Three-quarter Dirac points, Landau levels, and magnetization in 
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Kishigi, Keita; Hasegawa, Yūko

doi:10.1103/physrevb.96.085430

Cited by 11 publications

(25 citation statements)

References 75 publications

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“…It suggests distorted Dirac cone shown in Figure 13b. Moreover, recent realistic calculations of the energy band and Landau level structures in this system by Kishigi and Hasegawa support our experimental results and those interpreted qualitatively [53].…”

Section: Correction Of Dirac Conessupporting

confidence: 89%

Effects of Carrier Doping on the Transport in the Dirac Electron System α-(BEDT-TTF)2I3 under High Pressure

Tajima

2018

Crystals

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A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF) 2 I 3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. Moreover, the Dirac cones are highly tilted in a k-space. This system, thus, provides a testing ground for the investigation of physical phenomena in the multilayered, massless Dirac electron system with anisotropic Fermi velocity. Recently, the carrier injection into this system has been succeeded. Thus, the investigations in this system have expanded. The recent developments are remarkable. This effect exhibits peculiar (quantum) transport phenomena characteristic of electrons on the Dirac cone type energy structure. Keywords: α-(BEDT-TTF) 2 I 3 ; Dirac electron system; transport phenomena; inter-band effects of the magnetic field; carrier doping; quantum Hall effect

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Section: Correction Of Dirac Conessupporting

confidence: 89%

Effects of Carrier Doping on the Transport in the Dirac Electron System α-(BEDT-TTF)2I3 under High Pressure

Tajima

2018

Crystals

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“…We study the quantized energy at the three-quarter Dirac point in the presence of external magnetic field B. We obtain that the quantized energy is proportional to α 58)), which is consistent with the result obtained in the previous paper [11] by using the semiclassical quantization rule. We show that the zero mode exists by studying the finite-gap system.…”

Section: Discussionsupporting

confidence: 89%

“…The quantization of the energy in the three-quarter Dirac point in a magnetic field can be observed experimentally in quasi-two-dimensional organic superconductor α-(BEDT-TTF) 2 I 3 [11] and ultra cold Fermi gas on a tunable optical lattice [18].…”

Section: Discussionmentioning

confidence: 99%

“…Since the energy of the upper band depends linearly in three directions (for example, −q x and ±q y ) and quadratically in one direction (for example, +q x ) in that case, we call the critically tilted Dirac point as the "three-quarter Dirac point". [11] It has been known that when two-Dirac points merge at the time-reversal-invariant momentum, the energy depends linearly in two directions and quadratically in two directions, and it is called the semi-Dirac point [12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

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Energy quantization at the three-quarter Dirac point in a magnetic field

Hasegawa

Kishigi

2019

Phys. Rev. B

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The quantization of the energy in a magnetic field (Landau quantization) at a three-quarter Dirac point is studied theoretically. The three-quarter Dirac point is realized in the system of massless Dirac fermions with the critically tilted Dirac cone in one direction, where a linear term disappears and a quadratic term α2q 2x with a constant α2 plays an important role. The energy is obtained as En ∝ α 3 5 2 (nB) 4 5 , where n = 1, 2, 3, . . . , by means of numerically solving the differential equation. The same result is obtained analytically by adopting an approximation. The result is consistent with the semiclassical quantization rule studied previously. The existence of the n = 0 state is studied by introducing the energy gap due to the inversion-symmetry-breaking term, and it is obtained that the n = 0 state exists in one of a pair of three-quarter Dirac points, depending on the direction of the magnetic field when the energy gap is finite.

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“…7 In combination of the observed universal constant conductance and the pseudogap, our present optical study yields strong evidence of a single Dirac cone. In a theoretical study of uniaxial pressure, 40 it was recently predicted that α-(BEDT-TTF) 2 I 3 exhibits three-quarter Dirac points; further experiments have to show whether this is of relevance for the optical conductivity. Our conclusion from the optical spectra are further supported by suggestions that the massless Dirac electrons are strongly correlated due to the unscreened long-range Coulomb repulsion giving rise to an anomalous increase in ρ(T), 11 strong modification of the Fermi velocity 17 and excitonic mass generation at low T. 18 Theoretically, a gap opening due to spin-orbit coupling and/or merging of Dirac cones under strain in 2D topological organic materials have been discussed.…”

Section: Room-temperature Optical Conductivitymentioning

confidence: 99%

Optical signatures of energy gap in correlated Dirac fermions

Uykur

Kuntscher

et al. 2019

npj Quantum Mater.

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Dirac fermions attract considerable interest for several years and tremendous efforts are devoted to unveil the Dirac/Weyl semimetallic state in real crystalline systems. The behavior of Dirac fermions under strong correlations and in the proximity of other ordered states is under particular scrutiny as robust experimental signatures are scarce. α-(BEDT-TTF) 2 I 3 constitutes a superior model in this regard because the Dirac state occurs next to an electronically ordered ground state enabling us to investigate and deliberately vary the exotic properties in correlated Dirac fermions. The charge-ordered insulator gradually evolves to a metal when pressure is applied, and at low temperatures the electronic bands form tilted Dirac-like cones. Here, we present systematic lowtemperature infrared experiments on α-(BEDT-TTF) 2 I 3 in an extended pressure range. A metallic state with a frequency-independent optical conductivity indicates the coexistence of the trivial and massless Dirac electrons. We discover the opening of an energy gap due to correlated Dirac fermions at the boundary to the insulating state; it is gradually suppressed when pressure increases. The unique possibility of tuning the correlated Dirac state provides unprecedented insight into this novel electronic state and yields information relevant for Dirac electron systems in general.

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Three-quarter Dirac points, Landau levels, and magnetization in α−(BEDT−TTF)2I3

Cited by 11 publications

References 75 publications

Effects of Carrier Doping on the Transport in the Dirac Electron System α-(BEDT-TTF)2I3 under High Pressure

Effects of Carrier Doping on the Transport in the Dirac Electron System α-(BEDT-TTF)2I3 under High Pressure

Energy quantization at the three-quarter Dirac point in a magnetic field

Optical signatures of energy gap in correlated Dirac fermions

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