Alexey E. Kovalev

Superconducting state of the layered conductor α-(BEDT-TTF)2NH4Hg(SCN)4 in magnetic fields parallel to the layer plane

The superconductivity of the quasi two-dimensional (2D) organic compound α-(BEDT-TTF) 2 NH 4 Hg(SCN) 4 in the magnetic field applied exactly parallel to the conducting plane is studied through the measurement of the specific heat, thermal conductivity and ac susceptibility in accordance with the resistance, covering the whole temperature range. According to the bulk measurements, the upper critical field H c2 is close to the field giving the end-point of zero-resistance, while the onset-junction and midpoint criteria from the resistance measurement give notable overestimation of H c2 , indicating fluctuating and/or inhomogeneous contributions to superconductivity. The H c2 at low temperature (0.1 K) is isotropic within the 2D plane and comparable to the BCS Pauli paramagnetic limit, although no first-order transition feature is observed. The detailed resistive transition characteristics are presented.

Effect of an In-Plane Magnetic Field on the Interlayer Phase Coherence in the Extreme-2D Organic Superconductor κ-(BEDT-TTF)2Cu(NCS)2

Using a high-sensitivity cavity perturbation technique (40 to 180 GHz), we have probed the angle dependent interlayer magneto-electrodynamic response within the vortex state of the extreme two-dimensional organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. A previously reported Josephson plasma resonance [M. Mola et al., Phys. Rev.B62, 5965 (2000)] exhibits a dramatic re-entrant behavior for fields very close (< 1°) to alignment with the layers. In this same narrow angle range, a new resonant mode develops which appears to be associated with the non-equilibrium critical state. Fits to the angle dependence of the Josephson plasma resonance provide microscopic information concerning the superconducting phase correlation function within the vortex state. We also show that the effect of an in-plane magnetic field on the temperature dependence of the interlayer phase coherence is quite different from what we have previously observed for perpendicular magnetic fields.

Magnetic field studies of the peculiar electronic state in the /spl alpha/-(BEDT-TTF)/sub 2/MH/sub g/(SCN)/sub 4/ family

Summary form only given. The variety of magnetoresistance (MR) anomalies exhibited by the members of the /spl alpha/-(BEDT-TTF)/sub 2/MH/sub g/(SCN)/sub 4/ family with M=Tl, K or Rb is reviewed in the connection with possible modification of their electronic structure at low temperatures. Special attention is paid to the angular MR oscillations (AMRO) which provide indispensable information about the Fermi surface (FS). Two different types of AMRO are observed above and below the phase transition temperature, T/sub p/, respectively. The high-temperature AMRO are associated with the cylindrical FS enabling us to deduce the cylinder cross-section. At the same time, the low-temperature AMRO reveal an occurrence of a specific plane in the electronic system indicating that a new periodicity arises below T/sub p/. The cylindrical AMRO can be restored by high magnetic field or high pressure thus confirming the re-entrance into the high-temperature state. We present the results on the low temperature AMRO in all the three salts and analyze them in view of possible changes in the electronic system. Other peculiarities of both the semiclassical MR and quantum oscillations are also discussed within the proposed model.