Universal contributions to charge fluctuations in spin chains at finite temperature

• URL: http://arxiv.org/abs/2401.09548v2
• Date: Sun, 3 Mar 2024 00:10:27 GMT
• Title: Universal contributions to charge fluctuations in spin chains at finite temperature
• Authors: Kang-Le Cai and Meng Cheng
• Abstract summary: We show that $gamma(theta)$ only takes non-zero values at isolated points of $theta$, which is $theta=pi$ for all our examples. In two exemplary lattice systems we show that $gamma(pi)$ takes quantized values when the U(1) symmetry exhibits a specific type of 't Hooft anomaly with other symmetries.
• Score: 5.174839433707792
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: At finite temperature, conserved charges undergo thermal fluctuations in a quantum many-body system in the grand canonical ensemble. The full structure of the fluctuations of the total U(1) charge $Q$ can be succinctly captured by the generating function $G(\theta)=\left\langle e^{i \theta Q}\right\rangle$. For a 1D translation-invariant spin chain, in the thermodynamic limit the magnitude $|G(\theta)|$ scales with the system size $L$ as $\ln |G(\theta)|=-\alpha(\theta)L+\gamma(\theta)$, where $\gamma(\theta)$ is the scale-invariant contribution and may encode universal information about the underlying system. In this work we investigate the behavior and physical meaning of $\gamma(\theta)$ when the system is periodic. We find that $\gamma(\theta)$ only takes non-zero values at isolated points of $\theta$, which is $\theta=\pi$ for all our examples. In two exemplary lattice systems we show that $\gamma(\pi)$ takes quantized values when the U(1) symmetry exhibits a specific type of 't Hooft anomaly with other symmetries. In other cases, we investigate how $\gamma(\theta)$ depends on microscopic conditions (such as the filling factor) in field theory and exactly solvable lattice models.

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