3,766 research outputs found
Mathematical description of matter exchange between water components and adsorbing surface of filter medium of water purification units
The article presents the theory of mass transfer processes between water
polluting components and the adsorbing surface of filter medium of water
purification units
Orbitally induced hierarchy of exchange interactions in zigzag antiferromagnetic state of honeycomb silver delafossite Ag3Co2SbO6
We report the revised crystal structure, static and dynamic magnetic
properties of quasi-two dimensional honeycomb-lattice silver delafossite
Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent
with the onset of antiferromagnetic long range order at low temperatures with
N\'eel temperature TN ~ 21.2 K. In addition, the magnetization curves revealed
a field-induced (spin-flop type) transition below TN in moderate magnetic
fields. The GGA+U calculations show the importance of the orbital degrees of
freedom, which maintain a hierarchy of exchange interaction in the system. The
strongest antiferromagnetic exchange coupling was found in the shortest Co-Co
pairs and is due to direct and superexchange interactions between the
half-filled xz+yz orbitals pointing directly to each other. The other four out
of six nearest neighbor exchanges within the cobalt hexagon are suppressed,
since for these bonds active half-filled orbitals turned out to be parallel and
do not overlap. The electron spin resonance (ESR) spectra reveal a Gaussian
shape line attributed to Co2+ ion in octahedral coordination with average
effective g-factor g=2.3+/-0.1 at room temperature and shows strong divergence
of ESR parameters below 120 K, which imply an extended region of short-range
correlations. Based on the results of magnetic and thermodynamic studies in
applied fields, we propose the magnetic phase diagram for the new
honeycomb-lattice delafossite
Magnetic phase diagram of the frustrated S=1/2 chain magnet LiCu_2O_2
We present the results of the magnetization and dielectric constant
measurements on untwinned single crystal samples of the frustrated S=1/2 chain
cuprate LiCu_2O_2. Novel magnetic phase transitions were observed. A spin flop
transition of the spiral spin plane was observed for the field orientations
H||a,b. The second magnetic transition was observed at H~15 T for all three
principal field directions. This high field magnetic phase is discussed as a
collinear spin-modulated phase which is expected for an S=1/2 nearest-neighbor
ferromagnetic and next-nearest-neighbor antiferromagnetic chain system
Bifurcations and chaos in semiconductor superlattices with a tilted magnetic field
We study the effects of dissipation on electron transport in a semiconductor
superlattice with an applied bias voltage and a magnetic field that is tilted
relative to the superlattice axis.In previous work, we showed that although the
applied fields are stationary,they act like a THz plane wave, which strongly
couples the Bloch and cyclotron motion of electrons within the lowest miniband.
As a consequence,the electrons exhibit a unique type of Hamiltonian chaos,
which creates an intricate mesh of conduction channels (a stochastic web) in
phase space, leading to a large resonant increase in the current flow at
critical values of the applied voltage. This phase-space patterning provides a
sensitive mechanism for controlling electrical resistance. In this paper, we
investigate the effects of dissipation on the electron dynamics by modifying
the semiclassical equations of motion to include a linear damping term. We
demonstrate that even in the presence of dissipation,deterministic chaos plays
an important role in the electron transport process. We identify mechanisms for
the onset of chaos and explore the associated sequence of bifurcations in the
electron trajectories. When the Bloch and cyclotron frequencies are
commensurate, complex multistability phenomena occur in the system. In
particular, for fixed values of the control parameters several distinct stable
regimes can coexist, each corresponding to different initial conditions. We
show that this multistability has clear, experimentally-observable, signatures
in the electron transport characteristics.Comment: 14 pages 11 figure
The superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy
FeSe single crystals have been studied by soft point-contact
Andreev-reflection spectroscopy. Superconducting gap features in the
differential resistance dV/dI(V) of point contacts such as a characteristic
Andreev-reflection double-minimum structure have been measured versus
temperature and magnetic field. Analyzing dV/dI within the extended two-gap
Blonder-Tinkham-Klapwijk model allows to extract both the temperature and
magnetic field dependence of the superconducting gaps. The temperature
dependence of both gaps is close to the standard BCS behavior. Remarkably, the
magnitude of the double-minimum structure gradually vanishes in magnetic field,
while the minima position only slightly shifts with field indicating a weak
decrease of the superconducting gaps. Analyzing the dV/dI(V) spectra for 25
point contacts results in the averaged gap values = 1.8+/-0.4meV and
=1.0+/-0.2 meV and reduced values 2/kTc=4.2+/-0.9 and
2/kTc=2.3+/-0.5 for the large (L) and small (S) gap, respectively.
Additionally, the small gap contribution was found to be within tens of percent
decreasing with both temperature and magnetic field. No signatures in the dV/dI
spectra were observed testifying a gapless superconductivity or presence of
even smaller gaps.Comment: 8 pages, 4 figs., 3 tables. Shortened version without fig.4 and Table
3 is accepted for publication in Phys. Rev.
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