Large mass enhancement in RbOs2O6

TL;DR

This study reveals a large mass enhancement in the superconductor RbOs2O6, primarily due to electron-electron interactions, with implications for understanding its superconducting properties.

Contribution

The paper introduces a method to analyze bulk thermodynamic data to distinguish electron-phonon and other interaction contributions to mass enhancement in RbOs2O6.

Findings

Sommerfeld coefficient is about 4 times larger than band structure predictions.

Electron-phonon coupling constant lambda_ep is approximately 1.

Additional enhancement lambda_add is about 2.1, indicating other mechanisms.

Abstract

Heat capacity measurements on the recently discovered geometrically frustrated beta-pyrochlore superconductor RbOs2O6 (Tc=6.4 K) yield a Sommerfeld coefficient of 44 mJ/(molf.u. K^2). This is about 4 times larger than the one found in band structure calculations. In order to specify the enhancement due to electron-electron interactions, we have measured the electron-phonon enhancement. By a suitable analysis, an electron-phonon coupling constant lambda_ep = 1 +/- 0.1 is derived from the specific heat jump at Tc. This leaves a significant additional lambda_add = 2.1 +/- 0.3 for enhancement due to other mechanisms, possibly related to the triangular lattice. To arrive at these results, an appropriate analysis method for bulk thermodynamic data based on the condensation energy was applied.