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

本研究的目的是制备具有自旋/电荷密度波跃迁的有机导体和石墨的人工微结构，并通过处理空间边界条件来控制密度波的性质。为了实现人工微结构，我们开发了两种加工技术：电化学生长有机导体异质结构和氧等离子体刻蚀微细加工。除了人工结构外，我们还分别应用强磁场或强电场来局域化电子运动或引入空间不对称性。主要结果如下：1.采用电化学过生长技术成功地生长了(TMTSF)_2PF_6/(TMTSF)_2ClO_4异质结，并验证了生长后的异质结具有正常的体电性能。但在异质界面附近出现了许多尺寸为0.1~1μm的微裂纹。这一结果表明，在宏观尺度上利用电化学过度生长制备有机异质结构是困难的。2.我们建立了氧等离子体干法刻蚀制备石墨细线的工艺。利用微细加工抑制了涡流加热效应的石墨细丝样品，在单圈线圈技术产生的100T以上脉冲超强磁场作用下，对石墨的射频输运进行了测量。3.研究了α-(BEDT-TTf)_2KHg(SCN)_4的导电密度波相的电场效应。在沿堆积轴方向的强电场作用下，层间响应电流随磁场方向呈现出双分裂的Led共振。这一新现象可以用一对片状费米面上电子轨道的不对称性来解释。

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.