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Size-dependent transformation from triangular to rectangular fluxon lattice in Bi-2212 mesa structures
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
2012 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 400, 052022Article in journal (Refereed) Published
Abstract [en]

We present a systematic study of the field and size dependencies of the static fluxon lattice configuration in Bi-2212 intrinsic Josephson junctions and investigate conditions needed for the formation of a rectangular fluxon lattice required for a high power flux-flow oscillator. We fabricate junctions of different sizes from Bi2Sr2CaCu2O8+x and Bi1.75Pb0.25Sr2CaCu2O8+xsingle crystals using the mesa technique and study the Fraunhofer-like modulation of the critical current with magnetic field. The modulation can be divided into three regions depending on the formed fluxon lattice. At low field, no periodic modulation and no ordered fluxon lattice is found. At intermediate fields, modulation with half-flux quantum periodicity due to a triangular lattice is seen. At high fields, the rectangular lattice gives integer flux quantum periodicity. We present these fields in dependence on the sample size and conclude that the transitions between the regions depend only on λJ(Jc) and occur at about 0.4 and 1.3 fluxons per λJ, respectively. These numbers are universal for the measured samples and are consistent with performed numerical simulations.

Place, publisher, year, edition, pages
2012. Vol. 400, 052022
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-89383DOI: 10.1088/1742-6596/400/5/052022ISI: 000314977100461OAI: oai:DiVA.org:su-89383DiVA: diva2:617595
Conference
26th International Conference on Low Temperature Physics (LT26), Beijing, Peoples Republic of China, Aug 10-17, 2011
Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Intrinsic tunneling spectroscopic investigations of Bi2Sr2CaCu2O8+x superconductors: The fluxon lattice, resonant phenomena,flux-flow and current doping
Open this publication in new window or tab >>Intrinsic tunneling spectroscopic investigations of Bi2Sr2CaCu2O8+x superconductors: The fluxon lattice, resonant phenomena,flux-flow and current doping
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the tunneling between individual atomic layers in structures of Bi2Sr2CaCu2O8+x based high-temperature superconductors are experimentally studied employing the intrinsic Josephson effect. A special attention is paid on the fabrication of small mesa structures using micro and nanofabrication techniques.

Different resonant phenomena are studied in the dynamic fluxon state at high magnetic fields, including Eck-resonances and Fiske steps.

The periodic Fraunhofer-like modulation of the critical current of the junctions as a function of in-plane magnetic field is investigated. A transition from a modulation with a half flux quantum to a flux quantum periodicity is demonstrated with increasing field and decreasing junction length. It is interpreted in terms of the static fluxon lattice of stacked, strongly cou- pled intrinsic Josephson junctions and compared with theoretical predictions. A fluxon phase diagram is constructed. It is experimentally found that a stable rectangular fluxon lattice can be obtained at a flux density larger than 1.3 fluxons per Josephson penetration length and junction, Ф0Js. Numerical simulations have been carried out to complement the experimental data.

The resistive switching of mesas at high bias is studied. It is attributed to a persistent electri- cal doping of the crystal. Superconducting properties such as the critical current and tempera- ture and the tunneling spectra are analyzed at different doping states of the same sample. The dynamics of the doping is studied, and attributed to two mechanisms; a charge-transfer effect and oxygen reordering.

Place, publisher, year, edition, pages
Department of Physics, Stockholm University, 2013. 61 p.
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:su:diva-89385 (URN)
Presentation
2013-05-15, FA32, Fysikum, Albanova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

At the time of the defence the following paper was unpublihed and had a status as follows:

Paper 4: in Press

Available from: 2013-05-14 Created: 2013-04-23 Last updated: 2013-05-14Bibliographically approved
2. High-frequency phenomena in small Bi2Sr2CaCu2O8+x intrinsic Josephson junctions
Open this publication in new window or tab >>High-frequency phenomena in small Bi2Sr2CaCu2O8+x intrinsic Josephson junctions
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the tunneling between individual atomic layers in structures of Bi2Sr2CaCu2O8+x based high-temperature superconductors are experimentally studied employing the intrinsic Josephson effect. A special attention is paid to the fabrication of small mesa structures using micro and nanofabrication techniques.

In the first part of the thesis, the periodic Fraunhofer-like modulation of the critical current of the junctions as a function of in-plane magnetic field is investigated. A transition from a modulation with a half flux quantum to a flux quantum periodicity is demonstrated with increasing field and decreasing junction length. It is interpreted in terms of the transformation of the static fluxon lattice of stacked, strongly coupled intrinsic Josephson junctions and compared with theoretical predictions. A fluxon phase diagram is constructed.Numerical simulations have been carried out to complement the experimental data.

In the second part of the thesis, different resonant phenomena are studied in the dynamic flux-flow state at high magnetic fields, including Eck-resonances and Fiske steps. Different resonant modes and their velocities, including superluminal modes, are identified.

In the third part, different experiments attempting to detect radiation from small mesa structures using different setups based on hot-electron bolometer mixers and calorimeters are described. No distinct radiation with emission powers higher than about 500pW could be detected. Furthermore, the interaction with external GHz-radiation is studied. Resonances attributed to an induced flux-flow are observed, and the reflectivity of the sample can be tuned by switching mesas between the superconducting and quasiparticle state.

In the last part, the resistive switching of mesas at high bias is studied. It is attributed to a persistent electrical doping of the crystal. Superconducting properties such as the critical current and temperature and the tunneling spectra are analyzed at different doping states of the same sample. The dynamics of the doping is studied, and attributed to two mechanisms; a charge-transfer effect and oxygen reordering

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2015
Keyword
high-temperature superconductivity, Bi-2212, cuprates, intrinsic Josephson junctions, intrinsic tunneling, fluxons, flux-flow oscillator, THz-emission, cavity resonances, polaritons, electrical doping, micro/nano-fabrication
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-115582 (URN)978-91-7649-157-7 (ISBN)
Public defence
2015-05-20, sal FD41, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2015-04-28 Created: 2015-03-26 Last updated: 2015-05-05Bibliographically approved

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