Taturo Fukuda

Electron transport from a one-dimensional lead to a two-dimensional graphene sheet through a single site

The problem of electron transport through a graphene-based device is studied theoretically and numerically. The device is composed of a single central site, with a single energy level, which is connected to a one-dimensional lead, and a two-dimensional graphene sheet. The nonequilibrium Green function formalism is utilized in modeling the problem; the formulation and numerical calculations are carried out around a K-point, in the band structure of the graphene, where the Fermi energy is located. Particular importance is placed on the transmission and current–voltage (I–V) characteristics of the device under a small bias. We find that the graphene part causes the central transmission peak, originally due to the single energy level of the central site, to split into two peaks, leaving an anti-resonant, zero-transmission, dip between them; only one of these peaks contributes to the resultant current. There always appears an almost flat, practically zero-current, region on a rather large bias interval, centered around the Fermi energy of the graphene, in the I–V graphs.

Higher Harmonics Generation in a Two-Dimensional Electron Gas under a Quantizing Magnetic Field

Using the self-consistent linear response approximation, a linear integro-differential equation for electromagnetic waves propagating in a quasi-two-dimensional electron gas under a static uniform magnetic field and intense laser radiation is derived. From the inhomogeneous terms in the derived equation, possible higher harmonic generation due to the electrons is predicted.

Electromagnetic Waves in An Ideal Electron Gas at Finite Temperature

Thermal effects on the properties of the electromagnetic waves propagating in an electron gas have not been fully investigated. The finite temperature effects appear through the dielectric function of the electrons in the Maxwell equation that describes the electromagnetic field. Recently we calculated the dispersion relation of the electromagnetic wave propagating in an ideal electron gas at low temperatures using the self‐consistent linear response approximation and the Sommerfeld expansion. We shall discuss the implications of our results on various experimental situations including optical properties of plasma.

Quantum Many‐Body Virial Theorem And Matsubara Green’s Function

We discuss the quantum field theoretical formulation of the virial theorem on the basis of the canonical field theory of the generalized coordinate transformation and show the equation of motion of a charged Fermion system coupled to an electromagnetic field. Possible application to Fermion‐Boson mixtures is also discussed.

New Canonical Transformations to Eliminate External Fields in Quantum Many-Body Problems

The wave function of an electron in a time varying electric field, a static magnetic field and a impurity potential can be transformed to the wave function of an electron without the electric field. By a unitary transformation, the electric field can be rigorously eliminated.

Quasi‐Particle Lifetime of Quantum Coulomb Systems

A formula that relates the imaginary part of the proper self‐energy and the proper vertex part can be derived from the finite temperature generalized Ward‐Takahashi relation. Using the formula, the effects of the electron‐electron Coulomb interaction on the lifetime of the electron quasi‐particles can be calculated within the well‐established RPA scheme.