Large Transverse Thermoelectric Effect on Ferromagnetic Semimetal HgCr2Se4
Rifky Syariati and Fumiyuki Ishii

Nanomaterials Research Institute (NanoMaRi), Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192, Japan

Abstract

Some researchers studied the effect of the band gap on thermoelectric properties and concluded that the best materials must have a band gap greater than 6-10 kBT [1]. Today, heavily doped semiconductors are the main focus of the thermoelectric society, and opening a band gap is a proven way of increasing the Seebeck coefficients [2]. However, the presence of a band gap is not only the essential variable for obtaining large thermoelectric effect[3]. Semimetals, which have properties in between semiconductors and metals, would be the best potential candidate for having a large thermoelectric power factor without heavy doping [4]. The electrical conductivity of semimetals is comparable to those of heavily-doped semiconductors, and the thermal conductivity values in semimetals could also be small, especially if they consist of heavy elements [5]. One candidate material with ferromagnet and semimetallic properties is HgCr2Se4 [6]. The crystal of HgCr2Se4 also can be synthesized using the chemical vapor/transport method [7].

This study explores the transverse TE properties of HgCr2Se4, a ferromagnetic semimetal. The transverse thermoelectric properties of HgCr2Se4 were analyzed using density functional calculations and the semiclassical Boltzmann transport equation. At the Fermi level, the anomalous Nernst coefficient was significant. When assuming a relaxation time of 10 fs, the calculated anomalous Nernst coefficient of HgCr2Se4 was -74.38 muV/K at 100 K. The significant anomalous Nernst coefficient in HgCr2Se4 was attributed to the anomalous Nernst conductivity, which originates from the sharp slope near the Fermi level of the chemical potential dependence of the anomalous Hall conductivity and the Seebeck-induced effect. These results suggest that HgCr2Se4, as a ferromagnetic semimetal, has promising potential for application in thermoelectric devices.

References
[1] J. O. Sofo and J. D. Mahan. Phys. Rev. B 49, 4565 (1994).
[2] A. M. Dehkordi, M. Zebarjadi, J. He, T. M. Tritt. Mat. Sci. Eng. R 97, 1 (2015).
[3] M. Markov, X. Hu, H. C. Liu, N. Liu, S. J. Poon, K. Esfarjani, M. Zebarjadi. Sci. rep. 8, 9876 (2018).
[4] M. Markov, S. E, Rezaei, S.N. Sadeghi, K. Esfarjani, M. Zebarjadi . Phys. Mat. Rev. 3, 095401 (2019).
[5] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).
[6] C. Lin, C. Yi, Y. Shi, L. Zhang, G. Zhang, J. Muller, and Y. Li, Phys. Rev. B 94, 224404 (2016).
[7] J H. W. Lehmann and F. P. Emmenegger. Solid State Commun. 7, 965 (1969).

Keywords: thermoelectric, semimetal, anomalous Hall effect, anomalous Nernst effect

Topic: Modelling and Computational Physics