Quantum Physics of Spin Density Wave in Artificial Structures of Organic Conductors

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The purpose of the present research is to fabricate artificial microstructures of organic conductors and graphite, which show spin / charge density wave transitions, and to control density wave properties by handling the spatial boundary condition. To realize the artificial microstructures, we have developed two processing techniques, electrochemical overgrowth of hetero-structures of organic conductors and micro-fabrication by oxygen plasma etching. In addition to artificial structures, we have applied strong magnetic fields or strong electric fields to localize electron motion or to introduce spatial asymmetry, respectively. The main results are as the followings.1.We have successfully grown (TMTSF)_2PF_6/(TMTSF)_2ClO_4 hetero-junctions by the electrochemical overgrowth technique, and have checked the overgrown part shows normal bulk electronic properties without any damages. However there appear many micro-cracks with the size of 0.1〜1μm around the hetero-interface. This result suggests that it is difficult to fabricate the organic hetero-structures using the electrochemical overgrowth in macroscopic scale.2.We have established the technique to fabricate the graphite thin wires by the dry etching using oxygen plasma. Using the graphite thin wire samples, in which the eddy current heating effect is suppressed by the micro-fabrication, we have performed the RF transport measurement of graphite under pulsed ultra-high magnetic fields beyond 100T generated by the single-turn coil technique. We have revealed the existence of a new anomaly around 90T by avoiding heating effect.3.We have studied the electric field effect in conducting density wave phase of α-(BEDT-TTF)_2KHg(SCN)_4. Under strong electric fields along the stacking axis, the interlayer response current shows the doubly split Lebed resonances as a function of magnetic field orientations. This new phenomena is explained by the asymmetry of electron orbits on a pair of sheetlike Fermi surfaces.