Symmetry breaking driven by petahertz electron acceleration in a centrosymmetric organic superconductor

TL;DR

This study demonstrates that intense light can induce symmetry breaking and second harmonic generation in a centrosymmetric organic superconductor, revealing petahertz charge dynamics amplified by superconducting fluctuations.

Contribution

It provides the first observation of CEP-sensitive second harmonic generation in a centrosymmetric superconductor, indicating petahertz charge acceleration driven by superconducting fluctuations.

Findings

Observation of CEP-sensitive second harmonic generation in a superconductor.

Enhanced SHG near the superconducting transition temperature.

Indication of petahertz charge acceleration in a centrosymmetric system.

Abstract

Charge acceleration during an intense light field application to solids attracts much attention as elementary processes in high-harmonic generation and photoelectron emission [1-7]. For manipulating such attosecond dynamics of charge, carrier-envelope-phase (CEP:relative phase between carrier oscillation of light field and its envelope function) control has been employed in insulators, nanometal and graphene [8-10]. In superconducting materials, collective control of charge motion is expected because of its strongly coherent nature of quasi-particles. Here, in a layered organic superconductor, second harmonic generation (SHG) is observed by using a single-cycle 6 femtosecond near infrared pulse, which is in contrast to the common belief that even harmonics are forbidden in the centrosymmetric system. The SHG shows a CEP sensitive nature and an enhancement near the superconducting temperature. The result and its quantum many-body analysis indicate that a polarized current is induced by non-dissipative acceleration of charge, which is amplified by superconducting fluctuations. This will lead to petahertz functions of superconductors and of strongly correlated systems.