Two-dimensional materials exhibit unique properties, particularly in the thin limit. Td-MoTe2 is a transition metal dichalcogenide known as a type-II Weyl semimetal in the bulk form. It becomes superconducting at low temperatures, but the low critical temperature (Tc) around 100 mK makes it difficult to investigate its superconducting properties for pursuing signatures of topological superconductivity. On the other hand, a significant enhancement of Tc has recently been reported by decreasing the thickness of Td-MoTe2, the origin of which remains unclear. Td-MoTe2 is also attractive in spintronics owing to the low crystal symmetry and strong spin-orbit interaction, which generate unconventional spin Hall effect and spin-orbit torques. While there exist many studies on electronic and spintronic properties of bulk Td-MoTe2, few-layer Td-MoTe2 has scarcely been explored due to the instability of the material in the atmosphere and experimental difficulties in the device fabrication.
In this talk, focusing on superconducting and spin transport properties, I will first show the thickness dependence of superconducting properties in few-layer Td-MoTe2, and discuss a possible pairing symmetry by comparing the experimental data with the first principles calculation results. Exploiting enhanced superconductivity and the low crystal symmetry, we successfully demonstrated the giant superconducting nonreciprocal transport driven by the ratchet-like motion of superconducting vortices, and the gate modulation of nonreciprocal signals by reducing the sample thicknesses [1, 2]. In the second part, I will introduce unique spintronic properties of Td-MoTe2, and present our recent results on spin transport revealed by weak antilocalization measurements in few-layer samples, where spin relaxation time is also gate tunable, and a factor of three variation is possible in the monolayer limit.
[1] T. Wakamura et al., “Gate-tunable giant superconducting nonreciprocal transport in few-layer Td-MoTe2” Phys. Rev. Research. 6, 013132 (2024).
[2] T. Wakamura et al., “Superconducting properties of few-layer Td-MoTe2”, submitted.