Abstract
We analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced non-equilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.
Highlights
The application of a strong electromagnetic drive has emerged as a powerful new way to manipulate material properties [1, 2]
We analyze the competition between the enhanced Cooper pair formation and Cooper pair breaking and show that the enhancement of pairing can dominate in a broad parameter range resulting in signatures of superconductivity that appear at higher temperatures compared to equilibrium
In the slow drive limit, the pairing induced by the strongest instantaneous interaction dominates the Cooper pair formation which can be interpreted as a superconducting proximity effect in time rather than in space
Summary
We describe the consequences of different types of optically-accessible phonon nonlinearities. Since the photon momentum is negligible compared to the reciprocal lattice vector, the drive creates a coherent phonon state at zero momentum, QIqR=0(t) = E cos Ωt, where Ω is the drive frequency and E is proportional pump pulse coherently driven infrared phonons. There are three leading types of phonon nonlinearities which can have static and dynamic effects (Tab. I). There are two types of dynamical effects that can be distinguished: First, a simple modulation of system parameters, which makes system instantaneously more or less superconducting, and, second, dynamical squeezing of phonons, which is an explicitly quantum effect. Both dynamical effects lead to an increased superconducting instability temperature
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