Emergence of Quasi-two-dimensional Superconductivity in W-doped Bulk Noncentrosymmetric 3$R$-TaSe$_2$

Abstract

Noncentrosymmetric transition-metal dichalcogenides offer a rich environment for the study of unconventional superconducting phenomena. Here, we present a comprehensive analysis of single-crystalline W-doped 3$R$-TaSe$_2$, revealing weakly coupled anisotropic unconventional superconductivity at $T_c$ = 2.82(2) K, with an in-plane upper critical field exceeding the Pauli limit by 1.7 times. The angular dependence of the upper critical field, along with the observation of a Berezinskii-Kosterlitz-Thouless transition, reveals quasi-two-dimensional superconductivity. Crucially, magnetotransport reveals a distinct two-fold rotational symmetry within the superconducting state under in-plane fields, breaking the underlying three-fold lattice symmetry. These findings establish W-doped $3R\text{-TaSe}_2$ as a bulk model system for exploring intrinsic low-dimensional superconductivity and broken rotational symmetry, thus opening new directions for future quantum technologies.