Local dynamical lattice instabilities: Prerequisites for resonant pairing superconductivity

TL;DR

This paper explores how local lattice instabilities and charge fluctuations can facilitate non-phonon-mediated superconductivity, emphasizing the role of resonant pair tunneling and phase coherence in achieving high Tc without relying on traditional phonon mechanisms.

Contribution

It introduces a model where local dynamical lattice instabilities enable resonant pairing, providing a new pathway for superconductivity independent of phonon interactions.

Findings

Superconductivity can arise from local charge-lattice excitations coupled to lattice instabilities.

Resonant pair tunneling is crucial for establishing phase coherence in such systems.

A pseudogap phase persists above Tc, characterized by local pairing without global coherence.

Abstract

Fluctuating local diamagnetic pairs of electrons, embedded in a Fermi sea, are candidates for non-phonon-mediated superconductors without the stringent conditions on Tc which arise in phonon-mediated BCS classical low-Tc superconductors. The local accumulations of charge, from which such diamagnetic fluctuations originate, are irrevocably coupled to local dynamical lattice instabilities and form composite charge-lattice excitations of the system. For a superconducting phase to be realized, such excitations must be itinerant spatially phase-coherent modes. This can be achieved by resonant pair tunneling in and out of polaronic cation-ligand sites. Materials in which superconductivity driven by such local lattice instability can be expected, have a Tc which is controlled by the phase stiffness rather than the amplitude of the diamagnetic pair fluctuations. Above Tc, a pseudogap phase will be maintained up to a T*, where this pairing amplitude disappears. We discuss the characteristic local charge and lattice properties which characterize this pseudogap phase and which form the prerequisites for establishing a phase-coherent macroscopic superconducting state.