118 research outputs found
Revealing the magnetic proximity effect in EuS/Al bilayers through superconducting tunneling spectroscopy
A ferromagnetic insulator attached to a superconductor is known to induce an
exchange splitting of the Bardeen-Cooper-Schrieffer (BCS) singularity by a
magnitude proportional to the magnetization, and penetrating into the
superconductor to a depth comparable with the superconducting coherence length.
We study this long-range magnetic proximity effect in EuS/Al bilayers and find
that the exchange splitting of the BCS peaks is present already in the
unpolarized state of the ferromagnetic insulator (EuS), and is being further
enhanced when magnetizing the sample by a magnetic field. The measurement data
taken at the lowest temperatures feature a high contrast which has allowed us
to relate the line shape of the split BCS conductance peaks to the
characteristic magnetic domain structure of the EuS layer in the unpolarized
state. These results pave the way to engineering triplet superconducting
correlations at domain walls in EuS/Al bilayers. Furthermore, the hard gap and
clear splitting observed in our tunneling spectroscopy measurements indicate
that EuS/Al bilayers are excellent candidates for substituting strong magnetic
fields in experiments studying Majorana bound states.Comment: 9 pages, 4 color figure
Phonon-induced decay of the electron spin in quantum dots
We study spin relaxation and decoherence in a
GaAs quantum dot due to spin-orbit interaction. We derive an effective
Hamiltonian which couples the electron spin to phonons or any other fluctuation
of the dot potential. We show that the spin decoherence time is as large
as the spin relaxation time , under realistic conditions. For the
Dresselhaus and Rashba spin-orbit couplings, we find that, in leading order,
the effective magnetic field can have only fluctuations transverse to the
applied magnetic field. As a result, for arbitrarily large Zeeman
splittings, in contrast to the naively expected case
. We show that the spin decay is drastically suppressed for
certain magnetic field directions and values of the
Rashba coupling constant. Finally, for the spin coupling to acoustic phonons,
we show that
for all spin-orbit mechanisms in leading order in the
electron-phonon interaction.Comment: 5 pages, 1 figur
L-Drawings of Directed Graphs
We introduce L-drawings, a novel paradigm for representing directed graphs
aiming at combining the readability features of orthogonal drawings with the
expressive power of matrix representations. In an L-drawing, vertices have
exclusive - and -coordinates and edges consist of two segments, one
exiting the source vertically and one entering the destination horizontally.
We study the problem of computing L-drawings using minimum ink. We prove its
NP-completeness and provide a heuristics based on a polynomial-time algorithm
that adds a vertex to a drawing using the minimum additional ink. We performed
an experimental analysis of the heuristics which confirms its effectiveness.Comment: 11 pages, 7 figure
Nucleon Resonance Structure from CLAS and CLAS12 Experiments
The recent results on the photo- and electrocouplings extraction from the reaction of one- and two-pion photo- and electroproduction off protons in the resonances region are presented. The production of two charged pions is of particular importance for evaluation of the photocouplings for the Δ(1620)12 −, Δ(1700)32 −
Hanle Magnetoresistance in Thin Metal Films with Strong Spin-Orbit Coupling
We report measurements of a new type of magnetoresistance in Pt and Ta thin
films. The spin accumulation created at the surfaces of the film by the spin
Hall effect decreases in a magnetic field because of the Hanle effect,
resulting in an increase of the electrical resistance as predicted by Dyakonov
[PRL 99, 126601 (2007)]. The angular dependence of this magnetoresistance
resembles the recently discovered spin Hall magnetoresistance in Pt/Y3Fe5O12
bilayers, although the presence of a ferromagnetic insulator is not required.
We show that this Hanle magnetoresistance is an alternative, simple way to
quantitatively study the coupling between charge and spin currents in metals
with strong spin-orbit coupling.Comment: 13 pages, 3 figure
Theory of superfluidity and drag force in the one-dimensional Bose gas
The one-dimensional Bose gas is an unusual superfluid. In contrast to higher
spatial dimensions, the existence of non-classical rotational inertia is not
directly linked to the dissipationless motion of infinitesimal impurities.
Recently, experimental tests with ultracold atoms have begun and quantitative
predictions for the drag force experienced by moving obstacles have become
available. This topical review discusses the drag force obtained from linear
response theory in relation to Landau's criterion of superfluidity. Based upon
improved analytical and numerical understanding of the dynamical structure
factor, results for different obstacle potentials are obtained, including
single impurities, optical lattices and random potentials generated from
speckle patterns. The dynamical breakdown of superfluidity in random potentials
is discussed in relation to Anderson localization and the predicted
superfluid-insulator transition in these systems.Comment: 17 pages, 12 figures, mini-review prepared for the special issue of
Frontiers of Physics "Recent Progresses on Quantum Dynamics of Ultracold
Atoms and Future Quantum Technologies", edited by Profs. Lee, Ueda, and
Drummon
Strong interfacial exchange field in a heavy metal/ferromagnetic insulator system determined by spin Hall magnetoresistance
Spin-dependent transport at heavy metal/magnetic insulator interfaces is at
the origin of many phenomena at the forefront of spintronics research. A proper
quantification of the different interfacial spin conductances is crucial for
many applications. Here, we report the first measurement of the spin Hall
magnetoresistance (SMR) of Pt on a purely ferromagnetic insulator (EuS). We
perform SMR measurements in a wide range of temperatures and fit the results by
using a microscopic model. From this fitting procedure we obtain the
temperature dependence of the spin conductances (, and ),
disentangling the contribution of field-like torque (), damping-like
torque (), and spin-flip scattering (). An interfacial exchange field
of the order of 1 meV acting upon the conduction electrons of Pt can be
estimated from , which is at least three times larger than below the
Curie temperature. Our work provides an easy method to quantify this
interfacial spin-splitting field, which play a key role in emerging fields such
as superconducting spintronics and caloritronics, and topological quantum
computation.Comment: 15 pages, 3 figures, Supporting information included at the en
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