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Sequence of Quantum Phase Transitions in Bi2Sr2CaCu2O8+delta Cuprates Revealed by In Situ Electrical Doping of One and the Same Sample
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics. Universität Erlangen-Nürnberg, Germany.
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Number of Authors: 5
2016 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, no 6, 067001Article in journal (Refereed) Published
Abstract [en]

Our recently discovered electrical doping technique allows a broad-range variation of carrier concentration without changing the chemical composition. We show that it is possible to induce superconductivity in a nondoped insulating sample and to tune it reversibly all the way to an overdoped metallic state. This way, we can investigate the whole doping diagram of one and the same sample. Our study reveals two distinct critical points. The one at the overdoped side is associated with the onset of the pseudogap and with the metal-to-insulator transition in the c-axis transport. The other at optimal doping is associated with the appearance of a dressed electron energy. Our study confirms the existence of multiple phase transitions under the superconducting dome in cuprates.

Place, publisher, year, edition, pages
2016. Vol. 116, no 6, 067001
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-127346DOI: 10.1103/PhysRevLett.116.067001ISI: 000369737100007OAI: oai:DiVA.org:su-127346DiVA: diva2:911252
Available from: 2016-03-11 Created: 2016-03-02 Last updated: 2016-05-11Bibliographically approved
In thesis
1. Unraveling the cuprate superconductor phase diagram: Intrinsic tunneling spectroscopy and electrical doping
Open this publication in new window or tab >>Unraveling the cuprate superconductor phase diagram: Intrinsic tunneling spectroscopy and electrical doping
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2016. 77 p.
Keyword
Superconductivity, cuprates, intrinsic tunneling spectroscopy, Josephson junctions, mesa structures, micro/nanoscale fabrication, electrical doping, pseudogap, Bi-2212, Bi-2201
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-129270 (URN)978-91-7649-434-9 (ISBN)
Public defence
2016-06-13, sal FB54, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
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Available from: 2016-05-19 Created: 2016-04-19 Last updated: 2016-06-15Bibliographically approved

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Jacobs, ThorstenSimsek, YilmazKrasnov, Vladimir M.
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