Atomic-like spin noise in solid-state demonstrated with manganese in cadmium telluride

Spin noise spectroscopy is an optical technique which can probe spin resonances non-perturbatively. First applied to atomic vapours, it revealed detailed information about nuclear magnetism and the hyperfine interaction. In solids, this approach has been limited to carriers in semiconductor heterostructures. Here we show that atomic-like spin fluctuations of Mn ions diluted in CdT e (bulk and quantum wells) can be detected through the Kerr rotation associated to excitonic transitions. Zeeman transitions within and between hyperfine multiplets are clearly observed in zero and small magnetic fields and reveal the local symmetry because of crystal field and strain. The linewidths of these resonances are close to the dipolar limit. The sensitivity is high enough to open the way towards the detection of a few spins in systems where the decoherence due to nuclear spins can be suppressed by isotopic enrichment, and towards spin resonance microscopy with important applications in biology and materials science

Spatiotemporal electronic spin fluctuations in random nuclear fields in n-CdTe

We report on the dynamics of electron spins in n-doped CdTe layers that differs significantly from the expected response derived from the studies dedicated to electron spin relaxation in n-GaAs. At zero magnetic field, the electron spin noise spectra exhibit a two-peak structure - a zero-frequency line and a satellite - that we attribute to the electron spin precession in a frozen random nuclear spin distribution. This implies a surprisingly long electron spin correlation time whatever the doping level, even above the Mott transition. Using spatiotemporal spin noise spectroscopy, we demonstrate that the observation of a satellite in the spin noise spectra and a fast spin diffusion are mutually exclusive. This is consistent with a shortening of the electron spin correlation time due to hopping between donors. We interpret our data via a model assuming that the low temperature spin relaxation is due to hopping between donors in presence of hyperfine and anisotropic exchange interactions. Most of our results can be interpreted in this framework. First, a transition from inhomogeneous to homogeneous broadening of the spin noise peaks and the disappearance of the satellite are observed when the hopping rate becomes larger than the Larmor period induced by the local nuclear fields. In the regime of homogeneous broadening the ratio between the spin diffusion constant and the spin relaxation rate has a value in good agreement with the Dresselhaus constant. In the regime of inhomogeneous broadening, most of the samples exhibit a broadening consistent with the distribution of local nuclear fields. We obtain a new estimate of the hyperfine constants in CdTe and a value of 0.10 Tesla for the maximum nuclear field. Finally, our study also reveals a puzzle as our samples behave as if the active donor concentration was reduced by several orders of magnitudes with respect to the nominal values.Comment: 9 pages, 7 figure

Interchangeability of Biosimilars: What Level of Clinical Evidence is Needed to Support the Interchangeability Designation in the United States

A biosimilar is a biologic drug that is highly similar to a reference (originator) product, with no clinically meaningful differences between the two products in safety, purity, and potency . Regulatory approval of a biosimilar is based on analytical, structural, and functional comparisons with the reference product, comparative nonclinical (in vivo) studies, clinical pharmacokinetics and/or pharmacodynamics, and immunogenicity. In addition, comparative clinical efficacy and safety assessments are usually conducted and, taken together, comprise the totality of the evidence supporting biosimilarity. For a biosimilar to meet the additional designation of interchangeability in the United States (US), the applicant must demonstrate that the biological drug can be expected to produce the same clinical result as the reference product in any given patient and if the biological drug is administered more than once to an individual, the risk in terms of safety or diminished efficacy of alternating or switching between the use of the biological drug and the reference product is no greater than the risk of using the reference product without such alternation or switch . The challenges faced in conducting clinical studies to support a designation of interchangeability, as defined in the final interchangeability guidance from the US Food and Drug Administration, are considered. Potential alternative approaches to generating adequate and sufficient clinical data to support a designation of interchangeability are also presented

Simultaneous measurements of nuclear spin heat capacity, temperature and relaxation in GaAs microstructures

Heat capacity of the nuclear spin system (NSS) in GaAs-based microstructures has been shown to be much greater than expected from dipolar coupling between nuclei, thus limiting the efficiency of NSS cooling by adiabatic demagnetization. It was suggested that quadrupole interaction induced by some small residual strain could provide this additional reservoir for the heat storage. We check and validate this hypothesis by combining nuclear spin relaxation measurements with adiabatic remagnetization and nuclear magnetic resonance experiments, using electron spin noise spectroscopy as a unique tool for detection of nuclear magnetization. Our results confirm and quantify the role of the quadrupole splitting in the heat storage within NSS and provide additional insight into fundamental, but still actively debated relation between a mechanical strain and the resulting electric field gradients in GaAs.Comment: 11 pages, 4 figures, 1 tabl