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"Yu, M"
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Ultra-fast vortex motion in a direct-write Nb-C superconductor
The ultra-fast dynamics of superconducting vortices harbors rich physics generic to nonequilibrium collective systems. The phenomenon of flux-flow instability (FFI), however, prevents its exploration and sets practical limits for the use of vortices in various applications. To suppress the FFI, a superconductor should exhibit a rarely achieved combination of properties: weak volume pinning, close-to-depairing critical current, and fast heat removal from heated electrons. Here, we demonstrate experimentally ultra-fast vortex motion at velocities of 10–15 km s
−1
in a directly written Nb-C superconductor with a close-to-perfect edge barrier. The spatial evolution of the FFI is described using the edge-controlled FFI model, implying a chain of FFI nucleation points along the sample edge and their development into self-organized Josephson-like junctions (vortex rivers). In addition, our results offer insights into the applicability of widely used FFI models and suggest Nb-C to be a good candidate material for fast single-photon detectors.
To realize ultra-fast dynamics of superconducting vortices one needs to overcome the practical issue of flux-flow instability (FFI). Here, Dobrovolskiy et al. demonstrate ultra-fast vortex motion at 10-15 km/s velocity in a Nb-C superconductor where the FFI is described by the edge-controlled FFI model.
Journal Article
Data driven identification of networks of dynamic systems
\"The identification of network connected dynamic systems is currently a hot research topic within the community of systems and control. Other engineering areas, social sciences and system biology are putting a lot of effort in the study of network connected systems. Modeling such networks and the identification of these models from acquired measurements is crucial in the analysis or understanding of the dynamics. Based on these models, synthesis to modify the behavior of the network can also be performed. This book gives a unique overview of state of the art research in the field of identifying networks of linear dynamical systems. This overview combines many of the pioneering contributions from the authors with those of other researchers that play a crucial role in the development of this new field\"-- Provided by publisher.
Book
On massive higher spins and gravity. Part I. Spin 5/2
A
bstract
In this paper, we continue our investigation of gravitational interactions for massive higher spins extending our previous work on massive spin 3/2 and spin 2 to massive spin 5/2, including partially massless and massless limits. We use the gauge invariant frame-like description for massive fields, both for general analysis of possible vertices and for constructing the minimal vertex (i.e. vertex containing standard minimal interactions and non-minimal interactions with a minimum number of derivatives). In particular, we show that there is a special point
m
2
= 4Λ, which corresponds to the boundary of a unitary allowed region in
dS
4
, where minimal interactions disappear, leaving only non-minimal ones.
Journal Article
On massive higher spins and gravity. Part II. Spin 3
A
bstract
In this paper, we continue our investigation of gravitational interactions for massive higher spins, extending our recent work on massive spin 5/2 to massive spin 3, including its massless and partially massless limits. To construct the minimal gravitational interactions (i.e. vertexes containing both standard minimal interactions and non-minimal ones, which are necessary for any
s
≥ 5/2), we use a gauge invariant frame-like formalism. Similarly to the spin 5/2 case, there is a special point
m
2
= 6Λ, which corresponds to a boundary of the unitary allowed region in
dS
4
, where minimal interactions disappear, leaving only the non-minimal ones.
Journal Article
Partially massless spin 2 and supersymmetry
A
bstract
The very existence of partially massless spin 2 supermultiplet tell us that partially massless spin 2 has two natural super-partners: massless spin 3/2 and massive spin 3/2 with some special value of mass. As for any pair of fields connected by global supertransformations there are two natural questions: existence of the self-interaction and possibility to make supertransformations to be local by switching their interaction with massless spin 3/2 gravitino. At first, we consider a self-interaction for the partially massless spin 2 and massive spin 3/2 which may be considered as the first approximation to partially massless supergravity and provide a direct construction of the minimal (i.e. having no more than one derivative) vertex which resembles usual supergravity. Then we consider localization of global supersymmetry which connects partially massless spin 2 with its two possible super-partners — massless spin 3/2 and massive with special mass value. For the first case we also managed to construct a minimal vertex having no more that one derivative. Again this vertex can be considered as a part of what can be called partially massless
N
= 2 supergravity. As for the second case, the corresponding vertex does exist but it has higher derivative terms.
Journal Article
Partially massless spin 5/2 and supersymmetry
A
bstract
We elaborate on the partially massless spin 5/2 supermultiplet, which contains partially massless spin 5/2, massless and partially massless spin 2, as well as massless spin 3/2. We consider the global supertransformations connecting partially massless spin 5/2 to its two possible superpartners, massless and partially massless spin 2, and make them local by switching the interaction with the massless gravitino. We use a frame-like gauge-invariant formalism to describe free fields and the Fradkin-Vasiliev formalism to construct interactions, Due to the presence of the Stueckelberg fields in the gauge-invariant description of massive and partially massless fields, we face ambiguities related to field redefinitions. We use this freedom to simplify calculations. At the same time, we demonstrate how these ambiguities can be resolved using unfolded equations.
Journal Article
On massive higher spin supermultiplets in d = 4
A
bstract
In this work we discuss the cubic interactions for massless spin 3/2 gravitino with massive higher spin supermultiplets using three superblocks (2, 3/2), (5/2, 2) and (3, 5/2) as the first non-trivial examples. We use gauge invariant formalism for the massive higher spin fields and, as is common in such cases, we face an ambiguity related with the possible field redefinitions due to the presence of Stueckelberg fields. From one hand, we show how this ambiguity can be used as one more way to classify possible cubic vertices. We also note that all these field redefinitions do not change the part of the Lagrangian which appears in the unitary gauge (where all Stueckelberg fields are set to zero) so we still have some important independent results. From the other hand, we show how using the so-called unfolded formalism one can fix these ambiguities and obtain consistent deformations for all massive field gauge invariant curvatures which is the most important step in the Fradkin-Vasiliev formalism. Unfortunately, this works for the massive fields only so the way to construct deformations for the massless field curvatures is still has to be found.
Journal Article
Massless spin 2 interacting with massive higher spins in d = 3
A
bstract
In this paper we consider massless spin 2 interacting with the massive arbitrary spin fermions in
d
= 3. First of all, we study all possible deformations for the massive fermion unfolded equations in presence of a massless spin-2 field. We find three linearly independent solutions one of which corresponds to the standard gravitational interactions. Then for all three cases we reconstruct appropriate Lagrangian formulation.
Journal Article