Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli 620024, India.
J Phys Condens Matter. 2012 Apr 4;24(13):136002. doi: 10.1088/0953-8984/24/13/136002. Epub 2012 Mar 5.
We have investigated the effect of hydrostatic pressure as a function of temperature on the resistivity of a single crystal of the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7). Whereas a strong insulating behaviour is observed at all temperatures at ambient pressure, a clear transition into a metallic-like behaviour is induced when the sample is subjected to a pressure (P) of ~1.0 GPa at T < 70 K. A huge negative piezoresistance ~10(6) in the low temperature region at moderate pressures is observed. When the pressure is increased further (5.5 GPa), the high temperature polaronic state disappears and a metallic behaviour is observed. The insulator to metal transition temperature exponentially increases with pressure and the distinct peak in the resistivity that is observed at 1.0 GPa almost vanishes for P > 7.0 GPa. A modification in the orbital occupation of the e(g) electron between 3d(x(2)-y(2)) and 3d(z(2)-r(2)) states, as proposed earlier, leading to a ferromagnetic double-exchange phenomenon, can qualitatively account for our data.
我们研究了静水压力作为温度的函数对双层钙钛矿锰氧化物单晶（La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7)）电阻的影响。在常压下，所有温度下都观察到强烈的绝缘行为，而当样品在 T < 70 K 时承受约 1.0 GPa 的压力时，会诱导出明显的金属样行为。在中等压力下，低温区观察到巨大的负压阻效应~10(6)。当压力进一步增加（5.5 GPa）时，高温极化子态消失，观察到金属行为。从金属到绝缘的转变温度随压力呈指数增长，在 1.0 GPa 处观察到的电阻率明显峰值在 P > 7.0 GPa 时几乎消失。正如之前提出的，e(g)电子在 3d(x(2)-y(2))和 3d(z(2)-r(2))态之间的轨道占据的修改，导致了铁磁双交换现象，可以定性地解释我们的数据。
