225 research outputs found
Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films
Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in
contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and
out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films
using energy dependent soft x-ray momentum-resolved photoemission spectroscopy.
We show that the SS originates in nested regions confined to out-of-plane FSs,
which are drastically modified compared to in-plane FSs. From precise
reciprocal space maps in successive zones, we obtain the associated real space
compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis
quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a
SS and consistent with magneto-optic Kerr effect experiments. The results
reveal the importance of in-plane and out-of-plane FS mapping for ultrathin
films.Comment: 4 pages, 3 figure
Revisiting the valence-band and core-level photoemission spectra of NiO
We have re-examined the valence-band (VB) and core-level electronic structure
of NiO by means of hard and soft x-ray photoemission spectroscopy (PES). The
spectral weight of the lowest energy state found to be enhanced in the bulk
sensitive Ni 2p core-level PES. A configuration-interaction model including the
bound state screening has shown significant agreement with the core-level
spectra, and the off and on-resonance VB spectra. These results identify the
lowest energy state in core-level and VB-PES as the Zhang-Rice doublet bound
state, consistent with the spin-fermion model and recent ab initio calculation
with dynamical mean-field theory (LDA + DMFT).Comment: 4 pages, 3 figure
Experimental tests of reaction rate theory: Mu+H2 and Mu+D2
Copyright @ 1987 American Institute of Physics.Bimolecular rate constants for the thermal chemical reactions of muonium (Mu) with hydrogen and deuterium—Mu+H2→MuH+H and Mu+D2→MuD+D—over the temperature range 473–843 K are reported. The Arrhenius parameters and 1σ uncertainties for the H2 reaction are log A (cm3 molecule-1 s-1)=-9.605±0.074 and Ea =13.29±0.22 kcal mol-1, while for D2 the values are -9.67±0.12 and 14.73±0.40, respectively. These results are significantly more precise than those reported earlier by Garner et al. For the Mu reaction with H2 our results are in excellent agreement with the 3D quantum mechanical calculations of Schatz on the Liu–Siegbahn–Truhlar–Horowitz potential surface, but the data for both reactions compare less favorably with variational transition-state theory, particularly at the lower temperatures.NSERC (Canada) and the Petroleum Research Foundation of the Americal Chemical Society
Recoil effects of photoelectrons in a solid
High energy resolution C 1 photoelectron spectra of graphite were measured
at the excitation energy of 340, 870, 5950 and 7940eV using synchrotron
radiation. On increasing the excitation energy, i.e., increasing kinetic energy
of the photoelectron, the bulk origin C 1 peak position shifts to higher
binding energies. This systematic shift is due to the kinetic energy loss of
the high-energy photoelectron by kicking the atom, and is clear evidence of the
recoil effect in photoelectron emission. It is also observed that the
asymmetric broadening increases for the higher energy photoelectrons. All these
recoil effects can be quantified in the same manner as the M\"ossbauer effect
for -ray emission from nuclei embedded in crystals.Comment: 4 pages, 2 figure
Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO
The temperature () dependent metal-insulator transition (MIT) in VO is
investigated using bulk sensitive hard x-ray ( 8 keV) valence band, core
level, and V 2 resonant photoemission spectroscopy (PES). The valence
band and core level spectra are compared with full-multiplet cluster model
calculations including a coherent screening channel. Across the MIT, V 3
spectral weight transfer from the coherent ( final)
states at Fermi level to the incoherent ( final)
states, corresponding to the lower Hubbard band, lead to gap-formation. The
spectral shape changes in V 1 and V 2 core levels as well as the valence
band are nicely reproduced from a cluster model calculations, providing
electronic structure parameters. Resonant-PES finds that the
states resonate across the V 2 threshold in
addition to the and states. The results support
a Mott-Hubbard transition picture for the first order MIT in VO.Comment: 6 pages, 3 figures. to be published in Phys. Rev.
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