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Unusual two-dimensional behavior of iron-based superconductors with low anisotropy
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Institute of Metal Physics of National Academy of Sciences of Ukraine, Ukraine.ORCID-id: 0000-0002-7212-434x
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.ORCID-id: 0000-0003-4815-5856
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Antal upphovsmän: 92017 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 13, artikel-id 134512Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We study angular-dependent magnetoresistance in iron-based superconductors Ba1−xNaxFe2As2 and FeTe1−xSex. Both superconductors have relatively small anisotropies γ∼2 and exhibit a three-dimensional (3D) behavior at low temperatures. However, we observe that they start to exhibit a profound two-dimensional behavior at elevated temperatures and in applied magnetic field parallel to the surface. We conclude that the unexpected two-dimensional (2D) behavior of the studied low-anisotropic superconductors is not related to layeredness of the materials, but is caused by appearance of surface superconductivity when magnetic field exceeds the upper critical field Hc2(T) for destruction of bulk superconductivity. We argue that the corresponding 3D-2D bulk-to-surface dimensional transition can be used for accurate determination of the upper critical field.

Ort, förlag, år, upplaga, sidor
2017. Vol. 96, nr 13, artikel-id 134512
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
fysik
Identifikatorer
URN: urn:nbn:se:su:diva-149008DOI: 10.1103/PhysRevB.96.134512ISI: 000413050000004Scopus ID: 2-s2.0-85037116435OAI: oai:DiVA.org:su-149008DiVA, id: diva2:1158360
Tillgänglig från: 2017-11-20 Skapad: 2017-11-20 Senast uppdaterad: 2022-10-20Bibliografiskt granskad
Ingår i avhandling
1. Superradiant THz wave emission from arrays of Josephson junctions
Öppna denna publikation i ny flik eller fönster >>Superradiant THz wave emission from arrays of Josephson junctions
2020 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

High-power, continuous-wave, compact and tunable THz sources are needed for a large variety of applications. Development of power-efficient sources of electromagnetic radiation in the 0.1-10 THz range is a difficult technological problem, known as the “THz gap.” Josephson junctions allow creation of monochromatic THz sources with an inherently broad range of tunability. However, emission power from a single junction is too small. It can be amplified in a coherent superradiant manner by phase-locking of many junctions. In this case, the emission power should increase as a square of the number of phase-locked junctions.The aim of this thesis is to study a possibility of achieving coherent super-radiant emission with significant power and frequency tunability from Joseph-son junction arrays. Two types of devices are studied, based either on stacks (one-dimensional arrays) of intrinsic Josephson junctions naturally formed in single crystals of high-temperature cuprate superconductor Bi2Sr2CaCu2O8+x, or two-dimensional arrays of artificial low-temperature superconducting Nb/NbSi/Nb junctions. Micron-size junctions are fabricated using micro- and nanofabrication tools.The first chapter of this thesis describes the theory of Josephson junctions and how mutual coupling between Josephson junctions can lead to self-syn-chronization, facilitating the superradiant emission of electromagnetic radia-tion. The second chapter is focused on the technical aspects of this work, with detailed descriptions of sample fabrication and experimental techniques. The third chapter presents main results and discussion. It is demonstrated that de-vices based on high-Tc cuprates allow tunable emission in a very broad fre-quency range 1-11 THz. For low- Tc junction arrays synchronization of up to 9000 junctions is successfully achieved. It is argued that an unconventional traveling-waves mechanism facilitates the phase-locking of such huge arrays. The obtained results confirm a possibility of creation of high-power, continu-ous-wave, compact and tunable THz sources, based on arrays of Josephson junctions.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Physics, Stockholm University, 2020. s. 67
Nyckelord
Josephson junction, Superconductor, ThZ emission, high-Tc
Nationell ämneskategori
Fysik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:su:diva-181234 (URN)978-91-7911-178-6 (ISBN)978-91-7911-179-3 (ISBN)
Disputation
2020-09-09, sal FR4, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2020-08-17 Skapad: 2020-04-28 Senast uppdaterad: 2022-03-04Bibliografiskt granskad

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Kalenyuk, Aleksey A.Pagliero, AlessandroBorodianskyi, Evgenii A.Krasnov, Vladimir M.

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Physical Review B
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