105 research outputs found
YBaCuO/LaCaMnO bilayers: Interface coupling and electric transport properties
Heteroepitaxially grown bilayers of ferromagnetic LaCaMnO
(LCMO) on top of superconducting YBaCuO (YBCO) thin films were
investigated by focusing on electric transport properties as well as on
magnetism and orbital occupation at the interface. Transport measurements on
YBCO single layers and on YBCO/LCMO bilayers, with different YBCO thickness
and constant LCMO thickness \,nm, show a significant reduction of
the superconducting transition temperature only for \,nm,with
only a slightly stronger suppression in the bilayers, as compared to the
single layers. X-ray magnetic circular dichroism (XMCD) measurements confirm
recently published data of an induced magnetic moment on the interfacial Cu by
the ferromagnetically ordered Mn ions, with antiparallel alignment between Cu
and Mn moments. However, we observe a significantely larger Cu moment than
previously reported, indicating stronger coupling between Cu and Mn at the
interface. This in turn could result in an interface with lower transparency,
and hence smaller spin diffusion length, that would explain our electric
transport data, i.e.smaller suppression. Moreover, linear dichroism
measurements did not show any evidence for orbital reconstruction at the
interface, indicating that a large change in orbital occupancies through
hybridization is not necessary to induce a measurable ferromagnetic moment on
the Cu atoms.Comment: 8 Figure
Extremely Small Energy Gap in the Quasi-One-Dimensional Conducting Chain Compound SrNbO
Resistivity, optical, and angle-resolved photoemission experiments reveal
unusual one-dimensional electronic properties of highly anisotropic
SrNbO. Along the conducting chain direction we find an extremely small
energy gap of only a few meV at the Fermi level. A discussion in terms of
typical 1D instabilities (Peierls, Mott-Hubbard) shows that neither seems to
provide a satisfactory explanation for the unique properties of SrNbO.Comment: 4 pages, 3 figure
VocDoc, what happened to my voice? Towards automatically capturing vocal fatigue in the wild
Objective:
Voice problems that arise during everyday vocal use can hardly be captured by standard outpatient voice assessments. In preparation for a digital health application to automatically assess longitudinal voice data ‘in the wild’ – the VocDoc, the aim of this paper was to study vocal fatigue from the speaker’s perspective, the healthcare professional’s perspective, and the ‘machine’s’ perspective.
Methods:
We collected data of four voice healthy speakers completing a 90-min reading task. Every 10 min the speakers were asked about subjective voice characteristics. Then, we elaborated on the task of elapsed speaking time recognition: We carried out listening experiments with speech and language therapists and employed random forests on the basis of extracted acoustic features. We validated our models speaker-dependently and speaker-independently and analysed underlying feature importances. For an additional, clinical application-oriented scenario, we extended our dataset for lecture recordings of another two speakers.
Results:
Self- and expert-assessments were not consistent. With mean F1 scores up to 0.78, automatic elapsed speaking time recognition worked reliably in the speaker-dependent scenario only. A small set of acoustic features – other than features previously reported to reflect vocal fatigue – was found to universally describe long-term variations of the voice.
Conclusion:
Vocal fatigue seems to have individual effects across different speakers. Machine learning has the potential to automatically detect and characterise vocal changes over time.
Significance:
Our study provides technical underpinnings for a future mobile solution to objectively capture pathological long-term voice variations in everyday life settings and make them clinically accessible
Strong localization of electrons in quasi-one-dimensional conductors
We report on the experimental study of electron transport in sub-micron-wide
''wires'' fabricated from Si -doped GaAs. These quasi-one-dimensional
(Q1D) conductors demonstrate the crossover from weak to strong localization
with decreasing the temperature. On the insulating side of the crossover, the
resistance has been measured as a function of temperature, magnetic field, and
applied voltage for different values of the electron concentration, which was
varied by applying the gate voltage. The activation temperature dependence of
the resistance has been observed with the activation energy close to the mean
energy spacing of electron states within the localization domain. The study of
non-linearity of the current-voltage characteristics provides information on
the distance between the critical hops which govern the resistance of Q1D
conductors in the strong localization (SL) regime. We observe the exponentially
strong negative magnetoresistance; this orbital magnetoresistance is due to the
universal magnetic-field dependence of the localization length in Q1D
conductors. The method of measuring of the single-particle density of states
(DoS) in the SL regime has been suggested. Our data indicate that there is a
minimum of DoS at the Fermi level due to the long-range Coulomb interaction.Comment: 12 pages, 11 figures; the final version to appear in Phys. Rev.
Optical properties of structurally-relaxed Si/SiO superlattices: the role of bonding at interfaces
We have constructed microscopic, structurally-relaxed atomistic models of
Si/SiO superlattices. The structural distortion and oxidation-state
characteristics of the interface Si atoms are examined in detail. The role
played by the interface Si suboxides in raising the band gap and producing
dispersionless energy bands is established. The suboxide atoms are shown to
generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and
optical-absorption calculations at the Fermi Golden rule level are used to
demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue
shift in the spectrum, and (c) an enhancement of the absorption intensity in
the threshold-energy region. Some aspects of this behaviour appear not only in
the symmetry direction associated with the superlattice axis, but also in the
orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO
superlattices show clear optical enhancement and a shift of the optical
spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B
Self-energy of image states on copper surfaces
We report extensive calculations of the imaginary part of the electron
self-energy in the vicinity of the (100) and (111) surfaces of Cu. The
quasiparticle self-energy is computed by going beyond a free-electron
description of the metal surface, either within the GW approximation of
many-body theory or with inclusion, within the GW approximation, of
short-range exchange-correlation effects. Calculations of the decay rate of the
first three image states on Cu(100) and the first image state on Cu(111) are
also reported, and the impact of both band structure and many-body effects on
the electron relaxation process is discussed.Comment: 8 pages, 5 figures, to appear in Phys. Rev.
Magnetic Proximity Effect in YBa₂Cu₃O₇/La<sub>2/3</sub>Ca<sub>1/3</sub>MnO₃ and YBa₂Cu₃O₇/LaMnO₃₊ Superlattices
Using neutron reflectometry and resonant x-ray techniques we studied the magnetic proximity effect (MPE) in superlattices composed of superconducting YBa₂Cu₃O₇ and ferromagnetic-metallic La0.67Ca0.33MnO₃ or ferromagnetic-insulating LaMnO₃₊. We find that the MPE strongly depends on the electronic state of the manganite layers, being pronounced for the ferromagnetic-metallic La0.67Ca0.33MnO₃ and almost absent for ferromagnetic-insulating LaMnO₃₊. We also detail the change of the magnetic depth profile due to the MPE and provide evidence for its intrinsic nature
HESEB The Helmholtz state of the art Soft X Ray Undulator beamline at SESAME
SESAME and a consortium of five Helmholtz Centers are designing and installing a state of the art soft X Ray undulator beamline at the SESAME light source in Amman, Jordan. Funding is provided by the Helmholtz Association over a four year project cycle that started in January 2019. This is an interim report covering the first 36 months of the project where the construction and installation has been almost completed and commissioning and characterization of the beamline is about to start. Additionally, seminars, workshops, and a training program are part of the project aimed at establishing a broad user communit
Rethinking classification results based on read speech, or: why improvements do not always transfer to other speaking styles
Functional characterization of the diatom cyclin-dependent kinase A2 as a mitotic regulator reveals plant-like properties in a non-green lineage
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