Vortex Pinning and Sliding in Superconductors Charles Simon, laboratoire CRISMAT, CNRS

Laboratoire CRISMAT A. Pautrat C. Goupil Ecole Normale Supérieure Paris P. Mathieu LEMA Tours A. Ruyter L. Ammor Laboratoire Léon Brillouin A. Brûlet Institut Laue Langevin C. Dewhurst

I Introduction to vortex pinning and dynamics II A neutron diffraction study in low Tc materials III The peak effect in NbSe 2 IV The surface pinning in Bi-2212 V Conclusions

Vortex dynamics V B FLFL I V ff I (A) V (mV) 0.1 T 0.2 T 0.3 T I c (B) Nb-Ta 4.2 K V= R ff (B,T) (I-Ic(B,T)) E=B. V ff

 Typical disordered elastic system with pinning and sliding with the possibility to vary the intensity of the pinning by changing the magnetic field.  But from the beginning: problems (shape of the IV, …)  Here : Low temperature physics  Neutron scattering, very difficult but quite simple to interpret (10 years)

Neutron scattering B T B c2 B c1 Meissner Normal phase Niobium Nb-Ta Bi-2212

B(G) Cubitt, R. et al. Nature 365, (1993). T. Giamarchi and P. Le Doussal, Phys. Rev. Lett. 72, 1530 (1994). and Phys. Rev. B 52, 1242 (1995).

T. Klein et al., Nature 413, (2001) 404

Neutrons with current Nb-Ta singlecrystal P. Thorel and al., J. Phys. (Paris) 34, 447 (1973). A. Pautrat, Phys. Rev. Lett. 90, (2003).

Neutrons with current Nb-Ta singlecrystal

How flows the current?  Ic/2 I bulk =0 Ic/2 I bulk =(I-Ic) B neutrons curl B =   J tan  b y / B =   J x e / B A. Pautrat, et al. Phys. Rev. Lett. 90, (2003)

surface pinning (Pb-In) V(mV) I (A) Ic Ic (Amp) Surface treatments

Why surface pinning? Normal rough surface i c (A/m) = . sin  cr B 1000 Å MS length P. Mathieu et Y. Simon, Europhys Lett 5, 1988 ~ A/cm icic v  (  o  /B) 1/2  a o Boundary conditions n  cr

 / H C2  / B C2  = 1 Numerical solution of Ginzburg equations by Guilpin and Simon Nb film Quantitative prediction Quantitative analysis of the critical current due to vortex pinning by surface corrugation A.Pautrat, J. Scola, C. Goupil, Ch. Simon, C. Villard, B. Domengès, Y. Simon, B.Phys. Rev. B 69, (2004)

What happens at high current? V=R ff (I-Ic) V(mV) I(A)  (deg) I (Amp) V (  V) Smooth surface Rough surface  (deg) I (Amp) V (  V)  (deg) 0 A 20 A

Inhomogeneous critical current  (deg) V (  V) I c1 < I < I c2 I c1 I c2

The peak effect in NbSe 2 Metastable states of a flux-line lattice studied by transport and small-angle neutron A. Pautrat, J. Scola, Ch. Simon, P. Mathieu, A. Brûlet, C. Goupil, M. J. Higgins, Phys. Rev. B 71, (2005)

NbSe 2

Iron doped NbSe 2

T. Klein et al., Nature 413, (2001) 404

Bi-2212 Transport in the peak effect

Bi-2212 Persistence of an ordered flux line lattice above the second peak in Bi2Sr2CaCu2O8+δ A. Pautrat, Ch. Simon, C. Goupil, P. Mathieu, A. Brûlet, C. D. Dewhurst, and A. I. Rykov Phys. Rev. B 75, (2007)

Bi-2212 with columnar defects 5K 0.4T B  =1T Microbridge 50  m 20  m Surface vortex depinning in an irradiated single crystal microbridge of Bi2Sr2CaCu2O8+δ : Crossover from individual to collective bulk pinning A. Ruyter, D. Plessis, Ch. Simon, A. Wahl, and L. Ammor Phys. Rev. B 77, (2008)

Do columnar defects product bulk pinning? No, there is no bulk currents Do Columnar Defects Produce Bulk Pinning ? M. V. Indenbom, C. J. van der Beek, M. Konczykowski, and F. Holtzberg Phys. Rev. Lett. 84, 1792 (2000)

Reversible magnetization A. Wahl et al., Physica C (1995) R. J. Drost et al, PRB 58 R615 (1998)

 Very powerful technique  Surface currents  Peak effect = metastable states  What is the limit of this stability?  Noise measurements, ac response, Hall effects… Conclusions