87 research outputs found
Depth-resolved measurements of the Meissner screening profile in surface-treated Nb
We report depth-resolved measurements of the Meissner screening profile in
several surface-treated Nb samples using low-energy muon spin rotation
(LE-SR). In these experiments, implanted positive muons, whose stopping
depths below Nb's surface were adjusted between ~10 nm to ~150 nm, reveal the
field distribution inside the superconducting element via their spin-precession
(communicated through their radioactive decay products). We compare how the
field screening is modified by different surface treatments commonly employed
to prepare superconducting radio frequency (SRF) cavities used in accelerator
beamlines. In contrast to an earlier report [A. Romanenko et al., Appl. Phys.
Lett. 104 072601 (2014)], we find no evidence for any "anomalous" modifications
to the Meissner profiles, with all data being well-described by a London model.
Differences in screening properties between surface treatments can be explained
by changes to the carrier mean-free-paths resulting from dopant profiles near
the material's surface.Comment: 15 pages, 5 figures, 2 table
Thin film and surface preparation chamber for the low energy muons spectrometer
We have designed and constructed a thin film preparation chamber with base
pressure of ~mbar. Currently, the chamber is equipped with
two large area evaporators (a molecular evaporator and an electron-beam
evaporator), an ion sputtering gun, a thickness monitor and a substrate heater.
It is designed such that it can handle large area thin film samples with a
future possibility to transfer them in vacuum directly to the low energy muons
(LEM) spectrometer or to other advanced characterization facilities in the
Quantum Matter and Materials Center (QMMC) which will be constructed in 2024.
Initial commissioning of the chamber resulted in high quality, large area and
uniform molecular films of CuPc and TbPc on various substrate materials. We
present first results from low energy SR (LE-SR) measurements on
these films.Comment: 8 pages, 7 figures, muSR2020 conference proceeding
The elevated Curie temperature and half-metallicity in the ferromagnetic semiconductor LaEuO
Here we study the effect of La doping in EuO thin films using SQUID
magnetometry, muon spin rotation (SR), polarized neutron reflectivity
(PNR), and density functional theory (DFT). The SR data shows that the
LaEuO is homogeneously magnetically ordered up to its
elevated . It is concluded that bound magnetic polaron behavior does
not explain the increase in and an RKKY-like interaction is
consistent with the SR data. The estimation of the magnetic moment by DFT
simulations concurs with the results obtained by PNR, showing a reduction of
the magnetic moment per LaEuO for increasing lanthanum doping.
This reduction of the magnetic moment is explained by the reduction of the
number of Eu-4 electrons present in all the magnetic interactions in EuO
films. Finally, we show that an upwards shift of the Fermi energy with La or Gd
doping gives rise to half-metallicity for doping levels as high as 3.2 %.Comment: 7 pages, 11 figure
Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators
We combine low energy muon spin rotation (LE-SR) and soft-X-ray
angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and
electronic properties of magnetically doped topological insulators,
(Bi,Sb)Te. We find that one achieves a full magnetic volume fraction in
samples of (V/Cr)(Bi,Sb)Te at doping levels x 0.16.
The observed magnetic transition is not sharp in temperature indicating a
gradual magnetic ordering. We find that the evolution of magnetic ordering is
consistent with formation of ferromagnetic islands which increase in number
and/or volume with decreasing temperature. Resonant ARPES at the V edge
reveals a nondispersing impurity band close to the Fermi level as well as V
weight integrated into the host band structure. Calculations within the
coherent potential approximation of the V contribution to the spectral function
confirm that this impurity band is caused by V in substitutional sites. The
implications of our results on the observation of the quantum anomalous Hall
effect at mK temperatures are discussed
Meissner screening as a probe for inverse superconductor-ferromagnet proximity effects
Funding: We acknowledge the support of the EPSRC through Grants No. EP/I031014/1, No. EP/J01060X, No. EP/J010634/1, No. EP/L015110/1, No. EP/R031924/1, and No. EP/R023522/1. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 743791 (SUPERSPIN). R.S. acknowledges funding under ETH Zurich Postdoctoral Fellowship 20-1FEL-36.We present experimental results on the observed flux screening in proximity coupled superconductor-ferromagnet thin film structures using Nb and Co as the superconductor and ferromagnet respectively. Using the low-energy muon-spin rotation technique to locally probe the magnetic flux density, we find that the addition of the ferromagnet (F) increases the total flux screening inside the superconductor. Two contributions can be distinguished. One is consistent with the predicted spin-polarization (or magnetic proximity) effect, while the other is in line with the recently emerged electromagnetic (EM) proximity models. Furthermore, we show that the addition of a few nanometers of a normal metallic layer between the Nb and the Co fully destroys the contribution due to electromagnetic proximity. This is unanticipated by the current theory models in which the magnetization in the F layer is assumed to be the only driving force for the EM effect and suggests the role of additional factors. Further experiments to explore the influence of the direction of the F magnetization also reveal deviations from theory. These findings are an important step forward in improving the theoretical description and understanding of proximity coupled systems.Publisher PDFPeer reviewe
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