216 research outputs found
Closing and opening phase variability in dysphonia
Four examples of the use of vocal fold contact phase measurement are discussed for unilateral paresis. In each case this aspect of voice quality is of greater importance than the physical measurement of loudness and pitch related parameters. For three of the cases electro-stimulation has been used as a main part of the treatment. Phonation in both connected speech and, for comparison, in sustained sound production has been used with electro-laryngograph / egg signals providing the basis for measurement. The main new descriptors that have been found to be useful relate to: vocal fold closure and closure duration regularities and distributions; but reference is also made to related measures of peak acoustic amplitude. The new measures described give, in some cases, quite striking results that are of auditory significance and potentially of clinical value
First principles study of topological phase in chains of transition metals
Recent experiments have shown the signatures of Majorana bound states at the
ends of magnetic chains deposited on a superconducting substrate. Here, we
employ first principles calculations to directly investigate the topological
properties of transition metal nanochains (i.e., Mn, Cr, Fe and Co). In
contrast to the previous studies [Nadj-Perge et al. Science 346, 602 (2014) and
Ruby et al. Nano Lett. 17, 4473 (2017)], we found the exact tight binding
models in the Wannier orbital basis for the isolated chains as well as for the
surface--deposited wires. Based on these models, we calculate topological
invariant of phase for all systems. Our results for the isolated
chains demonstrate the existence of the topological phase only in the Mn and Co
systems. We considered also a non-collinear magnetic order as a source of the
non--trivial topological phase and found that this type of magnetic order is
not a stable ground state in the Fe and Co isolated chains. Further studies
showed that a coupling between the chain and substrate leads to strong
modification of the band structure. Moreover, the analysis of the topological
invariant indicates a possibility of emergence of the topological phase in all
studied nanochains deposited on the Pb surface. Therefore, our results
demonstrate an important role of the coupling between deposited atoms and a
substrate for topological properties of nanosystems.Comment: 11 pages, 7 figure
Fulde-Ferrell-Larkin-Ovchinnikov phase in the presence of pair hopping interaction
The recent experimental support for the presence of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in the CeCoIn5 directed the
attention towards the mechanisms responsible for this type of
superconductivity. We investigate the FFLO state in a model where
on--site/inter--site pairing coexists with repulsive pair hopping interaction.
The latter interaction is interesting in that it leads to pairing with nonzero
momentum of the Cooper pairs even in the absence of the external magnetic field
(the so-called eta-pairing). It turns out that depending on the strength of the
pair hopping interaction the magnetic field can induce one of two types of the
FFLO phase with different spatial modulations of the order parameter. It is
argued that the properties of the FFLO phase may give information about the
magnitude of the pair hopping interaction. We also show that eta-pairing and
d-wave superconductivity may coexist in the FFLO state. It holds true also for
superconductors which in the absence of magnetic field are of pure d-wave type.Comment: 16 pages, 8 figure
Interplay between pairing and correlations in spin-polarized bound states
We investigate the single and multiple defects embedded in a superconducting
host, studying interplay between the proximity induced pairing and
interactions. We explore influence of the spin-orbit coupling on energies,
polarization and spatial patterns of the bound (Yu-Shiba-Rusinov) states of
magnetic impurities in 2-dimensional square lattice. We also address the
peculiar bound states in the proximitized Rashba chain, resembling the Majorana
quasiparticles, focusing on their magnetic polarization which has been recently
reported by S. Jeon et al., [Science 358, 772 (2017)]. Finally, we study
leakage of these polarized Majorana quasiparticles on the side-attached
nanoscopic regions and confront them with the subgap Kondo effect near to the
singlet-doublet phase transition.Comment: 10 pages, 9 figure
Coexistence of superconductivity and incommensurate magnetic order
The influence of incommensurate spin density waves (SDW) on superconductivity
in unconventional superconductors is studied by means of the Bogolubov-de
Gennes (BdG) equations. Exploiting translational symmetries of a magnetically
ordered two-dimensional system we propose an approach that allows to solve the
BdG equations on much larger clusters than it is usually possible for
inhomogeneous systems. Applying this approach we demonstrate that the presence
of incommensurate spin density waves induces real-space inhomogeneity of the
superconducting order parameter even in the absence of external magnetic field.
In this case a homogeneous order parameter of the
Bardeen-Cooper-Schrieffer-type superconducting state is slightly modulated, or
equivalently, a small fraction of the charge carriers form Cooper pairs with
non-zero total momentum. However, when a sufficiently strong magnetic field is
applied, the homogeneous component of the order parameter is suppressed and the
system transits to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, where the
order parameter oscillates changing sign. We show that for s-wave pairing the
presence of external magnetic field diminishes the destructive influence of the
SDW order on superconductivity. A simple explanation of this effect is also
proposed.Comment: To appear in Phys. Rev.
Ab initio and nuclear inelastic scattering studies of FeSi/GaAs heterostructures
The structure and dynamical properties of the FeSi/GaAs(001) interface
are investigated by density functional theory and nuclear inelastic scattering
measurements. The stability of four different atomic configurations of the
FeSi/GaAs multilayers is analyzed by calculating the formation energies and
phonon dispersion curves. The differences in charge density, magnetization, and
electronic density of states between the configurations are examined. Our
calculations unveil that magnetic moments of the Fe atoms tend to align in a
plane parallel to the interface, along the [110] direction of the FeSi
crystallographic unit cell. In some configurations, the spin polarization of
interface layers is larger than that of bulk FeSi. The effect of the
interface on element-specific and layer-resolved phonon density of states is
discussed. The Fe-partial phonon density of states measured for the FeSi
layer thickness of three monolayers is compared with theoretical results
obtained for each interface atomic configuration. The best agreement is found
for one of the configurations with a mixed Fe-Si interface layer, which
reproduces the anomalous enhancement of the phonon density of states below 10
meVComment: 14 pages, 9 figures, 4 table
Origin of monoclinic distortion and its impact on the electronic properties in KO
We use the density functional theory and lattice dynamics calculations to
investigate the properties of potassium superoxide KO in which spin,
orbital, and lattice degrees of freedom are interrelated and determine the
low-temperature phase. After calculating phonon dispersion relations in the
high-temperature tetragonal structure, we identify a soft phonon mode
leading to the monoclinic symmetry and optimize the crystal geometry
resulting from this mode. Thus we reveal a displacive character of the
structural transition with the group-subgroup relation between the tetragonal
and monoclinic phases. We compare the electronic structure of KO with
antiferromagnetic spin order in the tetragonal and monoclinic phases. We
emphasize that realistic treatment of the electronic structure requires
including the local Coulomb interaction in the valence orbitals of the
O ions. The presence of the `Hubbard' leads to the gap opening at the
Fermi energy in the tetragonal structure without orbital order but with weak
spin-orbit interaction. We remark that the gap opening in the tetragonal phase
could also be obtained when the orbital order is initiated in the calculations
with a realistic value of . Finally, we show that the local Coulomb
interactions and the finite lattice distortion, which together lead to the
orbital order via the Jahn-Teller effect, are responsible for the enhanced
insulating gap in the monoclinic structure.Comment: accepted by Physical Review
Phononic drumhead surface state in distorted kagome compound RhPb
RhPb was initially recognized as one of a CoSn-like compounds with
symmetry, containing an ideal kagome lattice of -block atoms. However,
theoretical calculations predict the realization of the phonon soft mode which
leads to the kagome lattice distortion and stabilization of the structure with
symmetry [A. Ptok et al., Phys. Rev. B 104, 054305 (2021)]. Here,
we present the single crystal x-ray diffraction results supporting this
prediction. Furthermore, we discuss the main dynamical properties of RhPb with
symmetry. The bulk phononic dispersion curves contain several
flattened bands, Dirac nodal lines, and triple degenerate Dirac points. As a
consequence, the phononic drumhead surface state is realized for the (100)
surface, terminated by the zigzag-like edge of Pb honeycomb sublattice.Comment: 10 pages, 7 figure
- …