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Kundu S, Hossain A, S PK, Das R, Baenitz M, Baker PJ, Orain JC, Joshi DC, Mathieu R, Mahadevan P, Pujari S, Bhattacharjee S, Mahajan AV, Sarma DD. Signatures of a Spin-1/2 Cooperative Paramagnet in the Diluted Triangular Lattice of Y_{2}CuTiO_{6}. PHYSICAL REVIEW LETTERS 2020; 125:117206. [PMID: 32975979 DOI: 10.1103/physrevlett.125.117206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 06/11/2020] [Accepted: 08/04/2020] [Indexed: 06/11/2023]
Abstract
We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-1/2 system: Y_{2}CuTiO_{6}. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale (-θ_{CW}) of ∼134 K. We observe scaling collapses of the magnetic field and temperature dependent magnetic heat capacity and magnetization data, respectively, in conformity with expectations from the random singlet physics. Our experiments establish the suppression of any freezing scale, if at all present, by more than 3 orders of magnitude, opening a plethora of interesting possibilities such as disorder stabilized long range quantum entangled ground states.
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Affiliation(s)
- S Kundu
- Department of Physics, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India
| | - Akmal Hossain
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
| | - Pranava Keerthi S
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
| | - Ranjan Das
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
| | - M Baenitz
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Peter J Baker
- ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX110QX, United Kingdom
| | | | - D C Joshi
- Department of Engineering Sciences, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
| | - Roland Mathieu
- Department of Engineering Sciences, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
| | - Priya Mahadevan
- S. N. Bose National Center for Basic Sciences, Block-JD, Salt Lake, Kolkata-700106, India
| | - Sumiran Pujari
- Department of Physics, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India
| | - Subhro Bhattacharjee
- International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru 560089, India
| | - A V Mahajan
- Department of Physics, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India
| | - D D Sarma
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India
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Kawamura H, Uematsu K. Nature of the randomness-induced quantum spin liquids in two dimensions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:504003. [PMID: 31470422 DOI: 10.1088/1361-648x/ab400c] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The nature of the randomness-induced quantum spin liquid state, the random-singlet state, is investigated in two dimensions (2D) by means of the exact-diagonalization and the Hams-de Raedt methods for several frustrated lattices, e.g. the triangular, the kagome and the J 1-J 2 square lattices. Properties of the ground state, the low-energy excitations and the finite-temperature thermodynamic quantities are investigated. The ground state and the low-lying excited states consist of nearly isolated singlet-dimers, clusters of resonating singlet-dimers, and orphan spins. Low-energy excitations are either singlet-to-triplet excitations, diffusion of orphan spins accompanied by the recombination of nearby singlet-dimers, creation or destruction of resonating singlet-dimers clusters. The latter two excitations give enhanced dynamical 'liquid-like' features to the 2D random-singlet state. Comparison is made with the random-singlet state in a 1D chain without frustration, the similarity and the difference between in 1D and in 2D being highlighted. Frustration in a wide sense, not only the geometrical one but also including the one arising from the competition between distinct types of interactions, play an essential role in stabilizing this frustrated random singlet state. Recent experimental situations on both organic and inorganic materials are reviewed and discussed.
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Affiliation(s)
- Hikaru Kawamura
- Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
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Riedl K, Valentí R, Winter SM. Critical spin liquid versus valence-bond glass in a triangular-lattice organic antiferromagnet. Nat Commun 2019; 10:2561. [PMID: 31189897 PMCID: PMC6561973 DOI: 10.1038/s41467-019-10604-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 05/15/2019] [Indexed: 11/23/2022] Open
Abstract
In the quest for materials with unconventional quantum phases, the organic triangular-lattice antiferromagnet κ-(ET)2Cu2(CN)3 has been extensively discussed as a quantum spin liquid (QSL) candidate. The description of its low temperature properties has become, however, a particularly challenging task. Recently, an intriguing quantum critical behaviour was suggested from low-temperature magnetic torque experiments. Here we highlight significant deviations of the experimental observations from a quantum critical scenario by performing a microscopic analysis of all anisotropic contributions, including Dzyaloshinskii-Moriya and multi-spin scalar chiral interactions. Instead, we show that disorder-induced spin defects provide a comprehensive explanation of the low-temperature properties. These spins are attributed to valence bond defects that emerge spontaneously as the QSL enters a valence-bond glass phase at low temperature. This theoretical treatment is applicable to a general class of frustrated magnetic systems and has important implications for the interpretation of magnetic torque, nuclear magnetic resonance, thermal transport and thermodynamic experiments.
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Affiliation(s)
- Kira Riedl
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438, Frankfurt am Main, Germany.
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438, Frankfurt am Main, Germany
| | - Stephen M Winter
- Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438, Frankfurt am Main, Germany.
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Hörmann M, Wunderlich P, Schmidt KP. Dynamic Structure Factor of Disordered Quantum Spin Ladders. PHYSICAL REVIEW LETTERS 2018; 121:167201. [PMID: 30387667 DOI: 10.1103/physrevlett.121.167201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Indexed: 06/08/2023]
Abstract
We investigate the impact of quenched disorder on the zero-temperature dynamic structure factor of two-leg quantum spin ladders. Using linked-cluster expansions and bond-operator mean-field theory, huge effects on individual quasiparticles but also on composite bound states and two-quasiparticle continua are observed. This leads to intriguing quantum structures in dynamical correlation functions well observable in spectroscopic experiments.
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Affiliation(s)
- Max Hörmann
- Institute for Theoretical Physics, FAU Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Paul Wunderlich
- Institute for Theoretical Physics, FAU Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - K P Schmidt
- Institute for Theoretical Physics, FAU Erlangen-Nürnberg, 91058 Erlangen, Germany
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5
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Vasseur R, Potter AC, Parameswaran SA. Quantum criticality of hot random spin chains. PHYSICAL REVIEW LETTERS 2015; 114:217201. [PMID: 26066454 DOI: 10.1103/physrevlett.114.217201] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Indexed: 06/04/2023]
Abstract
We study the infinite-temperature properties of an infinite sequence of random quantum spin chains using a real-space renormalization group approach, and demonstrate that they exhibit nonergodic behavior at strong disorder. The analysis is conveniently implemented in terms of SU(2)_{k} anyon chains that include the Ising and Potts chains as notable examples. Highly excited eigenstates of these systems exhibit properties usually associated with quantum critical ground states, leading us to dub them "quantum critical glasses." We argue that random-bond Heisenberg chains self-thermalize and that the excited-state entanglement crosses over from volume-law to logarithmic scaling at a length scale that diverges in the Heisenberg limit k→∞. The excited state fixed points are generically distinct from their ground state counterparts, and represent novel nonequilibrium critical phases of matter.
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Affiliation(s)
- R Vasseur
- Department of Physics, University of California, Berkeley, California 94720, USA
- Materials Science Division, Lawrence Berkeley National Laboratories, Berkeley, California 94720, USA
| | - A C Potter
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - S A Parameswaran
- Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
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Vieira AP. Low-energy properties of aperiodic quantum spin chains. PHYSICAL REVIEW LETTERS 2005; 94:077201. [PMID: 15783847 DOI: 10.1103/physrevlett.94.077201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2003] [Indexed: 05/24/2023]
Abstract
We investigate the low-energy properties of antiferromagnetic quantum XXZ spin chains with couplings following two-letter aperiodic sequences, by an adaptation of the Ma-Dasgupta-Hu renormalization-group method. For a given aperiodic sequence, we argue that, in the easy-plane anisotropy regime, intermediate between the XX and Heisenberg limits, the general scaling form of the thermodynamic properties is essentially given by the exactly known XX behavior, providing a classification of the effects of aperiodicity on XXZ chains. As representative illustrations, we present analytical and numerical results for the low-temperature thermodynamics and the ground-state correlations for couplings following the Fibonacci quasiperiodic structure and a binary Rudin-Shapiro sequence, whose geometrical fluctuations are similar to those induced by randomness.
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Affiliation(s)
- André P Vieira
- Instituto de Física da Universidade de São Paulo, Caixa Postal 66318, 05315-970, São Paulo, Brazil
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Ghosh S, Rosenbaum TF, Aeppli G, Coppersmith SN. Entangled quantum state of magnetic dipoles. Nature 2003; 425:48-51. [PMID: 12955135 DOI: 10.1038/nature01888] [Citation(s) in RCA: 279] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2003] [Accepted: 07/07/2003] [Indexed: 11/09/2022]
Abstract
Free magnetic moments usually manifest themselves in Curie laws, where weak external magnetic fields produce magnetizations that vary as the reciprocal of the temperature (1/T). For a variety of materials that do not display static magnetism, including doped semiconductors and certain rare-earth intermetallics, the 1/T law is replaced by a power law T(-alpha) with alpha < 1. Here we show that a much simpler material system-namely, the insulating magnetic salt LiHo(x)Y(1-x)F(4)-can also display such a power law. Moreover, by comparing the results of numerical simulations of this system with susceptibility and specific-heat data, we show that both energy-level splitting and quantum entanglement are crucial to describing its behaviour. The second of these quantum mechanical effects-entanglement, where the wavefunction of a system with several degrees of freedom cannot be written as a product of wavefunctions for each degree of freedom-becomes visible for remarkably small tunnelling terms, and is activated well before tunnelling has visible effects on the spectrum. This finding is significant because it shows that entanglement, rather than energy-level redistribution, can underlie the magnetic behaviour of a simple insulating quantum spin system.
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Affiliation(s)
- S Ghosh
- James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA
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Wessel S, Normand B, Sigrist M, Haas S. Order by disorder from nonmagnetic impurities in a two-dimensional quantum spin liquid. PHYSICAL REVIEW LETTERS 2001; 86:1086-1089. [PMID: 11178016 DOI: 10.1103/physrevlett.86.1086] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2000] [Indexed: 05/23/2023]
Abstract
We consider doping of nonmagnetic impurities in the spin-1/2, 1/5-depleted square lattice. This structure, whose undoped phase diagram offers both magnetically ordered and spin-liquid ground states, is realized physically in CaV4O9. Doping into the ordered phase results in a progressive loss of order, which becomes complete at the percolation threshold. By contrast, doping into the spin liquids creates a phase of weak but long-ranged antiferromagnetic order, a true order-by-disorder phenomenon. We study the phase diagram of the doped system by computing the static susceptibility and staggered magnetization using a stochastic series-expansion quantum Monte Carlo technique.
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Affiliation(s)
- S Wessel
- Department of Physics and Astronomy, University of Southern California, Los Angeles 90089-0484, USA
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McKenzie RH. Exact Results for Quantum Phase Transitions in Random XY Spin Chains. PHYSICAL REVIEW LETTERS 1996; 77:4804-4807. [PMID: 10062635 DOI: 10.1103/physrevlett.77.4804] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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11
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Nguyen TN, Lee PA, zur Loye HC. Design of a Random Quantum Spin Chain Paramagnet: Sr
3
CuPt
0.5
Ir
0.5
O
6. Science 1996. [DOI: 10.1126/science.271.5248.489] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Tu N. Nguyen
- T. N. Nguyen and H.-C. zur Loye, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Patrick A. Lee
- P. A. Lee, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Hans-Conrad zur Loye
- T. N. Nguyen and H.-C. zur Loye, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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