Thermal Conductivity of Mg-doped CuGeO_3

TL;DR

This study investigates how Mg doping and magnetic fields influence thermal conductivity in CuGeO3, revealing that spin excitations contribute coherently to heat transport above the spin-Peierls transition and that doping affects the spin gap and heat transport properties.

Contribution

It provides new insights into the effects of Mg doping and magnetic fields on spin-mediated heat transport in CuGeO3, highlighting the robustness of the spin gap and its impact on phonon heat conduction.

Findings

Spin excitations contribute coherently to heat transport above T_SP.

Mg doping suppresses T_SP but not T^*, the temperature where the spin gap opens.

The spin gap enhances phonon heat transport, creating an unusual peak that diminishes with doping and magnetic fields.

Abstract

The thermal conductivity $\kappa$ is measured in a series of Cu_1-xMg_xGeO_3 single crystals in magnetic fields up to 16 T. It has turned out that heat transport by spin excitations is coherent for lightly doped samples, in which the spin-Peierls (SP) transition exists, at temperatures well above the SP transition temperature T_SP. Depression of this spin heat transport appears below T^*, at which the spin gap locally opens. T^* is not modified with Mg-doping and that T^* for each Mg-doped sample remains as high as T_SP of pure CuGeO_3, in contrast to T_SP which is strongly suppressed with Mg-doping. The spin-gap opening enhances phonon part of the heat transport because of reduced scattering by the spin excitations, producing an unusual peak. This peak diminishes when the spin gap is suppressed both in magnetic fields and with the Mg-doping.