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|Date and time:||7th Jan. (Mon.) 16:15 ` 17:15|
|Place:||Seminar room 732, Faculty of Science, University of Hyogo|
|Title:||Theoretical study of α-(BEDT-TTF)2I3 with the over-tilted Dirac cones|
|Speaker:||Prof. Keita Kishigi (Kumamoto University)|
From the extended Hückel method for α-(BEDT-TTF)2I3 under the uniaxial pressure along y-axis, the Dirac cones are over-tilted till 2.3 kbar, where some theoretical results have been obtained[1-3].
We have found that the Dirac cones are critically tilted at 2.3kbar, where the dispersion is quadratic in one direction and linear in the other three directions. We named this band crossing points and the Dirac cones as three-quarter Dirac points and the three-quarter Dirac cones. We have also shown the Landau levels by using the tight-binding model and the 2×2 three-quarter Dirac Hamiltonian. In ref , we have studied the Landau levels of the three-quarter Dirac cones in detail.
When the Dirac cones are over-tilted, the compensated metallic state is realized.
Especially, above 0.2 kbar, the Fermi surface of two electron pockets are changed to one electron pocket, i.e., Lifshitz transitions happen.
We have quantum-mechanically calculated the de Haas van Alphen (dHvA) oscillations.
Near the Lifshitz transitions, the Fourier components corresponding to the 3/2 and 5/2 areas of the hole pocket are enhanced.
It is not expected in the conventional Lifshitz and Kosevich formula of the dHvA oscillations.
 Kishigi and Hasegawa, Phys. Rev. B 96, 085430 (2017).
 Hasegawa and Kishigi, arxiv1809.02276.
 Kishigi and Hasegawa, unpublished.
 Lifshitz, Sov.Phys. JETP 11, 1130 (1960).
 Lifshitz and Kosevich, Sov. Phys. JETP 2, 636 (1956).
Toru Sakai(University of Hyogo, QST SPring-8)|
Kenji Tsutsui(QST Pring-8)
Hiroki Nakano(University of Hyogo)