Abstract
Abstract
We report a detailed study of moderate-coupling superconductivity coexisting with charge-density-wave (CDW) order in single-crystalline
$$1T\text {-Cu}_x\text {TiSe}_2$$
(
$$x = 0\text {--}0.1$$
) down to
$$60\text { mK}$$
. Millikelvin specific-heat measurements on underdoped samples reveal a sharp superconducting anomaly with a vanishing residual electronic specific heat coefficient (
$$\gamma _r \rightarrow 0$$
) in the ground state, signaling a fully gapped superconducting state clear of uncondensed normal electrons. Concurrently, distinct thermodynamic anomalies near
$$200\text { K}$$
and
$$25\text { K}$$
confirm the robust persistence of CDW order in the undoped and underdoped regimes, respectively. Upper critical-field measurements display a nearly temperature-independent anisotropy,
$$H_{\text {c2}}^{ab}/H_{\text {c2}}^c \simeq 1.7$$
, consistent with conventional single-gap
s
-wave pairing. Analysis of the reduced specific-heat jump,
$$\Delta C_{\text {el}}/\gamma _n T_{\text {c}}$$
, alongside the Werthamer-Helfand-Hohenberg (WHH) framework, establishes moderate electron-phonon coupling (
$$\lambda _{\text {el-ph}} = 0.62$$
) and conventional superconductivity coexisting with a partially suppressed CDW state. These findings present
$$1T\text {-Cu}_x\text {TiSe}_2$$
as a clean model platform for investigating the systematic modulation of competing quantum phases via transition-metal intercalation, offering a strategic framework for the architectural design of low-dimensional functional electronics.