Single gap superconductivity in beta-Bi2Pd

TL;DR

This study investigates beta-Bi2Pd superconductors and finds that, despite previous suggestions of multi-gap behavior, it exhibits conventional single-gap s-wave superconductivity based on various bulk and surface measurements.

Contribution

The paper provides comprehensive experimental evidence showing beta-Bi2Pd is a single-gap superconductor, challenging earlier multi-gap claims.

Findings

Calorimetric measurements show a single superconducting gap.

Upper critical field and lower critical field analyses indicate single-gap behavior.

Scanning tunneling spectroscopy detects a standard BCS density of states.

Abstract

beta-Bi2Pd compound has been proposed as another example of a multi-gap superconductor [Y. Imai et al., J. Phys. Soc. Jap. 81, 113708 (2012)]. Here, we report on measurements of several important physical quantities capable to show a presence of multiple energy gaps on our superconducting single crystals of beta-Bi2Pd with the critical temperature Tc close to 5 K. The calorimetric study via a sensitive ac technique shows a sharp anomaly at the superconducting transition, however only a single energy gap is detected. Also other characteristics inferred from calorimetric measurements as the field dependence of the Sommerfeld coefficient and the temperature and angular dependence of the upper critical magnetic field point unequivocally to standard single s-wave gap superconductivity. The Hall-probe magnetometry provides the same result from the analysis of the temperature dependence of the lower critical field. A single-gapped BCS density of states is detected by the scanning tunneling spectroscopy measurements. Then, the bulk as well as the surface sensitive probes evidence a standard conventional superconductivity in this system where the topologically protected surface states have been recently detected by ARPES [M. Sakano et al., Nature Comm. 6, 8595 (2015)] .