N. S. Sullivan

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 {micro}eV, broadening the search range to 1.9-3.3 {micro}eV. In addition, we report first results from an improved analysis technique.

Electron correlation in the second Landau level: a competition between many nearly degenerate quantum phases.

At a very low-temperature of 9 mK, electrons in the second Landau level of an extremely high-mobility two-dimensional electron system exhibit a very complex electronic behavior. With a 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 nu=2+2/5 state separated from the even-denominator nu=2+1/2 state by an insulating phase and a nu=2+2/7 and nu=2+1/5 state surrounded by such phases. A developing plateau at nu=2+3/8 points to the existence of other even-denominator states.

Results from a High-Sensitivity Search for Cosmic Axions

We report the first results of a high-sensitivity

Proposal for Axion Dark Matter Detection Using an LC Circuit

(\ensuremath{\sim}{10}^{\ensuremath{-}23}\mathrm{W})

Experimental Constraints on the Axion Dark Matter Halo Density

search for light halo axions through their conversion to microwave photons. At the 90% confidence level, we exclude a Kim-Shifman-Vainshtein-Zakharov axion of mass

Search for nonvirialized axionic dark matter

2.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}

Experimental studies of the fractional quantum Hall effect in the first excited Landau level

to

Design and performance of the ADMX SQUID-based microwave receiver

3.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\mathrm{eV}

Very high sensitivity ac capacitance bridge for the dielectric study of molecular solids at low temperatures

as the dark matter in the halo of our galaxy.

Precise and efficient in situ ortho — para-hydrogen converter

We show that dark matter axions cause an oscillating electric current to flow along magnetic field lines. The oscillating current induced in a strong magnetic field B0 produces a small magnetic field Ba. We propose to amplify and detect Ba using a cooled LC circuit and a very sensitive magnetometer. This appears to be a suitable approach to searching for axion dark matter in the 10(-7) to 10(-9)  eV mass range.