3,075 research outputs found
Balanced double-loop mesoscopic interferometer based on Josephson proximity nanojunctions
We report on the fabrication and characterization of a two-terminal
mesoscopic interferometer based on three V/Cu/V Josephson junctions having
nanoscale cross-section. The junctions have been arranged in a double-ring
geometry realized by metallic thin film deposition through a suspended mask
defined by electron beam lithography. Although a significant amount of
asymmetry between the critical current of each junction is observed we show
that the interferometer is able to suppress the supercurrent to a level lower
than 6 parts per thousand, being here limited by measurement resolution. The
present nano-device is suitable for low-temperature magnetometric and
gradiometric measurements over the micrometric scale.Comment: 5 pages, 4 figure
Highly-sensitive superconducting quantum interference proximity transistor
We report the design and implementation of a high-performance superconducting
quantum interference proximity transistor (SQUIPT) based on aluminum-copper
(Al-Cu) technology. With the adoption of a thin and short copper nanowire we
demostrate full phase-driven modulation of the proximity-induced minigap in the
normal metal density of states. Under optimal bias we record unprecedently high
flux-to-voltage (up to 3 mV/) and flux-to-current (exceeding 100
nA/) transfer function values at sub-Kelvin temperatures, where
is the flux quantum. The best magnetic flux resolution (as low as 500
n at 240 mK, being limited by the room temperature
pre-amplification stage) is reached under fixed current bias. These figures of
merit combined with ultra-low power dissipation and micrometer-size dimensions
make this mesoscopic interferometer attractive for low-temperature applications
such as the investigation of the magnetization of small spin populations.Comment: 7 pages, 5 color figure
Phase-driven collapse of the Cooper condensate in a nanosized superconductor
Superconductivity can be understood in terms of a phase transition from an
uncorrelated electron gas to a condensate of Cooper pairs in which the relative
phases of the constituent electrons are coherent over macroscopic length
scales. The degree of correlation is quantified by a complex-valued order
parameter, whose amplitude is proportional to the strength of the pairing
potential in the condensate. Supercurrent-carrying states are associated with
non-zero values of the spatial gradient of the phase. The pairing potential and
several physical observables of the Cooper condensate can be manipulated by
means of temperature, current bias, dishomogeneities in the chemical
composition or application of a magnetic field. Here we show evidence of
complete suppression of the energy gap in the local density of quasiparticle
states (DOS) of a superconducting nanowire upon establishing a phase difference
equal to pi over a length scale comparable to the superconducting coherence
length. These observations are consistent with a complete collapse of the
pairing potential in the center of the wire, in accordance with theoretical
modeling based on the quasiclassical theory of superconductivity in diffusive
systems. Our spectroscopic data, fully exploring the phase-biased states of the
condensate, highlight the profound effect that extreme phase gradients exert on
the amplitude of the pairing potential. Moreover, the sharp magnetic response
observed near the onset of the superconducting gap collapse regime can be
exploited to realize ultra-low noise magnetic flux detectors.Comment: 7 pages, 5 color figures plus supporting inf
Instanton counting on compact manifolds
In this thesis we analyze supersymmetric gauge theories on compact manifolds and their relation with representation theory of infinite Lie algebras associated to conformal field theories, and with the computation of geometric invariants and superconformal indices.
The thesis contains the work done by the candidate during the doctorate programme at SISSA under the supervision of A. Tanzini and G. Bonelli.
\u2022 in Chapter 2, we consider N = 2 supersymmetric gauge theories on four manifolds admitting an isometry. Generalized Killing spinor equations are derived from the consistency of supersymmetry algebrae and solved in the case of four manifolds admitting a U(1) isometry. This is used to explicitly compute the supersymmetric path integral on S2
7 S2 via equivariant localization. The building blocks of the resulting partition function are shown to contain the three point functions and the conformal blocks of Liouville Gravity.
\u2022 in Chapter 3, we provide a contour integral formula for the exact partition function of N = 2 supersymmetric U(N) gauge theories on compact toric four-manifolds by means of supersymmetric localisation. We perform the explicit evaluation of the contour integral for U(2) N = 2 17 theory on P2 for all instanton numbers. In the zero mass case, corresponding to the N = 4 supersymmetric gauge theory, we obtain the generating function of the Euler characteristics of instanton moduli spaces in terms of mock-modular forms. In the decoupling limit of infinite mass we find that the generating function of local and surface observables computes equivariant Donaldson invariants, thus proving in this case a long-standing conjecture by N. Nekrasov. In the case of vanishing first Chern class the resulting equivariant Donaldson polynomials are new.
\u2022 in Chapter 4, we explore N = (1, 0) superconformal six-dimensional theories arising from M5 branes probing a transverse Ak singularity. Upon circle compactification to five dimensions, we describe this system with a dual pq-web of five-branes and propose the spectrum of basic five-dimensional instanton operators driving global symmetry enhancement. For a single M5 brane, we find that the exact partition function of the 5d quiver gauge theory matches the 6d (1, 0) index, which we compute by letter counting. We finally show which relations among vertex correlators of qW algebrae are implied by the S-duality of the pq-web
ENERGY LANDSCAPES. The design of landscape architecture by the shape of energy infrastructure
The contribution constitutes a synthesis of the doctoral research work carried out, at the mid-doctoral stage.
The short text introduces the research topics related to the design of new renewable energy landscapes, stating the methodological aspects. Furthermore, it briefly describes the four sections into which the doctoral thesis is planned to be structured
How big is a house? The dimension of contemporary dwelling space
During recent decades, the attempt to design minimal spaces has become a challenge for architects. This phenomenon is first and foremost a reflection of a society that is liquid, as the philosopher Bauman describes it. Therefore, the meaning of the home and its use today have completely changed compared to the past. Within this context, the Italian law defining minimum standards for living spaces has still not been updated since the 1970s. The contribution invites a reflection on the new possibilities that minimum dwelling offers to contemporary society
Advanced Anti-Windup Techniques for the Limitation of the Effects of the Actuator Saturation
In this thesis an industrial issue is analysed. The issue consist on the undesirable effect of actuator sturation. Two approaches are given to solve the issue: an accurate inertia identification algorithm based on the DFT coefficient; and advanced anti-windup compensators. The principle of the modern anti-windup (DLAW and MRAW, LMI-based design approach), and a systematic design design procedure for the observer-based anti-windup are given. Simulation and test results are also given.ope
Modality Mix of RFID Regulation
This paper provides a general reflection on how law must manage the evolution oftechnology. By the example of radio frequency identification (RFID), it analyses the necessity ofRFID regulation based on Lessig’s four modalities law, norms, market and architecture. This papersuggests that a trade-off between or complementing of the four modalities is necessary for a holisticregulation of RFID. To support this claim, various topics of the draft recommendation on theimplementation of privacy, data protection and information security principles in RFID applicationsby the European Commission of February 2008 are cross-examined with and attributed to one ofthe four modalities. This paper concludes that the draft recommendation does not provide precisesupplementing legislation to justify its implementation. Many law-related issues of the draftrecommendation can be traded off against or complemented by the other three modalities norms,market and architecture
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