Research of the electronstates on strongly correlated electron systems under static and dynamic extreme condition

(1)压力和磁场对钙钛矿锰氧化物的影响为了研究压力对金属-绝缘体(M-I)转变的影响，测量了Eu_&lt；0.58&gt；sr_&lt；0.42&gt；MnO_3的磁致伸缩和磁化强度。在2T和6K附近的常压下，观察到的磁致伸缩为0.04%。在0.5T场强下，La_&lt；0.1&gt；Ce_&lt；0.4&gt；Sr_&lt；0.5&gt；MnO_3的饱和磁化强度随压力的增加而增大，在1.5T和5.0T场强下，饱和磁化强度减小。另一方面，在1.8GPa压力下，研究了静水压力对PZT材料电阻的影响。随着压力的增加，居里温度升高。由类近藤效应产生的-logT项的系数随压力的增加而减小，电阻最高温度向低温方向移动。虽然很大的负压系数的来源尚不清楚，但可以说这一特殊现象归因于某种磁相互作用。(2)对单晶UnI_2Si_2的磁相变及相关现象进行了高压研究。我们发现P-T和B-T磁相图之间的相似之处。根据计算结果，确定了抑制简单反铁磁性的临界压强为3.2 Gpa。在100K附近出现了一个小的反常现象，这可以归因于ILSDW相和UAF相之间的压力感生磁序-有序相变。根据磁弹性现象、热力学方程和理论方法，推导出加压可以抑制这一中间相。

(1) Effect of pressure and magnetic field on the perovskite manganese oxidesMagnetostriction and magnetization of Eu_<0.58>Sr_<0.42>MnO_3 were measured under hydrostatic pressures up to 2 GPa in order to investigate the effect of pressure on the metal-insulator (M-I) transition. At ambient pressure, around 2 T and 6 K, where the field-induced M-I transition was previously reported, the observed magnetostriction was to be 0.04 %. With increasing pressure, the saturation magnetization increased at a field of 0.5 T, whereas it decreased at field of 1.5 and 5.0 T.On the other hand, the influence of hydrostatic pressure on electrical resistance of La_<0.1>Ce_<0.4>Sr_<0.5>MnO_3 were investigated under pressures up to 1.8 GPa. With increasing pressure, Curie temperature increases. It is also found that the coefficient of -logT term originated from Kondo-like effect decreases with increasing pressure and the resistance maximum temperature shifts largely to lower temperature. Though the origin of the large negative pressure coefficient cannot be clearly solved, it can be said that the peculiar phenomenon is ascribed to some kind of magnetic interactions.(2) High-pressure studies on the magnetic phase transitions and related phenomena in the single crystalline UNi_2Si_2Measurement of electrical resistance and thermal expansion under high pressure and high magnetic field were performed. We found that the analogy between the p-T and B-T magnetic phase diagrams. From the results, the critical pressure for suppression of simple antiferromagnetism in UNi_2Si_2 was determined as 3.2 GPa. It is also found that a small anomaly appears around 100 K.The resistance anomaly can be attributed to the pressure-induced magnetic order-order phase transition between ILSDW and UAF phases. In terms of magnetoelastic phenomena, thermodynamic equations and theoretical approach, it is deduced that this intermediate phase would be suppressed by applying pressure.