ABSTRACT
We investigate the electron-phonon coupling in CH_{3}NH_{3}PbX_{3} lead halide perovskites through the observation of Landau levels and high-order excitons at weak magnetic fields, where the cyclotron energy is significantly smaller than the longitudinal optical phonon energy. The reduced masses of the carriers and the exciton binding energies obtained from these data are clearly influenced by polaron formation. We analyze the field-dependent polaronic and excitonic properties, and show that they can be quantitatively reproduced by the Fröhlich large polaron model.
ABSTRACT
We exploit an intense terahertz magnetic near field combined with femtosecond laser excitation to break the symmetry of photoinduced spin reorientation paths in ErFeO_{3}. We succeed in aligning macroscopic magnetization reaching up to 80% of total magnetization in the sample to selectable orientations by adjusting the time delay between terahertz and optical pump pulses. The spin dynamics are well reproduced by equations of motion, including time-dependent magnetic potential. We show that the direction of the generated magnetization is determined by the transient direction of spin tilting and the magnetic field at the moment of photoexcitation.
ABSTRACT
We studied the optical responses of organic-inorganic halide perovskite CH3NH3PbBr3 single crystals doped with heterovalent Bi3+ ions (electron densities up to 2.3 × 1012 cm-3). The Bi doping causes no significant changes in the band gap energy but leads to an enhanced Urbach tail and photoluminescence blue shift. On the basis of the time-resolved photoluminescence measurements, we attribute the PL response to a shorter carrier lifetime induced by Bi doping, which results in a reduced photon recycling effect (i.e., the repeated emission and reabsorption of photons inside the crystal). We discuss the physical relation between Bi concentration and the optical and electric properties of Bi-doped CH3NH3PbBr3 and reveal the unique nature of the Bi3+ ion as a dopant in halide perovskites.
ABSTRACT
A flake of monolayer graphene was sandwiched between boron nitride sheets. Temperature dependent Shubnikov-de Haas measurements were performed to access how this technique influences the electronic properties of the graphene sample. The maximum mobility found in this configuration was approximately 105 cm2 Vs -1. From the phase of the oscillations a Berry phase ß of 1/2 was obtained indicating the presence of Dirac fermions. We obtained Fermi velocities around [Formula: see text] m s-1 which imply hopping energies close to 2.5 eV. Furthermore, the carrier lifetime is typically higher than that found in graphene supported by SiO2, reaching values higher than 700 fs.
ABSTRACT
Electronic transport properties of a bundle of Si nanochains/nanowires were investigated. Si nanochains and nanowires were grown via a self-organized vapor-liquid-solid process and located on a pair of electrodes with a gap of several hundred nanometers. Unstable and a variety of current-voltage (I-V) characteristics were observed and some of those were Coulomb staircase-like. In addition, fluctuations which were seemingly random but partly and partially reproducible were observed in I-V curves of a parallel junction of a nanochain and a nanowire.
