Theory of superconductivity in hole-doped monolayer MoS2

Abstract

We theoretically investigate the Cooper-pair symmetry to be realized in hole-doped monolayer MoS2 by solving linearized BCS gap equations on the three-orbital attractive Hubbard-like model in the presence of the atomic spin-orbit coupling. In hole-doped monolayer MoS2, both spin-orbit coupling and the multi-orbital effects are more prominent than those of electron-doped system. Near the valence band edge, the Fermi surfaces are composed of three different types of hole pockets, namely, one mainly consisting of the almost spin-degenerate |d z 2 orbital near Γ point, and the others of the spin-split upper and lower bands near K and K ′ points arising from the |d x 2 −y 2 and |dxy orbitals. The number of relevant Fermi pockets increases with increase of the doping. At very low doping, the upper split bands of |d x 2 −y 2 and |dxy are concerned, yielding extremely low Tc due to small density of states of the split bands. For further doping, the conventional spin-singlet state (SS) appears in the Γ pocket, which has a mixture of the spin-triplet (orbital-singlet) (ST-OS) and spinsinglet (orbital-triplet) (SS-OT) states in the K and K ′ pockets. The ratio of the mixture depends on the relative strength of the interactions, and the sign of the exchange interactions. Moderately strong ferromagnetic exchange interactions even lead to the pairing state with the dominant ST-OS state over the conventional SS one. With these observations, we expect that the fascinating pairing with relatively high Tc emerges at high doping that involves all the three Fermi pockets.

Experimental consequences of Bogoliubov Fermi surfaces

“…The pairing of electrons with additional internal degrees of freedom resulting, e.g., from different orbitals or basis sites, can lead to qualitatively new pairing states. Such pairing states have for example been proposed for iron-based superconductors [2][3][4][5][6][7][8][9], Cu x Bi 2 Se 3 [10,11], cubic systems such as half-Heusler compounds [12][13][14][15][16][17][18][19][20][21], UPt 3 [22,23], transition-metal dichalcogenides [24,25], and twisted bilayer graphene [26][27][28]. It has been shown that in centrosymmetric multiband superconductors that break TRS, point and line nodes are generically "inflated," by interband pairing, into Fermi surfaces of Bogoliubov quasiparticles [29,30].…”

Engineering nodal topological phases in Ising superconductors by magnetic superstructures

“…The rich electronic properties of TMDs have stimulated several proposals for topological and unconventional superconductivity [16][17][18][19][20][21][22][23][24][25][26]. In [27,28] it was proposed that an Ising spin-orbit coupled monolayer TMD (e.g.…”

Spin and Orbital Susceptibilities in Hole-Doped Monolayer Superconductor MoS2 with Ising-Type Spin–Orbit Coupling

“…Since the Ising-type SOC locks the electron spin in the out-of-plane direction, the in-plane spin susceptibility is expected to be enhanced in contrast to the Rashba SOC systems. The layered transition-metal dichalcogenides (TMDCs), MX 2 (M = Mo, W and X = S, Se, and Te) are new platform for exotic superconductivity in context of noncentrosymmetric Ising-type spin-orbit physics [19][20][21][22][23][24][25]. The representative material of the TMDCs, MoS 2 , shows the electric-field-induced electron-doped superconductivity, whose in-plane upper critical field is about three times larger than the Pauli limit at 1.5 K due to the Isingtype SOC [26,27].…”

“…The representative material of the TMDCs, MoS 2 , shows the electric-field-induced electron-doped superconductivity, whose in-plane upper critical field is about three times larger than the Pauli limit at 1.5 K due to the Isingtype SOC [26,27]. The hole-doped TMDCs would be much interesting because of the multi-orbital features in the valence bands originating from the transition-metal d orbitals with relatively strong SOC [23,25]. Thin layer NbSe 2 and TaS 2 belonging to a family of TMDCs (the former can be viewed as heavily hole-doped MoS 2 ) also exhibit the large in-plane upper critical field.…”