800 research outputs found
Optical control of magnetization of micron-size domains in antiferromagnetic NiO single crystals
We propose Raman-induced collinear difference-frequency generation (DFG) as a
method to manipulate dynamical magnetization. When a fundamental beam
propagates along a threefold rotational axis, this coherent second-order
optical process is permitted by angular momentum conservation through the
rotational analogue of the Umklapp process. As a demonstration, we
experimentally obtained polarization properties of collinear magnetic DFG along
a [111] axis of a single crystal of antiferromagnetic NiO with micro
multidomain structure, which excellently agreed with the theoretical
prediction.Comment: 11 pages, 3 figures, submitted to Physical Review Letter
The Yellow Excitonic Series of Cu2O Revisited by Lyman Spectroscopy
We report on the observation of the yellow exciton Lyman series up to the
fourth term in Cu2O by time-resolved mid-infrared spectroscopy. The dependence
of the oscillator strength on the principal quantum number n can be well
reproduced using the hydrogenic model including an AC dielectric constant, and
precise information on the electronic structure of the 1s exciton state can be
obtained. A Bohr radius a_{1s}=7.9 A and a 1s-2p transition dipole moment
\mu_{1s-2p}= 4.2 eA were found
Dimensionality dependence of optical nonlinearity and relaxation dynamics in cuprates
Femtosecond pump-probe measurements find pronounced dimensionality dependence
of the optical nonlinearity in cuprates. Although the coherent two-photon
absorption (TPA) and linear absorption bands nearly overlap in both quasi-one
and two-dimensional (1D and 2D) cuprates, the TPA coefficient is one order of
magnitude smaller in 2D than in 1D. Furthermore, picosecond recovery of optical
transparency is observed in 1D cuprates, while the recovery in 2D involves
relaxation channels with a time scales of tens of picoseconds. The experimental
results are interpreted within the two-band extended Hubbard model.Comment: 10 pages, 4 figure
An Anomalous Phase in the Relaxor Ferroelectric Pb(ZnNb)O
X-ray diffraction studies on a Pb(ZnNb)O (PZN) single
crystal sample show the presence of two different structures. An outer-layer
exists in the outer most 10 to 50~m of the crystal, and undergoes a
structural phase transition at the Curie temperature K. The
inside phase is however, very different. The lattice inside the crystal
maintains a cubic unit cell, while ferroelectric polarization develops below
. The lattice parameter of the cubic unit cell remains virtually a
constant, i.e., much less variations compared to that of a typical relaxor
ferroelectric, in a wide temperature range of 15 K to 750 K. On the other hand,
broadening of Bragg peaks and change of Bragg profile line-shapes in both
longitudinal and transverse directions at clearly indicate a structural
phase transition occurring.Comment: to be submitted for PR
Testing the validity of THz reflection spectra by dispersion relations
Complex response function obtained in reflection spectroscopy at terahertz
range is examined with algorithms based on dispersion relations for integer
powers of complex reflection coefficient, which emerge as a powerful and yet
uncommon tools in examining the consistency of the spectroscopic data. It is
shown that these algorithms can be used in particular for checking the success
of correction of the spectra by the methods of Vartiainen et al [1] and
Lucarini et al [2] to remove the negative misplacement error in the terahertz
time-domain spectroscopy.Comment: 17 pages, 4 figure
Neutron Diffraction Study of Field Cooling Effects on Relaxor Ferroelectrics Pb[(Zn_{1/3} Nb_{2/3})_{0.92} Ti_{0.08}] O_{3}
High-temperature (T) and high-electric-field (E) effects on Pb[(Zn_{1/3}
Nb_{2/3})_{0.92} Ti_{0.08}]O_3 (PZN-8%PT) were studied comprehensively by
neutron diffraction in the ranges 300 <= T <= 550 K and 0 <= E <= 15 kV/cm. We
have focused on how phase transitions depend on preceding thermal and
electrical sequences. In the field cooling process (FC, E parallel [001] >= 0.5
kV/cm), a successive cubic (C) --> tetragonal (T) --> monoclinic (M_C)
transition was observed. In the zero field cooling process (ZFC), however, we
have found that the system does not transform to the rhombohedral (R) phase as
widely believed, but to a new, unidentified phase, which we call X. X gives a
Bragg peak profile similar to that expected for R, but the c-axis is always
slightly shorter than the a-axis. As for field effects on the X phase, we found
an irreversible X --> M_C transition via another monoclinic phase (M_A) as
expected from a previous report [Noheda et al. Phys. Rev. Lett. 86, 3891
(2001)]. At a higher electric field, we confirmed a c-axis jump associated with
the field-induced M_C --> T transition, which was observed by strain and x-ray
diffraction measurements.Comment: 8 pages, 9 figures, revise
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