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Ch. Simon laboratoire CRISMAT CNRS-ENSICAEN

"vortex pinning by surface irregularities and vortex dynamics in NbSe 2 and Bi-2212 what is the peak effect?". Ch. Simon laboratoire CRISMAT CNRS-ENSICAEN. Laboratoire CRISMAT A. Pautrat C. Goupil J. Scola Ecole Normale Supérieure Paris P. Mathieu. LEMA Tours A. Ruyter

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Ch. Simon laboratoire CRISMAT CNRS-ENSICAEN

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  1. "vortex pinning by surface irregularities and vortex dynamics in NbSe2 and Bi-2212 what is the peak effect?" Ch. Simon laboratoire CRISMAT CNRS-ENSICAEN

  2. Laboratoire CRISMAT A. Pautrat C. Goupil J. Scola Ecole Normale Supérieure Paris P. Mathieu LEMA Tours A. Ruyter Laboratoire Léon Brillouin A. Brûlet Tata Inst. Bombay S. Bhattacharya

  3. V(mV) Ic I (A) Collective pinning bulk vs surface pinning (Pb-In) Larkin Ovchinikov 1979 Fp = (npfp 2/ 2 Vc)1/2 Vc a C662 C44 Surface treatments Ic (Amp)

  4. q cr n Boundary conditions ic lvl (moe/B)1/2 ao P. Mathieu et Y. Simon, Europhys Lett 5, 1988 ~ 0-100 A/cm B Why surface pinning? Usually rough surface  1000 Å ic (A/m) = e . sin qcr MS length

  5. T = 4.2 K 5.2 K 6.2 K Ic (mA) B (Gauss) k = 1 e / HC2 B / BC2 Magnitude of surface pinning Nb film Numerical solution of Ginzburg equations by Guilpin and Simon

  6. q (deg) X (mm) Damaged Surface Ic (mA) T = 4.2 K Vierge B (Gauss) Quantitative?

  7. V V Linear I I V I Voltage current curves « Flux flow » hysteretic « Flux Creep U(I) »

  8. VL Voltmeter J Neutron scattering !

  9. Classical case Nb-Ta singlecrystal

  10. neutrons w B Ic/2 Ic/2 Ibulk=0 Ibulk=(I-Ic) Ic/2 Ic/2 How flows the current? curl B = m0J tan (Dw) = by / B = m0Jxe / B

  11. 0 A Rough surface Smooth surface 20 A w (deg) V=Rff (I-Ic) V (mV) V (mV) V(mV) Dw (deg) Dw (deg) I(A) I (Amp) I (Amp) What happens at high current?

  12. V (mV) Dw (deg) Ic2 Ic2 Ic1 Ic1 < I < Ic2 Inhomogeneous critical current

  13. Surface pinning in NbSe2

  14. The peak effect in NbSe2

  15. FC I<Ic I>Ic 0A

  16. B W/2 W/4 W/4 - b2 +b1 - b2 « Flux lines »

  17. Bi-2212 Transport in the peak effect

  18. Conclusions • Surface pinning dominates in a lot of samples: • Pb-In, Pb-Ta, etc.., Nb • NbSe2 • Bi-2212 • The peak effect is surface pinning

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