Theory of Laser-Controlled Competing Superconducting and Charge Orders

TL;DR

This paper explores how a laser field can dynamically control and switch between superconducting and charge-density wave orders in a correlated electron system, revealing resonance effects and the role of induced pairing.

Contribution

It introduces a theoretical framework showing how laser frequency detuning can selectively enhance or suppress competing orders via induced $ ext{eta}$ pairing in an attractive Hubbard model.

Findings

Red-detuned light enhances CDW and suppresses SC.

Blue-detuned light suppresses CDW and enhances SC.

Light-induced superconductivity can emerge from a CDW state.

Abstract

We investigate the nonequilibrium dynamics of competing coexisting superconducting (SC) and charge-density wave (CDW) orders in an attractive Hubbard model. A time-periodic laser field $\vec{A}(t)$ lifts the SC-CDW degeneracy, since the CDW couples linearly to the field ($\vec{A}$), whereas SC couples in second order ($\vec{A}^2$) due to gauge invariance. This leads to a striking resonance: When the photon energy is red-detuned compared to the equilibrium single-particle energy gap, CDW is enhanced and SC is suppressed, while this behavior is reversed for blue detuning. Both orders oscillate with an emergent slow frequency, which is controlled by the small amplitude of a third induced order, namely $\eta$ pairing, given by the commutator of the two primary orders. The induced $\eta$ pairing is shown to control the enhancement and suppression of the dominant orders. Finally, we demonstrate that light-induced superconductivity is possible starting from a predominantly CDW initial state.