Large Transverse and Longitudinal Magneto‐Thermoelectric Effect in Polycrystalline Nodal‐Line Semimetal Mg₃Bi₂

Abstract

Topological semimetals provide new opportunities for exploring new thermoelectric phenomena, because of their exotic and nontrivial electronic structure topology around the Fermi surface. In this study, we report on the discovery of giant transverse and longitudinal magneto-thermoelectric (MTE) effects in Mg3Bi2, which is predicted to be a type-II nodal-line semimetal in the absence of spin-orbit coupling (SOC). The maximum transverse power factor is 2182 μWm −1 K −2 at 13.5 K and 6 Tesla. The longitudinal power factor reaches up to 3043 μWm −1 K −2 at 15 K and 13 Tesla, which is 20 times higher than in a zero-strength magnetic field and is also comparable to state-of-the-art MTE materials. By compensating Mg loss in the Mg-rich conditions for turning carrier concentration, the sample obtained in this work shows a large linear non-saturating magnetoresistance of 940% under a field of 14 Tesla. This is a two-orders-of-magnitude increase with respect to the normal Mg-deficiency Mg3Bi2 sample. Using density functional calculations, we attribute the underlying mechanism to the parent nodal-line electronic structure without SOC and the anisotropic Fermi surface shape with SOC, highlighting the essential role of high carrier mobility and open electron orbits in moment space. Our work offers a new avenue toward highly efficient thermoelectric materials through the design of Fermi surfaces with special topological electronic structures in novel quantum materials.

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

“…Fermi energy tuning) was effective in suppressing Mg vacancies and optimizing carrier mobility. 19 The electron mobility increased by an order of magnitude, boosting magnetoresistance (MR) by 940% and vastly improving both the transverse thermopower (127 μV K −1 ) and transverse power factor (2182 μW m −1 K −2 ) at 13.5 K and 6 Tesla, rendering the Mg 3+ δ Bi 2 a promising transverse thermoelectric material. However, two open questions remain.…”

Cryogenic thermoelectric enhancements in SbCl3-doped porous Bi0.85Sb0.15 alloys

“…S10g (ESI †). The PF first increases and then decreases with the increasing magnetic field, reaching the highest value of 71.5 mW cm À1 K À2 at 0.2 T. The PF under a magnetic field of the x = 1 sample is markedly higher than that of other cryogenic TE materials, such as Cd 3 As 2 (14 mW cm À1 K À2 , 9 T), 58 Mg 3 Sb 2 (30 mW cm À1 K À2 , 13 T), 59 etc. Fig.…”

Experimental Realization of Spin‐Polarized States on Mg3Bi2 Surface

“…As shown in Figure 1a, Mg 3 Bi 2 has a trigonal crystal structure (space group P3m1) with the lattice constants a ¼ b ¼ 4.702 Å and c ¼ 7.436 Å. [20][21][22][23][24][25][26][27][28] The centrosymmetric unit cell contains five alternating Mg and Bi layers stacking along the [001] direction. The bulk Brillouin zone and the projection on (001) surface with high-symmetry points are plotted in Figure 1b.…”