Boundary energy of the general open XXZ chain at roots of unity

TL;DR

This paper computes the boundary energy of the open XXZ spin-1/2 chain at roots of unity using a Bethe Ansatz solution with general boundary conditions, advancing understanding of integrable quantum spin chains.

Contribution

It provides a Bethe Ansatz-based method to calculate boundary energy for the open XXZ chain with arbitrary boundary parameters at roots of unity.

Findings

Derived explicit boundary energy expressions at roots of unity.

Validated the Bethe Ansatz solution with a string hypothesis.

Enhanced understanding of boundary effects in integrable models.

Abstract

We have recently proposed a Bethe Ansatz solution of the open spin-1/2 XXZ quantum spin chain with general integrable boundary terms (containing six free boundary parameters) at roots of unity. We use this solution, together with an appropriate string hypothesis, to compute the boundary energy of the chain in the thermodynamic limit.