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Dipartimento di Fisica

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Light-induced high temperature superconductivity in alkali fullerides A3C60
Speaker Speaker: Dr. Andrea Nava
Affiliato Affiliato: SISSA - Trieste
Data Evento Mercoledì 24 Maggio 2017, alle ore 16.00 - Aula Seminari del Dipartimento di Fisica, Cubo 31 C, Piano IV
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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 (IR) 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 IR 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 TO 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 t1u half-filled state to a higher-energy empty t1g state, dramatically lowered in energy by the large dipole-dipole interaction acting in conjunction with Jahn Teller effect within the enormously degenerate manifold of (t1u)2(t1g)1 states. Both long-lived and entropy-rich because they are triplets, the IR-induced excitons act as a sort of cooling mechanism that permits transient superconductive signals to persist up to much larger temperatures.