arXiv subjects

B. P. Cowan

Publications and source records attributed to B. P. Cowan.

2 recordsLinked to original sources

arXiv2025

Thermodynamic Evidence for Density Wave Order in Two Dimensional 4He Supersolid

We previously reported the discovery of a two dimensional $^{4}$He supersolid; a state with intertwined density wave and superfluid order, observed in the second layer of $^{4}$He adsorbed on graphite. In this Letter we provide direct evidence for the density wave order, obtained by doping the layer with a small concentration of $^{3}$He atoms (impuritons). The heat capacity, magnetization and NMR relaxation times of the $^{3}$He were measured over a wide temperature range from 200 $μ$K to 500 mK. They provide evidence for changes in the ground state in the second layer film as the amount of $^{4}$He is increased at various fixed $^{3}$He doses. Clear evidence is obtained for a solid second layer film, matching the r\a'egime of superfluid response previously observed in pure $^{4}$He films.

cond-mat.other↗

arXiv2007

A nuclear magnetic resonance spectrometer for operation around 1 MHz with a sub 10 mK noise temperature based on a two stage dc SQUID

We have developed a nuclear magnetic resonance spectrometer with a series tuned input circuit for measurements on samples at millikelvin temperatures based on an integrated two-stage superconducting quantum interference device current sensor, with an energy sensitivty e = 26 +/-1 h when operated at 1.4K. To maximise the sensitivity both the NMR pickup coil and tuning capacitor need to be cooled, and the tank circuit parameters should be chosen to equalise the contributions from circulating current noise and voltage noise in the SQUID. A noise temperature TN = 7 +/-2 mK was measured, at a frequency of 0.884 MHz, with the circuit parameters close to optimum.

cond-mat.supr-con↗