121 research outputs found
A method to estimate weight and dimensions of aircraft gas turbine engines. Volume 3: Programmer's manual
For abstract, see N77-25171
Interplay Between Yu-Shiba-Rusinov States and Multiple Andreev Reflections
Motivated by recent scanning tunneling microscopy experiments on single
magnetic impurities on superconducting surfaces, we present here a
comprehensive theoretical study of the interplay between Yu-Shiba-Rusinov bound
states and (multiple) Andreev reflections. Our theory is based on a combination
of an Anderson model with broken spin degeneracy and nonequilibrium Green's
function techniques that allows us to describe the electronic transport through
a magnetic impurity coupled to superconducting leads for arbitrary junction
transparency. Using this combination we are able to elucidate the different
tunneling processes that give a significant contribution to the subgap
transport. In particular, we predict the occurrence of a large variety of
Andreev reflections mediated by Yu-Shiba-Rusinov bound states that clearly
differ from the standard Andreev processes in non-magnetic systems. Moreover,
we provide concrete guidelines on how to experimentally identify the subgap
features originating from these tunneling events. Overall, our work provides
new insight into the role of the spin degree of freedom in Andreev transport
physics.Comment: 15 pages, 10 figure
Microwave spectroscopy reveals the quantum geometric tensor of topological Josephson matter
Quantization effects due to topological invariants such as Chern numbers have become very relevant in many systems, yet key quantities such as the quantum geometric tensor providing local information about quantum states remain experimentally difficult to access. Recently, it has been shown that multiterminal Josephson junctions constitute an ideal platform to synthesize topological systems in a controlled manner. We theoretically study properties of Andreev states in topological Josephson matter and demonstrate that the quantum geometric tensor of Andreev states can be extracted by synthetically polarized microwaves. The oscillator strength of the absorption rates provides direct evidence of topological quantum properties of the Andreev states.publishe
Tunneling processes between Yu-Shiba-Rusinov bound states
Very recent experiments have reported the tunneling between Yu-Shiba-Rusinov
(YSR) bound states at the atomic scale. These experiments have been realized
with the help of a scanning tunneling microscope where a superconducting tip is
functionalized with a magnetic impurity and is used to probe another magnetic
impurity deposited on a superconducting substrate. In this way it has become
possible to study for the first time the spin-dependent transport between
individual superconducting bound states. Motivated by these experiments, we
present here a comprehensive theoretical study of the tunneling processes
between YSR bound states in a system in which two magnetic impurities are
coupled to superconducting leads. Our theory is based on a combination of an
Anderson model with broken spin degeneracy to describe the impurities and
nonequilibrium Green's function techniques to compute the current-voltage
characteristics. This combination allows us to describe the spin-dependent
transport for an arbitrary strength of the tunnel coupling between the
impurities. We first focus on the tunnel regime and show that our theory
naturally explains the experimental observations of the appearance of current
peaks in the subgap region due to both the direct and thermal tunneling between
the YSR states in both impurities. Then, we study in detail the case of
junctions with increasing transparency, which has not been experimentally
explored yet, and predict the occurrence of a large variety of (multiple)
Andreev reflections mediated by YSR states that give rise to a very rich
structure in the subgap current. In particular, we predict the occurrence of
multiple Andreev reflections that involve YSR states in different impurities.
These processes have no analogue in single-impurity junctions and they are
manifested as current peaks with negative differential conductance for subgap
voltages.Comment: 16 pages, 9 figures. arXiv admin note: text overlap with
arXiv:2005.0649
Spin-dependent tunneling between individual superconducting bound states
Magnetic impurities on superconductors induce discrete bound levels inside
the superconducting gap, known as Yu-Shiba-Rusinov (YSR) states. YSR levels are
fully spin-polarized such that the tunneling between YSR states depends on
their relative spin orientation. Here, we use scanning tunneling spectroscopy
to resolve the spin dynamics in the tunneling process between two YSR states by
experimentally extracting the angle between the spins. To this end, we exploit
the ratio of thermally activated and direct spectral features in the
measurement to directly extract the relative spin orientation between the two
YSR states. We find freely rotating spins down to 7mK, indicating a purely
paramagnetic nature of the impurities. Such a non-collinear spin alignment is
essential not only for producing Majorana bound states but also as an outlook
manipulating and moving the Majorana state onto the tip.Comment: 22 pages, 7 figures, including supplementary materia
A Large Hadron Electron Collider at CERN
This document provides a brief overview of the recently published report on
the design of the Large Hadron Electron Collider (LHeC), which comprises its
physics programme, accelerator physics, technology and main detector concepts.
The LHeC exploits and develops challenging, though principally existing,
accelerator and detector technologies. This summary is complemented by brief
illustrations of some of the highlights of the physics programme, which relies
on a vastly extended kinematic range, luminosity and unprecedented precision in
deep inelastic scattering. Illustrations are provided regarding high precision
QCD, new physics (Higgs, SUSY) and electron-ion physics. The LHeC is designed
to run synchronously with the LHC in the twenties and to achieve an integrated
luminosity of O(100) fb. It will become the cleanest high resolution
microscope of mankind and will substantially extend as well as complement the
investigation of the physics of the TeV energy scale, which has been enabled by
the LHC
Monitoring groundwater storage changes in the highly seasonal humid tropics: Validation of GRACE measurements in the Bengal Basin
International audienceSatellite monitoring of changes in terrestrial water storage provides invaluable information regarding the basin-scale dynamics of hydrological systems where ground-based records are limited. In the Bengal Basin of Bangladesh, we test the ability of satellite measurements under the Gravity Recovery and Climate Experiment (GRACE) to trace both the seasonality and trend in groundwater storage associated with intensive groundwater abstraction for dry-season irrigation and wet-season (monsoonal) recharge. We show that GRACE (CSR, GRGS) datasets of recent (2003 to 2007) groundwater storage changes (ΔGWS) correlate well (r = 0.77 to 0.93, p value < 0.0001) with in situ borehole records from a network of 236 monitoring stations and account for 44% of the total variation in terrestrial water storage (ΔTWS) highest correlation (r = 0.93, p value < 0.0001) and lowest root-mean-square error (<4 cm) are realized using a spherical harmonic product of CSR. Changes in surface water storage estimated from a network of 298 river gauging stations and soil-moisture derived from Land Surface Models explain 22% and 33% of ΔTWS, respectively. Groundwater depletion estimated from borehole hydrographs (-0.52 ± 0.30 km3 yr-1) is within the range of satellite-derived estimates (-0.44 to -2.04 km3 yr-1) that result from uncertainty associated with the simulation of soil moisture (CLM, NOAH, VIC) and GRACE signal-processing techniques. Recent (2003 to 2007) estimates of groundwater depletion are substantially greater than long-term (1985 to 2007) mean (-0.21 ± 0.03 km3 yr-1) and are explained primarily by substantial increases in groundwater abstraction for the dry-season irrigation and public water supplies over the last two decades
Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland Ice Sheet
The Greenland Ice Sheet (GrIS) is currently losing ice mass. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission Gravity Recovery and Climate Experiment (GRACE), surface mass balance (SMB) output of the Regional Atmospheric Climate Model v. 2 (RACMO2), and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. We find that the mean rate of mass variations in Greenland observed by GRACE was between −277 and −269 Gt yr−1 in 2003–2012. This estimate is consistent with the sum (i.e., −304±126 Gt yr−1) of individual contributions – surface mass balance (SMB, 216±122 Gt yr−1) and ice discharge (520±31 Gt yr−1) – and with previous studies. We further identify a seasonal mass anomaly throughout the GRACE record that peaks in July at 80–120 Gt and which we interpret to be due to a combination of englacial and subglacial water storage generated by summer surface melting. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO2.3, SNOWPACK, and MAR3.9). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast and northwest parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few gigatonnes) and does not explain the seasonal differences between the total mass and SMB signals. With the improved quantification of meltwater storage at the seasonal scale, we highlight its importance for understanding glacio-hydrological processes and their contributions to the ice sheet mass variability
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