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DIRECT OBSERVATION OF JOSEPHSON VORTICES
Young Scientist Contest 2016 of the Belgian Physical Society DIRECT OBSERVATION OF JOSEPHSON VORTICES presented by Lise SERRIER-GARCIA Lise SERRIER-GARCIA, Tristan CREN, Dimitri RODITCHEV, FranΓ§ois DEBONTRIDDER, Christophe BRUN, Juan Carlos CUEVAS, Vagner H. L. BESSA, Milorad MILOΕ EVIΔ Institute for Nanoscale Physics and Chemistry, Leuven, Belgium Institut des Nanosciences de Paris, CNRS-UPMC, Paris, France, Departamento de FΓsica TeΓ³rica de la Materia Condensada, Universidad AutΓ³noma de Madrid, SPAIN Departement Fysica, Universiteit Antwerpen, BELGIUM
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The supercurrent is zero at each step of quantum flux.
JOSEPHSON EFFECT πΌ πππ₯ πΌ π superconductor tunneling barrier Superconducting Quantum Interference Device (SQUID) A very sensitive sensor of extremely subtle magnetic fields magnetic field πΌ πππ₯ πΌ π = sin Ξπ =sinβ‘( π π 0 ) magnetic flux: π= π΅ π quantum flux: π 0 = β 2π The supercurrent is zero at each step of quantum flux. 2
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SUPERCONDUCTING ELECTRODES
Si Pb ππππ π£πππ‘πππ ππ’πππππ‘ STM Non-superconducting metal Superconductor Insulator πΆβ π π ππ βπ ππ ππ 2 β β at T = 0 normalized conductance π=0.3 πΎ π π =7 πΎ Bias voltage (mV) Using scanning tunneling spectroscopy, we directly access to the local electronic density of states. 3
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NANOSTRUCTURES CONTROLLED BY PREPARATION CONDITIONS
1 x 1 Β΅mΒ² 2 x 2 Β΅mΒ² 1 x 1 Β΅mΒ² J. Phys. Chem C (2015) The lead on silicon growth follows a self-organisation. Temperature, pressure, quality and amount of lead determine the nanostructures. 4
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BUILDING A JOSEPHSON JUNCTION
π π β15 ππ nanostructure What? 4 π π β15 ππ thickness (nm) topography conductance nanostructure Phys Rev Lett (2013) Bias voltage (mV) Superconductivity is not limited to the nanostructures. 5
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JOSEPHSON JUNCTION The distance is reduced to few tens of nanometer
superconductor dβ45 ππ Josephson junction 1 conductance conductance conductance map superconductor Bias voltage (mV) The distance is reduced to few tens of nanometer creating a Josephson junction. 6
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JOSEPHSON JUNCTIONS WITH MAGNETIC FIELD
non-supercodnucting metal superconductors magnetic field 1 x 1 Β΅mΒ² 5 thickness (nm) topography Array of Josephson junctions. 7
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ABRIKOSOV AND JOSEPSHON VORTICES
Nat Phys (2015) 1 x 1 Β΅m2 magnetic field 0 mT 180 mT 60 mT 120 mT 1 conductance 8
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THE GINZBURG-LANDAU EQUATIONS
Minimizing the free energy of the Ginzburg-Landau theoryβ¦ π π =π πΉ(π) 2 + π 2 πΉ(π) π β β π π»β2π π΄ π πΉ π + Β΅ π΅ π 2 Condensation Kinetic Magnetic Phys Rev E (2012) Nat Phys (2015) Phys Rev B (2002) π» Current π π Phase π π Amplitude |Ξ¨ π | β¦ to simulate the Abrikosov vortices. 9
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SIMULATING THE SUPERCONDUCTORSβ¦
Abrikosov vortex Josephson junction 500 x 500 nm2 H = 120 mT Nat Phys (2015) 1 2Ο amplitude |Ο| phase Ο Ginzburg-Landau equations describe the superconductivity in the nanostructures but not in the Josephson junctions. 10
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β¦ SIMULATING THE JOSEPHSON EFFECTβ¦
Phase Ο Interference pattern J Superconductor 1 Josephson junction Superconductor βπ πππ£ =π π π βπ π π β 2π Δ§ π π π π π΄ . ππ π½ π = π 0 π β πβ π π 2 π π π 0 π β πβ π π 2 π π π sin βπ πππ£ π + π 0 11
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Simulations and experiments are in very good agreement.
β¦ TO SIMULATE THE JOSEPSHON VORTICES Josephson vortex 500 x 500 nm2 H = 120 mT Nat Phys (2015) 1 1 superconductivity conductance Simulations and experiments are in very good agreement. 12
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JOSEPSHON VORTICES IN ELECTRONIC CIRCUITS
Nat Phys (2015) πΌ 1 πΌ 2 πΌ Josephson vortices can be induced by supercurrents instead of magnetic field. 13
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THANK YOU FOR YOUR ATTENTION!
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JOSEPSHON VORTICES AS REAL VORTICES?
1 1 Currents Superconducting correlations π π
π π±= π β π β π π
π πΉ π 2 Δ§ππ π β π β π¨ π π = Δ§ πΏ 2π β 2π π΅π β π΅π=πΏ π· 0 a Josephson vortex corresponds to a quanta of magnetic flux.
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Josephson vortex cores have a normal state.
AN ELECTRONIC DENSITY OF STATES! superconductor Josephson junction normal layer Abrikosov vortex Josephson vortex x x x x x Josephson vortex cores have a normal state.
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ABRIKOSOV VORTICES supercurrents vortex core magnetic field
vortices in superconductors An Abrikosov vortex has: a normal core, supercurrents around it, one quantum of magnetic flux.
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