167 research outputs found
Quantitative Determination of the Mechanical Properties of Nanomembrane Resonators by Vibrometry In Continuous Light
We present an experimental study of the bending waves of freestanding
\ce{Si3N4} nanomembranes using optical profilometry in varying environments
such as pressure and temperature. We introduce a method, named Vibrometry in
Continuous Light (VICL) that enables us to disentangle the response of the
membrane from the one of the excitation system, thereby giving access to the
eigenfrequency and the quality () factor of the membrane by fitting a model
of a damped driven harmonic oscillator to the experimental data. The validity
of particular assumptions or aspects of the model such as damping mechanisms,
can be tested by imposing additional constraints on the fitting procedure. We
verify the performance of the method by studying two modes of a
thick \ce{Si3N4} freestanding membrane and find factors
of for both modes at room temperature. Finally, we observe a
linear increase of the resonance frequency of the ground mode with temperature
which amounts to for a ground mode
frequency of . This makes the nanomembrane resonators
suitable as high-sensitive temperature sensors
Creation of equal-spin triplet superconductivity at the Al/EuS interface
In conventional superconductors, electrons of opposite spins are bound into
Cooper pairs. However, when the superconductor is in contact with a
non-uniformly ordered ferromagnet, an exotic type of superconductivity can
appear at the interface, with electrons bound into three possible spin-triplet
states. Triplet pairs with equal spin play a vital role in low-dissipation
spintronics. Despite the observation of supercurrents through ferromagnets,
spectroscopic evidence for the existence of equal-spin triplet pairs is still
missing. Here we show a theoretical model that reveals a characteristic gap
structure in the quasiparticle density of states which provides a unique
signature for the presence of equal-spin triplet pairs. By scanning tunnelling
spectroscopy we measure the local density of states to reveal the spin
configuration of triplet pairs. We demonstrate that the Al/EuS interface causes
strong and tunable spin-mixing by virtue of its spin-dependent transmission.Comment: 10 pages, 4 figures, 17 pages supplementary information, 14
supplementary figure
Simulating bistable current-induced switching of metallic atomic contacts by electron-vibration scattering
We present a microscopic model, describing current-driven switching in
metallic atomic-size contacts. Applying a high current through an atomic-size
contact, creates a strong electronic nonequilibrium that excites vibrational
modes by virtue of the electron-vibration coupling. Using density functional
theory (DFT) in combination with the Landauer-B\"uttiker theory for
phase-coherent transport, expressed in terms of nonequilibrium Green's
functions (NEGFs), we study the current-induced forces arising from this
nonequilibrium and determine those vibrational modes which couple most strongly
to the electronic system. For single-atom lead (Pb) contacts we show specific
candidates for bistable switches, consisting of two similar atomic
configurations with differing electric conductance. We identify vibrational
modes that induce a transition between these configurations. Our results reveal
a possible origin of bistable switching in atomic-size contacts through
excitation of vibrations by inelastic electron scattering and underline the
power of the combined DFT-NEGF approach and statistical mechanics analysis of a
Langevin equation to overcome the time-scale gap between atomic motion and rare
switching events, allowing for an efficient exploration of the contacts'
configurational phase space
Interplay of Andreev reflection and Coulomb blockade in hybrid superconducting single electron transistors
We study the interplay between Coulomb blockade and superconductivity in a
tunable superconductor-superconductor-normal metal single-electron transistor.
The device is realized by connecting the superconducting island via an oxide
barrier to the normal metal lead and with a break junction to the
superconducting lead. The latter enables Cooper pair transport and (multiple)
Andreev reflection. We show that those processes are relevant also far above
the superconducting gap and that signatures of Coulomb blockade may reoccur at
high bias while they are absent for small bias in the strong-coupling regime.
Our experimental findings agree with simulations using a master equation
approach in combination with the full counting statistics of multiple Andreev
reflection.Comment: Manuscript only, supplement available upon reques
Microscopic theory of supercurrent suppression by gate-controlled surface depairing
Recently gate-mediated supercurrent suppression in superconducting
nano-bridges has been reported in many experiments. This could be either a
direct or an indirect gate effect. The microscopic understanding of this
observation is not clear till now. Using the quasiclassical Green's function
method, we show that a small concentration of magnetic impurities at the
surface of the bridges can significantly help to suppress superconductivity and
hence the supercurrent inside the systems while applying a gate field. This is
because the gate field can enhance the depairing through the exchange
interaction between the magnetic impurities at the surface and the
superconductor. We also obtain a \emph{symmetric} suppression of the
supercurrent with respect to the gate field, a signature of a direct gate
effect. Future experiments can verify our predictions by modifying the surface
with magnetic impurities
Spatial-temporally resolved high-frequency surface acoustic waves on silicon investigated by femtosecond spectroscopy
Various types of surface acoustic waves are generated by femtosecond pulses on bulk silicon with aluminium stripe transducers. Rayleigh and leaky longitudinal surface acoustic wave modes are detected in the time domain for various propagation distances. The modes are identified by measuring on various pitches and comparing the spectra with finite element calculations. The lifetimes of the modes are determined quantitatively by spatially separating pump and probe beam, showing a significant difference in the lifetimes of both modes. We were able to excite and measure Rayleigh modes with frequencies of up to 90 GHz using a 100 nm period grating.Fil: Schubert, Martin . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Grossmann, Martin . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Ristow, Oliver . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Hettich, Mike . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Bruchhausen, Axel Emerico. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Comisión Nacional de EnergÃa Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de FÃsica (Centro Atómico Bariloche); Argentina. Comisión Nacional de EnergÃa Atómica. Gerencia del Area de EnergÃa Nuclear. Instituto Balseiro; ArgentinaFil: Barretto, Elaine C. S. . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Scheer, Elke . University of Konstanz. Department of Physics and Center for Applied Photonics; AlemaniaFil: Gusev, Vitalyi . Université du Maine; Francia. Centre National de la Recherche Scientifique; FranciaFil: Dekorsy, Thomas . University of Konstanz. Department of Physics and Center for Applied Photonics; Alemani
Single-crystalline YIG nanoflakes with uniaxial in-plane anisotropy and diverse crystallographic orientations
We study Y3Fe5O12 (YIG) nanoflakes that we produce via mechanical cleaving
and exfoliation of YIG single crystals. By characterizing their structural and
magnetic properties, we find that these YIG nanoflakes have surfaces oriented
along unusual crystallographic axes and uniaxial in-plane magnetic anisotropy
due to their shape, both of which are not commonly available in YIG thin films.
These physical properties, combined with the possibility of picking up the YIG
nanoflakes and stacking them onto nanoflakes of other van der Waals materials
or pre-patterned electrodes or waveguides, open unexplored possibilities for
magnonics and for the realization of novel YIG-based heterostructures and
devices.Comment: 13 pages, 4 figure
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