Normal-mode splitting in the coupled system of hybridized nuclear magnons and microwave photons

In the weak ferromagnetic MnCO$_3$ system, a low-frequency collective spin excitation (magnon) is the hybridized oscillation of nuclear and electron spins coupled through the hyperfine interaction. By using a split-ring resonator, we performed transmission spectroscopy measurements of MnCO$_3$ system and observed, for the first time, avoiding crossing between the hybridized nuclear-electron magnon mode and the resonator mode in the NMR-frequency range. The splitting strength is quite large due to the large spin density of $^{55}$Mn, and the cooperativity value $C=0.2$ (magnon-photon coupling parameter) is close to the conditions of strong coupling. The results reveal a new class of spin systems, in which the coupling between nuclear spins and photons is mediated by electron spins via the hyperfine interaction, and in which the similar normal-mode splitting of the hybridized nuclear magnon mode and the resonator mode can be observed.Comment: 5 pages, 3 figure

Evidence for magnon BEC in superfluid 3He-A

International audienceThe phenomenon of phase-coherent precession of magnetization in superfluid 3He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession have been observed in 3He-B: homogeneously precessing domain (HPD); persistent signal formed byQ-balls at very low temperatures; coherent precession with fractional magnetization; and two new modes of the coherent precession in compressed aerogel. Here we demonstrate the evidence of magnons Bose-Einstein condensation in 3He-A in a compressed aerogel

Silicon Vibrating Wires at Low Temperatures

International audienceNowadays microfabrication techniques originating from micro-electronics enable to create mechanical objects of micron-size. The field of Micro-Electro Mechanical devices(MEMs) is continuously expanding, with an amazingly broad range of applications at room temperature. Vibrating objects (torsional oscillators, vibrating wires) widely used at low températures to study quantum fluids, can be replaced advantageously by Silicon MEMs. In this letter we report on the study of Silicon vibrating wire devices. A goal-post structure covered with a metal layer is driven at resonance by the Laplace force acting on a current in a magnetic field, while the induced voltage arising from the cut magnetic flux allows to detect the motion. The characteristics of the resonance have been studied from 10 mK to 30 K, in vacuum and in 4He gas. In this article, we focus on the results obtained above 1.5 K, in vacuum and gas, and introduce some features observed at lower temperatures. The resonant properties can be quantitatively understood by means of simple models, from the linear regime to a highly non-linear response at strong drives. We demonstrate that the non-linearity is mostly due to the geometry of the vibrators. We also show that in our device the friction mechanisms originate in the metallic layers, and can be fully characterized. The interaction with 4He gas is fit to theory without adjustable parameters

Heat capacity of adsorbed Helium-3 at ultra-low temperatures

International audienceWe report on direct measurements of the heat capacity of monolayers of 3He adsorbed on the surface of a cell filled with superfluid 3He. We found that at ultra low temperatures the surface 3He heat capacity dominates over the heat capacity of the bulk liquid 3He. The replacement of adsorbed 3He by 4He changes the heat capacity of the sample by an order of magnitude. These investigations were made in the framework of the "ULTIMA" project, a dark matter detector based on superfluid 3He in the limit of ultra low temperatures

ULTIMA: Magnetic field dependence of the calibration factor

International audienceULTIMA is a project which proposes to use superfluid 3He as a sensitive medium for direct dark matter search. In this paper we report on new, detailed calibrations of our bolometric cells as a function of the magnetic field. An influence on the order of 20% is observed for magnetic fields up to 330 mT. Simultaneous measurements of neutron capture and heater events, releasing both a well defined energy, show that the effect is similar for both, and that it is possible to maintain a good calibration by an appropriate correction

Magnetic susceptibility of liquid 3He

International audience3He is a model of Fermi liquid, isotropic, its Fermi temperature is attainable and the interaction between atoms can be controlled by changing the pressure on the liquid. In this paper we present accurate cw-NMR measurements of the nuclear magnetic susceptibility of liquid 3He as a function of temperature and pressure. The emphasis has been placed in reliable thermometry, 3He pressure measurements directly in the cell to increase the measuring range until solidification, and an accurate characterization of the NMR spectrometer. Our measurements give effective Fermi temperatures substantially lower than former results