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Electron-tunneling measurements of low-T-c single-layer Bi2+xSr2-yCuO6+delta: Evidence for a scaling disparity between superconducting and pseudogap states
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.ORCID-id: 0000-0002-7553-2816
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Visa övriga samt affilieringar
2012 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, Vol. 86, nr 21, artikel-id 214506Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We experimentally study intrinsic tunneling and high magnetic field (up to 65 T) transport characteristics of the single-layer cuprate Bi2+xSr2-yCuO6+delta, with a very low superconducting critical temperature T-c less than or similar to 4 K. It is observed that the superconducting gap, the collective bosonic mode energy, the upper critical field, and the fluctuation temperature range are scaling down with T-c, while the corresponding pseudogap characteristics remain the same as in high-T-c cuprates with 20 to 30 times higher T-c. The observed disparity of the superconducting and pseudogap scales clearly reveals their different origins.

Ort, förlag, år, upplaga, sidor
2012. Vol. 86, nr 21, artikel-id 214506
Nationell ämneskategori
Fysik
Forskningsämne
fysik
Identifikatorer
URN: urn:nbn:se:su:diva-86498DOI: 10.1103/PhysRevB.86.214506ISI: 000312290600002Scopus ID: 2-s2.0-84871071245OAI: oai:DiVA.org:su-86498DiVA, id: diva2:587156
Anmärkning

AuthorCount:10;

Tillgänglig från: 2013-01-14 Skapad: 2013-01-14 Senast uppdaterad: 2022-09-30Bibliografiskt granskad
Ingår i avhandling
1. Intrinsic tunneling spectroscopy of low-Tc cuprate superconductors: Pseudogap, fluctuations and electrical doping
Öppna denna publikation i ny flik eller fönster >>Intrinsic tunneling spectroscopy of low-Tc cuprate superconductors: Pseudogap, fluctuations and electrical doping
2014 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In this thesis, intrinsic tunneling and magnetic transport measurements of the cuprate superconductor Bi2+xSr2-yCuO6+δ (Bi-2201) are presented. The compound is characterized by a single-CuO2 plane, has a very low critical temperature Tc ~ 4K and a relatively low upper critical field Hc2 ~ 10T. Therefore, superconductivity can be suppressed even at low temperatures, which opens the possibility to study normal-state properties with a relatively low influence of thermal fluctuations. Understanding the mechanism of Tc suppression in this compound might help understanding the mechanism of high Tc in other cuprates. The measurements where performed on small mesa structures with areas less than a square micrometer, which allow for measurements with nearly no artifacts caused by heating or crystal defects.

This series of experiments demonstrate that all superconducting characteristics are reduced inproportion to Tc , but the corresponding c-axis pseudogap characteristics remains similar to that in high-Tc Bi-2212 and Bi-2223 compounds with 20-30 times larger Tc. This large disparity reveals that the pseudogap is not connected to superconductivity, instead it possibly represents a different spin-singlet order that is universal to all cuprates. Furthermore, the experiments show that the thermal fluctuation region is not extraordinary large in this compound and is therefore not a cause of the low Tc, which leads to the assumption that this is caused by a weaker coupling, resulting in a smaller Cooper pair energy.

In addition, the change of mesa properties by electrical doping is studied on this compound, as well as on Bi-2212. The superconducting and normal state properties can be altered in a similar way than by conventional doping, without the use of different samples. This makes doping dependent studies much simpler and helps to understand the puzzling behavior of existing states within these compounds.

Ort, förlag, år, upplaga, sidor
Stockholm University, 2014. s. 53
Nyckelord
Bi-2201, Bi-2212, low-Tc, cuprates, intrinsic tunneling, transport measurements, pseudogap, fluctuations, electrical doping
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:su:diva-108236 (URN)
Presentation
2014-10-15, A2:1041, Albanova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-11-04 Skapad: 2014-10-15 Senast uppdaterad: 2014-11-04Bibliografiskt granskad
2. Unraveling the cuprate superconductor phase diagram: Intrinsic tunneling spectroscopy and electrical doping
Öppna denna publikation i ny flik eller fönster >>Unraveling the cuprate superconductor phase diagram: Intrinsic tunneling spectroscopy and electrical doping
2016 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

High-temperature superconductors belong to the group of strongly correlated materials. In these compounds, complex repulsive electron interactions and a large number of degrees of freedom lead to a rich variety of states of matter. Exotic phases like the pseudogap, charge-, spin- and pair-density waves, but also the remarkable phenomenon of superconductivity emerge, depending on doping level and temperature. However, up to now it is unclear what exactly causes these states, to what extent they are coexisting or competing, and where their borders in the phase diagram lie. A better understanding could help in finding the mechanism behind high-temperature superconductivity, but would also provide a better insight into the puzzling behavior of strongly correlated materials.

This thesis tries to resolve some of these questions with focus on the underdoped pseudogap regime. Mesa structures of bismuth-based cuprate superconductors were studied using intrinsic tunneling, which allows spectroscopic characterizations of electronic density of states inside the material. A micro/nano fabrication method was developed to further reduce mesa areas into the sub square-micrometer range, in order to minimize the effect of crystal defects and measurement artifacts caused by heating induced by the measurement current.

The comparison of energy scales in Bi-2201 and Bi-2212 cuprates shows that the pseudogap phenomenon is not connected to superconductivity, but possibly represents a competing spin-singlet order that is universal to all cuprates. The analysis of the upper critical field in Bi-2201 reveals a low anisotropy, which gives evidence of paramagnetically limited superconductivity. Furthermore, a new electrical doping method is demonstrated, which enables the reversible tuning the doping level of Bi-2212 and study a broad doping range upon a single sample. Using this method, two distinct critical points were observed under the superconducting dome in the phase diagram: one at the overdoped side, associated with the onset of the pseudogap and a metal to insulator transition, and one at optimal doping, associated with an enhanced "dressed" electron energy. Finally, a novel angular-dependent magnetotunneling technique is introduced, which allows for the separation of the superconducting and non-superconducting contributions to the pseudogap phenomenon. The method reveals that after an abrupt decay of the energy gap for TTc, weak superconducting correlations persist up to several tens of degrees above Tc.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Physics, Stockholm University, 2016. s. 77
Nyckelord
Superconductivity, cuprates, intrinsic tunneling spectroscopy, Josephson junctions, mesa structures, micro/nanoscale fabrication, electrical doping, pseudogap, Bi-2212, Bi-2201
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:su:diva-129270 (URN)978-91-7649-434-9 (ISBN)
Disputation
2016-06-13, sal FB54, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2016-05-19 Skapad: 2016-04-19 Senast uppdaterad: 2022-02-23Bibliografiskt granskad

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Jacobs, ThorstenKatterwe, Sven OlofMotzkau, HolgerRydh, AndreasKrasnov, Vladimir M.

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