Journal Article

Spin–valley locking in the normal state of a transition-metal dichalcogenide superconductor

Balasubramanian, T., King, P. D. C., Collins-McIntyre, L. J., Balakrishnan, G., Wells, J. W., Cooil, S. P., Sunko, V., Hunvik, K. W. B., Riley, J. M., Mazzola, F., Leandersson, M., Bahramy, M. S., Hoesch, M., Kim, T. K., Bawden, L., Polley, C. M.

2016

Overview

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-NbSe 2 , 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 NbSe 2 and related TMDCs. The origin of intertwined electronic orders in transition-metal dichalcogenides has long been debated. Here, Bawden et al . report that the normal state, from which these phases emerge, is unexpectedly spin-polarized, with spins locked to both valley and layer pseudospins.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 639/301/119/1001 / 639/301/119/1003 / Electrons / Humanities and Social Sciences / multidisciplinary / Physics / Science / Symmetry