231 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
Evidence for mass renormalization in LaNiO$"" sub 3_: an in situ soft x-ray photoemission study of epitaxial films
We investigate the electronic structure of high-quality single-crystal
LaNiO (LNO) thin films using in situ photoemission spectroscopy (PES). The
in situ high-resolution soft x-ray PES measurements on epitaxial thin films
reveal the intrinsic electronic structure of LNO. We find a new sharp feature
in the PES spectra crossing the Fermi level, which is derived from the
correlated Ni 3 electrons. This feature shows significant enhancement
of spectral weight with decreasing temperature. From a detailed analysis of
resistivity data, the enhancement of spectral weight is attributed to
increasing electron correlations due to antiferromagnetic fluctuations.Comment: 4 pages, 4 figures. submitted to Phys. Rev.
Temperature-Dependence of Magnetically-Active Charge Excitations in Magnetite across the Verwey Transition
We have studied the electronic structure of bulk single crystals and
epitaxial films of magnetite FeO. Fe core-level spectra show clear
differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission
spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra
exhibit temperature ()-dependent charge excitations across the Verwey
transition at =122 K, which is missing in the surface-sensitive spectra.
An extended impurity Anderson model full-multiplet analysis reveals roles of
the three distinct Fe-species (A-Fe, B-Fe, B-Fe) below
for the Fe spectra, and its dependent evolution. The Fe
HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic
phase of magnetized 100-nm-thick films. The model calculations also reproduce
the MCD and identify the magnetically distinct sites associated with the charge
excitations. Valence band HAXPES shows finite density of states at for
the polaronic metal with remnant order above , and a clear gap formation
below . The results indicate that the Verwey transition is driven by
changes in the strongly correlated and magnetically active B-Fe and
B-Fe electronic states, consistent with resistivity and bulk-sensitive
optical spectra.Comment: 5 pages, 4 figures Accepted in Physical Review Letter
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