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arXiv · 2206.01656

Emergence of Kac-Moody Symmetry in Critical Quantum Spin Chains

Ruoshui Wang·Yijian Zou·Guifre Vidal
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Abstract

Given a critical quantum spin chain with a microscopic Lie-group symmetry, corresponding e.g. to $U(1)$ or $SU(2)$ spin isotropy, we numerically investigate the emergence of Kac-Moody symmetry at low energies and long distances. In that regime, one such critical quantum spin chain is described by a conformal field theory where the usual Virasoro algebra associated to conformal invariance is augmented with a Kac-Moody algebra associated to conserved currents. Specifically, we first propose a method to construct lattice operators corresponding to the Kac-Moody generators. We then numerically show that, when projected onto low energy states of the quantum spin chain, these operators indeed approximately fulfill the Kac-Moody algebra. The lattice version of the Kac-Moody generators allow us to compute the so-called level constant and to organize the low-energy eigenstates of the lattice Hamiltonian into Kac-Moody towers. We illustrate the proposal with the XXZ model and the Heisenberg model with a next-to-nearest-neighbor coupling.

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Ruoshui Wang, Yijian Zou, Guifre Vidal. 2022-06-03. Emergence of Kac-Moody Symmetry in Critical Quantum Spin Chains. https://doi.org/10.1103/physrevb.106.115111

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