Low-frequency Electronic Excitations Research Articles

Low-frequency excitation spectra in double-walled armchair carbon nanotubes

The low-frequency electronic excitations of the double-walled armchair carbon nanotubes are investigated by the random-phase approximation. Both the intertube atomic hoppings and the intertube $e\text{\ensuremath{-}}e$ interactions are included in the calculations simultaneously. The intertube atomic hoppings significantly alter the low-energy bands and thus enrich the low-frequency excitation spectra. There are more single-particle excitation channels and plasmon modes. These excitations strongly depend on the symmetric configurations of the double-walled system and the transferred momentum, such as the number, the existence, the strength, and the frequency of plasmon modes.

Electron decay rates in a zero-gap graphite layer

A 2D monolayer graphite exhibits rich Coulomb excitations and deexcitations, mainly owing to the zero-gap characteristic. The low-frequency electronic excitations include interband e–h excitations, intraband e–h excitations, and plasmon. The two latters are purely caused by temperature. The Coulomb decay rate strongly depends on temperature and wave vector (or energy), and the analytic formulas between them are absent. The Coulomb decay rate of the Fermi-momentum state only comes from the intraband e–h excitations. It grows quickly as temperature increases. Its value is close to the measured results of the layered graphite. As to other states, three kinds of electronic excitations make important contributions to the Coulomb decay rates and cause the novel dependence on wave vector. The Coulomb decay rate is much faster than the electron–phonon scattering rate. A 2D monolayer graphite quite differs from a 2D electron gas or a 1D gapless carbon nanotube in electronic excitations and deexcitations.

Electronic excitations of double-walled armchair carbon nanotubes

The low-frequency electronic excitations in double-walled armchair carbon nanotubes are studied within the random-phase approximation. The intertube atomic overlaps significantly affect the low-energy bands and thus enrich the low-frequency single-particle excitations and collective excitations. They induce more plasmon modes, reduce the plasmon strength, and change acoustic plasmons into optical plasmons. The predicted results could be verified by the electron-energy-loss spectroscopy.

Temperature-dependent electronic excitations in a 2D graphite layer

The low-frequency electronic excitations of a 2D graphite layer is studied within random-phase approximation. Temperature could induce free carriers and thus significantly changes low-energy excitation properties. There exist intraband and interband single-particle excitations (SPE) and collective excitations. Both intraband SPE and plasmon are purely caused by temperature. Electronic excitations strongly depend on temperature and momentum. The Fermi-momentum state only decay through the intraband e–h excitations. The decay rate of such state quickly grows as temperature increases. A single graphite layer quite differs from a 2D electron gas in electronic excitations and de-excitations.

Dynamics of layered Jahn–Teller crystals of rare-earth compounds (Review)

Spectroscopic data on crystals of rare-earth compounds having structural instability due to the cooperative Jahn–Teller effect are reviewed. Based on an analysis of these data, it is inferred that the dynamic coupling of low-frequency electronic excitations of the rare-earth ions with crystal lattice vibrations plays an essential role in the formation of the low-energy spectra of layered crystals. The role of this coupling in the formation of anomalies of various physical properties of crystals of rare-earth compounds with highly anisotropic structure is examined.

Temperature-Dependent Electronic Excitations of Carbon Toroids

Carbon toroids could exhibit rich inter-π-state and intra-π-state excitations at finite temperature. The low-frequency electronic excitations are characterized by the longitudinal angular momentum ( L ), mainly owing to the cylindrical symmetry. The L -decoupled plasmons strongly depend on temperature, toroid geometry, and intertoroid Coulomb coupling. Temperature could make the inter-π-state plasmons change into the intra-π-state plasmons, or directly induce the intra-π-state plasmons. It is very novel that temperature does not affect excitation spectra of armchair carbon toroids, such as plasmon peak and plasmon frequency. There are certain important differences between armchair and nonarmchair carbon toroids. Intertoroid Coulomb interactions for coaxial carbon toroids have been included. They significantly enhance plasmon peak and plasmon frequency. The low-frequency plasmons in a carbon toroid quite differ from the purely temperature-induced plasmons in a graphite sheet.

Low-frequency electronic excitations in doped carbon nanotubes

We study the low-frequency electronic excitations of a doped carbon nanotube. The longitudinal dielectric function, the loss function, and the plasmon frequencies are calculated within the random phase approximation. They strongly depend on the transferred momentum ( q), the transferred angular momentum ( L), the Fermi energy, and the nanotube geometry (the radius and the chiral angle). All the doped carbon nanotubes could exhibit the L=0 acoustic plasmon. There also exists the L=1 optical plasmon, when the Fermi energy is sufficiently high. There are several important differences between type-I nanotubes and type-II nanotubes. The local-field corrections on the loss spectra and the plasmon frequencies are discussed.

Temperature-Induced Plasmons in a Graphite Sheet

The low-frequency electronic excitations of a two-dimensional graphite sheet are studied within the self-consistent-field approach. A zero-gap graphite sheet only exhibits the interband e-h excitations at zero temperature. Electrons and holes grow rapidly as temperature increases from zero. Temperature induces the intraband excitations and thus the intraband plasmons. A graphite sheet is predicted to be the first undoped system which could exhibit the low-frequency plasmons purely due to temperature. Whether such plasmons exist are mainly determined by temperature and momentum. The temperature-induced plasmons in a graphite sheet are identified as the 2D plasmons from the momentum dependence of plasmon frequencies. They quite differ from the optical plasmons in the three-dimensional graphite or graphite intercalation compounds. The inelastic light scattering spectroscopies could be used to verify the temperature-induced plasmons.

Electronic excitations in coupled armchair carbon nanotubes

We study the low-frequency electronic excitations in two-dimensional armchair carbon nanotube superlattices. The characteristics of the electronic structures and the superlattice geometry are directly reflected in the electronic excitations. The excitation properties, the dielectric function, the excitation spectrum, and the plasmon frequency, strongly depend on the direction and the magnitude of the transferred momentum, and the nanotube radius. There are low-frequency plasmons except that the transferred momentum is perpendicular to the tubular axis. They belong to acoustic plasmons.