Thermal transport of Dirac fermions in multiband system

本工作的目的是阐明狄拉克费米子在多带系统中的热输运。目标材料是有机导体θ-（BEDT-TTF）_2I_3，它在压力下既有Dirac锥带又有通常的抛物线带。开始，我们研究了α-（BEDT-TTF）_2I_3的热输运，测量了α-（BEDT-TTF）_2I_3在压力下的热电势和能斯特效应。因为我们在这个系统中获得了令人惊讶的有趣结果，所以我们将研究集中在这种材料上。在量子极限区，观察到了极大的能斯特效应（> 1 mV/K），而不是塞贝克效应。这种不寻常的行为是由狄拉克费米子系统的零模（N=0）朗道能级特性的固有性质引起的。与石墨烯相比，高纯α-（BEDT-TTF）_2I_3晶体中的朗道能级的宽度和塞曼能隙是产生巨大能斯特信号的原因。

The purpose of this work is to clarify the thermal transport of Dirac fermions in multiband system. The target material is the organic conductor θ-(BEDT-TTF)_2I_3, which has both Dirac-cone band and usual parabolic band under pressure. To begin with, we study the thermal transport of α-(BEDT-TTF)_2I_3 in which only Dirac-cone band exists.We have measured the thermopower and Nernst effect of α-(BEDT-TTF)_2I_3 under pressure. Because we obtained surprisingly interesting results in this system, we concentrated our research on this material. In the quantum limit region, the extremely large Nernst effect (>1mV/K) rather than the Seebeck effect was observed. This unusual behavior results from the intrinsic nature of the zero-mode (N=0) Landau level characteristic of the Dirac fermion system. The possible origin of the giant Nernst signal compared with that of graphene is the sharp width of the Landau level and the Zeeman gap in high-puritygα-(BEDT-TTF)_2I_3 crystal.