Inducing Strong Superconductivity in WTe₂ by a Proximity Effect

Abstract

The search for proximity-induced superconductivity in topological materials has generated widespread interest in the condensed matter physics community. The superconducting states inheriting nontrivial topology at interfaces are expected to exhibit exotic phenomena such as topological superconductivity and Majorana zero modes, which hold promise for applications in quantum computation. However, a practical realization of such hybrid structures based on topological semimetals and superconductors has hitherto been limited. Here, we report the strong proximity-induced superconductivity in type-II Weyl semimetal WTe, in a van der Waals hybrid structure obtained by mechanically transferring NbSe onto various thicknesses of WTe. When the WTe thickness ( t) reaches 21 nm, the superconducting transition occurs around the critical temperature ( T) of NbSe with a gap amplitude (Δ) of 0.38 meV and an unexpected ultralong proximity length ( l) up to 7 μm. With the thicker 42 nm WTe layer, however, the proximity effect yields T ≈ 1.2 K, Δ = 0.07 meV, and a short l of less than 1 μm. Our theoretical calculations, based on the Bogoliubov-de Gennes equations in the clean limit, predict that the induced superconducting gap is a sizable fraction of the NbSe superconducting one when t is less than 30 nm and then decreases quickly as t increases. This agrees qualitatively well with the experiments. Such observations form a basis in the search for superconducting phases in topological semimetals.

Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2

“…3c. In the thick limit (N ≥3), we find that observed behavior shows excellent agreement with transport measurements of proximity-induced superconductivity in bulk WTe 2 flakes [24,25], extending the previous studies to the ultra-thin limit (see Supplementary Materials). For N < 3, we observe a more rapid decrease of the extracted gap as function of N which may be explained by the strong variation of the electronic structure of the WTe 2 in this thickness range, resulting in a larger mismatch of the WTe 2 and NbSe 2 Fermi surfaces and therefore a stronger dependence of the induced gap on N [26].…”

“…3c we also plot the 4.7 K WTe 2 proximity gaps found from this more detailed fitting and find no significant deviation from those previously determined by fitting the single-gap BCS theory. This observation is in qualitative agreement with theory which predicts the proximity-induced gap to approach that of the NbSe 2 as the WTe 2 layer thickness goes to zero [24].Finally, we consider the lateral variation of the superconducting gap from within the ML WTe 2 to the region occupied by the edge state. Figure 4c shows dI/dV spectra taken at 2.8 K along a line approaching the physical edge of the WTe 2 monolayer, similar to that shown in Fig.…”

“…The exfoliation procedure naturally produces terraces of varying thickness in our samples, enabling thickness-dependent gap measurement within a single sample. Figure 3b shows the superconducting gap measured on terraces of different numbers of WTe 2 layers N , revealing that the gap decreases with increasing N , as expected for decaying superconducting correlations near the boundary of a superconducting-metal interface [24]. To quantify this behavior, we fit the BCS model to each of the spectra in Fig.…”

Van der Waals 2D Transition Metal Tellurides

“…Several methods have been utilized for the transition into a superconductor, for instance, chemical doping, and proximity effect . Chemical doping through alkali intercalation is an efficient method to influence the superconductivity of TMTs, accompanying with the lattice strain and electron‐doping effect .…”

Engineering nodal topological phases in Ising superconductors by magnetic superstructures

“…Our proposal is based on two recent breakthroughs, the observation of Ising superconductivity in transition metal dichalcogenides (TMDs) [5][6][7][8][9][10][11][12] and the discovery of novel techniques to fabricate 2d magnetic structures on van der Waals materials [13]. Due to the inversion-breaking structure of monolayers, the quasiparticles experience strong valley-dependent out-of-plane spin-orbit coupling (SOC).…”