Monte Carlo Study of the Separation of Energy Scales in Quantum Spin 1/2 Chains with Bond Disorder

TL;DR

This study uses quantum Monte Carlo simulations to identify three distinct temperature regimes in disordered quantum spin chains, revealing observable features like specific heat peaks and Curie-like susceptibility behavior.

Contribution

It demonstrates, for the first time, the clear separation of temperature regimes in disordered spin chains through exact numerical analysis, including a realistic material model.

Findings

Identification of three temperature regimes with distinct thermodynamic behavior

Observation of specific heat peaks indicating regime crossovers

Curie-like susceptibility with varying constants in each regime

Abstract

One-dimensional Heisenberg spin 1/2 chains with random ferro- and antiferromagnetic bonds are realized in systems such as $Sr_3 CuPt_{1-x} Ir_x O_6$. We have investigated numerically the thermodynamic properties of a generic random bond model and of a realistic model of $Sr_3 CuPt_{1-x} Ir_x O_6$ by the quantum Monte Carlo loop algorithm. For the first time we demonstrate the separation into three different temperature regimes for the original Hamiltonian based on an exact treatment, especially we show that the intermediate temperature regime is well-defined and observable in both the specific heat and the magnetic susceptibility. The crossover between the regimes is indicated by peaks in the specific heat. The uniform magnetic susceptibility shows Curie-like behavior in the high-, intermediate- and low-temperature regime, with different values of the Curie constant in each regime. We show that these regimes are overlapping in the realistic model and give numerical data for the analysis of experimental tests.