||Three-quarter Dirac points, Landau levels, and magnetization in α-(BEDT-TTF)2I3
Kishigi, Keita ,
Hasegawa, Yasumasa ,
キシギ, ケイタ ,
ハセガワ, ヤスマサ ,
岸木, 敬太長谷川, 泰正
085430-23 , 2017-08-22 , American Physical Society
The energies as a function of the magnetic field (H) and the pressure are studied theoretically in the tight-bindingmodel for the two-dimensional organic conductor α-(BEDT-TTF)2I3, in which massless Dirac fermions arerealized. The effects of the uniaxial pressure (P) are studied by using the pressure-dependent hopping parameters.The system is semimetallic with the same area of an electron pocket and a hole pocket atP <3.0 kbar, where theenergies (ε0D) at the Dirac points locate below the Fermi energy (ε0F) when H = 0. We find that at P = 2.3 kbarthe Dirac cones are critically tilted. In that case a type of band crossing occurs at “three-quarter” Dirac points;i.e., the dispersion is quadratic in one direction and linear in the other three directions. We obtain magneticfield dependencies of the Landau levels (εn): εn − ε0D∝ (nH)4/5 at P = 2.3 kbar (three-quarter Dirac points)and |εn − ε0F| ∝ (nH)2 at P = 3.0 kbar (the critical pressure for the semimetallic state). We also study themagnetization as a function of the inverse magnetic field. We obtain two types of quantum oscillations. One isthe usual de Haas–van Alphen (dHvA) oscillation, and the other is the unusual dHvA-like oscillation which isseen even in the system without the Fermi surface.