Low-field and anomalous high-field Hall effect in (TMTSF)2ClO 4

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Abstract
We report the study of the Hall effect, at low temperature, in (TMTSF) 2ClO4 (slow-cooled state), up to 80 kOe, with the field perpendicular to the (a-b) plane. We show that the linear field dependence of the weak Hall resistance, up to 40 kOe, supports the interpretation of the conducting phase in terms of a quasi planar Fermi surface with a density of carriers corresponding to the stoechiometry of the salt. At higher field, a strong and sharp increase of the Hall constant, is the signature of a phase transition to a semi-metallic state. The transition magnetic field is very temperature dependent. Below 0.7 K, in the semi-metallic state, remarkable steps and plateaux, of the Hall resistance are observed, suggesting either the quantization of the Hall constant of carriers in weakly coupled (a-b) planes or the existence of a sequence of electron-hole instabilities (excitonic phases)