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