I13-1-Coherence
|
Open Access
Abstract: X-ray ptychography has revolutionized nanoscale phase contrast imaging at large-scale synchrotron sources in recent years. We present here the first successful demonstration of the technique in a small-scale laboratory setting. An experiment was conducted with a liquid metal-jet x-ray source and a single photon-counting detector with a high spectral resolution. The experiment used a spot size of
5
μ
m
to produce a ptychographic phase image of a Siemens star test pattern with a submicron spatial resolution. The result and methodology presented show how high-resolution phase contrast imaging can now be performed at small-scale laboratory sources worldwide.
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May 2021
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I05-ARPES
|
X.
Lou
,
T. l.
Yu
,
Y. h.
Song
,
C. h. P.
Wen
,
W. z.
Wei
,
A.
Leithe-Jasper
,
Z. f.
Ding
,
L.
Shu
,
S.
Kirchner
,
H. C.
Xu
,
R.
Peng
,
D. L.
Feng
Diamond Proposal Number(s):
[22518]
Abstract: CeOs
4
Sb
12
(COS) and
PrOs
4
Sb
12
(POS) are two representative compounds that provide the ideal vantage point to systematically study the physics of multi-
f
-electron systems. COS with Ce
4
f
1
, and POS with Pr
4
f
2
configurations show distinct properties of Kondo insulating and heavy fermion superconductivity, respectively. We unveiled the underlying microscopic origin by angle-resolved photoemission spectroscopy studies. Their eV-scale band structure matches well, representing the common characters of conduction electrons in
R
Os
4
Sb
12
systems (
R
=
rare
earth
). However,
f
electrons interact differently with conduction electrons in COS and POS. Strong hybridization between conduction electrons and
f
electrons is observed in COS with band dependent hybridization gaps, and the development of a Kondo insulating state is directly revealed. Although the ground state of POS is a singlet, finite but incoherent hybridization exists, which can be explained by the Kondo scattering with the thermally excited triplet crystalline electric field state. Our results help us to understand the intriguing properties in COS and POS, and provide a clean demonstration of the microscopic differences in heavy fermion systems with
4
f
1
and
4
f
2
configurations.
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Apr 2021
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I05-ARPES
|
R. C.
Vidal
,
H.
Bentmann
,
J. i.
Facio
,
T.
Heider
,
P.
Kagerer
,
C. I.
Fornari
,
T. R. F.
Peixoto
,
T.
Figgemeier
,
S.
Jung
,
Cephise
Cacho
,
B.
Büchner
,
J.
Van Den Brink
,
C. M.
Schneider
,
L.
Plucinski
,
E. F.
Schwier
,
K.
Shimada
,
M.
Richter
,
A.
Isaeva
,
F.
Reinert
Diamond Proposal Number(s):
[22468]
Abstract: Using angle-resolved photoelectron spectroscopy (ARPES), we investigate the surface electronic structure of the magnetic van der Waals compounds
MnBi
4
Te
7
and
MnBi
6
Te
10
, the
n
=
1
and 2 members of a modular
(
Bi
2
Te
3
)
n
(
MnBi
2
Te
4
)
series, which have attracted recent interest as intrinsic magnetic topological insulators. Combining circular dichroic, spin-resolved and photon-energy-dependent ARPES measurements with calculations based on density functional theory, we unveil complex momentum-dependent orbital and spin textures in the surface electronic structure and disentangle topological from trivial surface bands. We find that the Dirac-cone dispersion of the topologial surface state is strongly perturbed by hybridization with valence-band states for
Bi
2
Te
3
-terminated surfaces but remains preserved for
MnBi
2
Te
4
-terminated surfaces. Our results firmly establish the topologically nontrivial nature of these magnetic van der Waals materials and indicate that the possibility of realizing a quantized anomalous Hall conductivity depends on surface termination.
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Apr 2021
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
J.
Li
,
L.
Xu
,
M.
Garcia-Fernandez
,
A.
Nag
,
H. C.
Robarts
,
A. C.
Walters
,
X.
Liu
,
J.
Zhou
,
K.
Wohlfeld
,
J.
Van Den Brink
,
H.
Ding
,
K.-J.
Zhou
Open Access
Abstract: We explore the existence of the collective orbital excitations, orbitons, in the canonical orbital system
KCuF
3
using the Cu
L
3
-edge resonant inelastic x-ray scattering. We show that the nondispersive high-energy peaks result from the
Cu
2
+
d
d
orbital excitations. These high-energy modes display good agreement with the ab initio quantum chemistry calculation, indicating that the
d
d
excitations are highly localized. At the same time, the low-energy excitations present clear dispersion. They match extremely well with the two-spinon continuum following the comparison with Müller ansatz calculations. The localized
d
d
excitations and the observation of the strongly dispersive magnetic excitations suggest that the orbiton dispersion is below the resolution detection limit. Our results can reconcile with the strong local Jahn-Teller effect in
KCuF
3
, which predominantly drives orbital ordering.
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Mar 2021
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
J. q.
Lin
,
P.
Villar Arribi
,
G.
Fabbris
,
A. s.
Botana
,
D.
Meyers
,
H.
Miao
,
Y.
Shen
,
D. G.
Mazzone
,
J.
Feng
,
G. S.
Chiuzbaian
,
A.
Nag
,
A. C.
Walters
,
M.
Garcia-Fernandez
,
K.-J.
Zhou
,
J.
Pelliciari
,
I.
Jarrige
,
J. w.
Freeland
,
J.
Zhang
,
J. f.
Mitchell
,
V.
Bisogni
,
X.
Liu
,
M. r.
Norman
,
M. p. m.
Dean
Diamond Proposal Number(s):
[18519]
Abstract: The discovery of superconductivity in a
d
9
−
δ
nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni
L
-edge and O
K
-edge spectroscopy of the reduced
d
9
−
1
/
3
trilayer nickelates
R
4
Ni
3
O
8
(where
R
=
La
, Pr) and associated theoretical modeling. A magnon energy scale of
∼
80
meV
resulting from a nearest-neighbor magnetic exchange of
J
=
69
(
4
)
meV
is observed, proving that
d
9
−
δ
nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O
K
-edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.
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Feb 2021
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I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[20182]
Open Access
Abstract: A chiral bobber is a localized three-dimensional magnetization configuration, terminated by a singularity. Chiral bobbers coexist with magnetic skyrmions in chiral magnets, lending themselves to new types of skyrmion-complementary bits of information. However, the on-demand creation of bobbers, as well as their direct observation remained elusive. Here, we introduce a new mechanism for creating a stable chiral bobber lattice state via the proximity of two skyrmion species with comparable size. This effect is experimentally demonstrated in a
Cu
2
OSeO
3
/
[
Ta
/
CoFeB
/
MgO
]
4
heterostructure in which an exotic bobber lattice state emerges in the phase diagram of
Cu
2
OSeO
3
. To unambiguously reveal the existence of the chiral bobber lattice state, we have developed a novel characterization technique, magnetic truncation rod analysis, which is based on resonant elastic x-ray scattering.
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Jan 2021
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
A.
Nag
,
M.
Zhu
,
M.
Bejas
,
J.
Li
,
H. C.
Robarts
,
H.
Yamase
,
A. N.
Petsch
,
D.
Song
,
H.
Eisaki
,
A. C.
Walters
,
M.
Garcia-Fernandez
,
A.
Greco
,
S. M.
Hayden
,
K.
Zhou
Diamond Proposal Number(s):
[24587]
Open Access
Abstract: High
T
c
superconductors show a rich variety of phases associated with their charge degrees of freedom. Valence charges can give rise to charge ordering or acoustic plasmons in these layered cuprate superconductors. While charge ordering has been observed for both hole- and electron-doped cuprates, acoustic plasmons have only been found in electron-doped materials. Here, we use resonant inelastic x-ray scattering to observe the presence of acoustic plasmons in two families of hole-doped cuprate superconductors (
La
1.84
Sr
0.16
CuO
4
and
Bi
2
Sr
1.6
La
0.4
CuO
6
+
δ
), crucially completing the picture. Interestingly, in contrast to the quasistatic charge ordering which manifests at both Cu and O sites, the observed acoustic plasmons are predominantly associated with the O sites, revealing a unique dichotomy in the behavior of valence charges in hole-doped cuprates.
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Dec 2020
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I05-ARPES
|
Davide
Curcio
,
Alfred J. H.
Jones
,
Ryan
Muzzio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Charlotte E.
Sanders
,
Pavel
Dudin
,
Cephise
Cacho
,
Simranjeet
Singh
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jill A.
Miwa
,
Jyoti
Katoch
,
Soeren
Ulstrup
,
Philip
Hofmann
Diamond Proposal Number(s):
[20218]
Abstract: The presence of an electrical transport current in a material is one of the simplest and most important realizations of nonequilibrium physics. The current density breaks the crystalline symmetry and can give rise to dramatic phenomena, such as sliding charge density waves, insulator-to-metal transitions, or gap openings in topologically protected states. Almost nothing is known about how a current influences the electron spectral function, which characterizes most of the solid’s electronic, optical, and chemical properties. Here we show that angle-resolved photoemission spectroscopy with a nanoscale light spot provides not only a wealth of information on local equilibrium properties, but also opens the possibility to access the local nonequilibrium spectral function in the presence of a transport current. Unifying spectroscopic and transport measurements in this way allows simultaneous noninvasive local measurements of the composition, structure, many-body effects, and carrier mobility in the presence of high current densities. In the particular case of our graphene-based device, we are able to correlate the presence of structural defects with locally reduced carrier lifetimes in the spectral function and a locally reduced mobility with a spatial resolution of 500 nm.
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Dec 2020
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|
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Abstract: We performed x-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the (Bi,Sb)2(Se,Te)3 family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of ∼10−3 μB/at.
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Nov 2020
|
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I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[17737, 20810, 20855]
Abstract: We report the use of a surfactant molecule during the epitaxy of graphene on SiC(0001) that leads to the growth in an unconventional orientation, namely
R
0
°
rotation with respect to the SiC lattice. It yields a very high-quality single-layer graphene with a uniform orientation with respect to the substrate, on the wafer scale. We find an increased quality and homogeneity compared to the approach based on the use of a preoriented template to induce the unconventional orientation. Using spot profile analysis low-energy electron diffraction, angle-resolved photoelectron spectroscopy, and the normal incidence x-ray standing wave technique, we assess the crystalline quality and coverage of the graphene layer. Combined with the presence of a covalently bound graphene layer in the conventional orientation underneath, our surfactant-mediated growth offers an ideal platform to prepare epitaxial twisted bilayer graphene via intercalation.
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Sep 2020
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