High Sensitivity Magnetic Flux Sensors with Direct Voltage Readout Double Relaxation Oscillation SQUIDs

The experimental sensitivity of double relaxation oscillation SQUIDs (DROSs) has been compared with theory and with the results obtained by numerical simulations. The experimental sensitivity ranges from 60 to 13h, where h is Planck's constant, for relaxation frequencies from 0.4 up to 10 GHz. For low frequencies the DROS characteristics can be explained by thermal noise on the critical currents. For high frequencies, the voltage-flux characteristics and the sensitivity are limited by the plasma frequency. The cross-over frequency is at 2 GHz, which is about 2% of the plasma frequency of the DROS

Energetic perspective on emergent inductance exhibited by magnetic textures in the pinned regime

Spatially varying magnetic textures can exhibit electric-current-induced dynamics as a result of the spin-transfer torque effect. When such a magnetic system is electrically driven, an electric field is generated, which is called the emergent electric field. In particular, when magnetic-texture dynamics are induced under the application of an AC electric current, the emergent electric field also appears in an AC manner, notably, with an out-of-phase time profile, thus exhibiting inductor behaviour, often called an emergent inductor. Here we show that the emergent inductance exhibited by magnetic textures in the pinned regime can be explained in terms of the current-induced energy stored in the magnetic system. We numerically find that the inductance values defined from the emergent electric field and the current-induced magnetization-distortion energy, respectively, are in quantitative agreement in the so-called adiabatic limit. Our findings indicate that emergent inductors retain the basic concept of conventional inductors; that is, the energy is stored under the application of electric current

Superfluid Phase Stability of 3^3He in Axially Anisotropic Aerogel

Measurements of superfluid $^3$He in 98% aerogel demonstrate the existence of a metastable \emph{A}-like phase and a stable \emph{B}-like phase. It has been suggested that the relative stability of these two phases is controlled by anisotropic quasiparticle scattering in the aerogel. Anisotropic scattering produced by axial compression of the aerogel has been predicted to stabilize the axial state of superfluid $^3$He. To explore this possiblity, we used transverse acoustic impedance to map out the phase diagram of superfluid $^3$He in a $\sim 98$% porous silica aerogel subjected to 17% axial compression. We have previously shown that axial anisotropy in aerogel leads to optical birefringence and that optical cross-polarization studies can be used to characterize such anisotropy. Consequently, we have performed optical cross-polarization experiments to verify the presence and uniformity of the axial anisotropy in our aerogel sample. We find that uniform axial anisotropy introduced by 17% compression does not stabilize the \emph{A}-like phase. We also find an increase in the supercooling of the \emph{A}-like phase at lower pressure, indicating a modification to \emph{B}-like phase nucleation in \emph{globally} anisotropic aerogels.Comment: 4 pages, 4 figures, submitted to LT25 (25th International Conference on Low Temperature Physics