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Physical Processes in Disordered Superconductors

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Physical Processes in Disordered Superconductors COMENIUS UNIVERSITY IN BRATISLAVA FACULTY OF MATHEMATICS, PHYSICS AND INFORMATICS Physical processes in disordered superconductors 2016 RNDr. Martin Zemliˇckaˇ COMENIUS UNIVERSITY IN BRATISLAVA FACULTY OF MATHEMATICS, PHYSICS AND INFORMATICS Physical processes in disordered superconductors Dissertation thesis 4.1.3 Condensed matter physics and acoustics Department of experimental physics Bratislava, 2016 RNDr. Martin Zemliˇckaˇ 51249511 Comenius University in Bratislava Faculty of Mathematics, Physics and Informatics THESIS ASSIGNMENT Name and Surname: Mgr. Martin Žemlička Study programme: Condense Matter Physics and Acoustics (Single degree study, Ph.D. III. deg., full time form) Field of Study: Physics Of Condensed Matter And Acoustics Type of Thesis: Dissertation thesis Language of Thesis: English Secondary language: Slovak Title: Physical processes in disordered superconductors. Literature: 1. A Tholen, Parametric amplification with weak-link nonlinearity in superconducting microresonators, arXiv:0906.2744v2 2.G. Wendin, V.S. Shumeiko,Superconducting Quantum Circuits, Qubits and Computing arXiv:cond-mat/0508729v1 3. A. M. ZAGOSKIN, QUANTUM ENGINEERING, Cambridge University Press 2011 4. L. Skrbek a kol. Fyzika nízkých teplot, matfyzpress PRAHA 2011 Aim: The aim of the thesis is the examination of physical processes in disordered superconductors and nonlinear effects in superconducting nanostructures. Such structures can be applied as very sensitive detectors usable in astronomy, experimental physics or in quantum information processing. Tutor: doc. RNDr. Miroslav Grajcar, DrSc. Department: FMFI.KEF - Department of Experimental Physics Head of prof. Dr. Štefan Matejčík, DrSc. department: Assigned: 01.09.2012 Approved: 01.03.2012 prof. RNDr. Peter Kúš, DrSc. Guarantor of Study Programme Student Tutor 51249511 Univerzita Komenského v Bratislave Fakulta matematiky, fyziky a informatiky ZADANIE ZÁVEREČNEJ PRÁCE Meno a priezvisko študenta: Mgr. Martin Žemlička Študijný program: fyzika kondenzovaných látok a akustika (Jednoodborové štúdium, doktorandské III. st., denná forma) Študijný odbor: fyzika kondenzovaných látok a akustika Typ záverečnej práce: dizertačná Jazyk záverečnej práce: anglický Sekundárny jazyk: slovenský Názov: Physical processes in disordered superconductors. Fyzikálne procesy v neusporiadaných supravodičoch. Literatúra: 1. A Tholen, Parametric amplification with weak-link nonlinearity in superconducting microresonators, arXiv:0906.2744v2 2.G. Wendin, V.S. Shumeiko,Superconducting Quantum Circuits, Qubits and Computing arXiv:cond-mat/0508729v1 3. A. M. ZAGOSKIN, QUANTUM ENGINEERING, Cambridge University Press 2011 4. L. Skrbek a kol. Fyzika nízkých teplot, matfyzpress PRAHA 2011 Cieľ: Cieľom práce je skúmanie fyzikálnych procesov v neusporiadaných supravodičoch a nelineárnych javov v supravodivých nanoštruktúrach. Tieto môžu byť použité ako veľmi citlivé detektory, využiteľné v astronómii, experimentálnej fyzike, ako aj pri spracovaní kvantovej informácie. Školiteľ: doc. RNDr. Miroslav Grajcar, DrSc. Katedra: FMFI.KEF - Katedra experimentálnej fyziky Vedúci katedry: prof. Dr. Štefan Matejčík, DrSc. Dátum zadania: 01.09.2012 Dátum schválenia: 01.03.2012 prof. RNDr. Peter Kúš, DrSc. garant študijného programu študent školiteľ Abstract Author: RNDr. Martin Zemliˇckaˇ Title: Physical processes in disordered superconductors Supervisor: Prof. RNDr. Miroslav Grajcar, DrSc. University: Comenius university in Bratislava Faculty: Faculty of mathematics, physics and informatics Department: Department of experimental physics Field of science: 4.1.3. Condensed matter physics and acoustics Year: 2016 The submitted dissertation thesis deals with the experimental analysis of phys- ical processes and effects in highly disordered superconductors. We optimized the deposition process of MoC thin films in order to produce the samples with enhanced sheet resistance R and critical temperature Tc as highest as possible. Optimal parameters for magnetron sputtering of MoC were determined. The sputtering rate deposition was calibrated by AFM thickness measurement. Structure, stoichiometry and surface roughness of the prepared samples were analyzed by means of XRD, EDX and STM, determining that our samples have the cubic crystallographic δ-phase and have a surface with atomic flat areas. Their stoichiometry reveals decreased carbon content, caused probably due to vacancies in the crystal lattice. We measured the transport properties of samples with different thicknesses in a wide range of magnetic fields and obtained basic material parameters. We found that Tc is well correlated with R and kf l, even as sample thickness is varied. We showed that Finkelstein's formula can not be applied in order to explain the Tc suppression, despite the fact that it qualitatively well describes the transport properties of our samples as well as many other thin disordered films. Further analysis by STM was performed, demonstrating an increase of in-gap states with decreasing thickness. Moreover, vortex lattice was observed, proving the long range phase coherence ascribed to fermionic scenario of superconductor insulator transition (SIT). A more detailed view of the field induced SIT of 3 nm MoC thin film revealed the atypical normal state in high magnetic field in agreement with Altshuler-Aronov model of enhanced electron-electron interactions. Moreover, we showed that the interface between the thin film and the substrate plays role as possible pair-breaker. 5 The applicability of our thin films was outlined by the transport measurements of a nanobridge patterned in 10 nm MoC film, which exhibited quantum phase slip like behavior. The scattering effects were further analyzed by microwave measurements of CPW resonators. The decrease of the internal quality factor and the resonant fre- quency was described by modified Mattis-Bardeen theory with introduced finite quasiparticle lifetime. The results agreed with the Dynes phenomenological pa- rameter Γ obtained from STM. The developed model was applied also in order to describe results from terahertz spectroscopy of the complex conductivity. We used the same CPW technique for granular MgB2 superconductor, which showed periodic hysteretic detuning in magnetic field, characteristic of artificially prepared SQUID structures. A reasonable model of such behavior with percolation path interrupted by weak links between the grains was designed and successfully used in the fit. Keywords: thin film, supercoductivity, Mattis-Bardeen theory, quasiparticle lifetime, coplanar waveguide resonator, superconductor-insulator transition, nanowire, RF SQUID, MoC, MgB2 6 Abstrakt Autor: RNDr. Martin Zemliˇckaˇ N´azov: Fyzik´alneprocesy v neusporiadan´ych supravodiˇcoch Skoliteˇ ˇl: Prof. RNDr. Miroslav Grajcar, DrSc. Univerzita: Univerzita Komensk´ehov Bratislave Fakulta: Fakulta matematiky, fyziky a informatiky Katedra: Katedra experiment´alnejfyziky Studijn´yOdbor:ˇ 4.1.3. Fyzika kondenzovan´ych l´atok a akustika Rok: 2016 V predloˇzenejpr´acipojedn´avame o experiment´alnejanal´yzefyzik´alnych pro- cesov vo vysoko neusporiadan´ych supravodiˇcoch. Optimalizovali sme pr´ıpravu tenk´ych ˇ ˇ MoC vrstiev s cielom dosiahnut vzorky so zv´yˇsen´ymodporom na ˇstvorec R a s ˇco najvyˇsˇsoukritickou teplotou Tc. Urˇcilisme optim´alneparametre magnetr´onoveho napraˇsovania MoC vrstiev. R´ychlosˇt napraˇsovania bola kalibrovan´ameran´ımhr´ubky pomocou at´omov´ehosilov´ehomikroskopu (AFM). Strukt´uru,stechiometriuˇ a povr- chov´udrsnosˇt pripraven´ych vzoriek sme analyzovali pomocou XRD, EDX a STM met´od. Z v´ysledkov sme urˇcili, ˇze naˇse vzorky maj´ukubick´ukryˇstalografick´u ˇstrukt´urua atom´arnehladk´eoblasti. Stechiometrick´aanal´yzauk´azalazn´ıˇzen´yob- sah uhl´ıka, sp^osoben´ypravdepodobne kv^olivakanci´amv kryˇst´alovej mrieˇzke. Merali sme tieˇztransportn´evlastnosti vzoriek s r^oznymi hr´ubkami v ˇsirokom rozsahu hodn^otextern´ehomagnetick´ehopoˇla, z ˇcohosme z´ıskali z´akladn´ema- teri´alov´evlastnosti. Zistili sme, ˇze Tc v´yraznekoreluje s R a kf l, a to aj pre vzorky s odliˇsnouhr´ubkou. Uk´azalisme, ˇze Finkelsteinov model nie je moˇzn´e pouˇziˇt na popis potlaˇcenia Tc, napriek tomu, ˇzekvalitat´ıvnes´uhlas´ıs v´ysledkami transportn´ych meran´ına naˇsich vzork´ach, ako aj na vzork´ach pripraven´ych z in´ych neusporiadan´ych supravodiˇcov. Vykonali sme tieˇzanal´yzupomocou STM, ktor´a uk´azalan´arastvn´utro-medzerov´ych stavov so zniˇzuj´ucousa hr´ubkou. Navyˇsesme pozorovali mrieˇzkuv´ırov, ˇcodokazuje pr´ıtomnosˇt f´azovej koherencie prisl´uchaj´ucej fermi´onov´emu scen´aruprechodu supravodiˇc-izolant (S=I). Detailnejˇs´ı pohˇlad na poˇlom indukovan´yprechod S-I v 3 nm hrubej MoC vrstve uk´azalatypick´ynorm´alny stav vo vysok´ych magnetick´ych poliach v zhode s modelom Altshulera a Aronova popisuj´ucisiln´uelektr´on-elektr´onov´uinterakciu. Uk´azalisme navyˇse,ˇzerozhranie 7 podloˇzkya tenkej vrstvy hr´a´ulohu moˇzn´ehorozb´ıjaniaCooperov´ych p´arov. Apliko- vateˇlnosˇt naˇsich tenk´ych vrstiev sme uk´azalina v´ysledkoch transportn´ych meran´ı nano-most´ıka, pripraven´ehoelektr´onovou litografiou na 10 nm tenkej MoC vrstve, ktor´evykazovali pr´ıtomnosˇt kvantov´ehoprek´lzavania f´azy. Rozptylov´eefekty boli tieˇzanalyzovan´emikrovlnn´ymimeraniami koplan´arnych rezon´atorov. Potlaˇcenievn´utornejkvality a rezonanˇcnejfrekvencie sme pop´ısali modifikovan´ymmodelom Mattisa a Bardeena so zavedenou koneˇcnoudobou ˇzivota kv´aziˇcast´ıc.V´ysledkys´uhlasilis hodnotami Dynesovho fenomenologick´ehoparame- tra Γ, z´ıskan´ehopomocou STM. Vyvinut´ymodel
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