2,953 research outputs found
Blue Quantum Fog: Chiral Condensation in Quantum Helimagnets
It is shown that a condensation transition involving a chiral order parameter
can occur in itinerant helimagnets, in analogy to the transition between the
isotropic phase and the phase known as blue fog or blue phase III in
cholesteric liquid crystals. It is proposed that such a transition is the
explanation for recent neutron scattering results in MnSi. Predictions are made
that will allow to experimentally test this proposal.Comment: 4pp, 1 eps fi
Robust procedure for creating and characterizing the atomic structure of scanning tunneling microscope tips
Scanning tunneling microscopes (STM) are used extensively for studying and
manipulating matter at the atomic scale. In spite of the critical role of the
STM tip, the control of the atomic-scale shape of STM tips remains a poorly
solved problem. Here, we present a method for preparing tips {\it in-situ} and
for ensuring the crystalline structure and reproducibly preparing tip structure
up to the second atomic layer. We demonstrate a controlled evolution of such
tips starting from undefined tip shapes.Comment: 12 pages preprint-style; 5 figure
Robust quantum coherence above the Fermi sea
In this paper we present an experiment where we measured the quantum
coherence of a quasiparticle injected at a well-defined energy above the Fermi
sea into the edge states of the integer quantum Hall regime. Electrons are
introduced in an electronic Mach-Zehnder interferometer after passing through a
quantum dot that plays the role of an energy filter. Measurements show that
above a threshold injection energy, the visibility of the quantum interferences
is almost independent of the energy. This is true even for high energies, up to
130~eV, well above the thermal energy of the measured sample. This result
is in strong contradiction with our theoretical predictions, which instead
predict a continuous decrease of the interference visibility with increasing
energy. This experiment raises serious questions concerning the understanding
of excitations in the integer quantum Hall regime
Wavevector and Frequency Dependent Complex Dielectric Function and the Dynamical Structure Factor of Two-dimensional Weakly-coupled Quantum and Classical Hot Plasmas
Structural, optical and nanomechanical properties of (1 1 1) oriented nanocrystalline ZnTe thin films
Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films
of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported.
X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction.
The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap
showed strong thickness dependence. The average film hardness and Young’s modulus obtained from loaddisplacement
curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of
(1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly
that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth
indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from
the nanoscratch test was ∼0.4.Financial support
in the form of fellowships to MSRNK and SK from the
ACRHEM project of DRDO is acknowledged
Secondary arm coarsening and microsegregation in superalloy PWA-1480 single crystals: Effect of low gravity
Single crystal specimens of nickel base superalloy PWA-1480 were directionally solidified on ground and during low gravity (20 sec) and high gravity (90 sec) parabolic maneuver of KC-135 aircraft. Thermal profiles were measured during solidification by two in-situ thermocouples positioned along the sample length. The samples were quenched during either high or low gravity cycles so as to freeze the structures of the mushy zone developing under different gravity levels. Microsegregation was measured by examining the solutal profiles on several transverse cross-sections across primary dendrites along their length in the quenched mushy zone. Effect of gravity level on secondary arm coarsening kinetics and microsegregation have been investigated. The results indicate that there is no appreciable difference in the microsegregation and coarsening kinetics behavior in the specimens grown under high or low gravity. This suggests that short duration changes in gravity/levels (0.02 to 1.7 g) do not influence convection in the interdendritic region. Examination of the role of natural convection, in the melt near the primary dendrite tips, on secondary arm spacings requires low gravity periods longer than presently available on KC-135. Secondary arm coarsening kinetics show a reasonable fit with the predictions from a simple analytical model proposed by Kirkwood for a binary alloy
Universal quantum computation on a semiconductor quantum wire network
Universal quantum computation (UQC) using Majorana fermions on a 2D
topological superconducting (TS) medium remains an outstanding open problem.
This is because the quantum gate set that can be generated by braiding of the
Majorana fermions does not include \emph{any} two-qubit gate and also the
single-qubit phase gate. In principle, it is possible to create these
crucial extra gates using quantum interference of Majorana fermion currents.
However, it is not clear if the motion of the various order parameter defects
(vortices, domain walls, \emph{etc.}), to which the Majorana fermions are bound
in a TS medium, can be quantum coherent. We show that these obstacles can be
overcome using a semiconductor quantum wire network in the vicinity of an
-wave superconductor, by constructing topologically protected two-qubit
gates and any arbitrary single-qubit phase gate in a topologically unprotected
manner, which can be error corrected using magic state distillation. Thus our
strategy, using a judicious combination of topologically protected and
unprotected gate operations, realizes UQC on a quantum wire network with a
remarkably high error threshold of as compared to to
in ordinary unprotected quantum computation.Comment: 7 pages, 2 figure
Dissipate locally, couple globally: a sharp transition from decoupling to infinite range coupling in Josephson arrays with on-site dissipation
We study the T=0 normal to superconducting transition of Josephson arrays
with {\it on-site} dissipation. A perturbative renormalization group solution
is given. Like the previously studied case of {\it bond} dissipation (BD), this
is a "floating" to coupled (FC) phase transition. {\it Unlike} the BD
transition, at which {\it only} nearest-neighbor couplings become relevant,
here {\it all} inter-grain couplings, out to {\it infinitely} large distances,
do so simultaneously. We predict, for the first time in an FC transition, a
diverging spatial correlation length. Our results show the robustness of
floating phases in dissipative quantum systems.Comment: 7+ pages, 3 eps figures, Europhysics Letters preprint format, as
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