Optical excitation of phase modes in strongly disordered superconductors

According to the Goldstone theorem the breaking of a continuous U(1) symmetry comes along with the existence of low-energy collective modes. In the context of superconductivity these excitations are related to the phase of the superconducting (SC) order parameter and for clean systems are optically...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2014-05, Vol.89 (17), Article 174506
Main Authors: Cea, T., Bucheli, D., Seibold, G., Benfatto, L., Lorenzana, J., Castellani, C.
Format: Article
Language:English
Subjects:
Condensed matter
Devices
Displays
Excitation
Low energy
Superconductivity
Superconductors
Theorems
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Summary:According to the Goldstone theorem the breaking of a continuous U(1) symmetry comes along with the existence of low-energy collective modes. In the context of superconductivity these excitations are related to the phase of the superconducting (SC) order parameter and for clean systems are optically inactive; that is, single-mode excitations do not directly couple to light. Here we show that for strongly disordered superconductors phase modes acquire a dipole moment and appear as a subgap spectral feature in the optical conductivity. This finding is obtained with both a gauge-invariant random-phase approximation scheme based on a fermionic Bogoliubov-de Gennes state and a prototypical bosonic model for disordered superconductors. In the strongly disordered regime, where the system displays an effective granularity of the SC properties, the optically active dipoles are linked to the isolated SC islands, offering a new perspective for realizing microwave optical devices.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.89.174506