Anomalous Metallic State near the Mott Transition

Mott绝缘体是一种由于强关联而处于绝缘状态的物质，它超越了简单的能带理论。在这种Mott绝缘体中，电子自旋得以幸存，并实现了各种类型的磁性。一旦载流子被掺杂到这种Mott绝缘态，电流就会流动，金属态就会实现，在这种金属态下，导电和磁性的相互作用与掺杂到带状绝缘体中的载流子形成鲜明对比，因此被称为反常金属态(AMS)。实际上，在铜酸盐中实现的高温超导电性可以被认为是这个AMS状态的一个不好的状态。在其他过渡金属氧化物中观察到的各种有趣的特征也是这种AMS的另一个方面。从实验和理论上阐明AMS的真实本质是本研究的目标。三年来对这一方向的研究的第一个结果是几乎可比的…更详细的实验证明了铜酸盐中AMS的存在，包括低掺杂区的自旋能隙或赝能隙，以及霍尔系数在高温下的反常行为。从理论上讲，反铁磁涨落在高温下起着重要的作用，而在低温下，由于同样的反铁磁相互作用而形成的单重态是造成假能隙的原因。另一方面，在过渡金属氧化物中被研究最多的锰氧化物中，轨道自由度被认为是导致输运和磁性质的反常的原因，并且已经确定了巨磁电阻和电荷有序的原因。此外，在具有三重简并轨道的Ruthenide中，实验证实了三重态超导电性的稳定性，这揭示了具有轨道简并的量子流体的另一种新的可能性。这将是更深入地理解凝聚态物质的重要一步。较少

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