arXiv subjects

John Saunders

Publications and source records attributed to John Saunders.

23 records · Page 2Linked to original sources

arXiv2014

Frequency Dependence of the Supersolid Signature in Polycrystalline 4He

We report studies, using a two mode torsional oscillator, of the putative supersolid signature in polycrystalline 4He. Measurements at two frequencies enable us to eliminate the viscoelastic contribution to the signature, and other instrumental effects arising from the temperature dependent shear modulus of the sample. The complex response function of the sample, encoded via its effective moment of inertia, shows an unexpected and unexplained frequency dependence. This cannot be accounted for by glassy dynamics within the sample. The results do not rule out the possibility of supersolidity in bulk solid 4He. ?

cond-mat.other↗

arXiv2013

Study of superfluid $^3$He under nanoscale confinement. A new approach to the investigation of superfluid $^3$He films

We review recent experiments in which superfluid $^3$He has been studied under highly controlled confinement in nanofluidic sample chambers. We discuss the experimental challenges and their resolution. These methods open the way to a systematic investigation of the superfluidity of $^3$He films, and the surface and edge excitations of topological superfluids.

cond-mat.other↗

arXiv2013

Current Sensing Noise Thermometry: A fast practical solution to low temperature measurement

We describe the design and performance of a series of fast, precise current sensing noise thermometers. The thermometers have been fabricated with a range of resistances from 1.290 $Ω$ down to 0.2 m$\mathrmΩ$. This results in either a thermometer that has been optimised for speed, taking advantage of the improvements in superconducting quantum interference device (SQUID) noise and bandwidth, or a thermometer optimised for ultra-low temperature measurement, minimising the system noise temperature. By using a single temperature calibration point, we show that noise thermometers can be used for accurate measurements over a wide range of temperatures below 4 K. Comparisons with a melting curve thermometer, a calibrated germanium thermometer and a pulsed platinum nuclear magnetic resonance thermometer are presented. For the 1.290 $\mathrmΩ$ resistance we measure a 1 % precision in just 100 ms, and have shown this to be independent of temperature.

cond-mat.supr-con↗

arXiv2013

Micro-coil detection of Nuclear Magnetic Resonance for nanofluidic samples

We have developed a novel dc SQUID system with a micro-coil input circuit to act as a local probe of quantum matter and nanosystems. The planar niobium micro-coil pickup loop is located remotely from the SQUID, coupled through a superconducting twisted pair, enabling the sample to be at microkelvin temperatures. A high degree of coupling between the coil and the region of interest of similar dimensions (up to ~ 100 microns) can be achieved. We report nuclear magnetic resonance (NMR) measurements to characterise the sensitivity of these coils to 3He in the gas phase at 4.2 K in a 30 mT magnetic field.

cond-mat.supr-con↗

arXiv2013

A microkelvin cryogen-free experimental platform with integrated noise thermometry

We report experimental demonstration of the feasibility of reaching temperatures below 1 mK using cryogen-free technology. Our prototype system comprises an adiabatic nuclear demagnetisation stage, based on hyperfine-enhanced nuclear magnetic cooling, integrated with a commercial cryogen-free dilution refrigerator and 8 T superconducting magnet. Thermometry was provided by a current-sensing noise thermometer. The minimum temperature achieved at the experimental platform was 600 μK. The platform remained below 1 mK for over 24 hours, indicating a total residual heat-leak into the experimental stage of 5 nW. We discuss straightforward improvements to the design of the current prototype that are expected to lead to enhanced performance. This opens the way to widening the accessibility of temperatures in the microkelvin regime, of potential importance in the application of strongly correlated electron states in nanodevices to quantum computing.

physics.ins-det↗