975 research outputs found
First principles investigation of transition-metal doped group-IV semiconductors: RY (R=Cr, Mn, Fe; Y=Si, Ge)
A number of transition-metal (TM) doped group-IV semiconductors,
RY (R=Cr, Mn and Fe; Y=Si, Ge), have been studied by the first
principles calculations. The obtained results show that antiferromagnetic (AFM)
order is energetically more favored than ferromagnetic (FM) order in Cr-doped
Ge and Si with =0.03125 and 0.0625. In 6.25% Fe-doped Ge, FM interaction
dominates in all range of the R-R distances while for Fe-doped Ge at 3.125% and
Fe-doped Si at both concentrations of 3.125% and 6.25%, only in a short R-R
range can the FM states exist. In the Mn-doped case, the RKKY-like mechanism
seems to be suitable for the Ge host matrix, while for the Mn-doped Si, the
short-range AFM interaction competes with the long-range FM interaction. The
different origin of the magnetic orders in these diluted magnetic
semiconductors (DMSs) makes the microscopic mechanism of the ferromagnetism in
the DMSs more complex and attractive.Comment: 14 pages, 2 figures, 6 table
Internal Transitions of Two-Dimensional Charged Magneto-Excitons X-: Theory and Experiment
Internal spin-singlet and spin-triplet transitions of charged excitons X- in
magnetic fields in quantum wells have been studied experimentally and
theoretically. The allowed X- transitions are photoionizing and exhibit a
characteristic double-peak structure, which reflects the rich structure of the
magnetoexciton continua in higher Landau levels (LL's). We discuss a novel
exact selection rule, a hidden manifestation of translational invariance, that
governs transitions of charged mobile complexes in a magnetic field.Comment: 4 pages, 2 figures, submitted to Physica
Epitaxial Growth of the Diluted Magnetic Semiconductors CryGe1-y and CryMnxGe1-x-y
We report the epitaxial growth of CryGe1-y and CryMnxGe1-x-y(001) thin films
on GaAs(001), describe the structural and transport properties, and compare the
measured magnetic properties with those predicted by theory. The samples are
strongly p-type, and hole densities increase with Cr concentration. The
CryGe1-y system remains paramagnetic for the growth conditions and low Cr
concentrations employed (y < 0.04), consistent with density functional theory
predictions. Addition of Cr into the ferromagnetic semiconductor MnxGe1-x host
systematically reduces the Curie temperature and total magnetization.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Biaxial strain tuning of exciton energy and polarization in monolayer WS2
We perform micro-photoluminescence and Raman experiments to examine the
impact of biaxial tensile strain on the optical properties of WS2 monolayers. A
strong shift on the order of -130 meV per % of strain is observed in the
neutral exciton emission at room temperature. Under near-resonant excitation we
measure a monotonic decrease in the circular polarization degree under applied
strain. We experimentally separate the effect of the strain-induced energy
detuning and evaluate the pure effect coming from biaxial strain. The analysis
shows that the suppression of the circular polarization degree under biaxial
strain is related to an interplay of energy and polarization relaxation
channels as well as to variations in the exciton oscillator strength affecting
the long-range exchange interaction.Comment: 29 pages, 11 figure
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