Berry phase effects affect electron dynamics significantly when the topology of Brillouin zone is non-trivial. In this tutorial, I briefly introduce basic concepts about the quantum geometric phase (Berry phase) and its consequences in transport properties of Bloch electron.

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题目: Dynamics of antiferromagnets driven by spin current

主讲人: Ran Cheng

单位：Department of Physics, University of Texas, Austin, TX 78712, USA

时间: 2013年7月18日（周四） 14:00-17：00

地点: 李薰楼468房间

Abstract:

When a spin-polarized current flows through a ferromagnetic (FM) metal, angular momentum is transferred to the magnetization via spin transfer torques. In antiferromagnetic (AFM) materials, however, the corresponding problem is unsolved. We derive microscopically the dynamics of an AFM system driven by spin current generated by an attached FM polarizer, and find that the spin current exerts a driving force on the local staggered order parameter. The mechanism does not rely on the conservation of spin angular momentum, nor does it depend on the induced FM moments on top the AFM background. Two examples are studied: (i) A domain wall is accelerated to a terminal velocity by purely adiabatic effect and no Walker's break-down exists. (ii) Injection of spin imbalance significantly splits the spin wave spectrum; a spin current triggers spin wave instability above a threshold that depends on the ratio between the spin imbalance and anisotropy gap.

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