Two-fold symmetric superconductivity in few-layer NbSe2

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) have been attracting significant interest 1-8 due to a range of properties, such as layer-dependent inversion symmetry, valleycontrasted Berry curvatures, and strong spin-orbit coupling (SOC). Of particular interest is niobium diselenide (NbSe 2 ), whose superconducting state in few-layer samples is profoundly affected by an unusual type of SOC called Ising SOC 7 . Combined with the reduced dimensionality, the latter stabilizes the superconducting state against magnetic fields up to ~35 T and could lead to other exotic properties such as nodal and crystalline topological superconductivity 9-14 . Here, we report transport measurements of few-layer NbSe 2 under inplane external magnetic fields, revealing an unexpected two-fold rotational symmetry of the superconducting state. In contrast to the three-fold symmetry of the lattice, we observe that

Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe$_2$

“…The model proposed in Ref. [32] relies on the presence of pwave components in the pairing function, which might as well play a role in the anisotropy of the diode effect we observe here.…”

“…It is clear that further studies are needed to elucidate the role of the in-plane field in superconducting TMDs, which might be related to a possible Rashba-like component of the SOI [29,30]. In NbSe 2 such Rashba components can arise, e.g., due to ripples in the crystal [31] formed when stamping NbSe 2 on hBN [24], or due to the substrate [32]. The existence of a weak Rashba SOI component in NbSe 2 has, for example, been invoked to explain the apparent two-fold anisotropy of the magnetoresistance as a function of in-plane magnetic field [32].…”

“…In NbSe 2 such Rashba components can arise, e.g., due to ripples in the crystal [31] formed when stamping NbSe 2 on hBN [24], or due to the substrate [32]. The existence of a weak Rashba SOI component in NbSe 2 has, for example, been invoked to explain the apparent two-fold anisotropy of the magnetoresistance as a function of in-plane magnetic field [32]. The model proposed in Ref.…”

Controlling charge and spin transport in an Ising-superconductor Josephson junction

“…However, it is nontrivial to observe since spin-singlet superconductivity is typically destroyed by strong magnetic fields through orbital [1] or Zeeman-induced pair breaking [2,3]. Recently, superconductivity was experimentally realized in various two-dimensional transition-metal dichalcogenides [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In these materials, the orbital depairing effect from an in-plane magnetic field is suppressed due to their twodimensional nature.…”

“…Thus, these so-called Ising superconductors provide an ideal laboratory to study the interplay between superconductivity and ferromagnetism. Applying an in-plane magnetic field can induce triplet correlations [19,[24][25][26][27][28], mirage gaps [28], or a two-fold rotational symmetry of the superconducting state [14,15].…”