Unconventional particle-hole mixing in the systems with strong superconducting fluctuations

TL;DR

This paper investigates unconventional particle-hole mixing in systems with strong superconducting fluctuations, revealing a novel temperature dependence of the Bogoliubov angle in pseudogap states using a two-component model and renormalization group methods.

Contribution

It introduces a new understanding of particle-hole entanglement and the Bogoliubov angle behavior in high-temperature superconductors and ultracold fermion systems with strong fluctuations.

Findings

Identifies a non-BCS temperature dependence of the Bogoliubov angle in pseudogap states.

Uses a two-component model to analyze coexistence of pairs and single fermions.

Employs a self-consistent renormalization group approach for quantitative analysis.

Abstract

Development of the STM and ARPES spectroscopies enabled to reach the resolution level sufficient for detecting the particle-hole entanglement in superconducting materials. On a quantitative level one can characterize such entanglement in terms of the, so called, Bogoliubov angle which determines to what extent the particles and holes constitute the spatially or momentum resolved excitation spectra. In classical superconductors, where the phase transition is related to formation of the Cooper pairs almost simultaneously accompanied by onset of their long-range phase coherence, the Bogoliubov angle is slanted all the way up to the critical temperature Tc. In the high temperature superconductors and in superfluid ultracold fermion atoms near the Feshbach resonance the situation is different because of the preformed pairs which exist above Tc albeit loosing coherence due to the strong quantum fluctuations. We discuss a generic temperature dependence of the Bogoliubov angle in such pseudogap state indicating a novel, non-BCS behavior. For quantitative analysis we use a two-component model describing the pairs coexisting with single fermions and study their mutual feedback effects by the selfconsistent procedure originating from the renormalization group approach.