57,594 research outputs found
Properties of recent IBAD-MOCVD Coated Conductors relevant to their high field, low temperature magnet use
BaZrO3 (BZO) nanorods are now incorporated into production IBAD-MOCVD coated
conductors. Here we compare several examples of both BZO-free and
BZO-containing coated conductors using critical current (Ic) characterizations
at 4.2 K over their full angular range up to fields of 31 T. We find that BZO
nanorods do not produce any c-axis distortion of the critical current density
Jc(theta) curve at 4.2 K at any field, but also that pinning is nevertheless
strongly enhanced compared to the non-BZO conductors. We also find that the
tendency of the ab-plane Jc(theta) peak to become cusp-like is moderated by BZO
and we define a new figure of merit that may be helpful for magnet design - the
OADI (Off-Axis Double Ic), which clearly shows that BZO broadens the ab-plane
peak and thus raises Jc 5-30{\deg} away from the tape plane, where the most
critical approach to Ic occurs in many coil designs. We describe some
experimental procedures that may make critical current Ic tests of these very
high current tapes more tractable at 4.2 K, where Ic exceeds 1000 A even for 4
mm wide tape with only 1 micron thickness of superconductor. A positive
conclusion is that BZO is very beneficial for the Jc characteristics at 4.2 K,
just as it is at higher temperatures, where the correlated c-axis pinning
effects of the nanorods are much more obvious
Optically-controlled single-qubit rotations in self-assembled InAs quantum dots
We present a theory of the optical control of the spin of an electron in an
InAs quantum dot. We show how two Raman-detuned laser pulses can be used to
obtain arbitrary single-qubit rotations via the excitation of an intermediate
trion state. Our theory takes into account a finite in-plane hole -factor
and hole-mixing. We show that such rotations can be performed to high
fidelities with pulses lasting a few tens of picoseconds.Comment: 6 pages, 4 figures; minor changes, J-ref adde
Ghost excitonic insulator transition in layered graphite
Some unusual properties of layered graphite, including a linear energy
dependence of the quasiparticle damping and weak ferromagnetism at low doping,
are explained as a result of the proximity of a single graphene sheet to the
excitonic insulator phase which can be further stabilized in a doped system of
many layers stacked in the staggered () configuration
The Local Universe as Seen in Far-Infrared and in Far-Ultraviolet: A Global Point of View on the Local Recent Star Formation
We select far-infrared (FIR-60 microns) and far-ultraviolet (FUV-1530 A)
samples of nearby galaxies in order to discuss the biases encountered by
monochromatic surveys (FIR or FUV). Very different volumes are sampled by each
selection and much care is taken to apply volume corrections to all the
analyses. The distributions of the bolometric luminosity of young stars are
compared for both samples: they are found to be consistent with each other for
galaxies of intermediate luminosities but some differences are found for high
(>5 10^{10} L_sun) luminosities. The shallowness of the IRAS survey prevents us
from securing comparison at low luminosities (<2 10^9 L_sun). The ratio of the
total infrared (TIR) luminosity to the FUV luminosity is found to increase with
the bolometric luminosity in a similar way for both samples up to 5 10^{10}
L_sun. Brighter galaxies are found to have a different behavior according to
their selection: the L_TIR/L_FUV ratio of the FUV-selected galaxies brighter
than 5 10^{10} L_sun reaches a plateau whereas L_TIR/L_FUV continues to
increase with the luminosity of bright galaxies selected in FIR. The
volume-averaged specific star formation rate (SFR per unit galaxy stellar mass,
SSFR) is found to decrease toward massive galaxies within each selection. The
SSFR is found to be larger than that measured for optical and NIR-selected
sample over the whole mass range for the FIR selection, and for masses larger
than 10^{10} M_sun for the FUV selection. Luminous and massive galaxies
selected in FIR appear as active as galaxies with similar characteristics
detected at z ~ 0.7.Comment: 32 pages, 9 figures, to be published in the Astrophysical Journal
Supplement series dedicated to GALEX result
Evidence for a dynamical ground state in the frustrated pyrohafnate Tb2Hf2O7
We report the physical properties of Tb2Hf2O7 based on ac magnetic
susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal
magnetization M(H), and heat capacity C_p(T) measurements combined with muon
spin relaxation (\muSR) and neutron powder diffraction measurements. No
evidence for long-range magnetic order is found down to 0.1 K. However,
\chi_ac(T) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz)
indicating slow spin dynamics. The slow spin dynamics is further evidenced from
the \muSR data (characterized by a stretched exponential behavior) which show
persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data
collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering)
but no magnetic Bragg peaks. The analysis of the diffuse scattering data
reveals a dominant antiferromagnetic interaction in agreement with the negative
Weiss temperature. The absence of long-range magnetic order and the presence of
slow spin dynamics and persistent spin fluctuations together reflect a
dynamical ground state in Tb2Hf2O7.Comment: 11 pages and 8 figure
Charge order, dynamics, and magneto-structural transition in multiferroic LuFeO
We investigated the series of temperature and field-driven transitions in
LuFeO by optical and M\"{o}ssbauer spectroscopies, magnetization, and
x-ray scattering in order to understand the interplay between charge,
structure, and magnetism in this multiferroic material. We demonstrate that
charge fluctuation has an onset well below the charge ordering transition,
supporting the "order by fluctuation" mechanism for the development of charge
order superstructure. Bragg splitting and large magneto optical contrast
suggest a low temperature monoclinic distortion that can be driven by both
temperature and magnetic field.Comment: 4 pages, 3 figures, PRL in prin
Doping Dependence of Collective Spin and Orbital Excitations in Spin 1 Quantum Antiferromagnet LaSrNiO Observed by X-rays
We report the first empirical demonstration that resonant inelastic x-ray
scattering (RIXS) is sensitive to \emph{collective} magnetic excitations in
systems by probing the Ni -edge of LaSrNiO (). The magnetic excitation peak is asymmetric, indicating the
presence of single and multi spin-flip excitations. As the hole doping level is
increased, the zone boundary magnon energy is suppressed at a much larger rate
than that in hole doped cuprates. Based on the analysis of the orbital and
charge excitations observed by RIXS, we argue that this difference is related
to the orbital character of the doped holes in these two families. This work
establishes RIXS as a probe of fundamental magnetic interactions in nickelates
opening the way towards studies of heterostructures and ultra-fast pump-probe
experiments.Comment: 8 pages, 4 figures, see ancillary files for the supplemental materia
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