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H. Wang

Publications and source records attributed to H. Wang.

405 records · Page 23Linked to original sources
arXiv2003

Measuring Magnetostriction with an Atomic Force Microscope: Application to Wires in Ballistic Magnetoresistance

In this study we present a new method of measuring magnetostriction with an atomic force microscope adapted for the application magnetic fields. The experiment allows us to visualise, in an elegant and educational way how the lateral magnetoelastic shape changes take place on the sample surface when a magnetic field is applied. We have, furthermore, used this technique to observe magnetically induced strains as small as 5*10-8, and have measured Ni, permalloy and commercial Cu wires and films, as well as pure Cu and Pt wires, where results are in agreement with other methods of measurement. The applications are, moreover, relevant to studies of ballistic magnetoresistance, where we can draw conclusions involving the effect of the magnetically induced strains on magnetoresistance measured at the same time as magnestostriction.

cond-mat.mtrl-sci↗
arXiv2003

Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films

We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.

cond-mat.supr-con↗
arXiv2003

Quantum phase transition in superconducting Au0.7In0.3 films of very low normal-state sheet resistance

We report the observation of a quantum phase transition (QPT), tuned by a parallel magnetic field, between a superconducting and metallic state in Au0.7In0.3 films of very low normal-state sheet resistance (< 90 Ohms). These films can be modeled as a random array of superconductor-normal metal-superconductor (SNS) junctions. Electrical transport and tunneling measurements suggest that, in the metallic state, the film consists of superconducting In-rich grains not linked by Josephson coupling. Whether phase fluctuation, which is not expected to be strong in such an SNS junction system according to the phase-number uncertainty relation, or a different physical process drives the observed QPT is discussed.

cond-mat.supr-con↗
arXiv2002

On the Resummation of Large QCD Corrections to photon photon to b anti-b

We study the resummation of large QCD radiative corrections up to the next to leading logarithmic accuracy to the process photon photon to b anti-b; i.e., we resum logarithms of the type alpha_s^p log^{2p}{m^2/s} and alpha_s^p log^{2p-1}{m^2/s} (m is the quark mass). The only source of all the logarithms to this accuracy is the off-shell Sudakov form factor included into the triangle topologies of the one-loop box diagram. We prove that any other configurations of diagrams to this accuracy, either cancel in subgroups or develop a universal on-shell Sudakov exponent due to the final quark anti-quark lines. We study the mechanism of cancellations between the different diagrams, which leads to the simple resummed results. We show the cancellation explicitly at three loops for the leading and at two loops for the next-to-leading logarithms. We also point out the general mechanism responsible for it, and discuss how it can be extended to higher orders.

hep-ph↗
arXiv2001

Geometrical destruction of the global phase coherence in ultrathin superconducting cylinders

The global phase coherence in doubly-connected superconductors leads to fluxoid quantization, allowing the superfluid velocity vs to be controlled by an applied magnetic flux. In ultrasmall samples this quantization requirement leads, surprisingly, to the destruction of the phase coherence itself around half-integer flux quanta, because of the sample-size-induced growth in vs, as predicted by de Gennes. We report observations of the predicted phenomenon in ultrathin Al and Au0.7In0.3 cylinders, and the corresponding phase diagram for ultrathin superconducting cylinders. The new phase diagram features disconnected superconducting regions, as opposed to the single one seen in the conventional Little-Parks experiment.

cond-mat.supr-con↗
arXiv2001

On the Resummation of Large QCD Logarithms in Higgs -> 2 Photons Decay

We study the strong corrections to the Higgs coupling to two photons. This coupling is the dominant mechanism for Higgs production in photon-photon collisions. In addition, the two photon decay mode of the Higgs is an important and relatively background free channel of relevance at the LHC and the Tevatron. We develop a method for the resummation of large QCD corrections in the form of Sudakov-like logarithms of the type α_s^n\ln^{2n}(m/m_H) and α_s^n\ln^{2n-1}(m/m_H) (where m is the light quark mass) which can contribute to this process in certain models (for example, the MSSM for large tan β) up to next-to-leading-logarithmic (NLL) accuracy. The NLL correction is moderate, the substantial part of which comes from terms not related to running coupling effects.

hep-ph↗
arXiv2001

Antilambda production in Au+Au collisions at 11.7 A GeV/c

We present results from Experiment E917 for antilambda and antiproton production in Au+Au collisions at 11.7 A GeV. We have measured invariant spectra and yields for both species in central and peripheral collisions. We find that the antilambda/antiproton ratio near mid-rapidity increases from 0.26+0.19-0.15 in peripheral collisions to 3.6+4.7-1.8 in central collisions, a value that is substantially larger than current theoretical estimates.

nucl-ex↗
arXiv1999

Electric-octupole and pure-electric-quadrupole effects in soft-x-ray photoemission

Second-order [O(k^2), k=omega/c] nondipole effects in soft-x-ray photoemission are demonstrated via an experimental and theoretical study of angular distributions of neon valence photoelectrons in the 100--1200 eV photon-energy range. A newly derived theoretical expression for nondipolar angular distributions characterizes the second-order effects using four new parameters with primary contributions from pure-quadrupole and octupole-dipole interference terms. Independent-particle calculations of these parameters account for a significant portion of the existing discrepancy between experiment and theory for Ne 2p first-order nondipole parameters.

physics.atom-ph↗