Dawn of cavity spintronics
C-M. Hu · 2016
Heroes are not always stars. This we know from movie, but it is also true in the community of physicists. While stars are celebrated and attract fans, heroes are more personal, reflecting our own views on the meaning of life and value of work. We don’t know each other’s heroes, and their path may not be easy to follow. Some of them may even prefer to stay away from the spotlight. My heroes, in the field of spintronics, are Robert Silsbee and Mark Johnson. In 1979, Robert H. Silsbee, the 50-year old Cornell University professor on his sabbatical leave at the University of Paris-Sud, published an article in Physics Review B with the title Coupling between ferromagnetic and conduction-spin-resonance modes at a ferromagneticnormal-metal interface [1]. Using a clever experiment and a concise theoretical model, Silsbee et al. revealed two new physical characteristics of a spin current: (i) through the microwave excitation of ferromagnetic resonance (FMR), a spin current can be generated in a ferromagnetic metal, which will flow into an adjacent normal metal. (ii) Such a spin current pumped by FMR impacts the spin dynamics of electrons in the metal via the exchange interaction, which can be detected via an enhanced electron spin resonance. Several decades later, from these two effects came spin pumping [2] and spin torque [3], two seminal concepts of contemporary magnetism. Today, every conference on spintronics has celebrated talks of spin pumping. However, Silsbee et al.’s ground breaking paper has only been cited about 100 times in four decades. Not surprising, many students of today studying spin pumping have never read that paper, and some have never even heard of it. The same thing has happened in the history of cinematography. In an era when movie goers celebrate blockbusters of Steven Spielberg, George Lucas and Peter Jackson, few of us spend time at home enjoying Stanley Kubric’s 2001, the Space Odyssey, a ground breaking art work produced in 1968, which has inspired Spielberg and Lucas. Kubric directed only 16 movies in his life time. He was