Annealing of the torn vortex lattice in YBCO crystals Victoria Bekeris Gabriela Pasquini Laboratorio de Bajas Temperaturas, Depto. de Física, FCEyN, Universidad de Buenos Aires, Argentina. Partially supported by: Fundación Sauberán, UBACyT X200 V ictoria I. Bekeris Carlos E. Acha Gabriela Pasquini Hernán J. Ferrari Graduate Students Alejandro J. Moreno Guillermo A. Jorge Miguel Monteverde Undergraduate Students Claudio E. Chiliotte Victor Bettachini Group Members:
20
Embed
Annealing of the torn vortex lattice in YBCO crystals
Annealing of the torn vortex lattice in YBCO crystals. Laboratorio de Bajas Temperaturas, Depto. de Física, FCEyN, U niversidad de Buenos Aires, Argentina . Partially supported by: Fundación Sauberán, UBACyT X200. Victoria Bekeris Gabriela Pasquini. Group Members:. V ictoria I. Bekeris - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Annealing of the torn vortex lattice in YBCO crystals
Victoria Bekeris
Gabriela Pasquini
Laboratorio de Bajas Temperaturas, Depto. de Física, FCEyN, Universidad de Buenos Aires, Argentina.Partially supported by: Fundación Sauberán, UBACyT X200
Victoria I. Bekeris
Carlos E. Acha
Gabriela Pasquini
Hernán J. Ferrari
Graduate Students
Alejandro J. Moreno Guillermo A. Jorge
Miguel Monteverde
Gastón Garbarino
Undergraduate Students
Claudio E. Chiliotte
Victor Bettachini
Group Members:
Oscillatory dynamics organizes different robust vortex lattice configurations (VLC) in YBCO crystals
Key results:
Scenario
Annihilation or creation of VL defects (e.g.dislocations)play a major role in bulk VL response
Key results:
Repeated symmetrical shaking - small vortex excursions - heals the VL (annihilation of defects)
The lattice attains HIGHER MOBILITY LOWER PINNING POTENTIAL CURVATURE
Temporarily asymmetrical shaking or large vortex excursions tears the VL (creation of defects)
The lattice attains LOWER MOBILITY HIGHER PINNING POTENTIAL CURVATURE
Procedure :
- Experimental results compared with MD calculations
ac susceptibility measurements probe the VLC
- ’+ j ’’ (non-linear regime) mobility High |’| or low ’’ high effective Jc, low mobility
- R
ac (Campbell regime) effective pinning potential well
High |’| low real λac, high curvature of effective pinning wells L
Hdc
Hdc ~ 3 kOe Hac ~ 10 Oe 10-2Oe < Hac < 1 Oe>> >
YBa2Cu3O7 single crystalsI.V. Alexandrov et al. JETP Lett. 48, 493 (1988)
Measuring procedure
Initial state “Shaking” magnetic field “Probe” ac field
ac susceptibilitymeasurement to probe the order ofthe VL
t, N
Experimental results intwinned YBa2Cu3O7 single crystals
Twinned YBa2Cu3O7 ( 0.56 x 0.6 x 0.02 mm3 ) Tc= 92 K , T= 0.3 K ( 10%-90%)Hac // ĉ ,. Hdc = 3 kOe, =20 avoiding Bose transition.
YBa2Cu3O7 single crystalsI.V. Alexandrov et al. JETP Lett. 48, 493 (1988)
Annealed (Sy) and torn (Asy) vortex latticein a warming-cooling process
Sy : Reversible T cycle
Asy : Irreversible T cycle
• No further disordering as the PE temperature is reached
• relaxation mechanisms for VLC
• Same W-C curves (not shown) for ASY at T below onset PE are reversible
87,0 87,5 88,0 88,50,10
0,12
0,14
0,16
Sy
Asy
R/D
T (K)
Conclusions
• Oscillatory dynamics organizes the VL in YBCO crystals in different configurations (VLC) characterized by their mobility and effective pinning potentials wells.
• Molecular dynamics relates high (low) mobility with low (high) density of defects (e.g. dislocations).
• The system relaxes by thermal activation to more favorable VLC either from “over” ordered or from “over” disordered configurations, probably involving different mechanisms (e.g. elastic, plastic relaxation).
• There is no trivial relationship between VL mobility and pinning potential curvature, particularly near the PE region.
Thank you for your attention
Related researches (incomplete list):
U.Yaron et al. PRL 73 2748 (1994).
S.N Gordeev et al., Nature 385, 324 (1997).
G. Ravikumar et al., PRB 57, R11069 (1998).
W. Henderson et al., PRL 81, 2352 (1998).
Z.L. Xiao et al., PRL 83, 1664 (1999).
S.S Banerjee et al., PRB 59, 6043 (1999).
Y. Paltiel et al., Nature 403, 398 (2000).
X. Ling et al. PRL 86, 712 (2001).
P. Chaddah, PRB 62, 5361 (2000).
D. Stamopoulos et al. PRB 66 214521 (2002)
M. Chandran cond-mat/0407309.
................
- du/dt - L u + J x o + FT(t) =0
: viscosity, L : Labusch constant
u: vortex displacement, J: current density,FT(t): thermal force
ac2 = L
2 + 0 B / (4 L) = L2 + C
2
1 + = 1+ ´ + j ´´ = ∑ cn / (n + )
= R / 2 ac2
Paco de la CruzYanina FasanoMariela MenghiniCarlos BalseiroDaniel DomínguezEva Andrei Marcelo RozenbergPablo TamboreneaGustavo LozanoLiliana ArracheaJorge KurchanLeticia Cugiliangolo