4,886 research outputs found
Role of interactions in 87Rb-40K Bose-Fermi mixtures in a 3d optical lattice
We investigate the effect of interspecies interaction on a degenerate mixture
of bosonic 87Rb and fermionic 40K atoms in a three-dimensional optical lattice
potential. Using a Feshbach resonance, the 87Rb-40K interaction is tuned over a
wide range. Through an analysis of the 87Rb momentum distribution, we find a
pronounced asymmetry between strong repulsion and strong attraction. In the
latter case, the Bose-Hubbard parameters are renormalized due to self-trapping,
leading to a marked shift in the superfluid to Mott insulator transition with
increasing Bose-Fermi interaction.Comment: 5 pages, 4 figure
Quantum Coherence of Image-Potential States
The quantum dynamics of the two-dimensional image-potential states in front
of the Cu(100) surface is measured by scanning tunneling microscopy (STM) and
spectroscopy (STS). The dispersion relation and the momentum resolved
phase-relaxation time of the first image-potential state are determined from
the quantum interference patterns in the local density of states (LDOS) at step
edges. It is demonstrated that the tip-induced Stark shift does not affect the
motion of the electrons parallel to the surface.Comment: Submitted to Phys. Rev. Lett., 4 pages, 4 figures; corrected typos,
minor change
Large angle magnetization dynamics measured by time-resolved ferromagnetic resonance
A time-resolved ferromagnetic resonance technique was used to investigate the
magnetization dynamics of a 10 nm thin Permalloy film. The experiment consisted
of a sequence of magnetic field pulses at a repetition rate equal to the
magnetic systems resonance frequency. We compared data obtained by this
technique with conventional pulsed inductive microwave magnetometry. The
results for damping and frequency response obtained by these two different
methods coincide in the limit of a small angle excitation. However, when
applying large amplitude field pulses, the magnetization had a non-linear
response. We speculate that one possible cause of the nonlinearity is related
to self-amplification of incoherence, known as the Suhl instabilities.Comment: 23 pages, 8 figures, submitted to PR
Modification of spintronic terahertz emitter performance through defect engineering
Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for
the generation of THz radiation based on spin-to-charge conversion in the
layers. The key technological and scientific challenge of THz spintronic
emitters is to increase their intensity and frequency bandwidth. Our work
reveals the factors to engineer spintronic Terahertz generation by introducing
the scattering lifetime and the interface transmission for spin polarized,
non-equilibrium electrons. We clarify the influence of the electron-defect
scattering lifetime on the spectral shape and the interface transmission on the
THz amplitude, and how this is linked to structural defects of bilayer
emitters. The results of our study define a roadmap of the properties of
emitted as well as detected THz-pulse shapes and spectra that is essential for
future applications of metallic spintronic THz emitters.Comment: 33 pages, 13 figure
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