Superconductivity vs. Charge density wave in CuxTiSe2 single-crystals
We present heat capacity measurements on a series of superconducting CuxTiSe2 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 superconducting electronic
heat capacity as a function of normalized temperature T/Tc 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 2Δ/kBTc ≈ 3.7 for all samples.
Figure 1: Superconducting electronic heat capacity of sample A (open symbols) and corresponding single-gap α-model fit (thick line), compared to that of NbS2 (solid symbols) and α-model fit corresponding to the presence of two energy gaps or one anisotropic gap (thin line). Upper inset: Angular dependence of Tc at 0.15 T (symbols) and a Ginzburgh-Landau fit for a single-gap superconductor (line). Lower inset: Deviation function—(Tc2/Tc2GL)2 for sample A (open symbols) and Hc2/Hc2GL)2 for NbS2 solid symbols); the line is a guide to the eye.
Figure 2: The temperature dependence ΔC/T of samples A, B, C, and D in a temperature scale normalized to the Tc of each sample. Inset: The phase diagram as proposed by Morosan et al. and the critical temperature of our samples with respect to their copper content (large symbols).