arXiv subjects

N. S. Sullivan

Publications and source records attributed to N. S. Sullivan.

45 records · Page 3Linked to original sources

arXiv2004

Tilt Induced Localization and Delocalization in the Second Landau Level

We have investigated the behavior of electronic phases of the second Landau level under tilted magnetic fields. The fractional quantum Hall liquids at $ν=$2+1/5 and 2+4/5 and the solid phases at $ν=$2.30, 2.44, 2.57, and 2.70 are quickly destroyed with tilt. This behavior can be interpreted as a tilt driven localization of the 2+1/5 and 2+4/5 fractional quantum Hall liquids and a delocalization through melting of solid phases in the top Landau level, respectively. The evolution towards the classical Hall gas of the solid phases is suggestive of antiferromagnetic ordering.

cond-mat.mes-hall↗

arXiv2004

Electron correlation in the second Landau level; a competition between many, nearly degenerate quantum phases

At a very low temperature of 9mK, electrons in the 2nd Landau level of an extremely high mobility two-dimensional electron system exhibit a very complex electronic behavior. With varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed $ν=2+2/5$ state separated from the even-denominator $ν=2+1/2$ state by an insulating phase and a $ν=2+2/7$ and $ν=2+1/5$ state surrounded by such phases. A developing plateau at $ν=2+3/8$ points to the existence of other even-denominator states.

cond-mat.mes-hall↗

arXiv2003

An Improved RF Cavity Search for Halo Axions

The axion is a hypothetical elementary particle and cold dark matter candidate. In this RF cavity experiment, halo axions entering a resonant cavity immersed in a static magnetic field convert into microwave photons, with the resulting photons detected by a low-noise receiver. The ADMX Collaboration presents new limits on the axion-to-photon coupling and local axion dark matter halo mass density from a RF cavity axion search in the axion mass range 1.9-2.3 microeV, broadening the search range to 1.9-3.3 microeV. In addition, we report first results from an improved analysis technique.

astro-ph↗

arXiv2003

Orientational Ordering in Monolayers of Ortho-Para Hydrogen

We discuss orientational ordering in monolayers of solid hydrogen in view of recent experimental findings in NMR studies of (\QTR{it}{ortho)}$_{c}$-(\QTR{it}{para)}$_{1-c}$-hydrogen mixtures on boron nitride substrate. Analysis of the temperature-concentration behavior for the observed NMR frequency splitting is given on the basis of a two-dimension ($J=1)_{c}$-($J=0)_{1-c}$-rotor model with the quadrupolar coupling constant $Γ_{0}=0.50\pm 0.03$ $K$ and the crystalline field amplitude $V_{0}=0.70\pm 0.10$ $K$ derived from experiment. The two distinct para-rotational (PR) short-range ordered structures are described in terms of the local alignment and orientation of the polar principal axis, and are shown to be due to the interplay between the positive and negative crystalline fields. It is shown that the observed below the 2D site percolation threshold $c_{p}=0.72$ local structures are rather different from the ferromagnetic-type PR ordering suggested earlier by Harris and Berlinsky.

cond-mat.dis-nn↗

arXiv2002

New Evidence for Zero-Temperature Relaxation in a Spin-Polarized Fermi Liquid

Spin-echo experiments are reported for 3He-4He solutions under extremely high B/T conditions, B=14.75 T and T >= 1.73 mK. The 3He concentration x_3 was adjusted close to the value x_c = 3.8% at which the spin rotation parameter muM_0 vanishes. In this way the transverse and longitudinal spin diffusion coefficients D_perp, D_parallel were measured while keeping |muM_0| < 1. It is found that the temperature dependence of D_perp deviates strongly from 1/T^2, with anisotropy temperature T_a = 4.26 +/- 0.18 mK. This value is close to the theoretical prediction for dilute solutions, and suggests that spin current relaxation remains finite as the temperature tends to zero.

cond-mat↗

arXiv2002

Experimental Constraints on the Axion Dark Matter Halo Density

Most of the mass of the Milky Way galaxy is contributed by its halo, presumably in the form of non-interacting cold dark matter. The axion is a compelling cold dark matter candidate. We report results from a search which probes the local galactic halo axion density using the Sikivie RF cavity technique. Candidates over the frequency range 550$$ $\le$ f $\le$$$ 810 MHz (2.3$$ $μ$eV $\le$$$ m$_{a}$ $\le$ 3.4 $μ$eV) were investigated. The absence of a signal suggests that KSVZ axions contribute no more than 0.45 GeV/cm$^3$ of mass density to the local dark matter halo over this mass range.

astro-ph↗

arXiv2000

Electric field induced memory and aging effects in pure solid N_2

We report combined high sensitivity dielectric constant and heat capacity measurements of pure solid N_2 in the presence of a small external ac electric field in the audio frequency range. We have observed strong field induced aging and memory effects which show that field cooled samples may be prepared in a variety of metastable states leading to a free energy landscape with experimentally ``tunable'' barriers, and tunneling between these states may occur within laboratory time scales.

cond-mat.dis-nn↗

arXiv2000

A modified dual-slope method for heat capacity measurements of condensable gases

A high resolution non-adiabatic method for measuring the heat capacity ($C_v$) of bulk samples of condensable gases in the range 7.5-70 K is described. In this method $C_v$ is evaluated by directly comparing the heating and cooling rates of the sample temperature for two algebraically independent heat pulse sequences without explicit use of the thermal conductance between sample and thermal bath. A fully automated calorimeter for rapid measurement of $C_v$ of molecular solids utilizing this technique is presented.

cond-mat.mtrl-sci↗

arXiv1999

Dielectric anomalies of solid CO and N_2 in the audio frequency range

We report the first audio frequency dielectric constant measurements of CO and N_2 in their solid phases. We have observed several new features, including (1) strong hysteresis effects above an onset temperature $T_{h} \simeq 42 K$ in the β-phase of pure N_2, (2) absence of the expected short range antiferroelectric dipolar ordering in CO down to 4.2 K, and (3) anomalous temperature dependence of the dielectric constant in the α-phases of both CO and N_2. Quantum mechanical treatment of the molecular rotation explains some of the observed anomalies in the α-phase, but the strong hysteresis indicates that pure geometrical frustration plays a significant role in the β-phase.

cond-mat.mtrl-sci↗