159 research outputs found
Metallic ground state in an ion-gated two-dimensional superconductor
Recently emerging two-dimensional (2D) superconductors in atomically thin layers and at heterogeneous interfaces are attracting growing interest in condensed matter physics. Here, we report that an ion-gated zirconium nitride chloride surface, exhibiting a dome-shaped phase diagram with a maximum critical temperature of 14.8 kelvin, behaves as a superconductor persisting to the 2D limit. The superconducting thickness estimated from the upper critical fields is congruent to 1.8 nanometers, which is thinner than one unit-cell. The majority of the vortex phase diagram down to 2 kelvin is occupied by a metallic state with a finite resistance, owing to the quantum creep of vortices caused by extremely weak pinning and disorder. Our findings highlight the potential of electric-field-induced superconductivity, establishing a new platform for accessing quantum phases in clean 2D superconductors.</p
Superconductivity protected by spin-valley locking in ion-gated MoS2
Symmetry-breaking has been known to play a key role in noncentrosymmetric
superconductors with strong spin-orbit-interaction (SOI). The studies, however,
have been so far mainly focused on a particular type of SOI, known as Rashba
SOI, whereby the electron spin is locked to its momentum at a right-angle,
thereby leading to an in-planar helical spin texture. Here we discuss
electric-field-induced superconductivity in molybdenum disulphide (MoS2), which
exhibits a fundamentally different type of intrinsic SOI manifested by an
out-of-plane Zeeman-type spin polarization of energy valleys. We find an upper
critical field of approximately 52 T at 1.5 K, which indicates an enhancement
of the Pauli limit by a factor of four as compared to that in centrosymmetric
conventional superconductors. Using realistic tight-binding calculations, we
reveal that this unusual behaviour is due to an inter-valley pairing that is
symmetrically protected by Zeeman-type spin-valley locking against external
magnetic fields. Our study sheds a new light on the interplay of inversion
asymmetry with SOI in confined geometries, and its unprecedented role in
superconductivity.Comment: 37 pages, 11 figures,
http://meetings.aps.org/Meeting/MAR15/Session/G11.1
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