Optically induced superconductivity in striped La2-xBaxCuO4 by polarization-selective excitation in the near infrared

TL;DR

This study demonstrates that near-infrared laser pulses can enhance superconducting interlayer coupling in La2-xBaxCuO4, inducing superconductivity-like properties even above the critical temperature, with polarization playing a key role.

Contribution

It reveals polarization-dependent optical control of superconductivity and stripe order in cuprates, showing enhancement of interlayer coupling above Tc via near-infrared excitation.

Findings

Enhanced Josephson plasma resonance below Tc with near-infrared pulses.

Induction of plasma resonance above Tc, up to TSO=40 K.

Polarization perpendicular to planes is more effective for enhancement.

Abstract

We show that superconducting interlayer coupling, which coexists with and is depressed by stripe order in La1.885Ba0.115CuO4, can be enhanced by excitation with near-infrared laser pulses. For temperatures lower than Tc = 13 K, we observe a blue-shift of the equilibrium Josephson plasma resonance, detected by terahertz-frequency reflectivity measurements. Key to this measurement is the ability to probe the optical properties at frequencies as low as 150 GHz, detecting the weak interlayer coupling strengths. For T > Tc a similar plasma resonance, absent at equilibrium, is induced up to the spin-ordering temperature TSO = 40 K. These effects are reminiscent but qualitatively different from the light-induced superconductivity observed by resonant phonon excitation in La1.675Eu0.2Sr0.125CuO6.5. Importantly, enhancement of the below-Tc interlayer coupling and its appearance above Tc are preferentially achieved when the near-infrared pump light is polarized perpendicular to the superconducting planes, likely due to more effective melting of stripe order and the less effective excitation of quasiparticles from the Cooper pair condensate when compared to in-plane excitation.