Anomalous Metallic State near the Mott Transition

莫特绝缘体是物质的一种状态，由于强关联而绝缘，并且超出了简单的能带理论。在这种莫特绝缘体中，电子自旋存活下来，并实现了各种类型的磁性。一旦载流子被掺杂到这种莫特绝缘状态中，电流流动并且实现金属状态，在这种金属状态中，导电和磁性以基本方式相互作用，与掺杂半导体中的载流子掺杂到带绝缘体中形成鲜明对比，因此称为异常金属状态（AMS）。实际上，铜酸盐中实现的高温超导性可以看作是AMS态的基态之一。在其他过渡金属氧化物中观察到的各种有趣的特征也是AMS的另一个方面。从实验和理论两方面阐明AMS的真实性质是本研究项目的目标。朝着这个方向进行的3年研究的第一个结果是， 关于我们 详细研究了铜酸盐中的AMS实验，包括欠掺杂区的自旋能隙或伪能隙以及高温下霍尔系数的异常行为。理论上已经澄清，反铁磁波动在高温下起着重要的作用，而由于相同的反铁磁相互作用的单重态形成造成的赝间隙在低温下。另一方面，在过渡金属氧化物中研究最多的锰氧化物中，已经看到轨道自由度导致输运和磁性质的多样性，并且已经确定了巨磁阻和电荷有序的原因。此外，在具有三重态简并轨道的三重态超导体中，实验证实了三重态超导的稳定性，这一事实揭示了具有轨道简并的量子流体的另一种新的可能性。这将是对凝聚态物质更深入理解的重要一步。少

Mott insulator is the state of matter which is insulating due to strong correlations and is beyond the simple band theory. In this Mott insulator electronic spins survive and various types of magnetism are realized. Once carriers are doped into such Mott insulating state, electric current flows and the metallic state is achieved, in this metallic state the conduction and magnetism interplay in essential ways in sharp contrast to the carrier doping into the band insulators as in the doped semiconductors and hence called the Anomalous Mettalic State(AMS). Actually the high temperature superconductivity realized in cuprates can considered as one of the groudstates of this AMS State. Various intriguing features observed in other transition metal oxides are another aspects of this AMS as well. To elucidate the true nature of AMS both experimentally and theoretically was the target of this research project. The first of the results of 3-years studies toward this direction was the almost comp … More lete experimental identifications of AMS in cuprates including spin-gap or pseudo-gap in underdoped region and anomalous behaviors of Hall coefficient at elevated temperatures. Theoretically it has been clarified that antiferromagnetic fluctuations are playing important roles at high temperatures whereas singlet formations due to the same antiferromagnetic interactions are causing the pseudo-gap at low temperatures. On the other hand in the Manganites, which are most studied among transition metal oxides, the orbital degrees of freedom have been seen to lead to the versatality of both transport and magnetic properties and the causes of colossal magnetoresistance and charge ordering have been identified. Moreover in ruthenides with triply-degenerate orbitals the stability of triplet superconductivity has been confirmed experimentally, which fact has disclosed another novel possibility of quantum fluids with orbital degeneracy. This will be an important step toward deeper understanding of condensed matters. Less