Electron coherent and incoherent pairing instabilities in inhomogeneous bipartite and nonbipartite nanoclusters

TL;DR

This paper investigates electron pairing instabilities in inhomogeneous nanoclusters, revealing new mechanisms for pairing and phase transitions that differ from traditional superconductivity theories, with implications for high-temperature superconductors.

Contribution

It provides exact calculations of collective excitations and charge/spin gaps in nanoclusters, identifying conditions for phase transitions and a novel pairing mechanism in inhomogeneous systems.

Findings

Level crossing degeneracies influence pairing and magnetic transitions.

Charge and spin condensation mechanisms suggest alternative routes to superconductivity.

Phase diagrams relate to experimental observations in high T_c cuprates and transition metal oxides.

Abstract

Exact calculations of collective excitations and charge/spin (pseudo)gaps in an ensemble of bipartite and nonbipartite clusters yield level crossing degeneracies, spin-charge separation, condensation and recombination of electron charge and spin, driven by interaction strength, inter-site couplings and temperature. Near crossing degeneracies, the electron configurations of the lowest energies control the physics of electronic pairing, phase separation and magnetic transitions. Rigorous conditions are found for the smooth and dramatic phase transitions with competing stable and unstable inhomogeneities. Condensation of electron charge and spin degrees at various temperatures offers a new mechanism of pairing and a possible route to superconductivity in inhomogeneous systems, different from the BCS scenario. Small bipartite and frustrated clusters exhibit charge and spin inhomogeneities in many respects typical for nano and heterostructured materials. The calculated phase diagrams in various geometries may be linked to atomic scale experiments in high T$_c$ cuprates, manganites and other concentrated transition metal oxides.