Ising pairing in superconducting NbSe2 atomic layers

• Published in: Nature physics Vol. 12; no. 2; pp. 139 - 143
• Main Authors: Xi, Xiaoxiang, Wang, Zefang, Zhao, Weiwei, Park, Ju-Hyun, Law, Kam Tuen, Berger, Helmuth, Forró, László, Shan, Jie, Mak, Kin Fai
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.02.2016; Nature Publishing Group
• Subjects: 140/125; 639/301/119/995; 639/301/357/1018; Atomic; Atomic physics; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Coupling; Critical field (superconductivity); Electron spin; Electrons; Ising model; letter; Locking; Magnetic properties; Mathematical and Computational Physics; Molecular; Momentum; Monolayers; Optical and Plasma Physics; Physics; Quantum phenomena; Spin-orbit interactions; Studies; Superconductivity; Superconductors; Theoretical; Transition metal compounds; Zeeman effect
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys3538

The superconducting properties of NbSe 2 as it approaches the monolayer limit are investigated by means of magnetotransport measurements, uncovering evidence of spin–momentum locking. The properties of two-dimensional transition metal dichalcogenides arising from strong spin–orbit interactions and valley-dependent Berry curvature effects have recently attracted considerable interest 1 , 2 , 3 , 4 , 5 , 6 , 7 . Although single-particle and excitonic phenomena related to spin–valley coupling have been extensively studied 1 , 3 , 4 , 5 , 6 , the effects of spin–valley coupling on collective quantum phenomena remain less well understood. Here we report the observation of superconducting monolayer NbSe 2 with an in-plane upper critical field of more than six times the Pauli paramagnetic limit, by means of magnetotransport measurements. The effect can be interpreted in terms of the competing Zeeman effect and large intrinsic spin–orbit interactions in non-centrosymmetric NbSe 2 monolayers, where the electron spin is locked to the out-of-plane direction. Our results provide strong evidence of unconventional Ising pairing protected by spin–momentum locking, and suggest further studies of non-centrosymmetric superconductivity with unique spin and valley degrees of freedom in the two-dimensional limit.