4,254 research outputs found
Transport through side-coupled double quantum dots: from weak to strong interdot coupling
We report low-temperature transport measurements through a double quantum dot
device in a configuration where one of the quantum dots is coupled directly to
the source and drain electrodes, and a second (side-coupled) quantum dot
interacts electrostatically and via tunneling to the first one. As the interdot
coupling increases, a crossover from weak to strong interdot tunneling is
observed in the charge stability diagrams that present a complex pattern with
mergings and apparent crossings of Coulomb blockade peaks. While the weak
coupling regime can be understood by considering a single level on each dot, in
the intermediate and strong coupling regimes, the multi-level nature of the
quantum dots needs to be taken into account. Surprisingly, both in the strong
and weak coupling regimes, the double quantum dot states are mainly localized
on each dot for most values of the parameters. Only in an intermediate coupling
regime the device presents a single dot-like molecular behavior as the
molecular wavefunctions weight is evenly distributed between the quantum dots.
At temperatures larger than the interdot coupling energy scale, a loss of
coherence of the molecular states is observed.Comment: 9 pages, 5 figure
Effect of Disorder on the Quantum Coherence in Mesoscopic Wires
We present phase coherence time measurements in quasi-one-dimensional
mesoscopic wires made from high mobility two-dimensional electron gas. By
implanting gallium ions into a GaAs/AlGaAs heterojunction we are able to vary
the diffusion coefficient over 2 orders of magnitude. We show that in the
diffusive limit, the decoherence time follows a power law as a function of
diffusion coefficient as expected by theory. When the disorder is low enough so
that the samples are semi-ballistic, we observe a new and unexpected regime in
which the phase coherence time is independent of disorder. In addition, for all
samples the temperature dependence of the phase coherence time follows a power
law down to the lowest temperatures without any sign of saturation and strongly
suggests that the frequently observed low temperature saturation is not
intrinsic.Comment: 4 pages, 4 figure
Direct observation of the flux-line vortex glass phase in a type II superconductor
The order of the vortex state in La_{1.9} Sr_{0.1} CuO_{4} is probed using
muon spin rotation and small-angle neutron scattering. A transition from a
Bragg glass to a vortex glass is observed, where the latter is composed of
disordered vortex lines. In the vicinity of the transition the microscopic
behavior reflects a delicate interplay of thermally-induced and pinning-induced
disorder.Comment: 14 pages, 4 colour figures include
Magnetism in Semiconducting Molybdenum Dichalcogenides
Transition metal dichalcogenides (TMDs) are interesting for understanding
fundamental physics of two-dimensional materials (2D) as well as for many
emerging technologies, including spin electronics. Here, we report the
discovery of long-range magnetic order below TM = 40 K and 100 K in bulk
semiconducting TMDs 2H-MoTe2 and 2H-MoSe2, respectively, by means of muon
spin-rotation (muSR), scanning tunneling microscopy (STM), as well as density
functional theory (DFT) calculations. The muon spin rotation measurements show
the presence of a large and homogeneous internal magnetic fields at low
temperatures in both compounds indicative of long-range magnetic order. DFT
calculations show that this magnetism is promoted by the presence of defects in
the crystal. The STM measurements show that the vast majority of defects in
these materials are metal vacancies and chalcogen-metal antisites which are
randomly distributed in the lattice at the sub-percent level. DFT indicates
that the antisite defects are magnetic with a magnetic moment in the range of
0.9-2.8 mu_B. Further, we find that the magnetic order stabilized in 2H-MoTe2
and 2H-MoSe2 is highly sensitive to hydrostatic pressure. These observations
establish 2H-MoTe2 and 2H-MoSe2 as a new class of magnetic semiconductors and
opens a path to studying the interplay of 2D physics and magnetism in these
interesting semiconductors.Comment: 13 pages, 10 Figure
Kondo physics in the algebraic spin liquid
We study Kondo physics in the algebraic spin liquid, recently proposed to
describe [Phys. Rev. Lett. {\bf 98}, 117205 (2007)].
Although spin dynamics of the algebraic spin liquid is described by massless
Dirac fermions, this problem differs from the Pseudogap Kondo model, because
the bulk physics in the algebraic spin liquid is governed by an interacting
fixed point where well-defined quasiparticle excitations are not allowed.
Considering an effective bulk model characterized by an anomalous critical
exponent, we derive an effective impurity action in the slave-boson context.
Performing the large- analysis with a spin index , we
find an impurity quantum phase transition from a decoupled local-moment state
to a Kondo-screened phase. We evaluate the impurity spin susceptibility and
specific heat coefficient at zero temperature, and find that such responses
follow power-law dependencies due to the anomalous exponent of the algebraic
spin liquid. Our main finding is that the Wilson's ratio for the magnetic
impurity depends strongly on the critical exponent in the zero temperature
limit. We propose that the Wilson's ratio for the magnetic impurity may be one
possible probe to reveal criticality of the bulk system
Muons as Local Probes of Three-body Correlations in the Mixed State of Type-II Superconductors
The vortex glass state formed by magnetic flux lines in a type-II
superconductor is shown to possess non-trivial three-body correlations. While
such correlations are usually difficult to measure in glassy systems, the
magnetic fields associated with the flux vortices allow us to probe these via
muon-spin rotation measurements of the local field distribution. We show via
numerical simulations and analytic calculations that these observations provide
detailed microscopic insight into the local order of the vortex glass and more
generally validate a theoretical framework for correlations in glassy systems.Comment: 4+ pages, high-quality figures available on reques
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
- …