Low-temperature properties of finite XX-chains with additional Ising spin

Abstract

This is a theoretical study of quantum stationary states and thermodynamics of two exactly solvable quantum models: a finite XX-chain with an “offshoot” that is connected via ZZ-interaction (Ising) to one of the chain nodes, and two different finite XX-chains joined through an additional ZZ-spin. It is shown that the spectrum can have impurity levels localized near the impurity spin, and the conditions for their manifestation are determined. The field and temperature dependences of the main thermodynamic characteristics of the models are investigated.