# Surface energy and elementary excitations of the XXZ spin chain with arbitrary boundary fields

## TL;DR

This paper investigates the thermodynamic properties, surface energy, and elementary excitations of the XXZ spin chain with arbitrary boundary fields, showing that inhomogeneous terms can be neglected for large systems.

## Contribution

It provides new analytical results for surface energy and excitations in the XXZ spin chain with arbitrary boundary conditions, extending understanding of boundary effects.

## Key findings

- Inhomogeneous term contribution is negligible for large N.
- Surface energy induced by boundary fields is explicitly calculated.
- Elementary excitations are characterized under arbitrary boundary conditions.

## Abstract

The thermodynamic properties of the XXZ spin chain with integrable open boundary conditions at the gaped region (i.e., the anisotropic parameter $\eta$ being a real number) are investigated.It is shown that the contribution of the inhomogeneous term in the $T-Q$ relation of the ground state and elementary excited state can be neglected when the size of the system $N$ tends to infinity. The surface energy and elementary excitations induced by the unparallel boundary magnetic fields are obtained.