Nanocalorimetric Evidence for Nematic Superconductivity in the Doped Topological Insulator Sr$_{0.1}$Bi$_{2}$Se$_{3}$

TL;DR

This study provides bulk thermodynamic evidence for nematic superconductivity in Sr$_{0.1}$Bi$_{2}$Se$_{3}$, revealing a two-fold gap symmetry and a symmetry-breaking energy term, indicating a topological, nematic superconducting phase.

Contribution

First thermodynamic demonstration of nematic superconductivity in doped Bi$_2$Se$_3$ using high-resolution calorimetry, identifying a symmetry-breaking energy term and estimating its strength.

Findings

Evidence of two-fold rotational symmetry in the superconducting gap.

Detection of a small specific heat anomaly confirming bulk superconductivity.

Large basal-plane anisotropy of $H_{c2}$ attributed to nematic phase.

Abstract

Spontaneous rotational-symmetry breaking in the superconducting state of doped $\mathrm{Bi}_2\mathrm{Se}_3$ has attracted significant attention as an indicator for topological superconductivity. In this paper, high-resolution calorimetry of the single-crystal $\mathrm{Sr}_{0.1}\mathrm{Bi}_2\mathrm{Se}_3$ provides unequivocal evidence of a two-fold rotational symmetry in the superconducting gap by a \emph{bulk thermodynamic} probe, a fingerprint of nematic superconductivity. The extremely small specific heat anomaly resolved with our high-sensitivity technique is consistent with the material's low carrier concentration proving bulk superconductivity. The large basal-plane anisotropy of $H_{c2}$ is attributed to a nematic phase of a two-component topological gap structure $\vec{\eta} = (\eta_{1}, \eta_{2})$ and caused by a symmetry-breaking energy term $\delta (|\eta_{1}|^{2} - |\eta_{2}|^{2}) T_{c}$. A quantitative analysis of our data excludes more conventional sources of this two-fold anisotropy and provides the first estimate for the symmetry-breaking strength $\delta \approx 0.1$, a value that points to an onset transition of the second order parameter component below 2K.