Field-dependent spin and heat conductivities of dimerized spin-1/2 chains

TL;DR

This study investigates how magnetic fields influence spin and heat conductivities in dimerized spin-1/2 chains at finite temperatures, revealing enhancements in conductivities during phase transitions and highlighting the effects of magnetothermal coupling.

Contribution

The paper provides the first detailed analysis of field-dependent spin and heat conductivities in dimerized spin chains, including the impact of magnetothermal effects on thermal transport.

Findings

Conductivities are enhanced in the gapless phase, especially at low frequencies.

Magnetothermal effects suppress the field-induced increase in thermal conductivity.

Results align with recent experiments on spin ladder materials.

Abstract

We study the spin and heat conductivity of dimerized spin-1/2 chains in homogeneous magnetic fields at finite temperatures. At zero temperature, the model undergoes two field-induced quantum phase transitions from a dimerized, into a Luttinger, and finally into a fully polarized phase. We search for signatures of these transitions in the spin and heat conductivities. Using exact diagonalization, we calculate the Drude weights, the frequency dependence of the conductivities, and the corresponding integrated spectral weights. As a main result, we demonstrate that both the spin and heat conductivity are enhanced in the gapless phase and most notably at low frequencies. In the case of the thermal conductivity, however, the field-induced increase seen in the bare transport coefficients is suppressed by magnetothermal effects, caused by the coupling of the heat and spin current in finite magnetic fields. Our results complement recent magnetic transport experiments on spin ladder materials with sufficiently small exchange couplings allowing access to the field-induced transitions.