75 research outputs found
Thermalization of hot electrons via interfacial electron-magnon interaction
Recent work on layered structures of superconductors (S) or normal metals (N)
in contact with ferromagnetic insulators (FI) has shown how the properties of
the previous can be strongly affected by the magnetic proximity effect due to
the static FI magnetization. Here we show that such structures can also exhibit
a new electron thermalization mechanism due to the coupling of electrons with
the dynamic magnetization, i.e., magnons in FI. We here study the heat flow
between the two systems and find that in thin films the heat conductance due to
the interfacial electron-magnon collisions can dominate over the well-known
electron-phonon coupling below a certain characteristic temperature that can be
straightforwardly reached with present-day experiments. We also study the role
of the magnon band gap and the induced spin-splitting field induced in S on the
resulting heat conductance and show that heat balance experiments can reveal
information about such quantities in a way quite different from typical magnon
spectroscopy experiments
Cyclostationary measurement of low-frequency odd moments of current fluctuations
Measurement of odd moments of current fluctuations is difficult due to strict
requirements for band-pass filtering. We propose how these requirements can be
overcome using cyclostationary driving of the measured signal and indicate how
the measurement accuracy can be tested through the phase dependence of the
moments of the fluctuations. We consider two schemes, the mixing scheme and the
statistics scheme, where the current statistics can be accessed. We also
address the limitations of the schemes, due to excess noise and due to the
effects of the environment, and, finally, discuss the required measurement
times for typical setups.Comment: 13 pages, 3 figure
Thermopower induced by a supercurrent in superconductor-normal-metal structures
We examine the thermopower Q of a mesoscopic normal-metal (N) wire in contact
to superconducting (S) segments and show that even with electron-hole symmetry,
Q may become finite due to the presence of supercurrents. Moreover, we show how
the dominant part of Q can be directly related to the equilibrium supercurrents
in the structure. In general, a finite thermopower appears both between the N
reservoirs and the superconductors, and between the N reservoirs themselves.
The latter, however, strongly depends on the geometrical symmetry of the
structure.Comment: 4 pages, 4 figures; text compacted and material adde
Photon heat transport in low-dimensional nanostructures
At low temperatures when the phonon modes are effectively frozen, photon
transport is the dominating mechanism of thermal relaxation in metallic
systems. Starting from a microscopic many-body Hamiltonian, we develop a
nonequilibrium Green's function method to study energy transport by photons in
nanostructures. A formally exact expression for the energy current between a
metallic island and a one-dimensional electromagnetic field is obtained. From
this expression we derive the quantized thermal conductance as well as show how
the results can be generalized to nonequilibrium situations. Generally, the
frequency-dependent current noise of the island electrons determines the energy
transfer rate.Comment: 4 pages, 3 Fig
Thermal, electric and spin transport in superconductor/ferromagnetic-insulator structures
A ferromagnetic insulator (FI) attached to a conventional superconductor (S)
changes drastically the properties of the latter. Specifically, the exchange
field at the FI/S interface leads to a splitting of the superconducting density
of states. If S is a superconducting film, thinner than the superconducting
coherence length, the modification of the density of states occurs over the
whole sample. The co-existence of the exchange splitting and superconducting
correlations in S/FI structures leads to striking transport phenomena that are
of interest for applications in thermoelectricity, superconducting spintronics
and radiation sensors. Here we review the most recent progress in understanding
the transport properties of FI/S structures by presenting a complete
theoretical framework based on the quasiclassical kinetic equations. We discuss
the coupling between the electronic degrees of freedom, charge, spin and
energy, under non-equilibrium conditions and its manifestation in
thermoelectricity and spin-dependent transport.Comment: 117 pages, 33 figures. arXiv admin note: substantial text overlap
with arXiv:1706.0824
Signatures and characterization of dominating Kerr nonlinearity between two driven systems with application to a suspended magnetic beam
We consider a model of two harmonically driven damped harmonic oscillators
that are coupled linearly and with a cross-Kerr coupling. We show how to
distinguish this combination of coupling types from the case where a coupling
of optomechanical type is present. This can be useful for the characterization
of various nonlinear systems, such as mechanical oscillators, qubits, and
hybrid systems. We then consider a hybrid system with linear and cross-Kerr
interactions and a relatively high damping in one of the modes. We derive a
quantum Hamiltonian of a doubly clamped magnetic beam, showing that the
cross-Kerr coupling is prominent there. We discuss, in the classical limit,
measurements of its linear response as well as the specific higher-harmonic
responses. These frequency-domain measurements can allow estimating the
magnitude of the cross-Kerr coupling or its magnon population.Comment: 18 pages, 6 figure
- …