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Types of measurements in superconductivity

Types of measurements in superconductivity. Adrian Crisan School of Metallurgy and Materials, University of Birmingham, UK a nd National Institute of Materials Physics, Bucharest, Romania. CONTENTS. I. Transport measurements II. DC magnetization III. AC susceptibility.

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Types of measurements in superconductivity

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  1. Types of measurements in superconductivity Adrian Crisan School of Metallurgy and Materials, University of Birmingham, UK and National Institute of Materials Physics, Bucharest, Romania

  2. CONTENTS • I. Transport measurements • II. DC magnetization • III. AC susceptibility

  3. I. Transport measurements • Contacts: rather easy for wires/tapes (soldering with low temperature soldering alloys based on Indium), quite easy for bulk and melt-textured (Silver paste), and quite difficult for films • Need to use photolitography (photoresist S1818,UV400 Exposure Optics, Karl Suss MJB3 Mask Aligner, Microsposit MF-319 developer) and etching (Diluted Nitric acid 0.1% ) to produce micron-sized bridges

  4. An overview of 4 bridges after etching Karl Suss MJB3 Mask Aligner system

  5. Patterned sample with 4 wires connection on sample broad

  6. Rotator part of the PPMS with transport option

  7. Scheme of rotation measurement of YBCO bridge Quantum Design SQUID MPMS Q.D. PPMS looks rather similar

  8. Resistivity vs. temperature: Tc(H), magnetoresistance Resistivity transition of 1μm BZO-doped YBCO film in magnetic fields of 0, 0.5, 1, 2, 3, 4, 5 and 6 T with H//c Resistivity transition of 1μm BZO-doped YBCO film in magnetic fields of 0, 0.5, 1, 2, 3, 4, 5 and 6 T with H//ab

  9. Phase diagram of High-Tc superconductors The vortex lattice undergoes a first-order melting transition transforming the vortex solid into a vortex liquid [Fisher et al, PRB 43,130, 1991]. At low magnetic fields (approx 1 Oe in BSCCO [A.C. et al, SuST 24, 115001, 2011), there is a reentrance of the melting line [Blatter et al, PRB 54, 72, 1996]. The flux lines in the vortex -liquid are entangled resulting in an ohmic longitudinal response, hence the vortex liquid and normal metallic phases are separated by a crossover at Hc2. • Low enough currents • VL- linear dissipation: E ≈ J • VS (VGlass)- strongly nonlinear dissipation: E ≈ exp[-(JT/J)m]

  10. Vortex melting from transport measurements I-V curves of [(BaCuO2)2/(CaCuO2)2]×35 artificial superlattices in three magnetic fields. The dashed lines represent power-law fits at the chosen melting temperatures: a) B=0.55 kG, T between 57 and 79.8 K, Tm=72.8 K; b) B=4.4 kG, T between 55.85 and 78.1 K, Tm=70.9 K; and c) B=10.8 kG, T between 49.75 and 75.4 K, Tm=68.1 K. YBCO single-grain [A. C. et al, Physica C 313, 70, 1999] [A. C. et al, Physica C 355, 231, 2001]

  11. Above Tm(B), the I–V curves crossover from an Ohmic behaviour at low currents to a power-law relation at high currents and every I–V curve displays an upward curvature. Below Tm(B), the I–V curves show an exponential relation at low currents and a power-law behaviour at high currents, with a downward curvature, suggesting that the system approaches to a truly superconducting phase VG for J exponentially small. At Tm(B), where the crossover between downward and upward curvatures occurs, the whole I–V curve displays a power-law relation, which takes the form: V (I, T=Tm) ≈ I(z+1)/(d-1), where z is the critical dynamical exponent of VG, and d dimensionality of the system (3 in this case). Above Tm(B) and for low currents, the Ohmic region in the I–V curves, the linear resistance Rl(T) can be scaled as: Rl ≈ (T/Tm-1)n(z+2-d), where n is the static critical exponent.

  12. Fisher, Fisher, Huse scaling (PRB 43, 130, 1991)

  13. Angle dependence of critical current (15Ag/1mm BZO-doped YBCO)x2

  14. Dependence of Ic on the field orientation for (Ag/(YBCO+BZO))x3, showing a small anisotropy for intermediate fields.

  15. II. DC magnetization Jc=Ct.DM Depends strongly on sample geometry thin films; m=DM/2; d-thickness; a,b-rectangle dimension:

  16. Field dependence of the critical current at 77 K for some quasi-multilayers grown in Birmingham in comparison with some results of other EU groups (green and black symbols)

  17. Bulk pinning force • Fp=BxJc 2.33h1/2(1-h)2+1.5h(1-h)2+0.63h(1-h) Surface normal (65%), point normal (22%), volume Dk (13%) 3.15h1/2(1-h)2+0.57h(1-h)2+0.19h3/2(1-h) Surface normal (90%), point normal (8%), surface Dk (2%)

  18. III. AC susceptibility measurements • fundamental and 3rdharmonic • Quantum Design PPMS • (T) at various HDC, hac ( 15 Oe), f ( 10 kHz): Tc(H) • ”(hac), 3(hac) at various fixed T and HDC and varying f: Jc(T,HDC, f), Ueff(T,HDC) Tm is the on-set of third harmonic susceptibility 3(T) [A. C. et al., 2003 Appl. Phys. Lett. 83 506]

  19. Critical current density as function of temperature, field, and frequency, using AC susceptibility measurements • JC = h*/da (in A/cm2) • h* - position of maximum (in Oe) • d – film thickness (in cm) • - coefficient slightly dependent on geometry (approx. 0.9) • E.H. Brandt, Physical Review B • 49/13 (1994) 9024.

  20. Anderson-Kim Collective pinning Zeldov

  21. EXPERIMENTAL: A.C. et al, SuST 22, 045014, 2009

  22. Vortex melting line from ac susceptibility ” is a measure of total dissipation: -linear: Thermal Activated Flux Flow (TAFF) and Flux Flow (FF) -nonlinear:Flux Creep 3 is a measure on nonlinear dissipation (flux-creep) only [P. Fabricatore et al, PRB 50, 3189, 1994]

  23. -two-fluid: ab(T)= ab(0)[1–(T/Tc)4]-1/2 -3D XY : ab(T)= ab(0)[1–T/Tc]-1/3 -mean-field: ab(T)= ab(0)[1–T/Tc]-1/2 C 1/42 , cL = 0.15, =90

  24. Examples 3D XY Two-fluid gYBCO = 5.4 gTl:1223=12.6 [A. C. et al., 2003 Appl. Phys. Lett. 83 506] [A. C. et al., 2007 PRB 76 21258]

  25. n=9 9 HgBa2O2 13 14 9 8 c 6 9 a 8 10 Z O(1)2- OP (SC) Nh IP (AF) (n-2) -(z) OP (SC) O(2)2- HgBa2Can-1CunOy (with n ≥ 6 ) [A. C. et al., 2008 PRB 77 144518]

  26. Two-fluid (1245 and 1234) Magnetically-coupled pancake vortex molecules composed of two pancakes separated by the thin CRL, strongly coupled by Josephson coupling

  27. Ba2Ca3Cu4O8(O1−yFy)2 [ F(2y)-0234] • Ba2Can-1CunO2n+2 (n=3-5), F=0, samples are optimally doped with Tc larger than 105 K, but they are very unstable • The system becomes stable after substitution of F at the apical O site; underdoped states • F(2.0)-0234 is not a Mott insulator, but a SC with Tc=58 K • Thin CRL (0.74 nm) as compared with other multilayered cuprates • Allow the investigation of underdoped region by varying the F doping • 2y = 1.3, 1.6, 2.0 (105, 86, 58 K) [D. D. Shivagan,.., A.C., et al., SuST 24, 095002]

  28. Penetration depth: 3D XY critical fluctuations model • F(1.3)-0234 near-optimally-doped, enough carriers in both OP and IPs, 3D SC, strong Josephson coupling

  29. Penetration depth: mean-field model • F(1.6)-0234 under-doped; out of the region of critical fluctuations; rearrangement of Fermi surfaces through hybridization between OP and IP bands; OP Fermi surface has a 2D character, IP Fermi surface has a 3D character

  30. Penetration depth: two-fluid model • F(2.0)-0234 heavily under-doped; formal Cu valence is 2+, should be half-filled Mott insulator; evidence of self-doped thick IPs block, as compared with thin IP block of F(2.0)-0212 that shows 3D-2D cross-over • Absence of 3D-2D cross-over is a manifestation of cooperative coupling in CRL and IPs

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