Anomalous thermodynamics of a quantum spin system with large residual entropy

Richter J, Schulenburg J, Dmitriev DV, Krivnov VY, Schnack J (2020)
CONDENSED MATTER PHYSICS 23(4): 43710.

Zeitschriftenaufsatz | Veröffentlicht | Englisch
 
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Autor*in
Richter, J.; Schulenburg, J.; Dmitriev, D. V.; Krivnov, V. Ya.; Schnack, JürgenUniBi
Abstract / Bemerkung
In contrast to strongly frustrated classical systems, their quantum counterparts typically have a non-degenerate ground state. A counterexample is the celebrated Heisenberg sawtooth spin chain with ferromagnetic zigzag bonds J(1) and competing antiferromagnetic basal bonds J(2). At a quantum phase transition point vertical bar J(2)/J(1)vertical bar = 1/2, this model exhibits a flat one-magnon excitation band leading to a massively degenerate ground-state manifold which results in a large residual entropy. Thus, for the spin-half model, the residual entropy amounts to exactly one half of its maximum value lim(T)(->infinity) S(T)/N = ln 2. In the present paper we study in detail the role of the spin quantum number s and the magnetic field H in the parameter region around the transition (flat-band) point. For that we use full exact diagonalization up to N = 20 lattice sites and the finite-temperature Lanczos method up to N = 36 sites to calculate the density of states as well as the temperature dependence of the specific heat, the entropy and the susceptibility. The study of chain lengths up to N = 36 allows a careful finite-size analysis. At the flat-band point we find extremely small finite-size effects for spin s = 1/2, i.e., the numerical data virtually correspond to the thermodynamic limit. In all other cases the finite-size effects are still small and become visible at very low temperatures. In a sizeable parameter region around the flat-band point the former massively degenerate ground-state manifold acts as a large manifold of low-lying excitations leading to extraordinary thermodynamic properties at the transition point as well as in its vicinity such as an additional low-temperature maximum in the specific heat. Moreover, there is a very strong influence of the magnetic field on the low-temperature thermodynamics including an enhanced magnetocaloric effect.
Stichworte
quantum Heisenberg model; frustration; sawtooth chain; residual entropy
Erscheinungsjahr
2020
Zeitschriftentitel
CONDENSED MATTER PHYSICS
Band
23
Ausgabe
4
Art.-Nr.
43710
ISSN
1607-324X
eISSN
2224-9079
Page URI
https://pub.uni-bielefeld.de/record/2950747

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Richter J, Schulenburg J, Dmitriev DV, Krivnov VY, Schnack J. Anomalous thermodynamics of a quantum spin system with large residual entropy. CONDENSED MATTER PHYSICS. 2020;23(4): 43710.
Richter, J., Schulenburg, J., Dmitriev, D. V., Krivnov, V. Y., & Schnack, J. (2020). Anomalous thermodynamics of a quantum spin system with large residual entropy. CONDENSED MATTER PHYSICS, 23(4), 43710. doi:10.5488/CMP.23.43710
Richter, J., Schulenburg, J., Dmitriev, D. V., Krivnov, V. Y., and Schnack, J. (2020). Anomalous thermodynamics of a quantum spin system with large residual entropy. CONDENSED MATTER PHYSICS 23:43710.
Richter, J., et al., 2020. Anomalous thermodynamics of a quantum spin system with large residual entropy. CONDENSED MATTER PHYSICS, 23(4): 43710.
J. Richter, et al., “Anomalous thermodynamics of a quantum spin system with large residual entropy”, CONDENSED MATTER PHYSICS, vol. 23, 2020, : 43710.
Richter, J., Schulenburg, J., Dmitriev, D.V., Krivnov, V.Y., Schnack, J.: Anomalous thermodynamics of a quantum spin system with large residual entropy. CONDENSED MATTER PHYSICS. 23, : 43710 (2020).
Richter, J., Schulenburg, J., Dmitriev, D. V., Krivnov, V. Ya., and Schnack, Jürgen. “Anomalous thermodynamics of a quantum spin system with large residual entropy”. CONDENSED MATTER PHYSICS 23.4 (2020): 43710.

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