Helical thermoelectrics and refrigeration.

The thermoelectric properties of a three-terminal quantum spin Hall (QSH) sample are examined. The inherent helicity of the QSH sample helps to generate a large charge power efficiently. Along with charge the system can be designed to work as a highly efficient spin heat engine too. The advantage of a helical over a chiral sample is that, while a multiterminal quantum Hall sample can only work as a quantum heat engine due to broken time reversal (TR) symmetry, a multiterminal QSH system can work effectively as both a charge or spin heat engine and as a charge or spin refrigerator as the TR symmetry is preserved.