title: Spin-valley locking in the normal state of a transition-metal dichalcogenide superconductor.
abstract: Metallic transition-metal dichalcogenides (TMDCs) are benchmark systems for studying and controlling intertwined electronic orders in solids, with superconductivity developing from a charge-density wave state. The interplay between such phases is thought to play a critical role in the unconventional superconductivity of cuprates, Fe-based and heavy-fermion systems, yet even for the more moderately-correlated TMDCs, their nature and origins have proved controversial. Here, we study a prototypical example, 2H-NbSe2, by spin- and angle-resolved photoemission and first-principles theory. We find that the normal state, from which its hallmark collective phases emerge, is characterized by quasiparticles whose spin is locked to their valley pseudospin. This results from a combination of strong spin-orbit interactions and local inversion symmetry breaking, while interlayer coupling further drives a rich three-dimensional momentum dependence of the underlying Fermi-surface spin texture. These findings necessitate a re-investigation of the nature of charge order and superconducting pairing in NbSe2 and related TMDCs.
authors.affiliation: SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK.
authors.forename: L
authors.initials: L
authors.lastname: Bawden
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.
authors.forename: S P
authors.initials: SP
authors.lastname: Cooil
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.
authors.forename: F
authors.initials: F
authors.lastname: Mazzola
authors.affiliation: SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK.|Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Riley
authors.affiliation: SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK.
authors.forename: L J
authors.initials: LJ
authors.lastname: Collins-McIntyre
authors.affiliation: SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK.|Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01217 Dresden, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Sunko
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.
authors.forename: K W B
authors.initials: KW
authors.lastname: Hunvik
authors.affiliation: MAX IV Laboratory, Lund University, PO Box 118, 221 00 Lund, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Leandersson
authors.affiliation: MAX IV Laboratory, Lund University, PO Box 118, 221 00 Lund, Sweden.
authors.forename: C M
authors.initials: CM
authors.lastname: Polley
authors.affiliation: MAX IV Laboratory, Lund University, PO Box 118, 221 00 Lund, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Balasubramanian
authors.affiliation: Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK.
authors.forename: T K
authors.initials: TK
authors.lastname: Kim
authors.affiliation: Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK.
authors.forename: M
authors.initials: M
authors.lastname: Hoesch
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.
authors.forename: J W
authors.initials: JW
authors.lastname: Wells
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: G
authors.initials: G
authors.lastname: Balakrishnan
authors.affiliation: Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan.|RIKEN center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.
authors.forename: M S
authors.initials: MS
authors.lastname: Bahramy
authors.affiliation: SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK.
authors.forename: P D C
authors.initials: PD
authors.lastname: King