Seminarium Fizyki Materii Skondensowanej

The current through a helical edge state of a quantum-spin-Hallinsulator may be fully transmitted through a magnetically gappedregion due to a combination of spin-transfer torque and spinpumping. Using a scattering approach, we argue that in such asystem the current is effectively carried by electrons withenergies below the magnet-induced gap and well below the Fermienergy. This has striking consequences, such as the absence ofshot noise, an exponential suppression of thermal noise, and anobstruction of thermal transport. For two helical edges covered bythe same quantum magnet, the device can act as robust noiselesscurrent splitter.