Thermal Conductivity in the Bose-Einstein Condensed State of Triplons in the Bond-Alternating Spin-Chain System Pb2V3O9

TL;DR

This study investigates how thermal conductivity behaves in a spin-chain system during the Bose-Einstein Condensed state of triplons, revealing directional enhancement linked to magnetic interactions and supporting a two-fluid model analogy.

Contribution

It provides experimental evidence of directional thermal conductivity enhancement in the BEC state of triplons in Pb2V3O9, highlighting the role of magnetic interactions.

Findings

Thermal conductivity along spin-chains is enhanced in the BEC state.

Thermal conductivity perpendicular to chains is suppressed in the BEC state.

Results support a two-fluid model explanation for thermal transport in the BEC state.

Abstract

In order to clarify the origin of the enhancement of the thermal conductivity in the Bose-Einstein Condensed (BEC) state of field-induced triplons, we have measured the thermal conductivity along the [101] direction parallel to spin-chains, $kappa_{\|[101]}$, and perpendicular to spin-chains, $kappa_{\perp[101]}$, of the S=1/2 bond-alternating spin-chain system Pb2V3O9 in magnetic fields up to 14 T. With increasing field at 3 K, it has been found that both $kappa_{\|[101]}$ and $kappa_{\perp[101]}$ are suppressed in the gapped normal state in low fields. In the BEC state of field-induced triplons in high fields, on the other hand, $kappa_{\|[101]}$ is enhanced with increasing field, while $kappa_{\perp[101]}$ is suppressed. That is, the thermal conductivity along the direction, where the magnetic interaction is strong, is markedly enhanced in the BEC state. Accordingly, our results suggest that the enhancement of $kappa_{\|[101]}$ in the BEC state is caused by the enhancement of the thermal conductivity due to triplons on the basis of the two-fluid model, as in the case of the superfluid state of liquid 4He.