Mapping of the anomalous magnetotransport regime in theα−(BEDT−TTF)2MHg(SCN)4(M=K,Tl)organic conductors

Abstract

We present a comprehensive set of pulsed-magnetic-field measurements of the quasi-two-dimensional organic conductors $\ensuremath{\alpha}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}M\mathrm{Hg}(\mathrm{SCN}{)}_{4}$ $(M=\mathrm{K},\mathrm{Tl})$ to map out the boundaries of a high-field regime that was recently associated with the presence of the bulk quantum Hall effect. The phase inversion effect observed in the interplane magnetoresistivity and the behavior of quantum oscillations in the Hall potential are used to investigate the high-field region as a function of magnetic field, temperature, rotation angle, sweep rate, sample quality, and the anion of the charge-transfer salt. The inversion of the phase of the oscillations in ${\ensuremath{\rho}}_{\mathrm{zz}}$ is found to be directly related to the quality of the sample, and is suggested to be an intrinsic property of $\ensuremath{\alpha}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}M\mathrm{Hg}(\mathrm{SCN}{)}_{4}$ $(M=\mathrm{K},\mathrm{Tl}).$ A detailed mapping of the phase-inverted region indicates that its boundaries agree qualitatively with those of the recently proposed low-temperature--high-field state.