46 research outputs found
Strong Spin-Orbit Interaction Induced in Graphene by Monolayer WS
We demonstrate strong anisotropic spin-orbit interaction (SOI) in graphene
induced by monolayer WS. Direct comparison between graphene/monolayer
WS and graphene/bulk WS system in magnetotransport measurements reveals
that monolayer transition metal dichalcogenide (TMD) can induce much stronger
SOI than bulk. Detailed theoretical analysis of the weak-antilocalization
curves gives an estimated spin-orbit energy () higher than 10 meV.
The symmetry of the induced SOI is also discussed, and the dominant
symmetric SOI can only explain the experimental results.
Spin relaxation by the Elliot-Yafet (EY) mechanism and anomalous resistance
increase with temperature close to the Dirac point indicates Kane-Mele (KM) SOI
induced in graphene.Comment: 5 pages, 4 figure
Coherence-enhanced, phase-dependent dissipation in long SNS Josephson junctions: revealing Andreev Bound States dynamics
One of the best known causes of dissipation in ac driven quantum systems
stems from photon absorption. Dissipation can also be caused by the retarded
response to the time-dependent excitation, and in general gives insight into
the system's relaxation times and mechanisms. We address the dissipation in a
mesoscopic normal wire with superconducting contacts, that sustains a
supercurrent at zero frequency and that may be expected to remain
dissipationless at frequency lower than the superconducting gap. We probe the
high frequency linear response of a Normal/Superconductor ring to a
time-dependent flux by coupling it to a highly sensitive multimode microwave
resonator. Far from being the simple derivative of the current-phase relation,
the ring's ac susceptibility also displays a dissipative component whose phase
dependence is a signature of the dynamical processes occurring within the
Andreev spectrum. We show how dissipation is driven by the competition between
the two aforementioned mechanisms. Depending on the relative strength of those
contributions, dissipation can be maximal at , when the minigap closes, or
can be maximal near , when the dc supercurrent is maximal. We also find
that the dissipative response increases at low temperature and can even exceed
the normal state conductance. The results are confronted with predictions of
the Kubo linear response and time-dependent Usadel equations. This experiment
shows the power of the ac susceptibility measurement of individual hybrid
mesoscopic systems in probing in a controlled way the quantum dynamics of ABS.
By spanning different physical regimes, our experiments provide a unique access
to inelastic scattering and spectroscopy of an isolated quantum coherent
system. This technique should be a tool of choice to investigate topological
superconductivity and detect the topological protection of edge states
Novel transport phenomena in graphene induced by strong spin-orbit interaction
Graphene is known to have small intrinsic spin-orbit Interaction (SOI). In
this review, we demonstrate that SOIs in graphene can be strongly enhanced by
proximity effect when graphene is deposited on the top of transition metal
dichalcogenides. We discuss the symmetry of the induced SOIs and differences
between TMD underlayers in the capacity of inducing strong SOIs in graphene.
The strong SOIs contribute to bring novel phenomena to graphene, exemplified by
robust supercurrents sustained even under tesla-range magnetic fields.Comment: 14 pages, 7 figure
Strain superlattices and macroscale suspension of Graphene induced by corrugated substrates
We investigate the organized formation of strain, ripples and suspended
features in macroscopic CVD-prepared graphene sheets transferred onto a
corrugated substrate made of an ordered arrays of silica pillars of variable
geometries. Depending on the aspect ratio and sharpness of the corrugated
array, graphene can conformally coat the surface, partially collapse, or lay,
fakir-like, fully suspended between pillars over tens of micrometers. Upon
increase of pillar density, ripples in collapsed films display a transition
from random oriented pleats emerging from pillars to ripples linking nearest
neighboring pillars organized in domains of given orientation.
Spatially-resolved Raman spectroscopy, atomic force microscopy and electronic
microscopy reveal uniaxial strain domains in the transferred graphene, which
are induced and controlled by the geometry. We propose a simple theoretical
model to explain the transition between suspended and collapsed graphene. For
the arrays with high aspect ratio pillars, graphene membranes stays suspended
over macroscopic distances with minimal interaction with pillars tip apex. It
offers a platform to tailor stress in graphene layers and open perspectives for
electron transport and nanomechanical applications
Spin-dependent recombination probed through the dielectric polarizability.
Despite residing in an energetically and structurally disordered landscape, the spin degree of freedom remains a robust quantity in organic semiconductor materials due to the weak coupling of spin and orbital states. This enforces spin-selectivity in recombination processes which plays a crucial role in optoelectronic devices, for example, in the spin-dependent recombination of weakly bound electron-hole pairs, or charge-transfer states, which form in a photovoltaic blend. Here, we implement a detection scheme to probe the spin-selective recombination of these states through changes in their dielectric polarizability under magnetic resonance. Using this technique, we access a regime in which the usual mixing of spin-singlet and spin-triplet states due to hyperfine fields is suppressed by microwave driving. We present a quantitative model for this behaviour which allows us to estimate the spin-dependent recombination rate, and draw parallels with the Majorana-Brossel resonances observed in atomic physics experiments.This work was supported by the Engineering and Physical Sciences Research Council [Grants
No. EP/G060738/1]. A. D. C. acknowledges support from the E. Oppenheimer Foundation and St Catharine's
College, Cambridge. S. L. B. is grateful for support from the EPSRC Supergen SuperSolar Project, the Armourers
and Brasiers Gauntlet Trust and Magdalene College, Cambridge.This is the final published version of the article. It was originally published in Nature Communications (Bayliss et. al, Nature Communications 2015, 6, 8534, doi:10.1038/ncomms9534). The final version is available at http://dx.doi.org/10.1038/ncomms953
Spin-dependent recombination probed through the dielectric polarizability.
Despite residing in an energetically and structurally disordered landscape, the spin degree of freedom remains a robust quantity in organic semiconductor materials due to the weak coupling of spin and orbital states. This enforces spin-selectivity in recombination processes which plays a crucial role in optoelectronic devices, for example, in the spin-dependent recombination of weakly bound electron-hole pairs, or charge-transfer states, which form in a photovoltaic blend. Here, we implement a detection scheme to probe the spin-selective recombination of these states through changes in their dielectric polarizability under magnetic resonance. Using this technique, we access a regime in which the usual mixing of spin-singlet and spin-triplet states due to hyperfine fields is suppressed by microwave driving. We present a quantitative model for this behaviour which allows us to estimate the spin-dependent recombination rate, and draw parallels with the Majorana-Brossel resonances observed in atomic physics experiments.This work was supported by the Engineering and Physical Sciences Research Council [Grants
No. EP/G060738/1]. A. D. C. acknowledges support from the E. Oppenheimer Foundation and St Catharine's
College, Cambridge. S. L. B. is grateful for support from the EPSRC Supergen SuperSolar Project, the Armourers
and Brasiers Gauntlet Trust and Magdalene College, Cambridge.This is the final published version of the article. It was originally published in Nature Communications (Bayliss et. al, Nature Communications 2015, 6, 8534, doi:10.1038/ncomms9534). The final version is available at http://dx.doi.org/10.1038/ncomms953
Persistent currents in Moebius strips
Relation between the geometry of a two-dimensional sample and its equilibrium
physical properties is exemplified here for a system of non-interacting
electrons on a Moebius strip. Dispersion relation for a clean sample is derived
and its persistent current under moderate disorder is elucidated, using
statistical analysis pertinent to a single sample experiment. The flux
periodicity is found to be distinct from that in a cylindrical sample, and the
essential role of disorder in the ability to experimentally identify a Moebius
strip is pointed out.Comment: 5 pages, 4 figure
Enhanced shot noise of multiple Andreev reflections in a carbon nanotube quantum dot in SU(2) and SU(4) Kondo regimes
The sensitivity of shot noise to the interplay between Kondo correlations and
superconductivity is investigated in a carbon nanotube quantum dot connected to
superconducting electrodes. Depending on the gate voltage, the SU(2) and SU(4)
Kondo unitary regimes can be clearly identified. We observe enhancement of the
shot noise via the Fano factor in the superconducting state. Its divergence at
low bias voltage, which is more pronounced in the SU(4) regime than in the
SU(2) one, is larger than what is expected from proliferation of multiple
Andreev reflections predicted by the existing theories. Our result suggests
that Kondo effect is responsible for this strong enhancement