10,006 research outputs found
Orbital Floquet Engineering of Exchange Interactions in Magnetic Materials
We present a new scheme to control the spin exchange interactions between two
magnetic ions by manipulating the orbital degrees of freedom using a periodic
drive. We discuss two different protocols for orbital Floquet engineering. In
one case, we modify the properties of the ligand orbitals which mediate
magnetic interactions between two transition metal ions. While in the other
case, we mix the d orbitals on each magnetic ion. In contrast to previous works
on Floquet engineering of magnetic properties, the present scheme makes use of
the AC Stark shift of the states involved in the exchange process
Finding the Elusive Sliding Phase in the Superfluid-Normal Phase Transition Smeared by c-Axis Disorder
We consider a stack of weakly Josephson coupled superfluid layers with c-axis disorder in the form of random superfluid stiffnesses and vortex fugacities in each layer as well as random interlayer coupling strengths. In the absence of disorder this system has a 3D XY type superfluid-normal phase transition as a function of temperature. We develop a functional renormalization group to treat the effects of disorder, and demonstrate that the disorder results in the smearing of the superfluid-normal phase transition via the formation of a Griffiths phase. Remarkably, in the Griffiths phase, the emergent power-law distribution of the interlayer couplings gives rise to a sliding Griffiths superfluid, with a finite stiffness in the a-b direction along the layers, and a vanishing stiffness perpendicular to it
On symmetric intersecting families
We make some progress on a question of Babai from the 1970s, namely: for with , what is the largest possible cardinality
of an intersecting family of -element subsets of
admitting a transitive group of automorphisms? We give upper and lower bounds
for , and show in particular that as if and only if for some function
that increases without bound, thereby determining the threshold
at which `symmetric' intersecting families are negligibly small compared to the
maximum-sized intersecting families. We also exhibit connections to some basic
questions in group theory and additive number theory, and pose a number of
problems.Comment: Minor change to the statement (and proof) of Theorem 1.4; the authors
thank Nathan Keller and Omri Marcus for pointing out a mistake in the
previous versio
A Cloud Tracking Tool for Planetary Orbiter Images
During their operations phase, planetary missions continuously produce a wealth of data that tend to overwhelm research teams. Spectral imagers, in particular, produce data cubes in which the wavelength dimension adds to the two spatial dimensions. Tracking of atmospheric features in order to derive winds and the construction of global maps from such large data volumes becomes particularly time-consuming if done manually. This highlights the importance of automated procedures capable of analysing sequences of data cubes with minimal user interaction. A tool for cloud tracking for such a purpose is currently under development in our group. In its present state it is based on synthetic images and uses a simple method of multiple matrix comparison to derive wind components. Deriving winds from data from the Venus Express - Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) instrument will be a possible application. We shall present an overview of the method, its benchmarking and the current status and future development of the project
The Parallelometer: a mechanical device to study curvature
A simple mechanical device is introduced, the parallelometer, that can be
used to measure curvatures of surfaces. The device can be used as a practical
illustration of parallel transport of a vector and to study Berry phase shift
when it is carried along a loop on the surface. Its connection to the Foucault
pendulum is discussed. The experimental results can be successfully compared
with the theoretical expectations. The experiment is inexpensive and
conceptually easy to perform and understand for a beginner
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