Leveraging bipolar effect to enhance transverse thermoelectricity in semimetal Mg2Pb for cryogenic heat pumping

Toward high-performance thermoelectric energy conversion, the electrons and holes must work jointly like two wheels of a cart: if not longitudinally, then transversely. The bipolar effect — the main performance restriction in the traditional longitudinal thermoelectricity, can be manipulated to be a performance enhancer in the transverse thermoelectricity. Here, we demonstrate this idea in semimetal Mg 2 Pb. At 30 K, a giant transverse thermoelectric power factor as high as 400 μWcm −1 K −2 is achieved, a 3 orders-of-magnitude enhancement than the longitudinal configuration. The resultant specific heat pumping power is ~ 1 Wg −1 , higher than those of existing techniques at 10~100 K. A large number of semimetals and narrow-gap semiconductors making poor longitudinal thermoelectrics due to severe bipolar effect are thus revived to fill the conspicuous gap of thermoelectric materials for solid-state applications. Heat pumping is in high demand at cryogenic temperature, but whether thermoelectricity can take on cryogenic heat pumping is an open question. Here, the authors answer this question by leveraging bipolar effect to enhance transverse thermoelectricity in semimetal Mg 2 Pb for cryogenic heat pumping.