Metal -insulator -superconductor phase separation in the highly correlated organic conductors near the Mott transition.

本文系统地研究了有机Mott体系κ-（BEDT-TTF）_2[N（CN）_2]Br的宏观电子相分离。利用同步辐射扫描微区红外光谱仪（SMIS）获得了相分离的真实的空间成像。在有机Mott体系κ-[（h-BEDT-TTF）_（d-BEDT-TTF<1-x>）_x]_2Cu[N（CN）_2]Br的单晶表面上获得了电子相分离的实验证据，其带宽由氢化BEDT-TTF分子（h-BEDT-TTF）和氘代BEDT-TTF分子（d-BEDT-TTF）之间的取代比x控制。使用SR的SMIS测量使我们能够显示绝缘和金属区域的畴结构的宏观尺寸。这一发现并不排除每个区域或每个扫描点内存在纳米级不均匀性的可能性，因为所获得的光谱可能导致测量点中纳米级不均匀性的平均值。但核磁共振和磁化强度的结果与目前的结果之间的密切一致表明，相分离发生在宏观尺度上。微米尺度相分离的观察不同于最近在强关联过渡金属氧化物体系中发现的纳米尺度电子不均匀性，这是一种填充控制的Mott体系。因此，我们认为填充控制的Mott系统中存在纳米尺度的本征不均匀性，而不存在热力学相变，如果存在宏观不均匀性，那么宏观不均匀性应该伴随着带宽控制的Mott系统中的相变和非平衡态等临界现象.在本研究中发现的相分离的起源必须是反铁磁Mott绝缘体和超导相的双稳性只是在一级Mott转变。

Systematic investigation of the electronic phase separation on macroscopic scale has been performed in the organic Mott system κ-(BEDT-TTF)_2[N(CN)_2]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy (SMIS) using the synchrotron radiation (SR). Experimental evidence of the electronic phase separation has been obtained on the single crystal surface of the organic Mott system κ-[(h-BEDT-TTF)_<1-x>(d-BEDT-TTF)_x]_2Cu[N(CN)_2]Br, of which band width is controlled by the substitution ratio x between the hydrogenated BEDT-TTF molecule (h-BEDT-TTF) and the deuterated one (d-BEDT-TTF). SMIS measurements using SR enable us to show the macroscopic size of the domain structure of the insulating and metallic regions. This finding does not exclude the possibility of the nano-scale inhomogeneity inside each domains or each scanning spot because the obtained spectrum may result in the average of nano-scale inhomogeneity in the measured spot. But close agreement between the previous results of NMR and magnetization and present results suggests that the phase separation occurs on macroscopic scale. The observation of the micro-meter scale phase separation is different from the recent findings of the nano-scale electronic inhomogeneity in the strongly correlated transition metal oxide system, which is a filling controlled Mott system. We therefore expect that the nano-scale intrinsic inhomogeneity appears in the filling controlled Mott system without thermodynamic phase transition, and the macroscopic inhomogeneity, if it comes, should accompany the critical phenomena like as the phase transition and non-equilibrium state in the band width controlled Mott system. The origin of the phase separation found in this study must be the bistability of the antiferromagnetic Mott insulator and superconducting phases just at the first order Mott transition.