Square Root Of Magnetic Field Research Articles

Cyclotron-phonon resonance power absorption in free standing nanostructure of transparent conducting oxides

A theory of cyclotron-phonon resonance power absorption (CPRPA) in a free-standing nanostructure (FSNS) of transparent conducting oxides (TCO) is presented. An analytical expression for optical power absorption is obtained based on quantum mechanical perturbation technique for the case when electrons are scattered by bulk longitudinal polar optical phonons. The optical power absorption spectrum consists of a series of peaks due to electron transition between Landau levels with simultaneous absorption of photon and emission of phonon. The intensity and location of absorption peaks depends on the material parameters such as electron effective mass and LO-phonon energy. Frequency, temperature and thickness dependence of absorption power and the variation of full-width at half maximum (FWHM) of absorption peaks as a function of magnetic field, temperature, and number of Landau levels are presented. The FWHM of CPRPA peaks increases linearly with square root of magnetic field. Further, FWHM is independent of temperature and thickness of FSNS. The numerical results obtained for all TCOs confirm that CPRPA measurements would be useful in understanding optical absorption characteristics of TCOs in finite and zero magnetic fields.

Nonlinear optical absorption and cyclotron–impurity resonance in monolayer silicene

The magneto-optical transport properties in monolayer silicene subjected simultaneously to a perpendicular magnetic field and an electromagnetic wave (optical field) are theoretically studied. The nonlinear absorption coefficient is calculated using perturbation theory taking account of the electron–impurity scattering. The cyclotron–impurity resonance (CIR) is observed through the absorption spectrum. The photon energy at resonances is found to be proportional to the square root of magnetic field. This behaviour is similar to that in graphene but different from that in conventional low-dimensional semiconductors. The full width at half maximum (FWHM) of CIR peaks increases with increasing magnetic field by the laws FWHM [meV] ≈0.432B[T] and FWHM [meV] ≈0.215B[T] for one- and two-photon absorption, respectively. The obtained FWHM is about one order of magnitude smaller than it is in graphene monolayers. Moreover, the temperature dependence of the FWHM is similar to that in graphene but different from that in conventional low-dimensional semiconductors.

Weak antilocalization and localization in disordered and interacting Weyl semimetals

Using the Feynman diagram techniques, we derive the finite-temperature conductivity and magnetoconductivity formulas from the quantum interference and electron-electron interaction, for a three-dimensional disordered Weyl semimetal. For a single valley of Weyl fermions, we find that the magnetoconductivity is negative and proportional to the square root of magnetic field at low temperatures, as a result of the weak antilocalization. By including the contributions from the weak antilocalization, Berry curvature correction, and Lorentz force, we compare the calculated magnetoconductivity with a recent experiment. The weak antilocalization always dominates the magnetoconductivity near zero field, thus gives one of the transport signatures for Weyl semimetals. In the presence of strong intervalley scattering and correlations, we expect a crossover from the weak antilocalization to weak localization. In addition, we find that the interplay of electron-electron interaction and disorder scattering always dominates the conductivity at low temperatures and leads to a tendency to localization. Finally, we present a systematic comparison of the transport properties of single-valley Weyl fermions, 2D massless Dirac fermions, and 3D conventional electrons.

Nonlinear optical absorption in graphene via two-photon absorption process

Nonlinear optical absorption phenomena in monolayer graphene for scattering between carriers and K-optical phonons are studied via investigating the phonon-assisted cyclotron resonance (PACR) effect. The positions of the PACR peaks are indicated. Only principal transitions make a significant contribution to the optical absorption power. We found that with the increase of the magnetic field, the optical absorption spectrum increases in magnitude and also gives the blue-shift in both one- and two-photon absorption processes. Besides, the half-width is found to be almost independent from the change of temperature, but proportional to the square root of magnetic field, and this agrees with the previous experimental observations.

Shape of Disorder-Broadened Landau Subbands in Graphene

In this Letter, we calculate the density of states of graphene under a highly uniform magnetic field and white-noise random potential. We discover that the disorder-broadened zero-energy Landau band has a Gaussian shape and its width is proportional to the random potential variance and the square root of magnetic field. We also use the Wegner-type calculation to justify our simulation results.

Line-Width of Quantum Limit Cyclotron Resonance. II. Impurity and Carrier-Carrier Scatterings in Ge, InSb and GaAs

Cyclotron Resonance Line-Width (CRLW) has been studied in the quantum limit for impurity and carrier-carrier scatterings in Ge, InSb and GaAs. Ionized impurity and neutral impurity (electron-neutral donor and electron-neutral acceptor) scatterings have been examined with impurity scatterings. The dependences on temperature and magnetic field of CRLW for these two scatterings are similar to each other. From our experimental results it becomes clear that CRLW is approximately (1) independent of temperature and (2) proportional to the inverse of the square root of magnetic field. Electron momentum cross section by neutral acceptor is noted to be some orders of magnitude less as compared with that by neutral donor even in the quantum limit.

QUANTUM LIMIT CYCLOTRON RESONANCE IN GaAs AND Ge

A study of quantum limit cyclotron resonance linewidth has been carried out in n-GaAs and pure Ge. The relaxation time in the quantum limit derived from cyclotron resonance linewidth has been examined for neutral donor scattering in GaAs and for acoustic deformation potential scattering in Ge. Time-resolved far-infrared (513 to 84 μm) laser cyclotron resonance has been performed in pulsed band gap excitation. It is found that (1) The inverse relaxation time for neutral donor scattering is proportional to neutral donor concentration and the reciprocal of the square root of magnetic field, and independent of temperature. (2) The same for acoustic deformation potential scattering is proportional to temperature and the square root of magnetic field.

On intracluster Faraday rotation. II - Statistical analysis

The comparison of a reliable sample of radio source Faraday rotation measurements seen through rich clusters of galaxies, with sources seen through the outer parts of clusters and therefore having little intracluster Faraday rotation, indicates that the distribution of rotation in the former population is broadened, but only at the 80% level of statistical confidence. Employing a physical model for the intracluster medium in which the square root of magnetic field strength/turbulent cell per gas core radius number ratio equals approximately 0.07 microgauss, a Monte Carlo simulation is able to reproduce the observed broadening. An upper-limit analysis figure of less than 0.20 microgauss for the field strength/turbulent cell ratio, combined with lower limits on field strength imposed by limitations on the Compton-scattered flux, shows that intracluster magnetic fields must be tangled on scales greater than about 20 kpc.