255 research outputs found
Ferromagnetic insulator-based superconducting junctions as sensitive electron thermometers
We present an exhaustive theoretical analysis of charge and thermoelectric
transport in a normal metal-ferromagnetic insulator-superconductor (NFIS)
junction, and explore the possibility of its use as a sensitive thermometer. We
investigated the transfer functions and the intrinsic noise performance for
different measurement configurations. A common feature of all configurations is
that the best temperature noise performance is obtained in the non-linear
temperature regime for a structure based on an europium chalcogenide
ferromagnetic insulator in contact with a superconducting Al film structure.
For an open-circuit configuration, although the maximal intrinsic temperature
sensitivity can achieve nKHz, a realistic amplifying chain will
reduce the sensitivity up to KHz. To overcome this limitation
we propose a measurement scheme in a closed-circuit configuration based on
state-of-art SQUID detection technology in an inductive setup. In such a case
we show that temperature noise can be as low as nKHz. We also
discuss a temperature-to-frequency converter where the obtained thermo-voltage
developed over a Josephson junction operated in the dissipative regime is
converted into a high-frequency signal. We predict that the structure can
generate frequencies up to GHz, and transfer functions up to
GHz/K at around K. If operated as electron thermometer, the device
may provide temperature noise lower than nKHz thereby being
potentially attractive for radiation sensing applications.Comment: 11 pages, 10 color figure
Majorana bound states in hybrid 2D Josephson junctions with ferromagnetic insulators
We consider a Josephson junction consisting of superconductor/ferromagnetic
insulator (S/FI) bilayers as electrodes which proximizes a nearby 2D electron
gas. By starting from a generic Josephson hybrid planar setup we present an
exhaustive analysis of the the interplay between the superconducting and
magnetic proximity effects and the conditions under which the structure
undergoes transitions to a non-trivial topological phase. We address the 2D
bound state problem using a general transfer matrix approach that reduces the
problem to an effective 1D Hamiltonian. This allows for straightforward study
of topological properties in different symmetry classes. As an example we
consider a narrow channel coupled with multiple ferromagnetic superconducting
fingers, and discuss how the Majorana bound states can be spatially controlled
by tuning the superconducting phases. Following our approach we also show the
energy spectrum, the free energy and finally the multiterminal Josephson
current of the setup.Comment: 8 pages; 5 figure
Charge tunneling in fractional edge channels
We explain recent experimental observations on effective charge of edge
states tunneling through a quantum point contact in the weak backscattering
regime. We focus on the behavior of the excess noise and on the effective
tunneling charge as a function of temperature and voltage. By introducing a
minimal hierarchical model different filling factors, \nu=p/(2p+1), in the Jain
sequence are treated on equal footing, in presence also of non-universal
interactions. The agreement found with the experiments for \nu=2/3 and \nu=2/5
reinforces the description of tunneling of bunching of quasiparticles at low
energies and quantitatively defines the condition under which one expects to
measure the fundamental quasiparticle charge. We propose high-order current
cumulant measurement to cross-check the validity of the above scenario and to
better clarify the peculiar temperature behavior of the effective charges
measured in the experiments.Comment: 6 pages, 3 figure
Full Counting Statistics in Strongly Interacting Systems: Non-Markovian Effects
We present a theory of full counting statistics for electron transport
through interacting electron systems with non-Markovian dynamics. We illustrate
our approach for transport through a single-level quantum dot and a metallic
single-electron transistor to second order in the tunnel-coupling strength, and
discuss under which circumstances non-Markovian effects appear in the transport
properties.Comment: 4 pages, 2 figures, LaTeX; typos added, references adde
Bipolar thermoelectricity in S/I/NS and S/I/SN superconducting tunnel junctions
Recent studies have shown the potential for bipolar thermoelectricity in
superconducting tunnel junctions with asymmetric energy gaps. The
thermoelectric performance of these systems is significantly impacted by the
inverse proximity effects present in the normal-superconducting bilayer, which
is utilized to adjust the gap asymmetry in the junction. Here, we identify the
most effective bilayer configurations, and we find that directly
tunnel-coupling the normal metal side of the bilayer with the other
superconductor is more advantageous compared to the scheme used before. By
utilizing quasiclassical equations, we examined the nonlinear thermoelectric
junction performance as a function of the normal metal film thickness and the
quality of the normal-superconducting interface within the bilayer, thereby
determining the optimal design to observe and maximize this nonequilibrium
effect. Our results offer a roadmap to achieve improved thermoelectric
performance in superconducting tunnel junctions, with promising implications
for a number of applications.Comment: 5 pages, 3 figure
Microwave-assisted thermoelectricity in SIS' tunnel junctions
Asymmetric superconducting tunnel junctions with gaps
have been proven to show a peculiar nonlinear bipolar thermoelectric effect.
This arises due to the spontaneous breaking of electron-hole symmetry in the
system, and it is maximized at the matching-peak bias
. In this paper, we investigate the interplay of
photon-assisted tunneling (PAT) and bipolar thermoelectric generation. In
particular, we show how thermoelectricity, at the matching peak, is supported
by photon absorption/emission processes at the frequency-shifted sidebands
, . This represents a sort of
microwave-assisted thermoelectricity. We show the existence of multiple stable
solutions, being associated with different photon sidebands, when a load is
connected to the junction. Finally, we discuss how the nonlinear cooling
effects are modified by the PAT. The proposed device can detect millimeter
wavelength signals by converting a temperature gradient into a thermoelectric
current or voltage.Comment: 7 pages, 3 figure
Environmental induced renormalization effects in quantum Hall edge states
We propose a general mechanism for renormalization of the tunneling exponents
in edge states of the fractional quantum Hall effect. Mutual effects of the
coupling with out-of-equilibrium 1/f noise and dissipation are considered both
for the Laughlin sequence and for composite co- and counter-propagating edge
states with Abelian or non-Abelian statistics. For states with
counter-propagating modes we demonstrate the robustness of the proposed
mechanism in the so called disorder-dominated phase. Prototypes of these
states, such as \nu=2/3 and \nu=5/2, are discussed in detail and the rich
phenomenology induced by the presence of a noisy environment is presented. The
proposed mechanism justifies the strong renormalizations reported in many
experimental observations carried out at low temperatures. We show how
environmental effects could affect the relevance of the tunneling excitations,
leading to important implications in particular for the \nu=5/2 case.Comment: 14 pages, 4 figure
Non-equilibrium Plasmons in a Quantum Wire Single Electron Transistor
We analyze a single electron transistor composed of two semi-infinite one
dimensional quantum wires and a relatively short segment between them. We
describe each wire section by a Luttinger model, and treat tunneling events in
the sequential approximation when the system's dynamics can be described by a
master equation. We show that the steady state occupation probabilities in the
strongly interacting regime depend only on the energies of the states and
follow a universal form that depends on the source-drain voltage and the
interaction strength.Comment: 4 pages, 3 figures. To appear in the Phys. Rev. Let
- …