98 research outputs found
Strong orientational effect of stretched aerogel on the 3He order parameter
Deformation of aerogel strongly modifies the orientation of the order
parameter of superfluid 3He confined in aerogel. We used a radial squeezing of
aerogel to keep the orbital angular momentum of the 3He Cooper pairs in the
plane perpendicular to the magnetic field. We did not find strong evidence for
a "polar" phase, with a nodal line along the equator of the Fermi surface,
predicted to occur at large radial squeezing. Instead we observed 3He-A with a
clear experimental evidence of the destruction of the long-range order by
random anisotropy -- the Larkin-Imry-Ma effect. In 3He-B we observed and
identified new modes of NMR, which are impossible to obtain in bulk 3He-B. One
of these modes is characterized by a repulsive interaction between magnons,
which is suitable for the magnon Bose-Einstein condensation (BEC).Comment: 4 pages, 3 figures, revtex, submitted to PR
Vortex core transitions in superfluid 3He in globally anisotropic aerogels
Core structures of a single vortex in A-like and B-like phases of superfluid
3He in uniaxially compressed and stretched aerogels are studied by numerically
solving Ginzburg-Landau equations derived microscopically. It is found that,
although any uniaxial deformation leads to a wider A-like phase with the axial
pairing in the pressure-temperature phase diagram, the vortex core states in
the two phases in aerogel depend highly on the type of deformation. In a
compressed aerogel, the first-order vortex core transition (VCT) previously
seen in the bulk B phase appears at any pressure in the B-like phase while no
strange vortex core is expected in the corresponding A-like phase. By contrast,
in a stretched aerogel, the VCT in the B-like phase is lost while another VCT
is expected to occur between a nonunitary core and a polar one in the A-like
phase. Experimental search for these results is hoped to understand correlation
between superfluid 3He and aerogel structure.Comment: 7 pages, 6 figures Text was changed. Resubmitted versio
Bolometric calibration of a superfluid He detector for Dark Matter search: direct measurement of the scintillated energy fraction for neutron, electron and muon events
We report on the calibration of a superfluid He bolometer developed for
the search of non-baryonic Dark Matter. Precise thermometry is achieved by the
direct measurement of thermal excitations using Vibrating Wire Resonators
(VWRs). The heating pulses for calibration were produced by the direct quantum
process of quasiparticle generation by other VWRs present. The bolometric
calibration factor is analyzed as a function of temperature and excitation
level of the sensing VWR. The calibration is compared to bolometric
measurements of the nuclear neutron capture reaction and heat depositions by
cosmic muons and low energy electrons. The comparison allows a quantitative
estimation of the ultra-violet scintillation rate of irradiated helium,
demonstrating the possibility of efficient electron recoil event rejection.Comment: 17 pages, submitted to Nuc. Instr. Meth.
NMR in Superfluid A-like Phase of He Confined in Globally Deformed Aerogel in Tilted Magnetic Field
NMR spectra in superfluid A-like phases confined in axially deformed aerogel
in presence of a magnetic field inclined with respect to deformation axis is
considered. The characteristic features of dipole frequency shift in axially
compressed and axially stretched cases are compared. In particular, it is shown
that in axially stretched aerogel environment the stability region of
coherently spin precessing mode is rather narrow due to the U(1)LIM effect.Comment: 8 pages, 2 figure
New Chiral Phases of Superfluid 3He Stabilized by Anisotropic Silica Aerogel
A rich variety of Fermi systems condense by forming bound pairs, including
high temperature [1] and heavy fermion [2] superconductors, Sr2RuO4 [3], cold
atomic gases [4], and superfluid 3He [5]. Some of these form exotic quantum
states having non-zero orbital angular momentum. We have discovered, in the
case of 3He, that anisotropic disorder, engineered from highly porous silica
aerogel, stabilizes a chiral superfluid state that otherwise would not exist.
Additionally, we find that the chiral axis of this state can be uniquely
oriented with the application of a magnetic field perpendicular to the aerogel
anisotropy axis. At suffciently low temperature we observe a sharp transition
from a uniformly oriented chiral state to a disordered structure consistent
with locally ordered domains, contrary to expectations for a superfluid glass
phase [6].Comment: 6 pages, 4 figure, and Supplementary Informatio
Mass coupling and ^3$He in a torsion pendulum
We present results of the and period shift, , for He
confined in a 98% nominal open aerogel on a torsion pendulum. The aerogel is
compressed uniaxially by 10% along a direction aligned to the torsion pendulum
axis and was grown within a 400 m tall pancake (after compression) similar
to an Andronikashvili geometry. The result is a high pendulum able to
resolve and mass coupling of the impurity-limited He over the
whole temperature range. After measuring the empty cell background, we filled
the cell above the critical point and observe a temperature dependent period
shift, , between 100 mK and 3 mK that is 2.9 of the period shift
(after filling) at 100 mK. The due to the He decreases by an order
of magnitude between 100 mK and 3 mK at a pressure of bar. We
compare the observable quantities to the corresponding calculated and
period shift for bulk He.Comment: 8 pages, 3 figure
Orbital glass and spin glass states of 3He-A in aerogel
Glass states of superfluid A-like phase of 3He in aerogel induced by random
orientations of aerogel strands are investigated theoretically and
experimentally. In anisotropic aerogel with stretching deformation two glass
phases are observed. Both phases represent the anisotropic glass of the orbital
ferromagnetic vector l -- the orbital glass (OG). The phases differ by the spin
structure: the spin nematic vector d can be either in the ordered spin nematic
(SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN)
is formed under conventional cooling from normal 3He. The second phase (OG-SG)
is metastable, being obtained by cooling through the superfluid transition
temperature, when large enough resonant continuous radio-frequency excitation
are applied. NMR signature of different phases allows us to measure the
parameter of the global anisotropy of the orbital glass induced by deformation.Comment: 7 pages, 6 figures, Submitted to Pis'ma v ZhETF (JETP Letters
Electrospray Ionization with High-Resolution Mass Spectrometry as a Tool for Lignomics: Lignin Mass Spectrum Deconvolution
Capability to characterize lignin, lignocellulose, and their degradation products is essential for development of new renewable feedstocks. Electrospray ionization high-resolution time-offlight mass spectrometry (ESI HR TOF MS) method was developed expanding the lignomics toolkit while targeting the simultaneous detection of low and high molecular weight (MW) lignin species. The effect of a broad range of electrolytes and various ionization conditions on ion formation and ionization effectiveness was studied using a suite of mono-, di- and triarene lignin model compounds as well as intact lignin. Contrary to the previous studies, the positive ionization mode was found to be more effective for methoxy-substituted arenes and polyphenols, i.e., species of a broadly varied MW structurally similar to the native lignin. For the first time, we report an effective formation of multiply charged species of lignin with the subsequent mass spectrum deconvolution in the presence of 100 mmol·L-1 formic acid in the positive ESI mode. The developed method enabled the detection of lignin species with an MW between 150 and 9,000 Da or higher, depending on the mass analyzer. The obtained Mn and Mw values of 1,500 and 2,500 Da, respectively, were in good agreement with those determined by gel permeation chromatography. Furthermore, the deconvoluted ESI mass spectrum was similar to that obtained with matrixassisted laser desorption/ionization (MALDI) TOF MS, yet featuring a higher signal-to-noise ratio. The formation of multiply charged species was confirmed with ESI ion mobility HR Q-TOF MS
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