfrustrated spin models have been studied, with results that suggest that emergent spin liquid states can exist there. One of these is the square lattice $S=1/2$ XY model with ring exchange, tractable by quantum Monte Carlo without the sign problem [1]. The basic Hamiltonian is purported to harbor an isolated spin liquid point with emergent $U(1)$ gauge symmetry and spinons [2]. Using suggestions from analytical theory, we attempt to stabilize an extended region of spin liquid around this critical point by adding terms to the Hamiltonian, and increasing the dimensionality of the lattice. However, such modifications produce no spin liquid state. We therefore explore a version of the Hamiltonian on the kagome lattice, which with a particular diagonal interaction is exactly soluble analytically, and is argued to be in a stable spin liquid state with $Z_2$ gauge symmetry [3]. The Monte Carlo is able to simulate directly all parameter regions of this Hamiltonian to test this claim, and in addition is able to explore the adjacent superfluid and insulating phases and respective phase transitions. [1] Sandvik, Daul, Singh and Scalapino, Phys Rev. Lett. 89 247201 (2002). [2] Senthil et al., Science 303 1490 (2004). [3] Balents, Fisher and Girvin, Phys. Rev. B 65, 224412 (2002); Sheng and Balents, cond-mat/0408639. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:39PM |
Y3.00004: Spin liquid aspects of the two dimensional Heisenberg antiferromagnet Invited Speaker: Since it was established that the 2D quantum (S=1/2) Heisenberg antiferromagnet on a square lattice develop long range order at T=0, albeit with only 60\% of the classical moment, it was believed that the excitaitons of this model should be classical spin waves only weakly renormalised by quantum fluctuations. Through neutron scattering investigations of CFTD, an excellend physicsl realisation of the model system, we have recently discovered i) a moderate deviation from the spin wave prediction for the zone boundary energies and ii) a huge, 50\%, deviation in intensity at Q=(pi,0). We interpret this as signature of valence bond type correlations in the quantum fluctuating part of the ground state. Although the valence bond state lacks long range order, which must be introduced through a variational approach, our results suggest that it may actually be a better starting point for approaches to understand spin fluctuations upon hole-doping as in the high temperature superconducting cuprates. [Preview Abstract] |
Friday, March 25, 2005 1:39PM - 2:15PM |
Y3.00005: The quasiparticle spectrum termination in a quantum spin liquid Invited Speaker: Igor Zaliznyak The crossover from a single quasi-particle to a spin-continuum response was recently observed in the spin dynamics of the Haldane-chain antiferromagnet CsNiCl3 [1,2]. It can be understood as a manifestation, in the particular case of the quantum spin liquid, of the peculiar property of the quantum Bose liquids, the quasiparticle spectrum termination point. The spectrum termination was first predicted for the superfluid helium-4 [3], where it was extensively studied both theoretically and experimentally. The quantum-spin-liquid (QSL) state of the two-dimensional (2D) S=1/2 Heisenberg antiferromagnet (HAFM) is of particular interest, as it may be relevant to the type of high-temperature superconductivity found in the cuprates. An organo-metallic material piperazinium hexachlorodicuprate (PHCC) is among the best known examples of the 2D QSL [4]. The spin excitations in this material have spectral gap of about 1 meV above which they follow a nearly 2D- isotropic dispersion with a bandwidth slightly larger than the gap. Recent experiments indicate that a quasiparticle spectrum termination point also exists in the excitation spectrum of the 2D quantum spin liquid existing in PHCC [5]. It signals the failure of the Bose-quasiparticle description in an extended region of the system's phase space. REFERENCES [1] I. A. Zaliznyak, S.-H. Lee, in Y. Zhu (Ed.), Modern Techniques for Characterizing Magnetic Materials, Kluwer Academic, New York (2005). [2] I. A. Zaliznyak, S.-H. Lee and S. V. Petrov, Phys. Rev. Lett. 87, 017202 (2001); Phys. Rev. Lett. 91, 039902 (2003). [3] Landau \& Lifshitz, Course of Theoretical Physics (Statistical Physics, Part 2, by Lifshitz, E. M. \& Pitaevskii, L. P.) Vol. 9, 125-139 (Pergamon Press, Oxford, 1981). [4] Stone, M. B., Zaliznyak, I., Reich, D. H., and Broholm, C., Phys. Rev. B 64, 144405 (2001). [5] M. Stone, I. A. Zaliznyak, et. al., in preparation (2004). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700