1,912 research outputs found
Quantum detectors for the third cumulant of current fluctuations
We consider the measurement of the third cumulant of current fluctuations
arising from a point contact, employing the transitions that they cause in a
quantum detector connected to the contact. We detail two generic detectors: a
quantum two-level system and a harmonic oscillator. In these systems, for an
arbitrary relation between the voltage driving the point contact and the energy
scales of the detectors, the results can be expressed in terms of an effective
detector temperature T_eff. The third cumulant can be found from the dependence
of T_eff on the sign of the driving voltage. We find that proper ordering of
the fluctuation operators is relevant in the analysis of the transition rates.
This is reflected in the effective Fano factor for the third cumulant measured
in such setups: it depends on the ratio of the voltage and an energy scale
describing the circuit where the fluctuations are produced.Comment: 12+ pages, 8 figure
Slow Vibrations in Transport through Molecules
We show how one can measure the signal from slow jumps of a single molecule
between metastable positions using a setup where the molecule is fixed to one
lead, and one of the coupling strengths is controlled externally. Such a
measurement yields information about slow processes deforming the molecule in
times much longer than the characteristic time scales for the electron
transport process.Comment: 4 pages, 3 figure
Topologically protected surface Majorana arcs and bulk Weyl fermions in ferromagnetic superconductors
A number of ferromagnetic superconductors have been recently discovered which
are believed to be in the so-called "equal spin pairing" (ESP) state. In the
ESP state the Cooper pairs condense forming order parameters
which are decoupled
in the spin-sector. We show that these three-dimensional systems should
generically support topologically protected surface Majorana arcs and bulk Weyl
fermions as gapless excitations. Similar protected low-energy exotic
quasiparticles should also appear in the recently discovered
non-centrosymmteric superconductors in the presence of a Zeeman field. The
protected surface arcs can be probed by angle-resolved photoemission (ARPES) as
well as scanning tunneling microscope (STM) experiments.Comment: 5 pages and 2 figures; Figure 2 revised, typos correcte
Ultra-low dissipation Josephson transistor
A superconductor-normal metal-superconductor (SNS) transistor based on
superconducting microcoolers is presented. The proposed 4-terminal device
consists of a long SNS Josephson junction whose N region is in addition
symmetrically connected to superconducting reservoirs through tunnel barriers
(I). Biasing the SINIS line allows to modify the quasiparticle temperature in
the weak link, thus controlling the Josephson current. We show that, in
suitable voltage and temperature regimes, large supercurrent enhancements can
be achieved with respect to equilibrium, due to electron ``cooling'' generated
by the control voltage. The extremely low power dissipation intrinsic to the
structure makes this device relevant for a number of electronic applications.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter
Mesoscopic supercurrent transistor controlled by nonequilibrium cooling
The distinctive quasiparticle distribution existing under nonequilibrium in a
superconductor-insulator-normal metal-insulator-superconductor (SINIS)
mesoscopic line is proposed as a novel tool to control the supercurrent
intensity in a long Josephson weak link. We present a description of this
system in the framework of the diffusive-limit quasiclassical Green-function
theory and take into account the effects of inelastic scattering with arbitrary
strength. Supercurrent enhancement and suppression, including a marked
transition to a -junction are striking features leading to a fully tunable
structure. The role of the degree of nonequilibrium, temperature, and materials
choice as well as features like noise, switching time, and current and power
gain are also addressed.Comment: 8 pages, 9 figures, submitted to Journal of Low Temperature Physic
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