102 research outputs found
Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning
We study the general problem of a manifold of interacting elastic lines whose
spatial correlations are strongly affected by the competition between random
and ordered pinning. This is done through magneto-transport experiments with
YBa2Cu3O7-d thin films that contain a periodic vortex pinning array created via
masked ion irradiation, in addition to the native random pinning. The strong
field-matching effects we observe suggest the prevalence of periodic pinning,
and indicate that at the matching field each vortex line is bound to an
artificial pinning site. However, the vortex-glass transition dimensionality,
quasi-2D instead of the usual 3D, evidences reduced vortex-glass correlations
along the vortex line. This is also supported by an unusual angular dependence
of the magneto-resistance, which greatly differs from that of Bose-glass
systems. A quantitative analysis of the angular magnetoresistance allows us to
link this behaviour to the enhancement of the system anisotropy, a collateral
effect of the ion irradiation
Stoichiometry, structure, and transport in the quasi-one-dimensional metal, Li(0.9)Mo(6)O(17)
A correlation between lattice parameters, oxygen composition, and the
thermoelectric and Hall coefficients is presented for single-crystal
Li(0.9)Mo(6)O(17), a quasi-one-dimensional (Q1D) metallic compound. The
possibility that this compound is a compensated metal is discussed in light of
a substantial variability observed in the literature for these transport
coefficients.Comment: 5 pages, 4 Figures; Phys. Rev. B (in press
Synthesis of Multiple-Pattern Planar Antenna Arrays with Single Prefixed or Jointly Optimized Amplitude Distributions
This is the peer reviewed version of the following article:Brégains, J. C.; Trastoy, A.; Ares Pena, F. J.; Moreno Piquero, E. "Synthesis of multiple-pattern planar antenna arrays with single prefixed or jointly optimized amplitude distributions", Microwave and Optical Technology Letters, 74 - 78 Volume: 32, Issue: 1 , 5 Jan. 2002, which has been published in final form at DOI: 10.1002/mop.10094. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[Abstract] Previous work on the generation of multiple radiation patterns by a single linear array antenna with an unchanging excitation amplitude distribution is generalized to planar arrays. The amplitude distribution common to all of the excitation distributions can be prefixed or optimized jointly with the phase distributions
Beam Reconfiguration of Linear Arrays Using Parasitic Elements
This paper is a postprint of a paper submitted to and accepted for publication in journal Electronics Letters and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library - http://digital-library.theiet.org/content/journals/10.1049/el:20063674[Abstrac] An innovative method for linear arrays beam reconfiguration is presented. This pattern reconfigurability is achieved by a mechanical displacement of a parasitic array located in front of an active one. Two worked examples that use parallel dipoles are presented
Microwave neural processing and broadcasting with spintronic nano-oscillators
Can we build small neuromorphic chips capable of training deep networks with
billions of parameters? This challenge requires hardware neurons and synapses
with nanometric dimensions, which can be individually tuned, and densely
connected. While nanosynaptic devices have been pursued actively in recent
years, much less has been done on nanoscale artificial neurons. In this paper,
we show that spintronic nano-oscillators are promising to implement analog
hardware neurons that can be densely interconnected through electromagnetic
signals. We show how spintronic oscillators maps the requirements of artificial
neurons. We then show experimentally how an ensemble of four coupled
oscillators can learn to classify all twelve American vowels, realizing the
most complicated tasks performed by nanoscale neurons
Magnetic field frustration of the metal-insulator transition in V2 O3
Despite decades of efforts, the origin of metal-insulator transitions (MITs) in strongly correlated materials remains one of the main long-standing problems in condensed-matter physics. An archetypal example is V2O3, which undergoes simultaneous electronic, structural, and magnetic phase transitions. This remarkable feature highlights the many degrees of freedom at play in this material. In this work, acting solely on the magnetic degree of freedom, we reveal an anomalous feature in the electronic transport of V2O3: On cooling, the magnetoresistance changes from positive to negative values well above the MIT temperature, and shows divergent behavior at the transition. The effects are attributed to the magnetic field quenching antiferromagnetic fluctuations above the Néel temperature TN, and preventing long-range antiferromagnetic ordering below TN. In both cases, suppressing the antiferromagnetic ordering prevents the opening of the incipient electronic gap. This interpretation is supported by Hubbard model calculations which fully reproduce the experimental behavior. Our study sheds light on this classic problem providing a clear and physical interpretation of the nature of the metal-insulator transition.Fil: Trastoy, J.. University of California at San Diego; Estados UnidosFil: Camjayi, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Del Valle, J.. University of California at San Diego; Estados UnidosFil: Kalcheim, Y.. University of California at San Diego; Estados UnidosFil: Crocombette, J. P.. Université Paris-Saclay; FranciaFil: Gilbert, D.A.. University of Tennessee; Estados UnidosFil: Borchers, J.A.. Nist Center For Neutron Research; Estados UnidosFil: Villegas, J.E.. Université Paris-Saclay; FranciaFil: Ravelosona, D.. Center For Nanoscience And Nanotechnology; FranciaFil: Rozenberg, M.J.. Université Paris-Saclay; FranciaFil: Schuller, Ivan K.. University of California at San Diego; Estados Unido
A high-temperature superconducting weak-link defined by ferroelectric field-effect
In all-oxide ferroelectric (FE) - superconductor (S) bilayers, due to the low
carrier concentration of oxides compared to transition metals, the FE
interfacial polarization charges induce an accumulation (or depletion) of
charge carriers in the S. This leads either to an enhancement or a depression
of its critical temperature depending on FE polarization direction.Here we
exploit this effect at a local scale to define planar weak-links in
high-temperature superconducting wires. This is realized in
BiFeO3(FE)/YBa2Cu3O7(S)bilayers in which the remnant FE domain structure is
written at will by locally applying voltage pulses with a conductive-tip atomic
force microscope. In this fashion, the FE domain pattern defines a spatial
modulation of superconductivity. This allows us to write a device whose
electrical transport shows different temperature regimes and magnetic field
matching effects that are characteristic of Josephson coupled weak-links. This
illustrates the potential of the ferroelectric approach for the realization of
high-temperature superconducting devices
- …