Magnetic properties of layered superconductors
The organic superconductors (BEDT-TTF)[sub 2] Cu(SNC)[sub 2] and (TMTSF)[sub 2]ClO[sub 4], with T[sub c] = 10K and 1.2K, have layered and highly anisotropic crystal structures. This thesis describes AC magnetic susceptibility measurements on these materials which illustrate the consequences of the discrete layered structure for the magnetic properties of the superconducting state. A DC magnetic field applied parallel to the layers of either material causes the rapid suppression of the AC screening response, and this indicates that the pinning restoring force for vortex motion parallel to the layers is anomalously weak in this orientation. This is believed to be due to the small size of the interlayer coherence length relative to the layer spacing. A simple estimate based on the energy and length scales relevant to Josephson coupled layers gives the correct order of magnitude for the pinning force. Pinning for vortices oriented perpendicular to the layers is larger by a factor of 500 for BEDT and 25 for TMTSF. When the DC field is applied at an angle to the layers, the initial suppression of the susceptibility is identical to that for a field parallel to the layers; when the field component normal to the layers exceeds a threshold, a sharp recovery of screening occurs. These observations indicate that the field initially enters the sample only in the direction parallel to the layers. The recovery of screening signals field penetration in the perpendicular direction at higher field strength, and is due to the onset of pinning by in-plane vortex cores. This magnetic [open quotes]lock-in[close quotes] effect is a qualitatively new behavior and is a direct consequence of weak interlayer coupling. The London penetration depth associated with interlayer currents is found to be on the order of hundreds of microns, comparable to that of a Josephson junction, and two to three orders of magnitude larger than for conventional superconductors.
- Research Organization:
- Princeton Univ., NJ (United States)
- OSTI ID:
- 7302817
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BEDT-TTF
MAGNETIC PROPERTIES
TMTSF
ALTERNATING CURRENT
CHLORATES
COPPER COMPOUNDS
DIRECT CURRENT
JOSEPHSON EFFECT
LAYERS
LONDON EQUATION
MAGNETIC SUSCEPTIBILITY
CHLORINE COMPOUNDS
CURRENTS
ELECTRIC CURRENTS
EQUATIONS
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANIC SUPERCONDUCTORS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SELENIUM COMPOUNDS
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
360607* - Other Materials- Superconducting Properties- (1992-)
665411 - Basic Superconductivity Studies- (1992-)