|
|
Jung-Hwa
Kim
,
Darren C.
Peets
,
Manfred
Reehuis
,
Peter
Adler
,
Andrey
Maljuk
,
Tobias
Ritschel
,
Morgan C.
Allison
,
Jochen
Geck
,
Jose R. L.
Mardegan
,
Pablo J.
Bereciartua Perez
,
Sonia
Francoual
,
Andrew
Walters
,
Thomas
Keller
,
Paula M.
Abdala
,
Philip
Pattison
,
Pinder
Dosanjh
,
Bernhard
Keimer
Open Access
Abstract: Since the discovery of charge disproportionation in the
FeO
2
square-lattice compound
Sr
3
Fe
2
O
7
by Mössbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained “hidden” to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe
K
-edge resonant x-ray scattering to demonstrate checkerboard charge order in the
FeO
2
planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on “hidden order” in other materials.
|
Aug 2021
|
|
|
|
Yili
Cao
,
Kun
Lin
,
Sergii
Khmelevskyi
,
Maxim
Avdeev
,
Keith M.
Taddei
,
Qiang
Zhang
,
Qingzhen
Huang
,
Qiang
Li
,
Kenichi
Kato
,
Chiu Chung
Tang
,
Alexandra
Gibbs
,
Chin-Wei
Wang
,
Jinxia
Deng
,
Jun
Chen
,
Hongjie
Zhang
,
Xianran
Xing
Abstract: Super Invar (SIV), i.e., zero thermal expansion of metallic materials underpinned by magnetic ordering, is of great practical merit for a wide range of high precision engineering. However, the relatively narrow temperature window of SIV in most materials restricts its potential applications in many critical fields. Here, we demonstrate the controlled design of thermal expansion in a family of
R
2
(
Fe
,
Co
)
17
materials (
R
=
rare
Earth). We find that adjusting the Fe-Co content tunes the thermal expansion behavior and its optimization leads to a record-wide SIV with good cyclic stability from 3–461 K, almost twice the range of currently known SIV. In situ neutron diffraction, Mössbauer spectra and first-principles calculations reveal the
3
d
bonding state transition of the Fe-sublattice favors extra lattice stress upon magnetic ordering. On the other hand, Co content induces a dramatic enhancement of the internal molecular field, which can be manipulated to achieve “ultrawide” SIV over broad temperature, composition and magnetic field windows. These findings pave the way for exploiting thermal-expansion-control engineering and related functional materials.
|
Jul 2021
|
|
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.
|
May 2021
|
|
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.
|
Apr 2021
|
|
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.
|
Apr 2021
|
|
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.
|
Mar 2021
|
|
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.
|
Feb 2021
|
|
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.
|
Jan 2021
|
|
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.
|
Dec 2020
|
|
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.
|
Dec 2020
|
|
