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)
Hdc = 2 kOe
T (K) 87 89 91
Non-linear and Linear ac = ´+ i ´´
LinearHdc = 0 hac= 0.04 OeHdc = 2.2 kOe hac= 0.04 Oe
Non – linear Peak EffectHdc = 2.2 kOe hac= 3.4 Oe
No clear evidence of PE in linear regime
Non- linear response mobility
80 82 84 86 88 90-1,0
-0,8
-0,6
-0,4
'
T(K)
ZFC FacCC Des Ord
80 82 84 86 88 90
0,0
0,1
0,2
''
T(K)
ZFC FacCC Des Ord
Symmetricwave form
Asymmetric wave form
Sinusoidal, Triangular, Square Sawtooth, with variable asymmetry
S.O.V. et al PRL. 86, 504 (2001); PRB. 65 134513(2002).
Hdc = 3 kOe Hdc = 3 kOe
to increase mobility to order the VL to decrease mobility 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
In a general case:ac = R + i I
In Campbell regime it is real, = I / R <<1 (
ac2 = L
2 + B 0 / 4 L
L = Labusch parametercurvature 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)
Linear ac = ´+ i ´´
0,0
0,2-1,0
-0,6
-0,2
87 88 89 90 910,0
0,1
(b)
(a)
,, (arb
.uni
ts)
Sample B
Campbell
,,
Hdc
= 040 mOe
(c)
3.4 Oe
Campbell
,
T(K)
Campbell
Normalized real penetration depth, R / D,
for Sy and Asy VLC´s
G. Pasquini and V. Bekeris, PRB in press
86 870,08
0,10
0,12
0,14
0,16
87 880,10
0,12
0,14
0,16
0,18
(a)
Linear regimeh
ac = 40 mOe
Hdc
= 2200 Oe
R/ D
T(K)
Sy Asy
Sample A
(b)
R/ D
T(K)
Sample B
d
2 RD =( Rd/2)
1/2
Annealed (Sy) and torn (Asy) vortex latticein a warming-cooling process
Sy : Reversible T cycle
Asy : Irreversible T cycle
Slow ~ 2 hrs. cycleTini ~ 87.3 KT 1.3 KMeas freq: 30 kHz
87,0 87,5 88,0 88,50,10
0,12
0,14
0,16
Sy
Asy
R/D
T (K)
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
Acknowledgements