Second Anomaly in the Specific Heat of beta-Pyrochlore Oxide Superconductor KOs2O6

TL;DR

This study reveals a second anomaly in the specific heat of KOs2O6 superconductor, indicating a possible unknown phase transition that interacts with superconductivity and shows a larger electronic contribution compared to similar compounds.

Contribution

It reports the discovery of a second specific heat anomaly in KOs2O6 and explores its relation to superconductivity and electronic properties, which was not previously known.

Findings

Second specific heat peak at ~7.5 K below Tc

Second anomaly's behavior under magnetic fields suggests a separate phase transition

Large Sommerfeld coefficient indicating high electronic density of states

Abstract

Resistivity and specific heat have been measured on a single crystalline sample of the beta-pyrochlore oxide superconductor, KOs2O6. It is found that a second peak in specific heat, which may evidence an unknown phase transition, appears around Tp ~ 7.5 K below the superconducting transition temperature Tc = 9.53 K. Applying magnetic fields up to 14 T, Tc is reduced gradually down to 7.1 K, while Tp is raised a little and becomes even higher than Tc at 14 T, which implies that the second anomaly is not associated directly with the superconductivity. It is demonstrated, however, that there is significant communication between the two anomalies, suggesting that they come from the same electrons. It is also reported that the Sommerfeld coefficient ? in KOs2O6 is possibly much larger than in other members of beta-pyrochlore oxide superconductors, RbOs2O6 (Tc = 6.3 K) and CsOs2O6 (Tc = 3.3 K).