Triplon Spin Current*

Spin current is a central concept of modern spintronics. Spin Seebeck effect (SSE), i.e., the spin current generation driven by a thermal gradient is one of the representative methods of creating DC spin current. SSE has been investigated from the viewpoint of its potential applications such as temperature sensor. Therefore, so far famous functional magnets such as ferro or ferrimagnets have been the main targets in SSE experiments. However, in recent years, it is gradually revealed that SSE can be an excellent tool to observe fundamental magnetic natures of attractive magnets. Namely, SSE is very powerful to detect dynamical features of various magnets including spin liquids and frustrated magnets. In fact, using SSE, we have uncovered several new features of different magnetic states such as a 1D spin liquid and a spin-nematic liquid. In this meeting, I will report our recent work about the SSE in the dimerized spin-Peierls phase of a quantum spin chain magnet CuGeO₃, whose elementary excitations are given by spin-1 triplons. We observed a new spin current carried by triplon excitations for the first time and developed the microscopic theory of the triplon spin current. I will explain the essential aspects of the triplon spin current.