The Pressure Approach to the Origin of the Anomalous State in the Quasi-Two-Dimensional Organic Conductor α- (BERT-TTF) ₂KHg (SCN) ₄

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Quasi-two-dimensional conductor α- (BEDT-TTF) ₂KHg (SCN) ₄ has the so-called anomalous electronic state at low temperature, while the isostructural salt α- (BEDT-TTF) ₂NH₄Hg (SCN) ₄ shows a normal behavior. In order to investigate the anomalous state by pressure approach, we measured the angular dependence of magnetoresistance under pressure to probe the Fermi surface topology. In α- (BEDT-TTF) ₂KHg (SCN) ₄, pressure suppresses the anomalous state and resurrects the normal one. Above the critical pressure, we found a quasi-one-dimensional Fermi surface responsible for the anomalous state. A detailed analysis of the pressure dependence of magnetoresistance shows that pressurization enhances the warp of the planar Fermi surface. In α- (BEDT-TTF) ₂NH₄Hg (SCN) ₄, the higher harmonic components of the warping was found to be comparatively large.