Calculations of quantum oscillations in quasi-two-dimensional charge-transfer salts

A numerical model is used to derive the quantum oscillations in the magnetisation and magnetoresistance of quasi-two-dimensional alpha-phase BEDT-TTF charge-transfer salts in high magnetic fields. Recent experimental results are simulated and the standard Lifshitz-Kosevich formalism is shown to be no longer appropriate

Magnetic breakdown and quantum interference in the quasi-two-dimensional superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) in high magnetic fields

Magnetic breakdown phenomena have been investigated in the longitudinal magnetoresistance of the quasi-two-dimensional (Q2D) superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) in magnetic fields of up to 50 T, well above the characteristic breakdown field. The material is of great interest because its relatively simple Fermi surface, consisting of a closed Q2D pocket and an open Q1D band, is almost identical to the initial hypothetical breakdown network proposed by Pippard. Two frequencies are expected to dominate the magnetoresistance oscillations: the a frequency, corresponding to orbits around the closed pocket, and the beta frequency, corresponding to the simplest classical breakdown orbit. However, a beta - alpha frequency is in fact found to be the dominant high-frequency oscillation in the magnetoresistance. Numerical simulations, employing standard theories for calculating the density of states, indicate that a significant presence of the beta - alpha frequency (forbidden in the standard theories) can result simply from the frequency-mixing effects associated with the pinning of the chemical potential in a quasi-two-dimensional system. While this effect is able to account for the previous experimental observation of beta - alpha frequency oscillations of small amplitude in the magnetization, it cannot explain why such a frequency dominates the high-field magnetotransport spectrum. Instead we have extended the numerical simulations to include a quantum interference model adapted for longitudinal magnetoresistance in a quasi-two-dimensional conductor. The modified simulations are then able to account for most of the features of the experimental magnetoresistance data

The importance of edge states in the quantum Hall regime of the organic conductor alpha-(BEDT-TTF)(2)KHg(SCN)(4)

We report measurements of the longitudinal magnetoresistance rho(zz) and magnetization of alpha-(BEDT-TTF)(2)KHg(SCN)(4) in pulsed magnetic fields of up to 50 T and temperatures down to 400 mK, using samples of different purity. Below 2 K the amplitude of the Shubnikov-de Haas oscillations in rho(zz) is found to decrease dramatically with falling temperature. This effect is shown to coincide with quasipersistent eddy current resonances in the magnetization, which are a signature of the quantum Hall effect. Evidence is provided for the existence of a novel interplane conduction mechanism involving highly metallic edge states with supressed scattering at the surface of the sample (a so-called 'chiral Fermi liquid'), operational when the chemical potential is between Landau levels in the bulk of the material

Chiral Fermi liquids and a new version of the quantum Hall effect observed in organic conductors at very high magnetic fields

We present evidence for a new form of quantum Hall effect (QHE) in organic molecular metals, in which the chemical potential is pinned to quasi-one-dimensional states between sharp quasi-two-dimensional Landau levels over finite regions of magnetic fields. A dramatic change in the behaviour of the resistivity component rho(zz) occurs when the QHE is observed, suggesting the presence of a chiral Fermi liquid at the sample edges. (C) 1998 Elsevier Science B.V. All rights reserved

The quantum Hall effect and chiral Fermi liquids in a quasi-two-dimensional organic conductor at very high magnetic fields

The oscillations in the longitudinal magnetoresistance of alpha-(BEDT-TTF)(2)KHg(SCN)(4) are shown to be strongly attenuated with decreasing temperature if the sample is in a state where it displays the quantum Hall effect. We provide evidence that this is a direct consequence of the existence of a chiral Fermi liquid on the surface of the sample. (C) 1998 Elsevier Science B.V. All rights reserved