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Three-quarter Dirac points, Landau levels, and magnetization in α-(BEDT-TTF)2I3 岸木, 敬太 147885 長谷川, 泰正 147886 ハセガワ, ヤスマサ Hasegawa, Yasumasa Kishigi, Keita 147885 長谷川, 泰正 147886 ハセガワ, ヤスマサ Hasegawa, Yasumasa 428 application/pdf 論文(Article) The energies as a function of the magnetic field (H) and the pressure are studied theoretically in the tight-binding model for the two-dimensional organic conductor α-(BEDT-TTF)2I3, in which massless Dirac fermions are realized. 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 the energies (ε0D) at the Dirac points locate below the Fermi energy (ε0F) when H = 0. We find that at P = 2.3 kbar the 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 magnetic field 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 the magnetization as a function of the inverse magnetic field. We obtain two types of quantum oscillations. One is the usual de Haas–van Alphen (dHvA) oscillation, and the other is the unusual dHvA-like oscillation which is seen even in the system without the Fermi surface. https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.085430 journal article American Physical Society 2017-08-22 VoR application/pdf Physical Review B 96 085430-1 085430-23 24699950 https://kumadai.repo.nii.ac.jp/record/30274/files/PhysRevB.96.085430.pdf http://hdl.handle.net/2298/38481 https://kumadai.repo.nii.ac.jp/records/30274 eng ©2017 American Physical Society