48 research outputs found
4 electron temperature driven ultrafast electron localization
Valence transitions in strongly correlated electron systems are caused by
orbital hybridization and Coulomb interactions between localized and
delocalized electrons. The transition can be triggered by changes in the
electronic structure and is sensitive to temperature variations, applications
of magnetic fields, and physical or chemical pressure. Launching the transition
by photoelectric fields can directly excite the electronic states and thus
provides an ideal platform to study the correlation among electrons on
ultrafast timescales. The EuNi(SiGe) mixed-valence
metal is an ideal material to investigate the valence transition of the Eu ions
via the amplified orbital hybridization by the photoelectric field on
sub-picosecond timescales. A direct view on the 4 electron occupancy of the
Eu ions is required to understand the microscopic origin of the transition.
Here we probe the 4 electron states of EuNi(SiGe)
at the sub-ps timescale after photoexcitation by X-ray absorption spectroscopy
across the Eu -absorption edge. The observed spectral changes due to the
excitation indicate a population change of total angular momentum multiplet
states = 0, 1, 2, and 3 of Eu, and the Eu = 7/2 multiplet
state caused by an increase in 4 electron temperature that results in a 4
localization process. This electronic temperature increase combined with
fluence-dependent screening accounts for the strongly non-linear effective
valence change. The data allow us to extract a time-dependent determination of
an effective temperature of the 4 shell, which is also of great relevance in
the understanding of metallic systems' properties, such as the ultrafast
demagnetization of ferromagnetic rare-earth intermetallics and their
all-optical magnetization switching.Comment: 19 pages, 9 figure
Magnetic anisotropy driven by ligand in 4d transition metal oxide SrRuO3
The origin of magnetic anisotropy in magnetic compounds is a longstanding
issue in solid state physics and nonmagnetic ligand ions are considered to
contribute little to magnetic anisotropy. Here, we introduce the concept of
ligand driven magnetic anisotropy in a complex transition-metal oxide. We
conducted X ray absorption and X ray magnetic circular dichroism spectroscopies
at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic
variation of the sample thickness in the range below 10 nm allowed us to
control the localization of Ru 4d t2g states, which affects the magnetic
coupling between the Ru and O ions. We found that the orbital magnetization of
the ligand induced via hybridization with the Ru 4d orbital determines the
magnetic anisotropy in SrRuO3
Broken Screw Rotational Symmetry in the Near-Surface Electronic Structure of -Stacked Crystals
We investigate the electronic structure of - and
by angle-resolved photoemission spectroscopy (ARPES) and
photoemission intensity calculations. Although in bulk form, these materials
are expected to exhibit band degeneracy in the plane due to screw
rotation and time-reversal symmetries, we observe gapped band dispersion near
the surface. We extract from first-principles calculations the near-surface
electronic structure probed by ARPES and find that the calculated photoemission
spectra from the near-surface region reproduce the gapped ARPES spectra. Our
results show that the near-surface electronic structure can be qualitatively
different from the bulk one due to partially broken nonsymmorphic symmetries.Comment: 6+11 pages, 4+13 figure
Interfacial-hybridization-modified Ir Ferromagnetism and Electronic Structure in LaMnO/SrIrO Superlattices
Artificially fabricated 3/5 superlattices (SLs) involve both strong
electron correlation and spin-orbit coupling in one material by means of
interfacial 3-5 coupling, whose mechanism remains mostly unexplored. In
this work we investigated the mechanism of interfacial coupling in
LaMnO/SrIrO SLs by several spectroscopic approaches. Hard x-ray
absorption, magnetic circular dichroism and photoemission spectra evidence the
systematic change of the Ir ferromagnetism and the electronic structure with
the change of the SL repetition period. First-principles calculations further
reveal the mechanism of the SL-period dependence of the interfacial electronic
structure and the local properties of the Ir moments, confirming that the
formation of Ir-Mn molecular orbital is responsible for the interfacial
coupling effects. The SL-period dependence of the ratio between spin and
orbital components of the Ir magnetic moments can be attributed to the
realignment of electron spin during the formation of the interfacial molecular
orbital. Our results clarify the nature of interfacial coupling in this
prototypical 3/5 SL system and the conclusion will shed light on the
study of other strongly correlated and spin-orbit coupled oxide
hetero-interfaces
Histological and Nuclear Medical Comparison of Inflammation After Hemostasis with Non-Thermal Plasma and Thermal Coagulation
The objective of this study is to examine the invasiveness of hemostasis by non-thermal plasma (NTP) compared with hemostasis by thermal coagulation (TC). The inflammation recovery process after hemostasis by TC and NTP was compared by using histological methods and nuclear medical molecular imaging. The necrotic areas in the NTP group disappeared after 5 days, whereas they remained 15 days after hemostasis in the TC group. The accumulation of 2-deoxy-2-[F-18] fluoro-D-glucopyranose (F-18-FDG), which reflects the existence of inflammatory cells, was higher in the TC group than in the NTP group on day 15. Thus, this study indicates that hemostasis by NTP is less inflammatory than TC. This report is the first to evaluate inflammation that occurred after hemostasis with medical devices noninvasively