Bruce Moskowitz

Anomalous rf magnetoresistance in copper at 4 K

We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f=1.2 GHz and at 4.4 K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the dc magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the rf surface current, but is also typical of superconductors.

Analysis of a microwave cavity detector coupled to a noisy amplifier

Abstract In a class of detectors for light pseudocscalar particles, a microwave cavity traps photons produced by the interaction of the particles with a strong magnetic field. The cavity strongly influences the signal and noise properties of the amplifier coupled to its output. We present the theory of a noisy amplifier coupled to a microwave cavity, along with experimental data for a cryogenic GaAsFET amplifier. The signal-to-noise ratio of the cavity-amplifier system is determined, and applications to the measurement of amplifier parameters are discussed.

Cosmic axion searches

Abstract Axions may have been created in the big bang and condensed into galactic halos to constitute the “dark” matter implied by galactic rotation curves. Experimental efforts are underway to detect these cosmic axions by conversion in the presence of an applied magnetic field to microwave photons which may be trapped by a resonant cavity. Present limits on abundance and coupling are less than three orders of magnitude higher than the values expected for all dark matter being axions; only a small part of the available phase space has been searched so far. Possible detector improvements and related laser production experiments are also discussed.

Improved Limits from the Galactic Axion Search

Cold, light axions are a leading candidate for the composition of dark matter in the galactic halo. An experiment designed to detect the microwave conversion signal from galactic axions has searched the frequency range 1.1–2.5 GHz. The updated limits on axion density and coupling are presented, and improvements for a possible second-generation experiment are discussed.

Anomalous rf magnetoresistance in copper at 4/degree/K

We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f = 1.2 GHz and at 4.4/degree/K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the DC magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the TF surface current. 17 refs., 4 figs., 1 tab.