Prof Arzhang Ardavan

Abstract:

We have performed detailed studies of the angle- and temperature-dependent resistive upper critical fields in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. With the magnetic field lying in the conducting planes, our measurements show an upper critical field which comfortably exceeds the Pauli-paramagnetic limit in this material. We find no azimuthal angle dependence of the critical field, in spite of recent evidence that this material has gap nodes characteristic of d-wave superconductivity. We propose that the large critical fields may be due to a Fulde-Ferrell-Larkin-Ovchinnikov state which can exist in exactly in-plane fields because of the nature of the Fermi surface of κ-(BEDT-TTF)2Cu(NCS)2. © 1999 IOP Publishing Ltd.

Abstract:

We have performed ESR measurements on an alpha-(BEDT-TTF)(2)KHg(SCN)(4) Single crystal at temperatures down to 0.9 K. Two regions where the ESR intensity decreases were observed. One corresponds to the proposed SDW transition (T approximate to 9 K); the other takes place at T less than or equal to 2 K. A new resonance line appears below the transition temperature T approximate to 9 K; its intensity grows continuously as the temperature is lowered. We regard the decrease of the ESR line at very low temperatures as evidence of a further phase transition.

Abstract:

We experimentally demonstrate a mechanism for a new kind of magnetic resonance, the Fermi-surface traversal resonance (FTR). This is caused by the periodic traversal of carriers across quasi-one-dimensional (Q1D) sections of Fermi surface (FS) in an external magnetic field. Owing to the warping of the Q1D Fermi sheets, the real space velocities of the carriers oscillate as they cross the FS, generating resonances in the high frequency conductivity of the material. The results contain information about the FS, including the direction and harmonic content of the warping components. Using a rotating resonant-cavity system, FTRs have been observed in alpha-(BEDT-TTF)(2)KHg(SCN)(4).

Abstract:

A study of the electronic and superconducting properties of the organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2) in the millimetre-wave range is presented. The measurments are carried out using a single crystal in an unique rotating rectangular cavity. This novel technique provides information about the anisotropy of the magnetoresistance at GHz freqencies.

Abstract:

We describe a quantum-mechanical model of Fermi-surface traversal resonance (FTR), a magneto-optical resonance that occurs in quasi-one-dimensional metals. We show that the predictions of this model are in quantitative agreement with earlier semiclassical models of FTR. The agreement between the two approaches, whose starting assumptions are very different, demonstrates that it is a fundamental property of quasi-one-dimensional systems. © 1999 The American Physical Society.