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Séminaire MCBT

Mardi 4 juillet à 11h00,
Salle Louis Weil, E424

Orateur : Mauro M. Doria (Universite Federale de Rio de Janeiro)
"A new way to make a superconducting nano film resonate"


Resonance is one of the most fundamental and important concepts in physics with numerous applications in daily life. Resonance makes the blow of a wind destroy a bridge, allows for the tuning of a radio to a frequency, and also a nano size material to have a substantial increase of its superconducting critical temperature and other superconducting properties, as compared to the bulk. In resonance an input parameter brought to its resonance window makes a system produce a very large response (output). More than fifty years ago Thompson and Blatt have theoretically predicted that the width of a nano film is the input parameter to enhance its superconducting properties - this became known as shape resonance. The proposal of Thompson and Blatt started a new way to think on how to achieve high temperature superconductivity. One should look at nano size superconductors with quantum geometrical confinement. However the geometrical (nano width) window needed to enter the resonant regime is in general very narrow, and so difficult to achieve. For this reason we propose here a new way to produce superconducting resonances [1], which is through the implant of a thin insulating barrier in the middle of the film. We named them barrier resonances to differentiate from those found by Thompson and Blatt. Nevertheless shape and barrier resonances share a common origin, which is the quantum confinement regime. There, electronic discrete modes behave similarly to vibrating modes on a rope tied to two walls. Electrons occupy these modes and form Cooper pairs, the building blocks of the superconducting state. The quantum confinement regime is reached when the difference in energy between two consecutive electronic modes becomes larger than the superconducting gap. The nano film enters in resonance when a new electronic mode becomes accessible to superconductivity. Changing the size of the rope leads to shape resonance while introducing an obstacle in the middle of the rope gives the barrier resonances. The barrier resonance opens the route to superconducting state engineering by artificial heterostructures through barrier configurations, thus generating novel superconducting phenomena.


1 - Mauro M. Doria, Marco Cariglia, and Andrea Perali, “Multigap superconductivity and barrier-driven resonances in superconducting nanofilms with an inner potential barrier”, Physical Review B 94, 224513 (2016)

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