Radiative Higgs mode in photoinduced $\eta$ pairs

TL;DR

This paper reveals how a probe pulse can transiently break the $ta$ symmetry in a photoinduced $ta$-pairing state in the Hubbard chain, inducing Higgs oscillations and a distinctive negative optical conductivity signature.

Contribution

It demonstrates the dynamic breaking of $ta$ symmetry and identifies unique optical signatures of the photoinduced $ta$-pairing state in the Hubbard model.

Findings

Observation of dynamic Higgs oscillations in $ta$-pair correlations.

Detection of a sharp negative optical conductivity above the Mott gap.

Emission of photons at the Higgs frequency due to broadband probing.

Abstract

We demonstrate that the $\eta$ symmetry of the pump-induced $\eta$-pairing state in the Hubbard chain can be transiently broken by an additionally applied probe pulse. This leads to characteristic dynamic Higgs oscillations of the $\eta$-pair correlations during the probe pulse and a sharp dynamic negative optical conductivity $\sigma(\omega;t)$, which appears above the equilibrium Mott gap $\omega>\Delta_{\rm c}$, long after the pump pulse is finished. This negative peak in the real part of $\sigma(\omega;t)$ is a distinctive hallmark of the photoinduced $\eta$-pairing state, distinguishing it from parameter regimes dominated by incoherent doublon formation, which do not exhibit this feature. Remarkably, the broadband probe pulse then leads to the emission of photons with the Higgs frequency.