619 research outputs found
Magnetism and superconductivity driven by identical 4 states in a heavy-fermion metal
The apparently inimical relationship between magnetism and superconductivity
has come under increasing scrutiny in a wide range of material classes, where
the free energy landscape conspires to bring them in close proximity to each
other. This is particularly the case when these phases microscopically
interpenetrate, though the manner in which this can be accomplished remains to
be fully comprehended. Here, we present combined measurements of elastic
neutron scattering, magnetotransport, and heat capacity on a prototypical heavy
fermion system, in which antiferromagnetism and superconductivity are observed.
Monitoring the response of these states to the presence of the other, as well
as to external thermal and magnetic perturbations, points to the possibility
that they emerge from different parts of the Fermi surface. This enables a
single 4 state to be both localized and itinerant, thus accounting for the
coexistence of magnetism and superconductivity.Comment: 4 pages, 4 figure
Fast Mapping of Terahertz Bursting Thresholds and Characteristics at Synchrotron Light Sources
Dedicated optics with extremely short electron bunches enable synchrotron
light sources to generate intense coherent THz radiation. The high degree of
spatial compression in this so-called low-alpha optics entails a complex
longitudinal dynamics of the electron bunches, which can be probed studying the
fluctuations in the emitted terahertz radiation caused by the micro-bunching
instability ("bursting"). This article presents a "quasi-instantaneous" method
for measuring the bursting characteristics by simultaneously collecting and
evaluating the information from all bunches in a multi-bunch fill, reducing the
measurement time from hours to seconds. This speed-up allows systematic studies
of the bursting characteristics for various accelerator settings within a
single fill of the machine, enabling a comprehensive comparison of the measured
bursting thresholds with theoretical predictions by the bunched-beam theory.
This paper introduces the method and presents first results obtained at the
ANKA synchrotron radiation facility.Comment: 7 pages, 7 figures, to be published in Physical Review Accelerators
and Beam
Simultaneous Detection of Longitudinal and Transverse Bunch Signals at a Storage Ring
To understand and control the dynamics in the longitudinal phase space,
time-resolved measurements of different bunch parameters are required. For a
reconstruction of this phase space, the detector systems have to be
synchronized. This reconstruction can be used e.g. for studies of the
micro-bunching instability. It occurs if the interaction of the bunch with its
own radiation leads to the formation of sub-structures on the longitudinal
bunch profile. These sub-structures can grow rapidly -- leading to a
sawtooth-like behaviour of the bunch. At KARA, we use a fast-gated intensified
camera for energy spread studies, Schottky diodes for coherent synchrotron
radiation studies as well as electro-optical spectral decoding for longitudinal
bunch profile measurements. For a synchronization, a hardware synchronization
scheme is used which compensates for eventual hardware delays. In this paper,
the different experimental setups and their synchronization are discussed and
first results of synchronous measurements are presented
Classes on compactifications of the moduli space of curves through solutions to the quantum master equation
In this paper we describe a construction which produces classes in a
compactification of the moduli space of curves. This construction extends a
construction of Kontsevich which produces classes in the open moduli space from
the initial data of a cyclic A-infinity algebra. The initial data for our
construction is what we call a `quantum A-infinity algebra', which arises as a
type of deformation of a cyclic A-infinity algebra. The deformation theory for
these structures is described explicitly. We construct a family of examples of
quantum A-infinity algebras which extend a family of cyclic A-infinity
algebras, introduced by Kontsevich, which are known to produce all the
Miller-Morita-Mumford classes using his construction.Comment: This version includes an updated list of reference
Poisson-de Rham homology of hypertoric varieties and nilpotent cones
We prove a conjecture of Etingof and the second author for hypertoric
varieties, that the Poisson-de Rham homology of a unimodular hypertoric cone is
isomorphic to the de Rham cohomology of its hypertoric resolution. More
generally, we prove that this conjecture holds for an arbitrary conical variety
admitting a symplectic resolution if and only if it holds in degree zero for
all normal slices to symplectic leaves.
The Poisson-de Rham homology of a Poisson cone inherits a second grading. In
the hypertoric case, we compute the resulting 2-variable Poisson-de
Rham-Poincare polynomial, and prove that it is equal to a specialization of an
enrichment of the Tutte polynomial of a matroid that was introduced by Denham.
We also compute this polynomial for S3-varieties of type A in terms of Kostka
polynomials, modulo a previous conjecture of the first author, and we give a
conjectural answer for nilpotent cones in arbitrary type, which we prove in
rank less than or equal to 2.Comment: 25 page
Explaining Myanmar's Regime Transition: The Periphery is Central
In 2010, Myanmar (Burma) held its first elections after 22 years of direct military rule. Few compelling explanations for this regime transition have emerged. This article critiques popular accounts and potential explanations generated by theories of authoritarian âregime breakdownâ and âregime maintenanceâ. It returns instead to the classical literature on military intervention and withdrawal. Military regimes, when not terminated by internal factionalism or external unrest, typically liberalise once they feel they have sufficiently addressed the crises that prompted their seizure of power. This was the case in Myanmar. The military intervened for fear that political unrest and ethnic-minority separatist insurgencies would destroy Myanmarâs always-fragile territorial integrity and sovereignty. Far from suddenly liberalising in 2010, the regime sought to create a âdisciplined democracyâ to safeguard its preferred social and political order twice before, but was thwarted by societal opposition. Its success in 2010 stemmed from a strategy of coercive state-building and economic incorporation via âceasefire capitalismâ, which weakened and co-opted much of the opposition. Having altered the balance of forces in its favour, the regime felt sufficiently confident to impose its preferred settlement. However, the transition neither reflected total âvictoryâ for the military nor secured a genuine or lasting peace
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