Thickness-Dependent Tunneling Spectra of 2H-TaS₂

Transition metal dichalcogenide (TMD) superconductors have attracted much attention, in part due to the ease with which thin flakes can be mechanically exfoliated, and due to their strong Ising spin-orbit coupling (ISOC), expected unconventional electron pairing and topological states, making them a focus of interest in recent years.

2H-TaS₂ is a superconducting TMD with critical temperature T_c=800mK in bulk flakes, and greatly enhanced T_c in thinner samples, in stark contrast to the extensively studied TMD superconductor 2H-NbSe₂ which displays the opposite trend.

We measure the tunneling spectra of 2H-TaS₂ flakes of various thicknesses ranging from bulk to monolayer by fabricating van der Waals (vdW) tunnel junction heterostructures using mechanical exfoliation and dry transfer. The observed tunneling spectra cannot be fitted with a simple BCS model, and the superconducting gap increases from 160μeV in bulk samples to 480μeV in our thinnest samples.

We measure the spectra in different temperatures and magnetic fields in in-plane and out-of-plane orientations, revealing hints of two-band superconductivity, anisotropy of the order parameter and Ising protection of superconductivity up to a field of 8.5T in-plane in thin samples.

These measurements are the first detailed mapping of the thickness dependence of the spectrum of 2H-TaS₂ and may serve as the first step in its integration into the arsenal of vdW materials used in the fabrication of further, potentially more complicated nano-devices.