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Application of nano-scale Josephson junction as phase sensitive detector for analysis of vortex states in mesoscopic superconductors
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. (Experimental Condensed Matter Physics)
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. (Experimental Condensed Matter Physics)
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. (Experimental Condensed Matter Physics)
2010 (Engelska)Ingår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 570, nr 19, s. 890-892Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We study phase shifts in a Josephson junction induced by vortices in superconducting mesoscopic electrodes. The position of the vortices are controlled by suitable geometry of a nano-scale Nb–Pt1−xNix–Nb junction of the overlap type made by Focused Ion Beam (FIB) sculpturing. The vortex is kept outside the junction, parallel to the junction plane. From the measured Fraunhofer characteristics the entrance and exit of vortices are detected. By changing the bias current through the junction at constant magnetic field the vortices can be manipulated and the system can be switched between two consecutive vortex states which are characterized by different critical currents of the junction. A mesoscopic superconductor thus acts as a non-volatile memory cell in which the junction is used both for reading and writing information (vortex). Furthermore, we observe that the critical current density of Nb–Pt1−xNix–Nb junctions decreases non-monotonously with increasing Ni concentration. It exhibits a minimum at 40 at.% Ni, which is an indication of switching into the π state.

Ort, förlag, år, upplaga, sidor
2010. Vol. 570, nr 19, s. 890-892
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:su:diva-48326DOI: 10.1016/j.physc.2010.02.039OAI: oai:DiVA.org:su-48326DiVA, id: diva2:375197
Tillgänglig från: 2010-12-07 Skapad: 2010-12-07 Senast uppdaterad: 2022-02-24Bibliografiskt granskad
Ingår i avhandling
1. Mesoscopic phenomena in hybrid superconductor/ferromagnet structures
Öppna denna publikation i ny flik eller fönster >>Mesoscopic phenomena in hybrid superconductor/ferromagnet structures
2011 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis explores peculiar effects of mesoscopic structures revealed at low temperatures. Three particular systems are studied experimentally: Ferromagnetic thin films made of diluted Pt1-xNix alloy, hybrid nanoscale Nb-Pt1-xNix-Nb Josephson junctions, and planar niobium Josephson junction with barrier layer made of Cu or Cu0.47Ni0.53 alloy.

A cost-effective way is applied to fabricate the sputtered NixPt1-x thin films with controllable Ni concentration. 3D Focused Ion Beam (FIB) sculpturing is used to fabricate Nb-Pt1-xNix-Nb Josephson junctions. The planar junctions are made by cutting Cu-Nb or CuNi-Nb double layer by FIB.

Magnetic properties of PtNi thin films are studied via the Hall effect. It is found that films with sub-critical Ni concentration are superparamagnetic at low temperatures and exhibit perpendicular magnetic anisotropy. Films with over-critical Ni concentration are ferromagnetic with parallel anisotropy. At the critical concentration the films demonstrate canted magnetization with the easy axis rotating as a function of temperature. The magnetism appears via two consecutive crossovers, going from paramagnetic to superparamagnetic to ferromagnetic, and the extraordinary Hall effect changes sign at low temperatures.

Detailed studies of superconductor-ferromagnet-superconductor Josephson junctions are carried out depending on the size of junction, thickness and composition of the ferromagnetic layer. The junction critical current density decreases non-monotonically with increasing Ni concentration. It has a minimum at ~ 40 at.% of Ni which indicates a switching into the π state.

The fabricated junctions are used as phase sensitive detectors for analysis of vortex states in mesoscopic superconductors. It is found that the vortex induces different flux shifts, in the measured Fraunhofer modulation of the Josephson critical current, depending on the position of the vortex. When the vortex is close to the junction it induces a flux shift equal to Φ0/2 leading to switching of the junction into the 0-π state. By changing the bias current at constant magnetic field the vortices can be manipulated and the system can be switched between two consecutive vortex states. A mesoscopic superconductor can thus act as a memory cell in which the junction is used both for reading and writing information (vortex).

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Physics, Stockholm University, 2011. s. 117
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:su:diva-56629 (URN)978-91-7447-282-0 (ISBN)
Disputation
2011-05-26, FB51, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2011-05-04 Skapad: 2011-04-19 Senast uppdaterad: 2022-02-24Bibliografiskt granskad

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Golod, TarasRydh, AndreasKrasnov, Vladimir M.

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