515 research outputs found
Language of Lullabies: The Russification and De-Russification of the Baltic States
This article argues that the laws for promotion of the national languages are a legitimate means for the Baltic states to establish their cultural independence from Russia and the former Soviet Union
Engineering the spin polarization of one-dimensional electrons
We present results of magneto-focusing on the controlled monitoring of spin polarization within a one-dimensional (1D) channel, and its subsequent effect on modulating the spin-orbit interaction (SOI) in a 2D GaAs electron gas. We demonstrate that electrons within a 1D channel can be partially spin polarized as the effective length of the 1D channel is varied in agreement with the theoretical prediction. Such polarized 1D electrons when injected into a 2D region result in a split in the odd-focusing peaks, whereas the even peaks remain unaffected (single peak). On the other hand, the unpolarized electrons, achieved by reducing the effective length of the 1D channel, do not affect the focusing spectrum and the odd and even peaks remain as single peaks, respectively. The split in odd-focusing peaks is evidence of direct measurement of spin polarization within a 1D channel, where each sub-peak represents the population of a particular spin state. Confirmation of the spin splitting is determined by a selective modulation of the focusing peaks due to the Zeeman energy in the presence of an in-plane magnetic field. We suggest that the SOI in the 2D regime is enhanced by a stream of polarized 1D electrons. The spatial control of spin states of injected 1D electrons and the possibility of tuning the SOI may open up a new regime of spin-engineering with application in future quantum information schemes
Direct observation of exchange-driven spin interactions in one-dimensional system
We present experimental results of transverse electron focusing measurements performed on an ntype
GaAs based mesoscopic device consisting of one-dimensional (1D) quantum wires as injector
and detector. We show that non-adiabatic injection of 1D electrons at a conductance of e2/
h results in
a single first focusing peak, which transforms into two asymmetric sub-peaks with a gradual
increase in the injector conductance up to 2e2/
h , each sub-peak representing the population of spinstate
arising from the spatially separated spins in the injector. Further increasing the conductance
flips the spin-states in the 1D channel, thus reversing the asymmetry in the sub-peaks. On applying
a source-drain bias, the spin-gap, so obtained, can be resolved, thus providing evidence of exchange
interaction induced spin polarization in the 1D systems. V
A limiting velocity for quarkonium propagation in a strongly coupled plasma via AdS/CFT
We study the dispersion relations of mesons in a particular hot strongly
coupled supersymmetric gauge theory plasma. We find that at large momentum k
the dispersion relations become omega = v_0 k + a + b/k + ..., where the
limiting velocity v_0 is the same for mesons with any quantum numbers and
depends only on the ratio of the temperature to the quark mass T/m_q. We
compute a and b in terms of the meson quantum numbers and T/m_q. The limiting
meson velocity v_0 becomes much smaller than the speed of light at temperatures
below but close to T_diss, the temperature above which no meson bound states at
rest in the plasma are found. From our result for v_0, we find that the
temperature above which no meson bound states with velocity v exist is
T_diss(v) \simeq (1-v^2)^(1/4) T_diss, up to few percent corrections.We thus
confirm by direct calculation of meson dispersion relations a result inferred
indirectly in previous work via analysis of the screening length between a
static quark and antiquark in a moving plasma. Although we do not do our
calculations in QCD, we argue that the qualitative features of the dispersion
relation we compute, including in particular the relation between dissociation
temperature and meson velocity, may apply to bottomonium and charmonium mesons
propagating in the strongly coupled plasma of QCD. We discuss how our results
can contribute to understanding quarkonium physics in heavy ion collisions.Comment: 57 pages, 12 figures; references adde
Effect of Split Gate Size on the Electrostatic Potential and 0.7 Anomaly within Quantum Wires on a Modulation-Doped GaAs/AlGaAs Heterostructure
© 2016 American Physical Society. © 2016 American Physical Society.We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs/AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization decreases rapidly as the length of the split gates increases. However, for the subset of devices showing good quantization, there is no correlation between the electrostatic length of the one-dimensional channel (estimated using a saddle-point model) and the gate length. The variation in electrostatic length and the one-dimensional subband spacing for devices of the same gate length exceeds the variation in the average values between devices of different lengths. There is a clear correlation between the curvature of the potential barrier in the transport direction and the strength of the "0.7 anomaly": the conductance value of the 0.7 anomaly reduces as the barrier curvature becomes shallower. These results highlight the key role of the electrostatic environment in one-dimensional systems. Even in devices with clean conductance plateaus, random fluctuations in the background potential are crucial in determining the potential landscape in the active device area such that nominally identical gate structures have different characteristics
Anderson localization on the Cayley tree : multifractal statistics of the transmission at criticality and off criticality
In contrast to finite dimensions where disordered systems display
multifractal statistics only at criticality, the tree geometry induces
multifractal statistics for disordered systems also off criticality. For the
Anderson tight-binding localization model defined on a tree of branching ratio
K=2 with generations, we consider the Miller-Derrida scattering geometry
[J. Stat. Phys. 75, 357 (1994)], where an incoming wire is attached to the root
of the tree, and where outcoming wires are attached to the leaves of
the tree. In terms of the transmission amplitudes , the total
Landauer transmission is , so that each channel
is characterized by the weight . We numerically measure the
typical multifractal singularity spectrum of these weights as a
function of the disorder strength and we obtain the following conclusions
for its left-termination point . In the delocalized phase ,
is strictly positive and is associated with a
moment index . At criticality, it vanishes and is
associated with the moment index . In the localized phase ,
is associated with some moment index . We discuss the
similarities with the exact results concerning the multifractal properties of
the Directed Polymer on the Cayley tree.Comment: v2=final version (16 pages
Non-Perturbative Corrections and Modularity in N=1 Type IIB Compactifications
Non-perturbative corrections and modular properties of four-dimensional type
IIB Calabi-Yau orientifolds are discussed. It is shown that certain
non-perturbative alpha' corrections survive in the large volume limit of the
orientifold and periodically correct the Kahler potential. These corrections
depend on the NS-NS two form and have to be completed by D-instanton
contributions to transform covariantely under symmetries of the type IIB
orientifold background. It is shown that generically also the D-instanton
superpotential depends on the two-form moduli as well as on the complex
dilaton. These contributions can arise through theta-functions with the dilaton
as modular parameter. An orientifold of the Enriques Calabi-Yau allows to
illustrate these general considerations. It is shown that this compactification
leads to a controlled four-dimensional N=1 effective theory due to the absence
of various quantum corrections. Making contact to the underlying topological
string theory the D-instanton superpotential is proposed to be related to a
specific modular form counting D3, D1, D(-1) degeneracies on the Enriques
Calabi-Yau.Comment: 35 page
TeV-Scale Black Hole Lifetimes in Extra-Dimensional Lovelock Gravity
We examine the mass loss rates and lifetimes of TeV-scale extra dimensional
black holes (BH) in ADD-like models with Lovelock higher-curvature terms
present in the action. In particular we focus on the predicted differences
between the canonical and microcanonical ensemble statistical mechanics
descriptions of the Hawking radiation that results in the decay of these BH. In
even numbers of extra dimensions the employment of the microcanonical approach
is shown to generally lead to a significant increase in the BH lifetime as in
case of the Einstein-Hilbert action. For odd numbers of extra dimensions,
stable BH remnants occur when employing either description provided the highest
order allowed Lovelock invariant is present. However, in this case, the time
dependence of the mass loss rates obtained employing the two approaches will be
different. These effects are in principle measurable at future colliders.Comment: 27 pages, 9 figs; Refs. and discussion adde
Direct observation of spin polarization in GaAs quantum wires by transverse electron focusing
We present transverse electron focusing measurements in the two dimensional electrons gas formed at the interface of a GaAs/AlGaAs heterostructure. The experimental arrangement consists of two orthogonal quantum point contacts (QPCs), one acting as injector and the other as detector of the collimated 1D electrons as a function of transverse magnetic field. The focusing spectrum shows anomalous behaviour, the first and third focusing peaks split into two sub-peaks while second peak remains as a single peak. The observed splitting, a signature of spin states, arises from the spin-orbit interaction when the 1D electrons are injected into the 2D regime, thus allowing us to manipulate the spin states within the 1D channel
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