Quantum spin dynamics

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:

Angle-dependent magnetoresistance oscillations (AMROs) in kappa-(BEDT-TTF)(2)Cu(SCN)(2) have been observed in fields of up to 33 T. AMROs due to both open and closed Fermi surface sections have been measured simultaneously for the first time in an organic metal. This provides information concerning the low temperature Fermi surface and demonstrates the absence of a spin-density wave state in this material.

Abstract:

Using a variant of the Corbino geometry in pulsed magnetic fields of up to 60 T, we have made direct measurements of the Hall potential in (Formula presented) within the quantum Hall regime. This method enables the in-plane components of the resistivity tensor, which are normally very difficult to measure, to be investigated and the nonlinear behavior of the sample’s (Formula presented) characteristics to be studied. It is found that an increasing probability of magnetic breakdown at higher fields leads to a degradation of the quantum Hall effect. © 1999 The American Physical Society.