Superconductivity from Doublon Condensation in the Ionic Hubbard Model

TL;DR

This paper investigates how superconductivity emerges from doublon condensation in the ionic Hubbard model, revealing phase transitions from Mott insulator to superconductor driven by charge fluctuations and doublon-hole pairing.

Contribution

It introduces an effective Hamiltonian and slave boson approach to demonstrate superconductivity from doublon condensation in the ionic Hubbard model.

Findings

Phase transition from Mott insulator to paramagnetic insulator with doublon-hole pairs

Emergence of superconductivity driven by condensate of doublons and holes

High $T_c$ superconducting dome with $hc/e$ flux quantization

Abstract

In the ionic Hubbard model, the onsite repulsion $U$, which drives a Mott insulator and the ionic potential $V$, which drives a band insulator, compete with each other to open up a window of charge fluctuations when $U \sim V$. We study this model on square and cubic lattices in the limit of large $U$ and $V$, with $V\sim U$. Using an effective Hamiltonian and a slave boson approach with both doublons and holes, we find that the system undergoes a phase transition as a function of $V$ from an antiferromagnetic Mott insulator to a paramagnetic insulator with strong singlet correlations, which is driven by a condensate of "neutral" doublon-hole pairs. On further increasing $V$, the system undergoes another phase transition to a superconducting phase driven by condensate of "charged" doublons and holes. The superfluid phase, characterized by presence of coherent (but gapped) fermionic quasiparticle, and $hc/e$ flux quantization, has a high $T_c \sim t $ which shows a dome shaped behaviour as a function of $V$. The paramagnetic insulator phase has a deconfined U(1) gauge field and associated gapless photon excitations. We also discuss how these phases can be detected in the ultracold atom context.