Nature of the quantum metal in a two-dimensional crystalline superconductor

• Published in: Nature physics Vol. 12; no. 3; pp. 208 - 212
• Main Authors: Tsen, A. W., Hunt, B., Kim, Y. D., Yuan, Z. J., Jia, S., Cava, R. J., Hone, J., Kim, P., Dean, C. R., Pasupathy, A. N.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.03.2016; Nature Publishing Group
• Subjects: 639/301/357/1018; 639/766/119/1003; Atmosphere; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Crystal structure; Crystallization; Electrons; Fluctuation; Inert atmospheres; letter; Low temperature; Magnetic fields; Mathematical and Computational Physics; Metals; Molecular; Optical and Plasma Physics; Phase diagrams; Physics; Quantum physics; Superconductivity; Superconductors; Theoretical; Thin films; Two dimensional; Two dimensional materials
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys3579

Owing to electron localization, two-dimensional materials are not expected to be metallic at low temperatures, but a field-induced quantum metal phase emerges in NbSe 2 , whose behaviour is consistent with the Bose-metal model. Two-dimensional (2D) materials are not expected to be metals at low temperature owing to electron localization 1 . Consistent with this, pioneering studies on thin films reported only superconducting and insulating ground states, with a direct transition between the two as a function of disorder or magnetic field 2 , 3 , 4 , 5 , 6 . However, more recent works have revealed the presence of an intermediate quantum metallic state occupying a substantial region of the phase diagram 7 , 8 , 9 , 10 , whose nature is intensely debated 11 , 12 , 13 , 14 , 15 , 16 , 17 . Here, we observe such a state in the disorder-free limit of a crystalline 2D superconductor, produced by mechanical co-lamination of NbSe 2 in an inert atmosphere. Under a small perpendicular magnetic field, we induce a transition from superconductor to the quantum metal. We find a unique power-law scaling with field in this phase, which is consistent with the Bose-metal model where metallic behaviour arises from strong phase fluctuations caused by the magnetic field 11 , 12 , 13 , 14 .