Quantum spin dynamics

Abstract:

A new family of hydrated molecular metals based on the bis(ethylenethio- tetrathiafulvalene) (BET-TTF) donor was developed. A metal stable down to 0.5 K was obtained for the first time from this donor, perhaps due to the absence of disorder in the peripheral sulfur atoms. A hint of superconducting transition in some crystals of the BET-TTF2Br·3H2O salt was observed.

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.