Boundary contributions to specific heat and susceptibility in the spin-1/2 XXZ chain

TL;DR

This paper analytically derives the low-temperature boundary contributions to specific heat and susceptibility in the spin-1/2 XXZ chain, revealing universal and divergent behaviors caused by boundary effects and irrelevant operators.

Contribution

It provides the first exact low-temperature asymptotic analysis of boundary effects in the XXZ model using Abelian bosonization, confirming results with numerical simulations.

Findings

Boundary susceptibility diverges at low temperatures.

Boundary contributions are universal in the isotropic case.

Analytical results are supported by numerical simulations.

Abstract

Exact low-temperature asymptotic behavior of boundary contribution to specific heat and susceptibility in the one-dimensional spin-1/2 XXZ model with exchange anisotropy 1/2 < \Delta \le 1 is analytically obtained using the Abelian bosonization method. The boundary spin susceptibility is divergent in the low-temperature limit. This singular behavior is caused by the first-order contribution of a bulk leading irrelevant operator to boundary free energy. The result is confirmed by numerical simulations of finite-size systems. The anomalous boundary contributions in the spin isotropic case are universal.