Annealing of the torn vortex lattice in YBCO
Annealing of the torn vortex lattice in YBCO crystals Victoria Bekeris Gabriela Pasquini Laboratorio de Bajas Temperaturas, Depto. de Física, FCEy. N, Universidad de Buenos Aires, Argentina. Partially supported by: Fundación Sauberán, UBACy. T X 200 Group Members: 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
Key results: Oscillatory dynamics organizes different robust vortex lattice configurations (VLC) in YBCO crystals 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 : ac susceptibility measurements probe the VLC - ’+ j ’’ (non-linear regime) High | ’| or low ’’ high effective Jc, low mobility - Rac (Campbell regime) High | ’| mobility effective pinning potential well low real λac, high curvature of effective pinning wells L - Experimental results compared with MD calculations
Measuring procedure Initial state “Shaking” magnetic field Hdc ~ 3 k. Oe >> Hac ~ 10 Oe > “Probe” ac field 10 -2 Oe < Hac < 1 Oe Hdc ac susceptibility measurement to probe the order of the VL t, N YBa 2 Cu 3 O 7 single crystals I. V. Alexandrov et al. JETP Lett. 48, 493 (1988)
Experimental results in twinned YBa 2 Cu 3 O 7 single crystals Twinned YBa 2 Cu 3 O 7 ( 0. 56 x 0. 02 mm 3 ) Tc= 92 K , T= 0. 3 K ( 10%-90%) Hac // ĉ , . Hdc = 3 k. Oe, =20 avoiding Bose transition. YBa 2 Cu 3 O 7 single crystals I. V. Alexandrov et al. JETP Lett. 48, 493 (1988)
Non-linear and Linear ac = ´+ i ´´ Linear Hdc = 0 Hdc = 2. 2 k. Oe hac= 0. 04 Oe Hdc = 2 k. Oe Non – linear Peak Effect Hdc = 2. 2 k. Oe hac= 3. 4 Oe 87 89 T (K) 91 No clear evidence of PE in linear regime
Non- linear response Hdc = 3 k. Oe mobility Hdc = 3 k. Oe Symmetric wave form Sinusoidal, Triangular, Square S. O. V. et al PRL. 86, 504 (2001); PRB. 65 134513(2002). Asymmetric wave form Sawtooth, with variable asymmetry
to increase mobility to decrease mobility to order the VL to disorder the VL Molecular Dynamics Simulations S. O. Valenzuela Phys. Rev. Lett. 88, 247003 (2002)
Connection between attained mobility and effective pinning potential wells?
In Campbell regime: - du/dt - L u + J x o +FT(t) =0 u: vortex displacement, J: current density, FT(t): thermal force : viscosity, L : Labusch constant curvature effective wells 2 c = B 0 / 4 L
Linear ac = ´+ i ´´ In a general case: Campbell ac = R + i I In Campbell regime it is real, e = I / R <<1 (e 0. 07) ac 2 = L 2 + B 0 / 4 L L = Labusch parameter curvature pinning wells ac + sample geometry determines ac E. H. Brandt, Phys. Rev. B 50, 13833 (1994); ibid 49 9024 (1994); ibid 50 4034 (1994). C. J. van der Beek et al. , Phys. Rev. B 48, 3393 (1993)
Normalized real penetration depth, R / D, for Sy and Asy VLC´s D =( Rd/2) 1/2 2 R d G. Pasquini and V. Bekeris, PRB in press
Annealed (Sy) and torn (Asy) vortex lattice in a warming-cooling process Sy : Reversible T cycle Asy : Irreversible T cycle Slow ~ 2 hrs. cycle Tini ~ 87. 3 K T 1. 3 K Meas freq: 30 k. Hz
Annealed (Sy) and torn (Asy) vortex lattice in 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
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.
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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, R 11069 (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 ac 2 = L 2 + 0 B / (4 L) = L 2 + C 2 1 + = 1+ ´ + j ´´ = ∑ cn / ( n + ) = R / 2 ac 2
Acknowledgements Paco de la Cruz Yanina Fasano Mariela Menghini Carlos Balseiro Daniel Domínguez Eva Andrei Marcelo Rozenberg Pablo Tamborenea Gustavo Lozano Liliana Arrachea Jorge Kurchan Leticia Cugiliangolo
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