Far-infrared magneto-optical investigations of shallow donors in epitaxial GaN layers on sapphire were carried out by means of Fourier transform spectrometry up to 23 T. From the splitting of the donor p states in a magnetic field, the cyclotron effective mass for conduction electrons was found to be $m^{*}\text{=0.222\hspace{0.05em}}{\mathrm{m}}_{\mathrm{0}}.$ A precise determination of the mass was made possible by the high quality of the spectra and by taking into account high magnetic field data above 12 T.

A new method of measuring the dynamics of magnetization at arbitrary magnetic field is presented. It is illustrated by measuring the spin-lattice relaxation rate in paramagnetic ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Te in magnetic fields up to 25 T. At low fields, the spin-spin interaction of the Mn spins dominates the relaxation process; however, at high fields the relaxation of isolated spins can be observed. Among the spin clusters playing an important role as fast relaxation centers, exchange-coupled nearest-neighbor Mn pairs are identified, suggesting an important mixing of their states.

Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasiclassical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level $m=E_F/v_F^2$. DOI: http://dx.doi.org/10.1103/PhysRevB.82.165305 © 2010 The American Physical Society

In this work, we have prepared a series of polydimethylsiloxane (PDMS) composites containing various graphene flakes loadings (0.02–2 wt%), and their broadband optical properties are being investigated. We demonstrate the tunability and evolution of transmittance and reflection spectra of the composites in a wide spectral range (0.4–200 μm) as a function of graphene content. Using these data we derive the broadband wavelength-dependent absorption coefficient (α) values. Our results show that α is roughly constant in the visible and IR ranges, and, surprisingly, is approximately one order of magnitude lower in the terahertz regime, suggesting different terahertz radiation scattering mechanism in our composite. Our material could be useful for applications in optical communication, sensing or ultrafast photonics.

Far-infrared (FIR) measurements of electric-dipole spin resonance (EDSR) of donor-bound electrons in ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Se}$ ($x=0.10\mathrm{} \mathrm{and} 0.20$ are reported. The EDSR transition is allowed in ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Se}$ by the combined effects of spin-orbit interaction and the acentric uniaxial symmetry of this wurtzite system. The far-infrared EDSR is observed at magnetic fields of the order of 1 T, indicating extremely large effective $g$ factors (in excess of 100) due to contributions from the exchange interaction between the band electrons and the localized magnetic moments. Measurements as a function of temperature and frequency reveal a strong temperature dependence of the $g$-factors, and a dramatic increase in the strength of EDSR with frequency. Studies with linear and circular polarization were used to determine the selection rules governing EDSR, as well as the sign of the exchange integral for the conduction band of ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Se}$. EDSR is observed only in samples characterized by low resistivities (∼1 Ω cm at 77 K), with donor concentrations in the range of ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$. In addition to EDSR, the FIR magnetotransmission spectra show several other interesting features, which are interpreted in terms of conduction-electron cyclotron resonance and magnetic field dependence in the $1s\to 2p$ transitions of the donor levels.