Long after its discovery, superconductivity in alkali fullerides A3C60 still challenges conventional wisdom. The freshest inroad in such ever-surprising physics is the behaviour under intense infrared excitation. Signatures attributable to a transient superconducting state extending up to temperatures ten times higher than the equilibrium Tc=20 K have been discovered in K3C60 after ultra-short pulsed infrared irradiation-an effect which still appears as remarkable as mysterious. Motivated by the observation that the phenomenon is observed in a broad pumping frequency range that coincides with the mid-infrared electronic absorption peak still of unclear origin, rather than to transverse optical phonons as has been proposed, we advance here a radically new mechanism. First, we argue that this broad absorption peak represents a "super-exciton" involving the promotion of one electron from the t_1u half-filled state to a higher-energy empty t_1g state, dramatically lowered in energy by the large dipole-dipole interaction acting in conjunction with the Jahn-Teller effect within the enormously degenerate manifold of (t_1u)^2 x (t_1g)^1 states. Both long-lived and entropy-rich because they are triplets, the infrared-induced excitons act as a sort of cooling mechanism that permits transient superconductive signals to persist up to much higher temperatures.

Nava, A., Giannetti, C., Georges, A., Tosatti, E., Fabrizio, M., Cooling quasiparticles in A3C60 fullerides by excitonic mid-infrared absorption, <<NATURE PHYSICS>>, 2018; 14 (2): 154-159. [doi:10.1038/nphys4288] [http://hdl.handle.net/10807/113910]

Cooling quasiparticles in A3C60 fullerides by excitonic mid-infrared absorption

Nava, Andrea
Primo
;
Giannetti, Claudio
Secondo
;
2018

Abstract

Long after its discovery, superconductivity in alkali fullerides A3C60 still challenges conventional wisdom. The freshest inroad in such ever-surprising physics is the behaviour under intense infrared excitation. Signatures attributable to a transient superconducting state extending up to temperatures ten times higher than the equilibrium Tc=20 K have been discovered in K3C60 after ultra-short pulsed infrared irradiation-an effect which still appears as remarkable as mysterious. Motivated by the observation that the phenomenon is observed in a broad pumping frequency range that coincides with the mid-infrared electronic absorption peak still of unclear origin, rather than to transverse optical phonons as has been proposed, we advance here a radically new mechanism. First, we argue that this broad absorption peak represents a "super-exciton" involving the promotion of one electron from the t_1u half-filled state to a higher-energy empty t_1g state, dramatically lowered in energy by the large dipole-dipole interaction acting in conjunction with the Jahn-Teller effect within the enormously degenerate manifold of (t_1u)^2 x (t_1g)^1 states. Both long-lived and entropy-rich because they are triplets, the infrared-induced excitons act as a sort of cooling mechanism that permits transient superconductive signals to persist up to much higher temperatures.
Inglese
Nava, A., Giannetti, C., Georges, A., Tosatti, E., Fabrizio, M., Cooling quasiparticles in A3C60 fullerides by excitonic mid-infrared absorption, <<NATURE PHYSICS>>, 2018; 14 (2): 154-159. [doi:10.1038/nphys4288] [http://hdl.handle.net/10807/113910]
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