Heat Capacity of Single Crystal CuxTiSe2 Superconductors

TL;DR

This study measures the heat capacity of Cu$_x$TiSe$_2$ single crystals across various doping levels, revealing a consistent single s-wave superconducting gap with intermediate coupling strength, regardless of charge density wave suppression.

Contribution

It provides the first comprehensive heat capacity analysis of Cu$_x$TiSe$_2$ across different doping levels, demonstrating a universal superconducting gap structure.

Findings

Single s-wave gap observed across all doping levels.

Superconducting gap ratio 2Δ/kBTc = 3.7, indicating intermediate coupling.

Charge density wave order does not affect the superconducting gap structure.

Abstract

We present heat capacity measurements on a series of superconducting Cu$_x$TiSe$_2$ single crystals with different Cu content down to 600 mK and up to 1 T performed by ac microcalorimetry. The samples cover a large portion of the phase diagram from an underdoped to a slightly overdoped region with an increasing superconducting critical temperature and the charge density wave (CDW) order gradually suppressed. The electronic heat capacity as a function of normalized temperature $T/T_c$ shows no difference regardless of the concentration of copper, i.e., regardless of how much the CDW order is developed in the samples. The data analysis reveals consistently a single s-wave gap with an intermediate coupling strength $2\Delta/k_BT_c$ = 3.7 for all samples.