Extreme orbital $ab$-plane upper critical fields far beyond Pauli limit in 4$H_{b}$-Ta(S, Se)$_{2}$ bulk crystals

Abstract: Transition metal disulfides 4$H_{b}$-Ta(S, Se)${2}$ with natural heterostructure of 1${T}$- and 1${H}$-Ta(S, Se)${2}$ layers have became the focus of correlated materials their unique combinations of Mott physics and possible topological superconductivity. In this work, we study the upper critical fields $\mu_{0}H_{c2}$ of 4$H_{b}$-TaS${2}$ and 4$H{b}$-TaS${1.99}$Se${0.01}$ single crystals systematically. Transport measurements up to 35 T show that both of ${ab}$-plane and ${c}$-axis upper critical fields ($\mu_{0}H_{c2,ab}$ and $\mu_{0}H_{c2,c}$) for 4$H_{b}$-TaS${2}$ and 4$H{b}$-TaS${1.99}$Se${0.01}$ exhibit a linear temperature dependent behavior down to 0.3 K, suggesting the three-dimensional superconductivity with dominant orbital depairing mechanism in bulk 4$H_{b}$-Ta(S, Se)${2}$. However, the zero-temperature $\mu{0}H_{c2,ab}$(0) for both crystals are far beyond the Pauli paramagnetic limit $\mu_{0}H{\rm_{P}}$. It could be explained by the effects of spin-momentum locking in 1$H$-Ta(S, Se)$_{2}$ layers with local inversion symmetry broken and the relatively weak intersublattice interaction between 1$H$ layers due to the existence of 1$T$ layers.