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

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(SR)扫描微区红外光谱(SMIS)获得了相分离的实空间成像。在有机MoTt体系κ-[(h-BEDT-TTF)_&lt；1-x&gt；(d-BEDT-TTF)_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，其带宽由氢化分子(h-BEDT-TTf)和氢化分子(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区和金属区的磁畴结构的宏观尺寸。这一发现并不排除每个区域或每个扫描光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被测光点中纳米级不均匀性的平均值。但以前的核磁共振和磁化强度的结果与目前的结果非常吻合，表明相分离发生在宏观尺度上。在强关联过渡金属氧化物体系中观察到的微米级相分离与最近发现的纳米级电子不均匀是不同的，过渡金属氧化物体系是填充控制的Mott系统。因此，我们预计在没有热力学相变的填充控制的Mott体系中会出现纳米尺度的本征不均匀性，而宏观的不均匀性如果出现的话，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。本研究中发现的相分离的根源应该是反铁磁Mott绝缘体和超导相在一阶Mott转变处的双稳态。

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.