Transport evidence of asymmetric spin–orbit coupling in few-layer superconducting 1Td-MoTe2

Abstract

Two-dimensional transition metal dichalcogenides MX 2 ( M = W, Mo, Nb, and X = Te, Se, S) with strong spin–orbit coupling possess plenty of novel physics including superconductivity. Due to the Ising spin–orbit coupling, monolayer NbSe 2 and gated MoS 2 of 2 H structure can realize the Ising superconductivity, which manifests itself with in-plane upper critical field far exceeding Pauli paramagnetic limit. Surprisingly, we find that a few-layer 1 T d structure MoTe 2 also exhibits an in-plane upper critical field which goes beyond the Pauli paramagnetic limit. Importantly, the in-plane upper critical field shows an emergent two-fold symmetry which is different from the isotropic in-plane upper critical field in 2 H transition metal dichalcogenides. We show that this is a result of an asymmetric spin–orbit coupling in 1 T d transition metal dichalcogenides. Our work provides transport evidence of a new type of asymmetric spin–orbit coupling in transition metal dichalcogenides which may give rise to novel superconducting and spin transport properties.

Magnetoelectric effects in gyrotropic superconductors

“…In recent years, many noncentrosymmetric superconductors such as superconductors with chiral lattice structures [14][15][16][17], and superconducting transition metal dichalcogenides (TMDs) [18][19][20][21][22][23][24] have been discovered. Since these emergent noncentrosymmetric superconductors have different crystal symmetries, the SOC in these materials has different forms.…”

“…For example, superconductors with point group symmetry T and O, which belong to chiral (or enantiomorphic) point groups, have isotropic SOC in the form of v p • σ, where p is momentum, σ is the Pauli matrices, and v is the SOC strength [25]. On the other hand, multilayer 1T d -structure WTe 2 and MoTe 2 possess anisotropic SOC [24]. For atomically thin monolayer 2H-MoS 2 and 2H-NbSe 2 , Ising SOC [18][19][20][26][27][28] is present which pins electron spins to the out-of-plane directions.…”

Van der Waals 2D Transition Metal Tellurides

“…In recent year, TMTs have gained much attention with robust magnetic fields' susceptibility originated from the strong spin–orbit coupling . Few‐layer WTe 2 has the broken in‐plane mirror symmetry and strong Ising spin–orbit coupling, which induced the twofold symmetry in‐plane upper critical field beyond Pauli paramagnetic limit . Jarillo‐Herrero and co‐workers reported the electric field tunable intrinsic superconductivity of monolayer WTe 2 .…”

Phase Transition and Superconductivity Enhancement in Se‐Substituted MoTe2 Thin Films

“…Furthermore, no appreciable thermal hysteresis was observed in the temperature-dependent sheet resistance R s (T) curves ( Supplementary Figure 3) in superconducting MoSe x Te 2-x samples with x≤1.0, signifying no phase transition from 1T' to T d phase occurs 11,31 . Combined with the above STEM and XPS results, we can conclude that the T d phase (for x≤0.8) and 1T' phase (for x≤1.1)…”

“…The methods involve heating 19,20 , element doping 21,22 , chemical modifications 23,24 , laser irradiation 25 , strain 26 , and electrostatic gating 27 . Recently, the 1T'-to-T d phase transition driven by pressure 28 , thermo 29,30 , as well as dimensionality 11,31 in MX 2 has been reported. However, these strategies can only realize 2H-to-1T' or 1T'-to-T d phase transition.…”