0000000000315661
AUTHOR
Hartmut G. Roskos
Generation of a DC Fiske current by coupling of Bloch and in-plane cyclotron oscillations in a semiconductor superlattice
The coherent coupling between electron Bloch and in-plane cyclotron oscillations in semiconductor superlatices in tilted electric and magnetic fields induces a unidirectional quasi-DC current in analogy to the DC Fiske effect observed when a superconductor Josephson junction or a superfluid weak link is coupled to an electromagnetic respectively an acoustic resonator. In all cases, the coupling opens an elastic rectifying transport channel. We explore the effect for the case of a superlattice both experimentally and theoretically, and specifically address the influence of the coupling on the frequency of the magnetoBloch oscillations.
Picosecond energy relaxation in
Abstract Investigating the reflectance response dynamics of La 0.67 Ca 0.33 MnO 3 thin films after excitation by femtosecond laser pulses, we identify for the first time a picosecond relaxation step which only exists below the Curie temperature T C . The relaxation time increases from zero at T C to several picoseconds at low temperatures. The data can be explained with the existence of a magnetization-related effective energy gap, and assuming relaxation between these states to be mediated by a Frohlich-type electron–lattice interaction.
Combined investigation of collective amplitude and phase modes in a quasi-one-dimensional charge-density-wave system over a wide spectral range
We investigate experimentally both the amplitude and phase channels of the collective modes in the quasi-1D charge-density-wave (CDW) system, K0.3MoO3, by combining (i) optical impulsive-Raman pump-probe and (ii) terahertz time-domain spectroscopy (THz-TDS), with high resolution and a detailed analysis of the full complex-valued spectra in both cases. This allows an unequivocal assignment of the observed bands to CDW modes across the THz range up to 9 THz. We revise and extend a time-dependent Ginzburg-Landau model to account for the observed temperature dependence of the modes, where the combination of both amplitude and phase modes allows one to robustly determine the bare-phonon and elec…
Optical determination of the oxygen content of YBa2Cu3O6+x thin films by IR reflectance and transmittance measurements
Abstract Recent studies of the optical properties of YBa2Cu3O6+x (YBCO) single crystals by several authors have shown that the optical conductivity in the infrared spectral region is a sensitive function of the oxygen content of the samples. Infrared spectroscopy thus offers a possibility for oxygen concentration analysis and is an alternative to other methods such as (i) the X-ray determination of the length of the c-axis and (ii) spectroscopic ellipsometry at an electronic transition band centered around 4.1 eV whose strength decreases with increasing oxygen content. We explore the applicability of the IR optical method for the case of YBCO thin films of about 300 nm thickness which are e…