158 citations · 709 across the 28 of their papers we have counts for
23 papers · 1 filter
Band Structures of Edge Magnetoplasmon Crystals
Ken-ichi Sasaki
A two-dimensional electron gas in a static external magnetic field exhibits two distinct collective excitation modes. The lower frequency mode propagates along the periphery of the…
Suppression of Gate Screening on Edge Magnetoplasmons by Highly Resistive ZnO Gate
N. Kumada, N. -H. Tu, K. -i. Sasaki +5
We investigate a way to suppress high-frequency coupling between a gate and low-dimensional electron systems in the gigahertz range by measuring the velocity of edge magnetoplasmon…
Massive Dirac Fermions Signal in Raman Spectrum of Graphene
Ken-ichi Sasaki
Massless Dirac fermions in graphene can acquire a mass through different kinds of sublattice-symmetry-breaking perturbations, and there is a growing need to determine this mass usi…
Theory of a Carbon-Nanotube Polarization Switch
Ken-ichi Sasaki, Yasuhiro Tokura
Recently, it was suggested that the polarization dependence of light absorption to a single-walled carbon nanotube is altered by carrier doping. We specify theoretically the doping…
Theory of intraband plasmons in doped carbon nanotubes: rolled surface-plasmons of graphene
Ken-ichi Sasaki, Shuichi Murakami, Hideki Yamamoto
A single-wall carbon nanotube possesses two different types of plasmons specified by the wavenumbers in the azimuthal and axial directions. The azimuthal plasmon that is caused by…
Determination of intrinsic lifetime of edge magnetoplasmons
Ken-ichi Sasaki, Shuichi Murakami, Yasuhiro Tokura +1
It is known that peculiar plasmons whose frequencies are purely imaginary exist in the interior of a two-dimensional electronic system described by the Drude model. We show that wh…
Effects of Screening on Propagation of Graphene Surface Plasmons
Ken-ichi Sasaki, Norio Kumada
Electromagnetic fields bound tightly to charge carriers in a two-dimensional sheet, namely surface plasmons, are shielded by metallic plates that are a part of a device. It is show…
Valley-antisymmetric potential in graphene under dynamical deformation
Ken-ichi Sasaki, Yasuhiro Tokura, Hideki Gotoh
When graphene is deformed in a dynamical manner, a time-dependent potential is induced for the electrons. The potential is antisymmetric with respect to valleys, and some straightf…
Topological Raman Band in Carbon Nanohorn
Ken-ichi Sasaki, Yoshiaki Sekine, Kouta Tateno +1
Raman spectroscopy has been used in chemistry and physics to investigate the fundamental process involving light and phonons (quantum of lattice vibration). The carbon nanohorn int…
The origin of Raman D Band: Bonding and Antibonding Orbitals in Graphene
Ken-ichi Sasaki, Yasuhiro Tokura, Tetsuomi Sogawa
In Raman spectroscopy of graphite and graphene, the band at cm is used as the indication of the dirtiness of a sample. However, our analysis suggests that the…
Decay and Frequency Shift of Inter and Intravalley Phonons in Graphene -Dirac Cone Migration-
K. Sasaki, K. Kato, Y. Tokura +2
By considering analytical expressions for the self-energies of intervalley and intravalley phonons in graphene, we describe the behavior of D, 2D, and D Raman bands with changes…
Pseudospin for Raman D Band in Armchair Graphene Nanoribbons
K. Sasaki, K. Kato, Y. Tokura +2
By analytically constructing the matrix elements of an electron-phonon interaction for the band in the Raman spectra of armchair graphene nanoribbons, we show that pseudospin a…
Electron Wave Function in Armchair Graphene Nanoribbons
K. Sasaki, K. Wakabayashi, T. Enoki
By using analytical solution of a tight-binding model for armchair nanoribbons, it is confirmed that the solution represents the standing wave formed by intervalley scattering and…
Polarization Dependence of Raman Spectra in Strained Graphene
K. Sasaki, K. Wakabayashi, T. Enoki
The polarization dependences of the G, D, and 2D (G) bands in Raman spectra at graphene bulk and edge are examined theoretically. The 2D and D bands have different selection rul…
Soliton Trap in Strained Graphene Nanoribbons
Ken-ichi Sasaki, Riichiro Saito, Mildred S. Dresselhaus +2
The wavefunction of a massless fermion consists of two chiralities, left-handed and right-handed, which are eigenstates of the chiral operator. The theory of weak interactions of e…
Chiral Gauge Theory for Graphene Edge
Ken-ichi Sasaki, Katsunori Wakabayashi
An effective-mass theory with a deformation-induced (an axial) gauge field is proposed as a theoretical framework to study graphene edge. Though the gauge field is singular at edge…
Berry's Phase for Standing Wave Near Graphene Edge
Ken-ichi Sasaki, Katsunori Wakabayashi, Toshiaki Enoki
Standing waves near the zigzag and armchair edges, and their Berry's phases are investigated. It is suggested that the Berry's phase for the standing wave near the zigzag edge is t…
Identifying the Orientation of Edge of Graphene Using G Band Raman Spectra
K. Sasaki, R. Saito, K. Wakabayashi +1
The electron-phonon matrix elements relevant to the Raman intensity and Kohn anomaly of the G band are calculated by taking into account the effect of the edge of graphene. The ana…
Kohn Anomalies in Graphene Nanoribbons
Ken-ichi Sasaki, Masayuki Yamamoto, Shuichi Murakami +6
The quantum corrections to the energies of the point optical phonon modes (Kohn anomalies) in graphene nanoribbons are investigated. We show theoretically that the longitudinal…
Hamiltonian decomposition for bulk and surface states
Ken-ichi Sasaki, Yuji Shimomura, Yositake Takane +1
We demonstrate that a tight-binding Hamiltonian with nearest- and next-nearest-neighbor hopping integrals can be decomposed into bulk and boundary parts in a general lattice system…
Magnetism as a mass term of the edge states in graphene
Ken-ichi Sasaki, Riichiro Saito
The magnetism by the edge states in graphene is investigated theoretically. An instability of the pseudo-spin order of the edge states induces ferrimagnetic order in the presence o…
Stabilization mechanism of edge states in graphene
K. Sasaki, S. Murakami, R. Saito
It has been known that edge states of a graphite ribbon are zero-energy, localized eigen-states. We show that next nearest-neighbor hopping process decreases the energy of the edge…
Re-parameterization Invariance in Fractional Flux Periodicity
Shuichi Murakami, Ken-ichi Sasaki, Riichiro Saito
We analyze a common feature of a nontrivial fractional flux periodicity in two-dimensional systems. We demonstrate that an addition of fractional flux can be absorbed into re-param…