Abstract
Unusual metallic states involving breakdown of the standard Fermi-liquid picture of long-lived quasiparticles in well-defined band states emerge at low temperatures near correlation-driven Mott transitions. Prominent examples are ill-understood metallic states in d- and f-band compounds near Mott-like transitions. Finding of superconductivity in solid O2 on the border of an insulator-metal transition at high pressures close to 96 GPa is thus truly remarkable. Neither the insulator-metal transition nor superconductivity are understood satisfactorily. Here, we undertake a first step in this direction by focussing on the pressure-driven insulator-metal transition using a combination of first-principles density-functional and many-body calculations. We report a striking result: the finding of an orbital-selective Mott transition in a pure p-band elemental system. We apply our theory to understand extant structural and transport data across the transition, and make a specific two-fluid prediction that is open to future test. Based thereupon, we propose a novel scenario where soft multiband modes built from microscopically coexisting itinerant and localized electronic states are natural candidates for the pairing glue in pressurized O2.
Highlights
The unique properties of high-pressure induced solid phases of molecular gases continue to evince keen and enduring interest in condensed matter physics
Electronic structure calculation based on generalized gradient approximation (GGA) shows that the nonmagnetic insulating state is energetically favored at pressures corresponding to the ε-phase[20, 21]
We have theoretically studied the insulator-metal transition in highly pressurized solid O2 using first-principles local-density-approximation plus dynamical-mean-field calculations
Summary
The unique properties of high-pressure induced solid phases of molecular gases continue to evince keen and enduring interest in condensed matter physics. The crucial difference in this case is that since the doped carriers can have either spin (↑, ↓) with equal probability, doping a Mott insulator, e.g., by holes, creates two available states at the Fermi energy This is at the heart of spectral weight transfer, a phenomenon ubiquitous to Mott, as opposed to band, insulators. The resulting metallic state upon doping can vary from a Fermi liquid at weak coupling to an exotic orbital-selective, non-Fermi liquid metal for stronger electron-electron interactions, as doping and temperature[25] are varied This fundamental difference between band and multi-orbital Mott-Hubbard insulators is of basic and practical interest. We show that sizable multiband electronic interactions are the clue to the insulating state of the ε-phase of solid oxygen and its evolution to a non-Fermi liquid metallic state at high pressures. In light of the discussion above, we study how an orbital-selective interplay between appreciable p-band itinerance and sizable, on-site Coulomb repulsion, U, plays a central role in this unique Mott transition in solid O2
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