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Coexistence of type-I and type-II superconductivity signatures in ZrB12 probed by muon spin rotation measurements
KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.ORCID iD: 0000-0002-3577-7966
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2020 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 14, article id 144523Article in journal (Refereed) Published
Abstract [en]

Superconductors usually display either type-I or type-II superconductivity and the coexistence of these two types in the same material, for example, at different temperatures, is rare in nature. We employed the muon spin rotation (mu SR) technique to unveil the superconducting phase diagram of the dodecaboride ZrB12 and obtained clear evidence of both type-I and type-II characteristics. Most important, we found a region showing unusual behavior where the usually mutually exclusive mu SR signatures of type-I and type-II superconductivity coexist. We reproduced that behavior in theoretical modeling that required taking into account multiple bands and multiple coherence lengths, which suggests that material has one coherence length larger and another smaller than the magnetic field penetration length (the type-1.5 regime). At stronger fields, a footprint of the type-II mixed state showing square flux-line lattice was also obtained using neutron diffraction.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2020. Vol. 102, no 14, article id 144523
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-286197DOI: 10.1103/PhysRevB.102.144523ISI: 000582413900008Scopus ID: 2-s2.0-85095452272OAI: oai:DiVA.org:kth-286197DiVA, id: diva2:1523589
Note

QC 20210128

Available from: 2021-01-28 Created: 2021-01-28 Last updated: 2022-06-25Bibliographically approved
In thesis
1. Topological excitations in field theory models of superconductivity and magnetism
Open this publication in new window or tab >>Topological excitations in field theory models of superconductivity and magnetism
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Topological excitations are subjects of intensive studies in physics and mathematics. In solid-state and soft matter physics, topological excitations can largely determine the thermodynamic and electromagnetic properties of materials, while in high energy physics they were theorized as particles. The corresponding theories are based on field models, which are among the pillars of theoretical physics.

Field theory models of superconductivity and magnetism are the theoretical basis for this work. Topological excitations in superconductors and magnets have been studied since the middle of the last century. Since then, a huge amount of work has been accumulated on vortices, Bloch points and skyrmions. In this popular topic, we discovered new phenomena. The main results are:

Discovery and theory of skyrmion braids in cubic chiral magnets. 

Coexistence of type-I and type-II superconductivity signatures in muon spin rotation measurements on ZrB_{12} explained by theoretical modeling of vortex states giving qualitative agreement. 

Theory and experimental evidence of magnetic field controlled pairwise interaction of skyrmions in cubic chiral magnets. 

Experimental observation of chiral bobbers predicted in theory by Rybakov et al. (2015). 

Theory of a new type of magnetic ordering - antichiral ferromagnetism - giving rise to unique skyrmions.  

Generalization of the Bogdanov-Yablonskii solution (1989) for classical models of magnets from the case of a skyrmion with a topological charge of -1 (+1) to the case of all integer charges. 

Positive answer to the Babaev-Faddeev-Niemi hypothesis (2002) on the existence of knot excitations in the superconducting state by demonstrating stable solutions in a model that takes into account the Andreev-Bashkin effect. 

Abstract [sv]

Topologiska excitationer har fått stor uppmärksamhet inom både fysik och matematik. I den kondenserade materiens fysik kan topologiska excitationer ha en avgörande roll för termodynamiska och elektromagnetiska egenskaper av material, medan dessa excitationer i högenergifysik var teoretisk betraktade som partiklar. De motsvarande teorierna är baserade på fältmodeller, vilka är av fundamental vikt för teoretisk fysik. Fältteoretiska modeller för supraledning och magnetism är de teoretiska utgångspunkterna för denna avhandling. 

Topologiska excitationer i supraledare och magneter har studerats sedan 50-talet. Sedan dess har en stor mängd arbete ägnats åt att studera virvlar, Bloch-punkter och skyrmioner. I detta populära forskningsområde har vår forskning lett till upptäckten av nya fenomen, de huvudsakliga resultaten är: 

Upptäckten av skyrmionflätor i kirala kubiska magneter och formuleringen av teorin rörande dessa.

Förklaring av samexisterande typ-1 och typ-2 supraledande signaturer i muon-spin-rotationsmätningar i ZrB_{12} genom teoretisk modellering av virveltillstånd som uppvisar kvalitativa överenstämmelser. 

Teoretiskt och experimentellt bevis för magnetisk justerbar skyrmion-skyrmion interaktion i kirala kubiska magneter. 

Experimentell observation av kirala flötesstrukturer förutspådd av Rybakov et el. (2015). 

Teori rörande anti-chiral ferromagnetism, en ny typ av magnetisk ordning som ger upphov till unika skyrmioner. 

Generalisering av Bogdanov-Yablonskii lösningen (1989) för klassiska modeller av magneter från fallet av en skyrmion med topologisk laddning-1 (+1) till alla heltalsladdningar.

Positivt besvarat Babaev-Faddeev-Niemi hypotesen (2002) rörande existensen av knutexcitationer i supraledare genom att ha demonstrerat stabila lösningar i en modell som tar i beaktande Andreev-Bashkin effekten.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2021. p. 51
Series
TRITA-SCI-FOU ; 2021:34
National Category
Physical Sciences
Research subject
Physics; Physics, Theoretical Physics
Identifiers
urn:nbn:se:kth:diva-301652 (URN)978-91-7873-981-3 (ISBN)
Public defence
2021-10-04, FP21 och via Zoom, Roslagstullsbacken 33, Stockholm, 11:45 (English)
Opponent
Supervisors
Available from: 2021-09-13 Created: 2021-09-09 Last updated: 2022-06-25Bibliographically approved

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Rybakov, Filipp N.Babaev, Egor

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