Vortex dynamics in superconductors in the presence of anisotropic pinning [Elektronische Ressource] / von Oleksiy K. Soroka

Sujets

• Physik

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2005
• Nombre de lectures: 6
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Vortex dynamics in superconductors in
the presence of anisotropic pinning
Dissertation
zur Erlangung des Grades
Doktor der Naturwissenschaften (Dr.rer.nat.)
am Fachbereich Physik
der Johannes Gutenberg-Universit¨ at Mainz
von
Oleksiy K. Soroka
geb.in Kremenec’(Ukraine)
Mainz, 2004Tag der Einreichung: 08.11.2004
Tag der mundlic¨ hen Prufung:¨ 15.03.2005Vortex dynamics in superconductors in
the presence of anisotropic pinning
Ph. D. thesis
by
Oleksiy K. Soroka
Mainz, 2004Contents
1 Basic concepts of superconductivity 1
1.1 Type II superconductors, vortices . . . ............... 3
1.2 Fluxpinningandcreep............. 6
1.3 High-temperature superconductors . ..... 8
2Guidedvortexmotion,theory 11
2.1 Introduction.............................. 1
2.2 TheFokker-Plankmethod........... 15
2.3 Nonlinear conductivity and resistivity tensors ........... 20
2.4 Calculationsusingmodelpotential ................. 2
2.5 Probability function and the average
pinningforce .................. 30
2.6 Additionalpoint-likepinning..................... 31
2.7 Conclusions........ 34
3 Guiding in YBCO 37
3.1 Twin formation in YBa Cu O .................. 37
2 3 7−δ
3.2 FilmpreparationandX-rayanalysis ..... 42
3.3 Magnetoresistivitymeasurements....... 49
4 Guiding in faceted Nb-films 55
¯4.1 Faceting of the Al O {1010}surface................ 5
2 3
iii CONTENTS
4.2 Samplepreparation.......................... 56
4.3 MagnetoresistivitymeasurementsI ...... 59
4.4 MagnetoresistivitymeasurementsI...... 67
4.5 Discusionoftheexperimentaldata................. 72
4.5.1 Guiding................. 72
4.5.2 Arheniusanalysis ........... 74
4.5.3 NatureofthepinninginfacetedNbfilms.......... 85
5 Conclusions 89
A 93
Bibliography 97List of Figures
1.1 H-T phase diagram of a superconductor .............. 2
1.2 H-T phase diagram of the type II superconductor ......... 4
1.3 Structureofanisolatedvortex.................... 5
1.4 PhenomenologicalphasediagramforHTSC ............ 9
2.1 Samplewithunidirectedpinningplanesinmagneticfield..... 16
2.2 System of coordinates xy associated with the pinning planes . . . 17
2.3 Model pinning potential U (x).................... 24p
2.4 The dependence of the probability functionν on the dimensionlessa
parameter f ................... 26
2.5 The temperature dependence of the probability function ν fora
different values of the parameter f ................. 27
0
−2.6 The temperature dependence of the odd componentν of the prob-
a
ability function for the different values of parameter j ...... 29
0
3.1 Unit cell of YBa Cu O ...................... 38
2 3 7−δ
3.2 Epitaxial relationship between the tetragonal phase and the or-
thorhombic phase of YBa Cu O ...... 39
2 3 7−δ
3.3 Twinning with (110)-plane as a twin wall .............. 40
3.4 Temperature dependences of lattice parameters for substrate ma-
terials having a perovskite-like structure and YBa Cu O .... 41
2 3 7−δ
iiiiv LIST OF FIGURES
3.5 Splitting of the reflections for the four possible twin orientations
of YBa Cu O ........................... 4
2 3 7−δ
3.6 A scan of the (hk2)-plane of YBa Cu O film grown on NdGaO 46
2 3 7−δ 3
3.7 Splitting of the reflections on the scan of the (hk2)-plane of YBa Cu O
2 3 7−δ
film grown on NdGaO ........................ 47
3
3.8 Splitting of the reflections on the scan of the (hk2)-plane of YBa Cu O
2 3 7−δ
film grown on SrTiO .............. 48
3
3.9 Structureasusedforthemagnetoresistivitymeasurements.... 49
3.10Samplemountedonthesampleholder ............... 50
3.11 Resistive superconductive transition of sample ak69 ........ 51
3.12 Resistive supe transition for sample ak81........ 51
3.13 Magnetic field dependence of the even longitudinal component of
the magnetoresistivity for the different transport current orienta-
tions for sample ak69 ......................... 53
3.14 Magnetic field dependencies of the even longitudinal components
of the magnetoresistivity for the sample ak81............ 53
3.15 Magnetic field dependencies of the odd longitudinal components of
the magnetoresistivity for the sample ak69 ............. 54
3.16 Magnetic field dependencies of the odd longitudinal components of
the magnetoresistivity for the sample ak81 ............. 54
¯4.1 Faceted surface of the (1010)-Al O substrate ........... 56
2 3
4.2 STM image of Nb-film deposited on the faceted Al O substrate
2 3
surface................................. 57
4.3 Hall structures as used for the magnetoresistivity measurements . 58
4.4 Superconductive transition in zero magnetic field of the three sam-
pleswithdifferenttransportcurentorientation.......... 60LIST OF FIGURES v
4.5 Temperature and magnetic field dependences of the even longitu-
+dinal magnetoresistivity component ρ for the different transport

curentorientations.......................... 61
4.6 Temperature and magnetic field dependences of the odd longitu-
−dinal magnetoresistivity component ρ for the different transport

curentorientations.......................... 63
4.7 Temperature and magnetic field dependences of the even transver-
+sal magnetoresistivity component ρ for the different transport
⊥
curentorientations.......................... 64
4.8 Temperature and magnetic field dependence of the odd transversal
−magnetoresistivity component ρ for the different transport cur-
⊥
rentorientations............................ 6
4.9 Superconductive transition in zero magnetic field for the different
transportcurrentorientations......... 68
4.10 Temperature dependence of the even longitudinal magnetoresistiv-
+ity component ρ for the different transport current orientations . 69

4.11 Temperature dependence of the odd longitudinal magnetoresistiv-
−ity component ρ for the different transport current orientations . 70

4.12 Temperature dependence of the even transversal magnetoresistiv-
+ity component ρ for the different transport current orientations . 71
⊥
4.13 Temperature dependence of the odd transversal magnetoresistivity
−component ρ for the different transport current orientations . . . 72
⊥
4.14 The dependence of the guiding angle β on temperature in two
experiments.............................. 73
4.15 Arrhenius plot of the even longitudinal magnetoresistivity in a
magnetic field ofµ H =0.007 T for the different transport current
0
orientations.............................. 75vi LIST OF FIGURES
4.16 Arrhenius plot of the even longitudinal magnetoresistivity in a
magnetic field ofµ H =0.015 T for the different transport current
0
orientations.............................. 76
4.17 Arrhenius plot of the even longitudinal magnetoresistivity in a
magnetic field ofµ H =0.030 T for the different transport current
0
orientations.............................. 76
4.18 Arrhenius plot of the even longitudinal magnetoresistivity for the
temperature range of 8.39 K> T> 8.29K............. 81
4.19 Calculated and measured dependences of the even longitudinal
magnetoresistivity on the temperature and its Arrhenius plot . . . 84
4.20 Distribution of the magnetic field density on the faceted surface . 86