Order in quantum compass and orbital $e_g$ models

5 Sep 2017, 11:30
20m
30 ()

30

oral Session 5

Speaker

Andrzej M. Oles (Jagiellonian University)

Description

Exchange interactions in orbital models are frustrated even on a square lattice, where two $T=1/2$ pseudospin components $T_i^{\gamma}(\theta)$ parameterized by angle $\theta\in(0,\pi/2]$ interact by terms $JT_i^{\gamma}(\theta)T_j^{\gamma}(\theta)$. Maximal frustration in the quantum compass model with $T_i^{\gamma}(\pi/2)\equiv\frac12\sigma_i^{\gamma}$, where $\sigma_i^{\gamma}$ is the Pauli matrix, is reduced to moderate frustration for the $e_g$ orbital model at $\theta=\pi/3$ [1]. We investigate thermodynamic phase transitions at temperature $T_c$ on an infinite square lattice by variational tensor network renormalization (VTNR) in imaginary time. From the linear susceptibility (order parameter) in the symmetric (symmetry-broken) phase the onset of nematic order in the quantum compass model is estimated at $T_c/J=0.0606(4)$ [2], in good agreement with Quantum Monte Carlo (QMC). For the 2D $e_g$ orbital model one finds: ($i$) a very accurate VTNR estimate of $T_c/J=0.3566\pm 0.0001$ while QMC fails due to the sign problem, and ($ii$) that the critical exponents are within the Ising universality class. Remarkably large difference in frustration and entanglement results in so distinct $T_c$. $ $ [1] L. Cincio, J. Dziarmaga, and A. M. Oleś, Phys. Rev. B **82**, 104416 (2010). [2] P. Czarnik, J. Dziarmaga, and A. M. Oleś, Phys. Rev. B **93**, 184410 (2016).

Primary author

Andrzej M. Oles (Jagiellonian University)

Co-authors

Jacek Dziarmaga (Jagiellonian University) Piotr Czarnik (Jagiellonian University)

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