Berlin 2024 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 75: Low Dimensional Systems

TT 75.4: Vortrag

Donnerstag, 21. März 2024, 15:45–16:00, H 3007

Mean-field theory for the thermodynamics of quantum spin systems — •Andreas Honecker — Laboratoire de Physique Théorique et Modélisation, CNRS UMR 8089, CY Cergy Paris Université, France

Many quantum-spin compounds realize a complex –typically higher-dimensional– exchange geometry. This poses a challenge for the theoretical description of their thermodynamic properties. Mean-field theory suggests itself as a flexible tool in this context. However, accuracy of simple single-site mean-field theory turns out to be disappointing for certain antiferromagnetic compounds with a low saturation field that are of potential interest for adiabatic demagnetization refrigeration [1]. We therefore revisit the mean-field approximation for the thermodynamic properties of the spin-1/2 Heisenberg ferro- and antiferromagnets on prototypical lattices such as the square, triangular, and simple cubic ones and benchmark it against numerical results obtained by quantum Monte Carlo simulations and exact diagonalization. We also discuss perspectives for improving the accuracy of mean-field methods.

[1] M. Tiwari, Mean-Field Theory for Quantum Spin Systems and the Magnetocaloric Effect, Ph.D. thesis, CY Cergy Paris Université (2022)

Keywords: Mean-field theory; quantum spin models; magnetocaloric effect