I21-Resonant Inelastic X-ray Scattering (RIXS)
|
C. D.
Dashwood
,
A.
Geondzhian
,
J. G.
Vale
,
A. C.
Pakpour-Tabrizi
,
C. A.
Howard
,
Q.
Faure
,
L. S. I.
Veiga
,
D.
Meyers
,
G. S.
Chiuzbaian
,
A.
Nicolaou
,
N.
Jaouen
,
R. B.
Jackman
,
A.
Nag
,
M.
Garcia-Fernandez
,
Ke-Jin
Zhou
,
A. C.
Walters
,
K.
Gilmore
,
D. F.
Mcmorrow
,
M. P. M.
Dean
Diamond Proposal Number(s):
[22695]
Open Access
Abstract: Interactions between electrons and lattice vibrations are responsible for a wide range of material properties and applications. Recently, there has been considerable interest in the development of resonant inelastic x-ray scattering (RIXS) as a tool for measuring electron-phonon (
e
-ph) interactions. Here, we demonstrate the ability of RIXS to probe the interaction between phonons and specific electronic states both near to, and away from, the Fermi level. We perform carbon
K
-edge RIXS measurements on graphite, tuning the incident x-ray energy to separately probe the interactions of the
π
∗
and
σ
∗
electronic states. Our high-resolution data reveal detailed structure in the multiphonon RIXS features that directly encodes the momentum dependence of the
e
-ph interaction strength. We develop a Green’s-function method to model this structure, which naturally accounts for the phonon and interaction-strength dispersions, as well as the mixing of phonon momenta in the intermediate state. This model shows that the differences between the spectra can be fully explained by contrasting trends of the
e
-ph interaction through the Brillouin zone, being concentrated at the
Γ
and
K
points for the
π
∗
states while being significant at all momenta for the
σ
∗
states. Our results advance the interpretation of phonon excitations in RIXS and extend its applicability as a probe of
e
-ph interactions to a new range of out-of-equilibrium situations.
|
Dec 2021
|
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I06-Nanoscience
|
Yujia
Wang
,
Qing
He
,
Wenmei
Ming
,
Mao-Hua
Du
,
Nianpeng
Lu
,
Clodomiro
Cafolla
,
Jun
Fujioka
,
Qinghua
Zhang
,
Ding
Zhang
,
Shengchun
Shen
,
Yingjie
Lyu
,
Alpha T.
N’diaye
,
Elke
Arenholz
,
Lin
Gu
,
Cewen
Nan
,
Yoshinori
Tokura
,
Satoshi
Okamoto
,
Pu
Yu
Open Access
Abstract: Epitaxial strain provides important pathways to control the magnetic and electronic states in transition-metal oxides. However, the large strain is usually accompanied by a strong reduction of the oxygen-vacancy formation energy, which hinders the direct manipulation of their intrinsic properties. Here, using a postdeposition ozone annealing method, we obtain a series of oxygen stoichiometric
SrCoO
3
thin films with the tensile strain up to 3.0%. We observe a robust ferromagnetic ground state in all strained thin films, while interestingly the tensile strain triggers a distinct metal-to-insulator transition along with the increase of the tensile strain. The persistent ferromagnetic state across the electrical transition therefore suggests that the magnetic state is directly correlated with the localized electrons, rather than the itinerant ones, which then calls for further investigation of the intrinsic mechanism of this magnetic compound beyond the double-exchange mechanism.
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May 2020
|
|
I05-ARPES
|
Raphael C.
Vidal
,
Alexander
Zeugner
,
Jorge I.
Facio
,
Rajyavardhan
Ray
,
M. Hossein
Haghighi
,
Anja U. b.
Wolter
,
Laura T.
Corredor Bohorquez
,
Federico
Caglieris
,
Simon
Moser
,
Tim
Figgemeier
,
Thiago R. F.
Peixoto
,
Hari Babu
Vasili
,
Manuel
Valvidares
,
Sungwon
Jung
,
Cephise
Cacho
,
Alexey
Alfonsov
,
Kavita
Mehlawat
,
Vladislav
Kataev
,
Christian
Hess
,
Manuel
Richter
,
Bernd
Büchner
,
Jeroen
Van Den Brink
,
Michael
Ruck
,
Friedrich
Reinert
,
Hendrik
Bentmann
,
Anna
Isaeva
Diamond Proposal Number(s):
[22468]
Open Access
Abstract: Combinations of nontrivial band topology and long-range magnetic order hold promise for realizations of novel spintronic phenomena, such as the quantum anomalous Hall effect and the topological magnetoelectric effect. Following theoretical advances, material candidates are emerging. Yet, so far a compound that combines a band-inverted electronic structure with an intrinsic net magnetization remains unrealized.
MnBi
2
Te
4
has been established as the first antiferromagnetic topological insulator and constitutes the progenitor of a modular
(
Bi
2
Te
3
)
n
(
MnBi
2
Te
4
)
series. Here, for
n
=
1
, we confirm a nonstoichiometric composition proximate to
MnBi
4
Te
7
. We establish an antiferromagnetic state below 13 K followed by a state with a net magnetization and ferromagnetic-like hysteresis below 5 K. Angle-resolved photoemission experiments and density-functional calculations reveal a topologically nontrivial surface state on the
MnBi
4
Te
7
(
0001
)
surface, analogous to the nonmagnetic parent compound
Bi
2
Te
3
. Our results establish
MnBi
4
Te
7
as the first band-inverted compound with intrinsic net magnetization providing a versatile platform for the realization of magnetic topological states of matter.
|
Dec 2019
|
|
I05-ARPES
|
Y. j.
Chen
,
L. x.
Xu
,
J. h.
Li
,
Y. w.
Li
,
H. y.
Wang
,
C. f.
Zhang
,
H.
Li
,
Y.
Wu
,
A. j.
Liang
,
C.
Chen
,
S. W.
Jung
,
C.
Cacho
,
Y. h.
Mao
,
S.
Liu
,
M. x.
Wang
,
Y. f.
Guo
,
Y.
Xu
,
Z. k.
Liu
,
L. x.
Yang
,
Y. l.
Chen
Diamond Proposal Number(s):
[23648, 24827]
Open Access
Abstract: The intrinsic magnetic topological insulator
MnBi
2
Te
4
exhibits rich topological effects such as quantum anomalous Hall effect and axion electrodynamics. Here, by combining the use of synchrotron and laser light sources, we carry out comprehensive and high-resolution angle-resolved photoemission spectroscopy studies on
MnBi
2
Te
4
and clearly identify its topological electronic structure. In contrast to theoretical predictions and previous studies, we observe topological surface states with diminished gap forming a characteristic Dirac cone. We argue that the topological surface states are mediated by multidomains of different magnetization orientations. In addition, the temperature evolution of the energy bands clearly reveals their interplay with the magnetic phase transition by showing interesting differences between the bulk and surface states, respectively. The investigation of the detailed electronic structure of
MnBi
2
Te
4
and its temperature evolution provides important insight into not only the exotic properties of
MnBi
2
Te
4
, but also the generic understanding of the interplay between magnetism and topological electronic structure in magnetic topological quantum materials.
|
Nov 2019
|
|
I09-Surface and Interface Structural Analysis
|
Benedikt P.
Klein
,
Nadine J.
Van Der Heijden
,
Stefan R.
Kachel
,
Markus
Franke
,
Claudio K.
Krug
,
Katharina K.
Greulich
,
Lukas
Ruppenthal
,
Philipp
Müller
,
Phil
Rosenow
,
Shayan
Parhizkar
,
Francois C.
Bocquet
,
Martin
Schmid
,
Wolfgang
Hieringer
,
Reinhard J.
Maurer
,
Ralf
Tonner
,
Christian
Kumpf
,
Ingmar
Swart
,
J. Michael
Gottfried
Diamond Proposal Number(s):
[16259]
Open Access
Abstract: The interaction of carbon-based aromatic molecules and nanostructures with metals can strongly depend on the topology of their π-electron systems. This is shown with a model system using the isomers azulene, which has a nonalternant π system with a 5-7 ring structure, and naphthalene, which has an alternant π system with a 6-6 ring structure. We found that azulene can interact much more strongly with metal surfaces. On copper (111), its zero-coverage desorption energy is 1.86 eV, compared to 1.07 eV for naphthalene. The different bond strengths are reflected in the adsorption heights, which are 2.30 Å for azulene and 3.04 Å for naphthalene, as measured by the normal incidence x-ray standing wave technique. These differences in the surface chemical bond are related to the electronic structure of the molecular π systems. Azulene has a lowlying LUMO that is close to the Fermi energy of Cu and strongly hybridizes with electronic states of the surface, as is shown by photoemission, near-edge x-ray absorption fine-structure, and scanning tunneling microscopy data in combination with theoretical analysis. According to density functional theory calculations, electron donation from the surface into the molecular LUMO leads to negative charging and deformation of the adsorbed azulene. Noncontact atomic force microscopy confirms the deformation, while Kelvin probe force microscopy maps show that adsorbed azulene partially retains its in-plane dipole. In contrast, naphthalene experiences only minor adsorption-induced changes of its electronic and geometric structure. Our results indicate that the electronic properties of metal-organic interfaces, as they occur in organic (opto)electronic devices, can be tuned through modifications of the π topology of the molecular organic semiconductor, especially by introducing 5-7 ring pairs as functional structural elements.
|
Feb 2019
|
|
I10-Beamline for Advanced Dichroism
|
Jason D.
Hoffman
,
Brian J.
Kirby
,
Jihwan
Kwon
,
Gilberto
Fabbris
,
D.
Meyers
,
John W.
Freeland
,
Ivar
Martin
,
Olle G.
Heinonen
,
Paul
Steadman
,
Hua
Zhou
,
Christian M.
Schlepütz
,
Mark P. m.
Dean
,
Suzanne G. e.
Te Velthuis
,
Jian-Min
Zuo
,
Anand
Bhattacharya
Diamond Proposal Number(s):
[9626]
Open Access
Abstract: Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects, and locally broken symmetries. We report on the discovery of a noncollinear magnetic structure in superlattices of the ferromagnetic metallic oxide La2/3Sr1/3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependence of the noncollinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni2+ states. Our work suggests a new approach to engineering noncollinear spin textures in metallic oxide heterostructures.
|
Nov 2016
|
|
I05-ARPES
|
A.
Tamai
,
Q. S.
Wu
,
I.
Cucchi
,
F. Y.
Bruno
,
S.
Riccò
,
T. K.
Kim
,
M.
Hoesch
,
C.
Barreteau
,
E.
Giannini
,
C.
Besnard
,
A. A.
Soluyanov
,
F.
Baumberger
Diamond Proposal Number(s):
[12404]
Open Access
Abstract: We report a combined experimental and theoretical study of the candidate type-II Weyl semimetal
MoTe2. Using laser-based angle-resolved photoemission, we resolve multiple distinct Fermi arcs on the inequivalent top and bottom (001) surfaces. All surface states observed experimentally are reproduced by an electronic structure calculation for the experimental crystal structure that predicts a topological Weyl semimetal state with eight type-II Weyl points. We further use systematic electronic structure calculations simulating different Weyl point arrangements to discuss the robustness of the identified Weyl semimetal state and the topological character of Fermi arcs in MoTe2.
|
Aug 2016
|
|
|
|
Abstract: Magnetite, Fe3O4, is the first magnetic material discovered and utilized by mankind in Ancient Greece, yet it still attracts attention due to its puzzling properties. This is largely due to the quest for a full and coherent understanding of the Verwey transition that occurs at TV=124K and is associated with a drop of electric conductivity and a complex structural phase transition. A recent detailed analysis of the structure, based on single crystal diffraction, suggests that the electron localization pattern contains linear three-Fe-site units, the so-called trimerons. Here, we show that whatever the electron localization pattern is, it partially survives up to room temperature as short-range correlations in the high-temperature cubic phase, easily discernible by diffuse scattering. Additionally, ab initio electronic structure calculations reveal that characteristic features in these diffuse scattering patterns can be correlated with the Fermi surface topology.
|
Mar 2014
|
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