Negative electronic compressibility and nanoscale inhomogeneity in ionic-liquid gated two-dimensional superconductors

Abstract

When the electron density of highly crystalline thin films is tuned by chemical doping or ionic liq- uid gating, interesting effects appear including unconventional superconductivity, sizeable spin-orbit coupling, competition with charge-density waves, and a debated low-temperature metallic state that seems to avoid the superconducting or insulating fate of standard two-dimensional electron systems. Some experiments also find a marked tendency to a negative electronic compressibility. We suggest that this indicates an inclination for electronic phase separation resulting in a nanoscopic inhomo- geneity. Although the mild modulation of the inhomogeneous landscape is compatible with a high electron mobility in the metallic state, this intrinsically inhomogeneous character is highlighted by the peculiar behaviour of the metal-to-superconductor transition. Modelling the system with super- conducting puddles embedded in a metallic matrix, we fit the peculiar resistance vs. temperature curves of systems like TiSe2, MoS2, and ZrNCl. In this framework also the low-temperature debated metallic state finds a natural explanation in terms of the pristine metallic background embedding non-percolating superconducting clusters. An intrinsically inhomogeneous character naturally raises the question of the formation mechanism(s). We propose a mechanism based on the interplay be- tween electrons and the charges of the gating ionic liquid.

substantially modified presentation: 12 pages 7 figures

References in corpus (10)

• Highly crystalline 2D superconductors
• Controlling many-body states by the electric-field effect in a two-dimensional material
• Metallic ground state in an ion-gated two-dimensional superconductor
• Electrostatically Induced Superconductivity at the Surface of WS${}_2$
• Influence of domain walls in the incommensurate charge density wave state of Cu intercalated 1$T$-TiSe${}_2$
• Quantum phase transitions in highly crystalline two-dimensional superconductors
• Intrinsic instability of electronic interfaces with strong Rashba coupling
• Observation of Quantum Griffiths Singularity and Ferromagnetism at Superconducting LaAlO3/SrTiO3(110) Interface
• Competition between electron pairing and phase coherence in superconducting interfaces
• Possible mechanisms of electronic phase separation in oxide interfaces

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• Direct evidence for two-gap superconductivity in hydrogen-intercalated titanium diselenide