Electronic transport properties of YBa_1tn2Cu_1tn3O_1tn7_1tn-_1tnx, PrBa_1tn2Cu_1tn2_1tn._1tn9Ga_1tn0_1tn._1tn1O_1tn7_1tn-_1tny trilayers and superlattices perpendicular to the layer structure [Elektronische Ressource] / vorgelegt von Hernán Rodríguez

Sujets

• Physik

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2004
• Nombre de lectures: 9
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Electronic transport properties of
YBa Cu O /PrBa Cu Ga O2 3 7−x 2 2.9 0.1 7−y
trilayers and superlattices perpendicular
to the layer structure
Dissertation
zur Erlangung des Grades
Doktor der Naturwissenschaften (Dr.rer.nat.)
am Fachbereich Physik
der Johannes Gutenberg-Universit¨at Mainz
vorgelegt von
Hern´an Rodr´ıguez
geb.in Bogot´a (Kolumbien)
Mainz, 2004
D77Tag der Einreichung : 05.07.2004
Tag der mu¨ndliche Pru¨fung : 14.10.2004Contents
1 Theoretical background 5
1.1 Superconductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Electron tunneling theory . . . . . . . . . . . . . . . . . . . . . . 6
1.3 The Josephson equations . . . . . . . . . . . . . . . . . . . . . . . 8
1.4 RCSJ Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5 The Bogoluibov de Gennes equations . . . . . . . . . . . . . . . . 11
1.6 Andreev reflections . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.7 Inhomogeneous superconductors . . . . . . . . . . . . . . . . . . . 16
1.8 Comparison between pair potential models and experiments . . . 19
2 Preparation and characterization 23
2.1 Preparation of HTSC superlattices . . . . . . . . . . . . . . . . . 23
2.2 Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.1 Magnetic susceptibility . . . . . . . . . . . . . . . . . . . . 26
2.2.2 X–ray diffraction . . . . . . . . . . . . . . . . . . . . . . . 27
2.3 Junction patterning . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3.1 Mesa structures . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.2 Wiring the junction . . . . . . . . . . . . . . . . . . . . . . 31
2.3.3 Process outline . . . . . . . . . . . . . . . . . . . . . . . . 32
2.4 Device design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.5 Differential conductance measurements . . . . . . . . . . . . . . . 34
3 Trilayers 37
3.1 Bonder–Tinkham–Klapwijk model . . . . . . . . . . . . . . . . . . 37
3.2 Properties of the barrier . . . . . . . . . . . . . . . . . . . . . . . 39
◦3.3 Results of trilayers prepared at T = 840 C . . . . . . . . . . . . 39s
3.4 Proximity effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.4.1 Conventional proximity effect . . . . . . . . . . . . . . . . 44
iiiCONTENTS
3.4.2 Proximity effect in HTSC’s . . . . . . . . . . . . . . . . . . 46
◦3.5 Results for trilayer grown at T = 760 C . . . . . . . . . . . . . . 48s
3.6 Zero bias conductance peak . . . . . . . . . . . . . . . . . . . . . 51
3.7 The Anderson–Appelbaum model . . . . . . . . . . . . . . . . . . 52
3.8 Comparison with experimental results . . . . . . . . . . . . . . . . 52
3.9 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4 Superlattices 59
4.1 In–plane and out–of–plane resistivity in superlattices . . . . . . . 59
4.2 Properties of the PrBa Cu Ga O barrier . . . . . . . . . . . 622 2.9 0.1 7−y
◦4.3 Conductivity measurements of superlattices prepared at T = 840 C 65s
4.4 Background conductance . . . . . . . . . . . . . . . . . . . . . . . 70
◦4.5 Conductivity measurements of superlattices prepared at T = 760 C 73s
4.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5 Optical properties 81
5.1 Two–dimensional antiferromagnets . . . . . . . . . . . . . . . . . 81
5.2 Two magnon interaction . . . . . . . . . . . . . . . . . . . . . . . 83
5.3 High frequency Raman scattering . . . . . . . . . . . . . . . . . . 84
6 Summary 89
Bibliography 93
ivList of Figures
1.1 Semiconductor model description for the SIN tunneling process. . 7
1.2 RCJS circuit for a Josephson junction. . . . . . . . . . . . . . . . 10
1.3 I–V characteristic of over– and underdamped cases in the RCJS
model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4 Schematic representation of the Andreev reflection process. . . . . 16
1.5 Calculation of the DOS for a 1–D superlattice. . . . . . . . . . . . 18
1.6 Density of states for a 1–D superlattice using a self–consistened
pair potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.7 Density of states of a LSCO single crystal. . . . . . . . . . . . . . 20
2.1 AFM pictures ofa STO substrate with and without thermal treat-
ment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2 Magnetic susceptibility of a YBCO thin film and low angle XRD
of a PBCO thin film. . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3 X–ray diffraction of the (YBCO) /(PBCO) superlattice. . . . . . 281 5
2.4 SEM picture of a mesa structure. . . . . . . . . . . . . . . . . . . 31
2.5 Mesa structure preparation. First step “ion milling”. . . . . . . . 32
2.6 Mesa structure preparation. Second step “window opening”. . . . 33
2.7 Mesa structure preparation. Third step “wiring”. . . . . . . . . . 34
2.8 Patterning process outline. . . . . . . . . . . . . . . . . . . . . . . 35
2.9 Top view of the device structure. . . . . . . . . . . . . . . . . . . 36
3.1 G(V) dependence on the parameter Z after the BTK model. . . . 38
3.2 R(T) dependence of PBCO and Gallium doped PBCO. . . . . . . 40
3.3 G(V) dependence of the (YBCO) /(PBCO) superlattice. . . . . 412 10
◦3.4 G(V)–T dependences of a trilayer grown at 840 C with 20 nm
PBCGO barrier.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.5 V–I characteristic of a trilayer with 20 nm PBCGO barrier. . . . 44
vLIST OF FIGURES
3.6 G(V) and BTK simulation of a trilayer with 20 nm PBCGO barrier 45
3.7 Profile of the superconducting order parameter across the SN in-
terface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.8 Profileofthesuperconducting orderparameterattheSN interface
depending on the parameters γ and γ . . . . . . . . . . . . . . . . 47B
◦3.9 G(V)dependencesofatrilayergrownat760 Cwith20nmPBCGO
barrier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.10 ParabolicfitofthedifferentialconductancebackgroundforaYBCO/
PBCGO/YBCO trilayer. . . . . . . . . . . . . . . . . . . . . . . . 50
3.11 Schematic calculation of the quantity ΔG. . . . . . . . . . . . . . 53
3.12 Temperature dependence of the zero bias conductance of a YBCO
/PBCGO/YBCO trilayer. . . . . . . . . . . . . . . . . . . . . . . 54
3.13 Differential conductance against the logarithmic scale of the bias
voltage at different temperatures. . . . . . . . . . . . . . . . . . . 55
3.14 Function G(V,T) against the logarithm of V at different temper-
atures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.15 G(V) dependence of a YBCO/PBCGO/YBCO trilayer for differ-
ent applied magnetic fields at T = 4 K. . . . . . . . . . . . . . . . 57
4.1 R (T) dependences of (YBCO) / (PBCO) superlattices. . . . . 60ab n m
4.2 R (T)dependenceof(YBCO) /(PBCO) superlatticeswith(2/3),c n m
(2/5) and (2/9) modulations. . . . . . . . . . . . . . . . . . . . . 61
4.3 R (T) dependence of the (YBCO) / (PBCGO) superlattice. . . 63c 4 12
4.4 Variable range hopping plot for the out–of–plane resistance. . . . 64
4.5 G(V) dependence of the (YBCO) /(PBCGO) superlattice. . . . 654 12
4.6 G(V) dependence of the (YBCO) /(PBCO) superlattice. . . . . 672 10
4.7 I–V characteristic of the (YBCO) /(PBCO) superlattice. . . . . 682 10
4.8 G(V) dependence of the (YBCO) /(PBCGO) superlattice. . . . 694 16
4.9 Dependence of G(V) with Z. . . . . . . . . . . . . . . . . . . . . . 72
4.10 G(V) dependence of the (YBCO) / (PBCGO) superlattice. . . . 744 12
4.11 Tunneling conductance of the (YBCO) /(PBCGO) superlattice. . 764 5
4.12 Temperature dependence of the superconducting gap. . . . . . . . 77
4.13 G(V) dependence ofthe (YBCO) /(PBCGO) superlattice atT =4 5
4 K. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.14 Profileoftheorderparameterattheinterfaceforsamplesprepared
◦ ◦at T = 840 C and T = 760 C. . . . . . . . . . . . . . . . . . . . 79s s
viLIST OF FIGURES
5.1 Phase diagram for hole–doped cuprates. . . . . . . . . . . . . . . 82
5.2 Simple picture of the AFM ordering in the CuO plane and the2
nonbonding hybridized wave function. . . . . . . . . . . . . . . . . 83
5.3 x–dopingdependenceoftheRamanspectraofY Pr Ba Cu Al Ox 1−x 2 3−y y 7
single crystals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.4 Raman spectra of a PBCO thin film and the (YBCO) /(PBCO)4 6
superlattice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.5 Temperaturedependenceofthetwomagnondampingandsuperex-
change energy of (YBCO) /(PBCO) superlattices. . . . . . . . . 874 m
viiLIST OF FIGURES
viiiList of Tables
3.1 Estimated γ and γ parameters for YBCO–noble metal junction . 47B
4.1 c–axis energy gap values from literature. . . . . . . . . . . . . . . 75
4.2 Normal conductance values for different multilayers. . . . . . . . . 79
ixLIST OF TABLES
x