Alexandra Palacio-Morales

Abstract:

Transition metal dichalcogenides (TMD) display a rich variety of electronic orders such as spin and charge orders, Ising superconductivity and topological properties. In the monolayer limit, these properties can be partially controlled by electric gates and adatoms deposition reaching a doping limit of 1·10¹⁴cm^-2 in NbSe₂ [1]. Monolayer NbSe₂ exhibits coexistence of a 3x3 charge density wave (CDW) and superconductivity with strong Ising spin orbit coupling, which locks the spin-momentum in the out-of-plane direction fully polarizing the bands at K and K’ [2]. Therefore, monolayer NbSe₂ superconductor shows an in-plane critical magnetic field much larger than the paramagnetic limit [3]. Moreover, theoretical studies in TMDs point out that a tuning of the Fermi energy may induce topological superconductivity carry out by the polarized bands [4].

Here, I present a new TMD-based system, (LaSe)_1.14(NbSe₂)₂: a misfit compound formed from the alternation of blocks of 2H-NbSe₂ and unit cells of LaSe rock salt. I will show that the band structure of the system behaves as monolayer NbSe₂ with a rigid doping of electrons per Nb. This doping, far beyond the doping limits obtained so far, changes the CDW periodicity into a 2x2 with very short coherence length [5] and introduces signatures of unconventional pairing.

References:

[1] X. Xi et al., Physical Review Letters 117, 106801 (2016)

[2] M. M. Ugeda et al., Nature Physics 12, 92 (2016)

[3] X. Xi et al., Nature Physics 12, 139-143 (2016)

[4] Y.-T. Hsu et al., Nature Communications 8, 14985 (2017)

[5] R. T. Leriche et al., Advance Functional Materials 31, 2007706 (2020)