Single-gap s-wave superconductivity in Cu$_x$TiSe$_2$

TL;DR

This study provides evidence that Cu$_x$TiSe$_2$ exhibits conventional s-wave superconductivity with a single gap, based on thermal conductivity measurements indicating a fully gapped Fermi surface.

Contribution

The paper demonstrates that Cu$_x$TiSe$_2$ has a single-gap s-wave superconducting state, contrasting with related materials showing multiple gaps.

Findings

No residual linear term in thermal conductivity at low T.

Magnetic field dependence consistent with a single, uniform gap.

Se 4$p$ band is below Fermi level, with Ti 3$d$ band responsible for superconductivity.

Abstract

The in-plane thermal conductivity $\kappa$ of the layered superconductor Cu$_x$TiSe$_2$ was measured down to temperatures as low as $T_c$/40, at $x$ = 0.06 near where the CDW order vanishes. The absence of a residual linear term at $ T \to 0$ is strong evidence for conventional s-wave superconductivity in this system. This is further supported by the slow magnetic field dependence, also consistent with a single gap, of uniform magnitude across the Fermi surface. Comparison with the closely related material NbSe$_2$, where the superconducting gap is three times larger on the Nb 4$d$ band than on the Se 4$p$ band, suggests that in Cu$_{0.06}$TiSe$_2$ the Se 4$p$ band is below the Fermi level and the Ti 3$d$ band is alone responsible for the superconductivity.