Two-Dimensional Vortex Melting in BEDT Organic Superconductors and NMR Relaxation Induced by Vortex Structure Defects
Résumé
We present experimental studies and a theoretical model of the 1H NMR relaxation rate (1yT1) in the BEDT organic superconductor in magnetic fields B perpendicular to the conducting layers. The curves T1−1 (T, B − const) show a pronounced peak, whose position Tm(B) coincides with a phase transition line as it has been revealed by other methods. The peak sharpens remarkably with decreasing B when the family of curves T1−1(T, B) converges to the field independent “master curve” below Tm. We show that the complex of experimental results cannot be interpreted as resulting from harmonic oscillations of a rigid vortex lattice, and suggest that the relaxation comes from the Brownian motion of highly diffusive point defects in decoupled 2D crystals of pancake vortices.
Mots clés
- Quantum fluctuations
- Superconducting materials
- Vortex structure defects
- Two dimensional
- Organic superconductors
- Magnetic coupling
- Point defects
- Phase transitions
- Phase diagrams
- Organic conductors
- Nuclear magnetic resonance
- Mathematical models
- Magnetic relaxation
- Magnetic fields
- Brownian movement
- Approximation theory
Domaines
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