Colossal Nernst power factor in topological semimetal NbSb2

Abstract

Today solid-state cooling technologies below liquid nitrogen boiling temperature (77 K), crucial to quantum information technology and probing quantum state of matter, are greatly limited due to the lack of good thermoelectric and/or thermomagnetic materials. Here, we report the discovery of colossal Nernst power factor of 3800 × 10−4 W m−1 K−2 under 5 T at 25 K and high Nernst figure-of-merit of 71 × 10−4 K−1 under 5 T at 20 K in topological semimetal NbSb2 single crystals. The observed high thermomagnetic performance is attributed to large Nernst thermopower and longitudinal electrical conductivity, and relatively low transverse thermal conductivity. The large and unsaturated Nernst thermopower is the result of the combination of highly desirable electronic structures of NbSb2 having compensated high mobility electrons and holes near Fermi level and strong phonon-drag effect. This discovery opens an avenue for exploring material option for the solid-state heat pumping below liquid nitrogen temperature.

A giant Nernst power factor and figure-of-merit in polycrystalline NbSb2 for Ettingshausen refrigeration

“…Above 100 K, the S xx decreases linearly with increasing temperature, reaching À20 mV K À1 at 300 K. When the magnetic field is applied, the S xx below 100 K is significantly enhanced, while that above 100 K is only slightly increased. Similar temperature-dependence and magnetic field-dependence have been also observed in single-crystalline NbSb 2 , 20 indicating that the grain boundary has little influence on the S xx .…”

“…For example, the S yx of polycrystalline NbSb 2 is 396 mV K À1 under 9 T at 21 K, which is 36% lower than that of single-crystalline NbSb 2 (616 mV K À1 ) under the same conditions. 20 Thus, the grain boundaries in polycrystalline NbSb 2 lead to decreased S yx .…”

“…For example, the s yy of polycrystalline NbSb 2 is 0.65 Â 10 6 S m À1 under 9 T at 21 K, which is 20% lower than that of single-crystalline NbSb 2 (0.81 Â 10 6 S m À1 ) under the same conditions. 20 Based on the S yx and s yy , the (PF) N of polycrystalline NbSb 2 is calculated and plotted in Fig. 3d.…”

Giant transverse thermoelectric effect induced by topological transition in polycrystalline Dirac semimetal Mg3Bi2

“…Overall, we attribute both the giant electron mobility and the enhanced thermoelectric performance in Mn-doped Mg 3+d Bi 2 to the topological phase transition from a Z 2 topological insulator to a Dirac semimetal. We calculated the transverse zT value for the obtained Mg 3+d Bi 2 :Mn 0.1 sample at 6 Tesla and the best zT is 0.025 at 15 K, which is comparable with the state-of-the-art transverse thermoelectric materials, such as single-crystal NbSb 2 (zT = 0.1, at 25 K), 42 PtSn 4 (zT = 0.01, at 15 K), 11 Mg 2 Pb (zT = 0.01, at 25 K), 21 YbMnBi 2 (zT = 0.002, at 175 K), 6 etc. (Fig.…”

“…Finally, transverse thermoelectric materials have great potential in thermoelectric energy conversion, especially in Recently, researchers suggested that the specific heat pumping powers of transverse thermoelectric materials are higher than those of liquid hydrogen and liquid nitrogen. 21,42 Additionally, compared with longitudinal thermoelectric devices, the transverse thermoelectric devices do not need both n and p types of thermoelectric materials for constructing one device, which significantly simplifies the thermoelectric module. The main problem in the future is that transverse thermoelectric materials still need a high magnetic field to achieve high performance.…”