B18-Core EXAFS
|
Manjil
Das
,
Sayantika
Bhowal
,
Jhuma
Sannigrahi
,
Abhisek
Bandyopadhyay
,
Anupam
Banerjee
,
Giannantonio
Cibin
,
Dmitry
Khalyavin
,
Niladri
Banerjee
,
Devashibhai
Adroja
,
Indra
Dasgupta
,
Subham
Majumdar
Diamond Proposal Number(s):
[17752]
Abstract: We address the concomitant metal-insulator transition (MIT) and antiferromagnetic ordering in the novel pyrochlore iridate
Eu
2
Ir
2
O
7
by combining x-ray absorption spectroscopy, x-ray and neutron diffractions, and density functional theory (DFT)-based calculations. The temperature dependent powder x-ray diffraction clearly rules out any change in the lattice symmetry below the MIT, nevertheless a clear anomaly in the Ir-O-Ir bond angle and Ir-O bond length is evident at the onset of MIT. From the x-ray absorption near edge structure (XANES) spectroscopic study of Ir-
L
3
and
L
2
edges, the effective spin-orbit coupling is found to be intermediate, at least quite far from the strong atomic spin-orbit coupling limit. Powder neutron diffraction measurement is in line with an all-in-all-out magnetic structure of the Ir-tetrahedra in this compound, which is quite common among rare-earth pyrochlore iridates. The sharp change in the Ir-O-Ir bond angle around the MIT possibly arises from the exchange striction mechanism, which favors an enhanced electron correlation via weakening of Ir-Ir orbital overlap and an insulating phase below
T
M
I
. The theoretical calculations indicate an insulating state for shorter bond angle validating the experimental observation. Our DFT calculations show a possibility of intriguing topological phase below a critical value of the Ir-O distance, which is shorter than the experimentally observed bond length. Therefore, a topological state may be realized in bulk
Eu
2
Ir
2
O
7
sample if the Ir-O bond length can be reduced by the application of sufficient external pressure.
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Apr 2022
|
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I06-Nanoscience
|
X.
Gu
,
C.
Chen
,
W. S.
Wei
,
L. L.
Gao
,
J. Y.
Liu
,
X.
Du
,
D.
Pei
,
J. S.
Zhou
,
R. Z.
Xu
,
Z. X.
Yin
,
W. X.
Zhao
,
Y. D.
Li
,
C.
Jozwiak
,
A.
Bostwick
,
E.
Rotenberg
,
D.
Backes
,
L. S. I.
Veiga
,
S.
Dhesi
,
T.
Hesjedal
,
G.
Van Der Laan
,
H. F.
Du
,
W. J.
Jiang
,
Y. P.
Qi
,
G.
Li
,
W. J.
Shi
,
Z. K.
Liu
,
Y. L.
Chen
,
L. X.
Yang
Diamond Proposal Number(s):
[27482]
Abstract: Crystal geometry can greatly influence the emergent properties of quantum materials. As an example, the kagome lattice is an ideal platform to study the rich interplay between topology, magnetism, and electronic correlation. In this work, combining high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structure of
X
Mn
6
Sn
6
(
X
=
Dy
,
Tb
,
Gd
,
Y
)
family compounds. We observe the Dirac fermion and the flat band arising from the magnetic kagome lattice of Mn atoms. Interestingly, the flat band locates in the same energy region in all compounds studied, regardless of their different magnetic ground states and
4
f
electronic configurations. These observations suggest a robust Mn magnetic kagome lattice across the
X
Mn
6
Sn
6
family, thus providing an ideal platform for the search for, and investigation of, new emergent phenomena in magnetic topological materials.
|
Apr 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Yingying
Peng
,
Leonardo
Martinelli
,
Qizhi
Li
,
Matteo
Rossi
,
Matteo
Mitrano
,
Riccardo
Arpaia
,
Marco
Moretti Sala
,
Qiang
Gao
,
Xuefei
Guo
,
Gabriella Maria
De Luca
,
Andrew
Walters
,
Abhishek
Nag
,
Andi
Barbour
,
Genda
Gu
,
Jonathan
Pelliciari
,
Nicholas B.
Brookes
,
Peter
Abbamonte
,
Marco
Salluzzo
,
Xingjiang
Zhou
,
Ke-Jin
Zhou
,
Valentina
Bisogni
,
Lucio
Braicovich
,
Steven
Johnston
,
Giacomo
Ghiringhelli
Diamond Proposal Number(s):
[20012]
Abstract: While electron-phonon coupling (EPC) is crucial for Cooper pairing in conventional superconductors, its role in high-
T
c
superconducting cuprates is debated. Using resonant inelastic x-ray scattering at the oxygen
K
edge, we study the EPC in
Bi
2
Sr
2
Ca
Cu
2
O
8
+
δ
(Bi2212) and
Nd
1
+
x
Ba
2
−
x
Cu
3
O
7
−
δ
(NBCO) at different doping levels ranging from heavily underdoped (
p
=
0.07
) to overdoped (
p
=
0.21
). We analyze the data with a localized Lang-Firsov model that allows for the coherent excitations of two phonon modes. While electronic band dispersion effects are non-negligible, we are able to perform a study of the relative values of EPC matrix elements in these cuprate families. In the case of NBCO, the choice of the excitation energy allows us to disentangle modes related to the CuO chains and the
Cu
O
2
planes. Combining the results from the two families, we find the EPC strength decreases with doping at
q
∥
=
(
−
0.25
,
0
)
r.l.u., but has a nonmonotonic trend as a function of doping at smaller momenta. This behavior is attributed to the screening effect of charge carriers. We also find that the phonon intensity is enhanced in the vicinity of the charge-density-wave excitations while the extracted EPC strength appears to be less sensitive to their proximity. By performing a comparative study of two cuprate families, we are able to identify general trends in the EPC for the cuprates and provide experimental input to theories invoking a synergistic role for this interaction in
d
-wave pairing.
|
Mar 2022
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[20426]
Open Access
Abstract: We report on the characterization of the growth of vacuum-deposited zinc phthalocyanine (ZnPc) thin films on glass through a combination of in situ grazing incidence x-ray scattering, x-ray reflectivity, and atomic force microscopy. We found that the growth at room temperature proceeds via the formation of two structurally unique substrate-induced interfacial layers, followed by the growth of the
γ
-ZnPc polymorph thereafter (thickness
≈
1.0
nm). As the growth of the bulk
γ
-ZnPc progresses, a substantial out-of-plane lattice strain (
≈
15
%
relative to
γ
-ZnPc powder) is continually relaxed during the thin film growth. The rate of strain relaxation was slowed after a thickness of
≈
13
nm, corresponding to the transition from layer growth to island growth. The findings reveal the real-time microstructural evolution of ZnPc and highlight the importance of substrate-induced strain on thin film growth.
|
Mar 2022
|
|
I11-High Resolution Powder Diffraction
|
Abstract: The Heisenberg pyrochlore antiferromagnet
Gd
2
Pt
2
O
7
is one of a series of gadolinium pyrochlore compounds with a variety of B-site cations. Despite the expected simplicity of a spin-only
Gd
3
+
Heisenberg interaction model, the gadolinium pyrochlore series exhibits various complex magnetic ground states at low temperature.
Gd
2
Pt
2
O
7
displays the highest temperature magnetic order of the series with
T
N
=
1.6
K, which has been attributed to enhanced superexchange pathways facilitated by empty
5
d
e
g
Pt orbitals. In this study, we use various neutron scattering techniques on an isotopically enriched polycrystalline
160
Gd
2
Pt
2
O
7
sample to examine the magnetic structure and spin-wave excitation spectrum below
T
N
in order to extract the dominant exchange interactions. We find that the ground-state magnetic structure is the Palmer-Chalker state previously seen in
Gd
2
Sn
2
O
7
with an associated gapped excitation spectrum consistent with enhanced exchange interactions between further near-neighbor
Gd
3
+
ions. We confirm this exchange model with analysis of the magnetic diffuse scattering in the paramagnetic regime using polarized neutrons.
|
Mar 2022
|
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I05-ARPES
|
Xian P.
Yang
,
Harrison
Labollita
,
Zi-Jia
Cheng
,
Hari
Bhandari
,
Tyler A.
Cochran
,
Jia-Xin
Yin
,
Md. Shafayat
Hossain
,
Ilya
Belopolski
,
Qi
Zhang
,
Yuxiao
Jiang
,
Nana
Shumiya
,
Daniel
Multer
,
Maksim
Liskevich
,
Dmitry A.
Usanov
,
Yanliu
Dang
,
Vladimir N.
Strocov
,
Albert V.
Davydov
,
Nirmal J.
Ghimire
,
Antia S.
Botana
,
M. Zahid
Hasan
Diamond Proposal Number(s):
[29230]
Abstract: Layered transition metal dichalcogenides have a rich phase diagram and they feature two-dimensionality in numerous physical properties.
Co
1
/
3
NbS
2
is one of the newest members of this family where Co atoms are intercalated into the van der Waals gaps between
NbS
2
layers. We study the three-dimensional electronic band structure of
Co
1
/
3
NbS
2
using both surface and bulk sensitive angle-resolved photoemission spectroscopy. We show that the electronic bands do not fit into the rigid band shift picture after the Co intercalation. Instead,
Co
1
/
3
NbS
2
displays a different orbital character near the Fermi level compared to the pristine
NbS
2
compound and has a clear band dispersion in the
k
z
direction despite its layered structure. Our photoemission study demonstrates the out-of-plane electronic correlations introduced by the Co intercalation, thus offering a different perspective on this compound. Finally, we propose how Fermi level tuning could lead to exotic phases such as spin density wave instability.
|
Mar 2022
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[18786]
Abstract: Crystallographic analysis and thermoelectric studies of solid solutions
Rh
1
−
x
Ir
x
Te
2
(
0
≤
x
≤
1
)
are reported. All compositions show layered structures belonging to the
P
¯
3
m
1
space group at room temperature.
IrTe
2
presents a first-order phase transition from the hexagonal to the triclinic lattice (
P
¯
1
space group), which is monitored by synchrotron radiation x-ray powder diffraction. In the cooling-down process the transition appears at 240 K while in the warming-up process it begins at 280 K, showing a remarkable hysteresis. All compositions show a strong metallic behavior with enhanced Pauli paramagnetism and two regimes in the electrical resistivity. These regimes are associated with electron-electron scattering (at low temperature
ρ
∼
T
2
) and electron-phonon coupling (higher temperatures
ρ
∼
T
). The Seebeck coefficient shows hole-type carriers for all the compounds.
|
Mar 2022
|
|
|
|
Open Access
Abstract: In condensed matter systems, the electronic degrees of freedom are often entangled to form complex composites, known as hidden orders, which give rise to unusual properties, while escaping detection in conventional experiments. Here we demonstrate the existence of hidden
k
-space magnetoelectric multipoles in nonmagnetic systems with broken space-inversion symmetry. These
k
-space magnetoelectric multipoles are reciprocal to the real-space charge dipoles associated with the broken inversion symmetry. Using the prototypical ferroelectric
PbTiO
3
as an example, we show that their origin is a spin asymmetry in momentum space resulting from the broken space inversion symmetry associated with the ferroelectric polarization. In
PbTiO
3
, the
k
-space spin asymmetry corresponds to a pure
k
-space magnetoelectric toroidal moment, which can be detected using magnetic Compton scattering, an established tool for probing magnetism in ferromagnets or ferrimagnets with a net spin polarization, which has not been exploited to date for nonmagnetic systems. In particular, the
k
-space magnetoelectric toroidal moment combined with the spin-orbit interaction manifest in an antisymmetric magnetic Compton profile that can be reversed using an electric field. Our work suggests an experimental route to directly measuring and tuning hidden
k
-space magnetoelectric multipoles via specially designed magnetic Compton scattering measurements.
|
Mar 2022
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[8858, 9902]
Abstract: We studied in situ the local atomic structure evolution of an equiatomic
Zr
50
Cu
50
metallic glassy alloy under high pressure compression inside a diamond anvil cell using synchrotron x-ray total scattering. The empirical potential structure refinement method was used to reconstruct the three-dimensional atomic models at each pressure step, and to analyze the spatially averaged local atomic structure configurations. The interatomic distances of different atomic pairs are reduced at different rates with increasing pressure and the Cu-Cu pairs exhibit the highest percentage reduction. Between ambient pressure and 36.85 GPa, the atomic separation of the Cu-Cu pairs is reduced by ∼12% compared to ∼5% for Zr-Zr and Zr-Cu pairs. Such disproportional decrease in interatomic distance results in inhomogeneous atom reconfiguration in the short atomic range. With the increase of pressure, the Zr atoms move preferentially towards the Zr-Zr pairs, while the Cu atoms move preferentially towards the Cu-Cu pairs, creating inhomogeneous atom reconfiguration with positive short-range order coefficients of 0.0309 and 0.0464 for Zr-Zr and Cu-Cu respectively, but a negative value of −0.0464 for Zr-Cu pairs. Voronoi tessellation method was also used to study the evolution of the short-range atom packing versus pressure, elucidating the cause for the bimodal distribution of the bond angle distributions. The research sheds light on understanding of the atomic reconfiguration of equiatomic alloys under high pressure.
|
Feb 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[25355, 13812]
Abstract: Recent progress in the growth and characterization of thin-film
VO
2
has shown its electronic properties can be significantly modulated by epitaxial matching. To throw new light on the concept of “Mott engineering,” we develop a symmetry-consistent approach to treat structural distortions and electronic correlations in epitaxial
VO
2
films under strain, and compare our design with direct experimental probes. We find strong evidence for the emergence of correlation-driven charge order deep in the metallic phase, and our results indicate that exotic phases of
VO
2
can be controlled with epitaxial stabilization.
|
Jan 2022
|
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