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Coherent generation of phonon-polaritons in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions
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.
2011 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 83, no 10, 100510Article in journal (Refereed) Published
Abstract [en]

The Bi2Sr2CaCu2O8+x high-temperature superconductor represents a natural layered metamaterial composed of metallic CuO bilayers sandwiched between ionic BiO planes. Each pair of CuO bilayers forms an atomic-scale Josephson junction. Here we employ the intrinsic Josephson effect for in situ generation and self-detection of electromagnetic waves in Bi2Sr2CaCu2O8+x single crystals. We observe that electromagnetic waves form polaritons with several transverse optical phonons. This indicates the presence of unscreened polar response in cuprates, which may lead to unusually strong electron-phonon interaction. Our technique can provide intense local sources of coherent, monochromatic phonon-polaritons with kW/cm2 power densities.

Place, publisher, year, edition, pages
2011. Vol. 83, no 10, 100510
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-62392DOI: 10.1103/PhysRevB.83.100510ISI: 000288510800001OAI: oai:DiVA.org:su-62392DiVA: diva2:441561
Available from: 2011-09-16 Created: 2011-09-16 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena
Open this publication in new window or tab >>Properties of small Bi2Sr2CaCu2O8 intrinsic Josephson junctions: confinement, flux-flow and resonant phenomena
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, intrinsic Josephson junctions, naturally formed in the strongly anisotropic high-temperature superconductor Bi2Sr2CaCu2O8 (Bi-2212), are studied experimentally. For this purpose, small mesa structures are fabricated on the surface of single crystals using micro- and nano-fabrication tools, focused ion beam is used to reduce the area of the mesa-structures down to ≈ 1 × 1 μm2.

The properties of charge transport across copper-oxide layers inside the mesas are studied by intrinsic tunneling spectroscopy. Temperature, bias and magnetic field dependences of current-voltage characteristics are examined.

In the main part of the thesis, the behavior of intrinsic Josephson junctions in magnetic fields B parallel to the copper-oxide planes is studied. Parallel magnetic fields penetrate the junctions in the form of Josephson vortices (fluxons). At high magnetic fields, fluxons are arranged in a regular lattice and are accelerated by a sufficient high transport current. As the fluxon lattice is moving through the mesa, it emits electromagnetic waves in the important THz frequency range. Properties of Bi-2212 mesas in this flux-flow regime are studied in this thesis.

The following new observations were made during the course of this work: a crossover from thermal activation above Tc to quantum tunneling below Tc is seen in the interlayer transport-mechanism, the Fraunhofer pattern of Ic(B) is observed clearly in Bi-2212, superluminal electromagnetic cavity resonances and phonon-polaritons are observed in Bi-2212.

It is argued that the employed technique for miniaturization of mesas and the obtained results can be useful for a better understanding of fundamental properties of high-temperature superconductors and for the realizations of coherent flux-flow oscillators and coherent phonon-polariton generators in the important THz frequency range.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 105 p.
Keyword
high-temperature superconductivity, intrinsic Josephson junctions, tunneling, fluxons, flux-flow oscillator, THz-emission, cavity resonances, polaritons, micro/nano-fabrication
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-62583 (URN)978-91-7447-358-2 (ISBN)
Public defence
2011-10-27, FB41, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript. Available from: 2011-10-05 Created: 2011-09-23 Last updated: 2011-10-07Bibliographically approved
2. 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
3. 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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