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.