1,686 research outputs found
Magnetic field - temperature phase diagram of quasi-two-dimensional organic superconductor lambda-(BETS)_2 GaCl_4 studied via thermal conductivity
The thermal conductivity kappa of the quasi-two-dimensional (Q2D) organic
superconductor lambda-(BETS)_2 GaCl_4 was studied in the magnetic field H
applied parallel to the Q2D plane. The phase diagram determined from this bulk
measurement shows notable dependence on the sample quality. In dirty samples
the upper critical field H_{c2} is consistent with the Pauli paramagnetic
limiting, and a sharp change is observed in kappa(H) at H_{c2 parallel}. In
contrast in clean samples H_{c2}(T) shows no saturation towards low
temperatures and the feature in kappa(H) is replaced by two slope changes
reminiscent of second-order transitions. The peculiarity was observed below ~
0.33T_c and disappeared on field inclination to the plane when the orbital
suppression of superconductivity became dominant. This behavior is consistent
with the formation of a superconducting state with spatially modulated order
parameter in clean samples.Comment: 10 pages, 8 figures, new figure (Fig.5) and references added, title
change
Superconductivity in an organic insulator at very high magnetic fields
We investigate by electrical transport the field-induced superconducting
state (FISC) in the organic conductor -(BETS)FeCl. Below 4 K,
antiferromagnetic-insulator, metallic, and eventually superconducting (FISC)
ground states are observed with increasing in-plane magnetic field. The FISC
state survives between 18 and 41 T, and can be interpreted in terms of the
Jaccarino-Peter effect, where the external magnetic field {\em compensates} the
exchange field of aligned Fe ions. We further argue that the Fe
moments are essential to stabilize the resulting singlet, two-dimensional
superconducting stateComment: 9 pages 3 figure
Dependence of the Superconducting Transition Temperature of MgB2 on Pressure to 20 GPa
The dependence of Tc on nearly hydrostatic pressure has been measured for an
isotopically pure (11B) MgB2 sample in a helium-loaded diamond-anvil-cell to
nearly 20 GPa. Tc decreases monotonically with pressure from 39.1 K at ambient
pressure to 20.9 K at 19.2 GPa. The initial dependence is the same as that
obtained earlier (dTc/dP = -1.11(2) K/GPa) on the same sample in a He-gas
apparatus to 0.7 GPa. The observed pressure dependence Tc(P) to 20 GPa can be
readily described in terms of simple lattice stiffening within standard
phonon-mediated BCS superconductivity.Comment: 9 pages, 3 figure
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