24,430 research outputs found
Electronic nematicity and its relation to quantum criticality in Sr_3Ru_2O_7 studied by thermal expansion
We report high-resolution measurements of the in-plane thermal expansion
anisotropy in the vicinity of the electronic nematic phase in SrRuO
down to very low temperatures and in varying magnetic field orientation. For
fields applied along the c-direction, a clear second-order phase transition is
found at the nematic phase, with critical behavior compatible with the
two-dimensional Ising universality class (although this is not fully
conclusive). Measurements in a slightly tilted magnetic field reveal a broken
four-fold in-plane rotational symmetry, not only within the nematic phase, but
extending towards slightly larger fields. We also analyze the universal scaling
behavior expected for a metamagnetic quantum critical point, which is realized
outside the nematic region. The contours of the magnetostriction suggest a
relation between quantum criticality and the nematic phase.Comment: 8 pages, 12 Figures, invited paper at QCNP 2012 conferenc
Symmetry-breaking lattice distortion in Sr_3Ru_2O_7
The electronic nematic phase of SrRuO is investigated by
high-resolution in-plane thermal expansion measurements in magnetic fields
close to 8 T applied at various angles off the c-axis. At
we observe a very small () lattice distortion which
breaks the four-fold in-plane symmetry, resulting in nematic domains with
interchanged - and b-axis. At the domains are
almost fully aligned and thermal expansion indicates an area-preserving lattice
distortion of order which is likely related to orbital
ordering. Since the system is located in the immediate vicinity to a
metamagnetic quantum critical end point, the results represent the first
observation of a structural relaxation driven by quantum criticality.Comment: 4 pages, 5 figures, PRL accepte
Anisotropy of the low-temperature magnetostriction of Sr3Ru2O7
We use high-resolution capacitive dilatometry to study the low-temperature
linear magnetostriction of the bilayer ruthenate SrRuO as a
function of magnetic field applied perpendicular to the ruthenium-oxide planes
(). The relative length change is detected either
parallel or perpendicular to the c-axis close to the metamagnetic region near
B=8 T. In both cases, clear peaks in the coefficient at three subsequent metamagnetic transitions are observed. For , the third transition at 8.1 T bifurcates at temperatures below 0.5
K. This is ascribed to the effect of an in-plane uniaxial pressure of about 15
bar, unavoidable in the dilatometer, which breaks the original fourfold
in-plane symmetry.Comment: 3 pages, 3 Figures, Manuscript for Proceedings of the International
Conference on Quantum Criticality and Novel Phases (QCNP09, Dresden
Multiple metamagnetic quantum criticality in SrRuO
Bilayer strontium ruthenate SrRuO displays pronounced non-Fermi
liquid behavior at magnetic fields around 8 T, applied perpendicular to the
ruthenate planes, which previously has been associated with an itinerant
metamagnetic quantum critical end point (QCEP). We focus on the magnetic
Gr\"uneisen parameter , which is the most direct probe to
characterize field-induced quantum criticality. We confirm quantum critical
scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked
by two ordered phases A and B, identified previously by neutron scattering. In
addition we find evidence for a QCEP at 7.53(2) T and determine the quantum
critical regimes of both instabilities and the effect of their superposition
A Study of Linear Approximation Techniques for SAR Azimuth Processing
The application of the step transform subarray processing techniques to synthetic aperture radar (SAR) was studied. The subarray technique permits the application of efficient digital transform computational techniques such as the fast Fourier transform to be applied while offering an effective tool for range migration compensation. Range migration compensation is applied at the subarray level, and with the subarray size based on worst case range migration conditions, a minimum control system is achieved. A baseline processor was designed for a four-look SAR system covering approximately 4096 by 4096 SAR sample field every 2.5 seconds. Implementation of the baseline system was projected using advanced low power technologies. A 20 swath is implemented with approximately 1000 circuits having a power dissipation of from 70 to 195 watts. The baseline batch step transform processor is compared to a continuous strip processor, and variations of the baseline are developed for a wide range of SAR parameters
Holographic Recording Materials Development
Organic photorefractive materials were evaluated for application in a reversible holographic memory system. Representative indigo and thioindigo derivatives and several stilbene derivatives were studied as well as 15, 16-dialkyldihydropyrene derivatives the following goals were achieved: (1) the successful writing of phase holograms in a thioindigo/polymer gel system, (2) the successful writing and erasing of phase holograms in a variety of indigo/polymer gel and indigo/solid polymer systems, and (3) the identification of indigoid dyes and 15, 16-dialkyldihydropyrene derivatives as materials potentially suitable for utilization in an operational system. Photochemical studies of the stilbene, indigo, thioindigo, and dialkyldihydropyrene derivatives in solution and in a variety of polymer matrix materials were conducted with the goal of optimizing the photorefractive behavior of the chemical system as a whole. The spectroscopic properties required of optimal photorefractive materials were identified, and it was shown that both the indigoid dyes and the dialkyldihydropyrenes closely match the required properties
Photon Statistics of a Single Atom Laser
We consider a laser model consisting of a single four-level or three-level atom, an optical cavity, and an incoherent pump. Results for photon statistics for varying pump levels are obtained using a quantum trajectory algorithm. In particular, we calculate the mean photon number, Fano factor (which is the variance over the mean). We examine that the behavior of the single-atom device as β, the fraction of spontaneous emission into the lasing mode, is varied. Typical values considered for β are 0.01\u3cβ\u3c1.0. We find that for large enough β, lasing action, with properties similar to those predicted by semiclassical theories that factorize atom-field correlations and use a small-noise approximation, can occur. Squeezing can occur as β is increased. There is no evidence of a sharp phase transition from weakly excited thermal light to coherent light at a particular pump power. This is consistent with work on many-atom lasers with β values in the range considered here. As β is increased, the output goes from quasithermal light to coherent and finally to squeezed light, progressing into a fully quantum-mechanical regime. We also consider the effects of cavity damping and spontaneous emission rates on these results
Initial bound state studies in light-front QCD
We present the first numerical QCD bound state calculation based on a
renormalization group-improved light-front Hamiltonian formalism. The QCD
Hamiltonian is determined to second order in the coupling, and it includes
two-body confining interactions. We make a momentum expansion, obtaining an
equal-time-like Schrodinger equation. This is solved for quark-antiquark
constituent states, and we obtain a set of self-consistent parameters by
fitting B meson spectra.Comment: 38 pages, latex, 5 latex figures include
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