“Our theory laid a foundation for measurement of this current and quantitative theory about spin transport.”

Because it is a really nice paper! But seriously, I believe it’s because it addressed a major conceptual confusion within a field of research that is rapidly expanding.

It is closer to the latter. We tried to put the spin current concept on a firm basis conforming to the standard transport theory.

A major concern of spintronics is transport of spin, and spin current is the concept describing this process. Our theory laid a foundation for measurement of this current and quantitative theory about spin transport.

We were investigating the inverse spin Hall effect (ISHE), and found that the result was incompatible with the spin Hall effect coefficient that had been calculated earlier. The Onsager relation dictates that they should be the same up to a point. We found that the problem stems from the spin current definition that people (including us) have been using.

Our earlier semi-classical theory had suggested that the conventional spin current might be better revised to give a proper connection with the standard spin-continuity equation. We were then convinced that the spin current definition must be revised in order to fix a whole array of problems.