Spin-valley locking in the normal state of a transition-metal dichalcogenide superconductor
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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 andorigins 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 characterised 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 spintexture. These findings necessitate a re-investigation of the nature of charge order and superconducting pairing in NbSe2 and related TMDCs.
Bawden , L , Cooil , S P , Riley , J M , Collins-McIntyre , L J , Sunko , V , Hunvik , K , Leandersson , M , Polley , C M , Balasubramanian , T , Kim , T K , Hoesch , M , Wells , J W , Balakrishnan , G , Bahramy , M S & King , P D 2016 , ' Spin-valley locking in the normal state of a transition-metal dichalcogenide superconductor ' , Nature Communications , vol. 7 , 11711 . https://doi.org/10.1038/ncomms11711
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