Tuning Metastable Light-Induced Superconductivity in K3 C60 with a Hybrid CO2 -Ti: Sapphire Laser
2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings (2021)
Abstract:
High power mid-infrared light pulses of tunable pulse length were generated to stabilize light-induced superconductivity in K3C60 for nanoseconds. This metastable state showed a vanishing electrical resistance at five times the material's equilibrium critical temperature.Evidence for metastable photo-induced superconductivity in K3C60
Nature Physics Springer Nature 17:5 (2021) 611-618
Abstract:
Excitation of high-Tc cuprates and certain organic superconductors with intense far-infrared optical pulses has been shown to create non-equilibrium states with optical properties that are consistent with transient high-temperature superconductivity. These non-equilibrium phases have been generated using femtosecond drives, and have been observed to disappear immediately after excitation, which is evidence of states that lack intrinsic rigidity. Here we make use of a new optical device to drive metallic K3C60 with mid-infrared pulses of tunable duration, ranging between one picosecond and one nanosecond. The same superconducting-like optical properties observed over short time windows for femtosecond excitation are shown here to become metastable under sustained optical driving, with lifetimes in excess of ten nanoseconds. Direct electrical probing, which becomes possible at these timescales, yields a vanishingly small resistance with the same relaxation time as that estimated by terahertz conductivity. We provide a theoretical description of the dynamics after excitation, and justify the observed slow relaxation by considering randomization of the order-parameter phase as the rate-limiting process that determines the decay of the light-induced superconductor.Analytical solution for the steady states of the driven Hubbard model
Physical Review B American Physical Society 103:3 (2021) 35146
Abstract:
Under the action of coherent periodic driving a generic quantum system will undergo Floquet heating and continuously absorb energy until it reaches a featureless thermal state. The phase-space constraints induced by certain symmetries can, however, prevent this and allow the system to dynamically form robust steady states with off-diagonal long-range order. In this work, we take the Hubbard model on an arbitrary lattice with arbitrary filling and, by simultaneously diagonalizing the two possible SU(2) symmetries of the system, we analytically construct the correlated steady states for different symmetry classes of driving. This construction allows us to make verifiable, quantitative predictions about the long-range particle-hole and spin-exchange correlations that these states can possess. In the case when both SU(2) symmetries are preserved in the thermodynamic limit we show how the driving can be used to form a unique condensate which simultaneously hosts particle-hole and spin-wave order.Lieb's Theorem and Maximum Entropy Condensates
Quantum 5 (2021)
Abstract:
Coherent driving has established itself as a powerful tool for guiding a many-body quantum system into a desirable, coherent non-equilibrium state. A thermodynamically large system will, however, almost always saturate to a featureless infinite temperature state under continuous driving and so the optical manipulation of many-body systems is considered feasible only if a transient, prethermal regime exists, where heating is suppressed. Here we show that, counterintuitively, in a broad class of lattices Floquet heating can actually be an advantageous effect. Specifically, we prove that the maximum entropy steady states which form upon driving the ground state of the Hubbard model on unbalanced bi-partite lattices possess uniform off-diagonal long-range order which remains finite even in the thermodynamic limit. This creation of a 'hot' condensate can occur on any driven unbalanced lattice and provides an understanding of how heating can, at the macroscopic level, expose and alter the order in a quantum system. We discuss implications for recent experiments observing emergent superconductivity in photoexcited materials.Tuning Metastable Light-Induced Superconductivity in K3C60 with a Hybrid CO2-Ti:Sapphire Laser
Optica Publishing Group (2021) ff1a.5