颗粒间隧穿体系H-A模型的磁电阻翻转效应

Inversed magnetoresistance effects in the H-A model for intergranular tunneling

基于HELMAN-ABELES模型,超越传统的一级近似,对磁场相关库仑阻塞下体系的磁输运性质进行了系统的理论分析.我们发现,磁场相关的库仑能隙将引起低温下的正磁电阻发散行为,该行为与自旋极化引起的低温负磁电阻相互竞争,使体系的宏观磁电阻随参数的区域变化呈现出复杂的特征.我们分析了该正磁电阻出现的根本原因,从而指出影响磁电阻的因素除了传统的自旋极化率之外,还有与之效果相反的自旋相关库仑能隙的作用,后者为颗粒体系中的磁电阻效应提供了新的可能来源.

This work is based on the HELMAN-ABELES model and we exceed the traditional first-ordered approximation to systematically analyze magnetotransport properties with spin-dependent Coulomb gap. We found that the global magnetoresistnace exhibits complex characteristics in the different regions of parameters due to the competition between the divergent positive magnetoresistance caused by spin-dependent Coulomb gap and the negative magnetoresistance by spin polarization at low temperature. The underlying reasons for the divergent positive MR are discussed. The spin-dependent Coulomb gap can serve as a new potential MR source in granular systems.