I06-Nanoscience
|
G.
Awana
,
R.
Fujita
,
A.
Frisk
,
P.
Chen
,
Q.
Yao
,
A. J.
Caruana
,
C. J.
Kinane
,
N.-J.
Steinke
,
S.
Langridge
,
P.
Olalde-Velasco
,
S. S.
Dhesi
,
G.
Van Der Laan
,
X. F.
Kou
,
S. L.
Zhang
,
T.
Hesjedal
,
D.
Backes
Diamond Proposal Number(s):
[23748]
Open Access
Abstract: An elegant approach to overcome the intrinsic limitations of magnetically doped topological insulators is to bring a topological insulator in direct contact with a magnetic material. The aspiration is to realize the quantum anomalous Hall effect at high temperatures where the symmetry-breaking magnetic field is provided by a proximity-induced magnetization at the interface. Hence, a detailed understanding of the interfacial magnetism in such heterostructures is crucial, yet its distinction from structural and magnetic background effects is a rather nontrivial task. Here, we combine several magnetic characterization techniques to investigate the magnetic ordering in
MnTe
/
Bi
2
Te
3
heterostructures. A magnetization profile of the layer stack is obtained using depth-sensitive polarized neutron reflectometry. The magnetic constituents are characterized in more detail using element-sensitive magnetic x-ray spectroscopy. Magnetotransport measurements provide additional information about the magnetic transitions. We find that the supposedly antiferromagnetic MnTe layer does not exhibit an x-ray magnetic linear dichroic signal, raising doubt that it is in its antiferromagnetic state. Instead, Mn seems to penetrate into the surface region of the
Bi
2
Te
3
layer. Furthermore, the interface between MnTe and
Bi
2
Te
3
is not abrupt, but extending over
∼
2.2
nm. These conditions are the likely reason that we do not observe proximity-induced magnetization at the interface. Our findings illustrate the importance of not solely relying on one single technique as proof for proximity-induced magnetism at interfaces. We demonstrate that a holistic, multitechnique approach is essential to gain a more complete picture of the magnetic structure in which the interface is embedded.
|
May 2022
|
|
I11-High Resolution Powder Diffraction
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[14061, 17673, 16390]
Open Access
Abstract: The similar electronic structures of Bi3+ and Pb2+ have motivated researchers to explore bismuth-based perovskite compounds, which in the past decade has been further fuelled by the demand for developing lead-free piezoceramics. The difficulty in stabilizing the perovskite phase in bismuth based compounds has directed most research activities towards exploring two main compounds - multiferroic BiFeO3 and relaxor ferroelectric Na1/2Bi1/2TiO3 and their derivatives. In recent years, quenching these materials from the sintering temperature or from the paraelectric phase (above the Curie temperature, Tc) has resulted in a plethora of fundamentally interesting and technologically relevant advances, including enhanced thermal depolarization temperature, high Tc, giant strain and control over the atomic structure and electrical conductivity at the domain wall. In this contribution, a brief overview of quenching piezoceramics is presented, with majority of the discussion encompassing salient features of quenching lead-free perovskite structured Na1/2Bi1/2TiO3- and BiFeO3- based materials. For each material system, the influence of quenching on phase transitions, domain switching behavior and electromechanical properties are presented, apart from outlining the current understanding of the underlying mechanisms. The review provides guidelines for further exploration of the quenching strategy for improving the functionality of Bi-based piezoceramics.
|
May 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Nimrod
Bachar
,
Kacper
Koteras
,
Jakub
Gawraczynski
,
Waldemar
Trzciński
,
Józef
Paszula
,
Riccardo
Piombo
,
Paolo
Barone
,
Zoran
Mazej
,
Giacomo
Ghiringhelli
,
Abhishek
Nag
,
Ke-Jin
Zhou
,
José
Lorenzana
,
Dirk
Van Der Marel
,
Wojciech
Grochala
Diamond Proposal Number(s):
[24869]
Open Access
Abstract: Charge-transfer insulators are the parent phase of a large group of today's unconventional high-temperature superconductors. Here we study experimentally and theoretically the interband excitations of the charge-transfer insulator silver fluoride
AgF
2
, which has been proposed as an excellent analog of oxocuprates. Optical conductivity and resonant inelastic x-ray scattering on
AgF
2
polycrystalline sample show a close similarity with that measured on undoped
La
2
CuO
4
. While the former shows a charge-transfer gap
∼
3.4
eV, larger than in the cuprate,
d
d
excitations are nearly at the same energy in the two materials. Density functional theory and exact diagonalization cluster computations of the multiplet spectra show that
AgF
2
is more covalent than the cuprate, in spite of the larger fundamental gap. Furthermore, we show that
AgF
2
is at the verge of a charge-transfer instability. The overall resemblance of our data on
AgF
2
to those published previously on
La
2
CuO
4
suggests that the underlying charge-transfer insulator physics is the same, while
AgF
2
could also benefit from a proximity to a charge density wave phase as in
BaBiO
3
. Therefore, our work provides a compelling support to the future use of fluoroargentates for materials' engineering of novel high-temperature superconductors.
|
May 2022
|
|
I06-Nanoscience
|
Filip
Krizek
,
Sonka
Reimers
,
Zdeněk
Kašpar
,
Alberto
Marmodoro
,
Jan
Michalička
,
Ondřej
Man
,
Alexander
Edström
,
Oliver J.
Amin
,
Kevin W.
Edmonds
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Jan
Zubáč
,
Domink
Kriegner
,
Dina
Carbone
,
Jakub
Železný
,
Karel
Výborný
,
Kamil
Olejník
,
Vít
Novák
,
Jan
Rusz
,
Juan-Carlos
Idrobo
,
Peter
Wadley
,
Tomas
Jungwirth
Diamond Proposal Number(s):
[22437]
Open Access
Abstract: The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its physical fundamentals to applications in information technologies. Here, we explore antiferromagnetic CuMnAs in which imaging by x-ray photoemission reveals the presence of magnetic textures down to nanoscale, reaching the detection limit of this established microscopy in antiferromagnets. We achieve atomic resolution by using differential phase-contrast imaging within aberration-corrected scanning transmission electron microscopy. We identify abrupt domain walls in the antiferromagnetic film corresponding to the Néel order reversal between two neighboring atomic planes. Our work stimulates research of magnetic textures at the ultimate atomic scale and sheds light on electrical and ultrafast optical antiferromagnetic devices with magnetic field–insensitive neuromorphic functionalities.
|
Apr 2022
|
|
I05-ARPES
|
M.
Berben
,
S.
Smit
,
C.
Duffy
,
Y.-T.
Hsu
,
L.
Bawden
,
F.
Heringa
,
F.
Gerritsen
,
S.
Cassanelli
,
X.
Feng
,
S.
Bron
,
E.
Van Heumen
,
Y.
Huang
,
F.
Bertran
,
T. K.
Kim
,
C.
Cacho
,
A.
Carrington
,
M. S.
Golden
,
N. E.
Hussey
Abstract: Once doped away from their parent Mott insulating state, the hole-doped cuprates enter into many varied and exotic phases. The onset temperature of each phase is then plotted versus
p
—the number of doped holes per copper atom—to form a representative phase diagram. Apart from differences in the absolute temperature scales among the various families, the resultant phase diagrams are strikingly similar. In particular, the
p
values corresponding to optimal doping (
p
opt
∼
0.16
) and to the end of the pseudogap phase
(
p
∗
∼
0.19
–
0.20
)
are essentially the same for all cuprate families bar one: the single-layer Bi-based cuprate
Bi
2
+
z
−
y
Pb
y
Sr
2
−
x
−
z
La
x
CuO
6
+
δ
(Bi2201). This anomaly arises partly due to the complex stoichiometry of this material and also to the different
p
values inferred from disparate (e.g., bulk or surface) measurements performed on samples with comparable superconducting transition temperatures
T
c
. Here, by combining measurements of the in-plane resistivity in zero and high magnetic fields with angle-resolved photoemission spectroscopy studies in the superconducting and normal state, we argue that the phase diagram of Bi2201 may in fact be similar to that realized in other families. This study therefore brings Bi2201 into the fold and supports the notion of universality of
p
opt
and
p
∗
in all hole-doped cuprates.
|
Apr 2022
|
|
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.
|
Apr 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[24593]
Open Access
Abstract: The microscopic origins of emergent behaviours in condensed matter systems are encoded in their excitations. In ordinary magnetic materials, single spin-flips give rise to collective dipolar magnetic excitations called magnons. Likewise, multiple spin-flips can give rise to multipolar magnetic excitations in magnetic materials with spin S ≥ 1. Unfortunately, since most experimental probes are governed by dipolar selection rules, collective multipolar excitations have generally remained elusive. For instance, only dipolar magnetic excitations have been observed in isotropic S = 1 Haldane spin systems. Here, we unveil a hidden quadrupolar constituent of the spin dynamics in antiferromagnetic S = 1 Haldane chain material Y2BaNiO5 using Ni L3-edge resonant inelastic x-ray scattering. Our results demonstrate that pure quadrupolar magnetic excitations can be probed without direct interactions with dipolar excitations or anisotropic perturbations. Originating from on-site double spin-flip processes, the quadrupolar magnetic excitations in Y2BaNiO5 show a remarkable dual nature of collective dispersion. While one component propagates as non-interacting entities, the other behaves as a bound quadrupolar magnetic wave. This result highlights the rich and largely unexplored physics of higher-order magnetic excitations.
|
Apr 2022
|
|
I10-Beamline for Advanced Dichroism
|
Kook Tae
Kim
,
Margaret R.
Mccarter
,
Vladimir A.
Stoica
,
Sujit
Das
,
Christoph
Klewe
,
Elizabeth P.
Donoway
,
David M.
Burn
,
Padraic
Shafer
,
Fanny
Rodolakis
,
Mauro A. P.
Gonçalves
,
Fernando
Gómez-Ortiz
,
Jorge
Íñiguez
,
Pablo
García-Fernández
,
Javier
Junquera
,
Sandhya
Susarla
,
Stephen W.
Lovesey
,
Gerrit
Van Der Laan
,
Se Young
Park
,
Lane W.
Martin
,
John W.
Freeland
,
Ramamoorthy
Ramesh
,
Dong Ryeol
Lee
Diamond Proposal Number(s):
[24797]
Open Access
Abstract: Resonant elastic X-ray scattering (REXS) offers a unique tool to investigate solid-state systems providing spatial knowledge from diffraction combined with electronic information through the enhanced absorption process, allowing the probing of magnetic, charge, spin, and orbital degrees of spatial order together with electronic structure. A new promising application of REXS is to elucidate the chiral structure of electrical polarization emergent in a ferroelectric oxide superlattice in which the polarization vectors in the REXS amplitude are implicitly described through an anisotropic tensor corresponding to the quadrupole moment. Here, we present a detailed theoretical framework and analysis to quantitatively analyze the experimental results of Ti L-edge REXS of a polar vortex array formed in a PbTiO3/SrTiO3 superlattice. Based on this theoretical framework, REXS for polar chiral structures can become a useful tool similar to x-ray resonant magnetic scattering (XRMS), enabling a comprehensive study of both electric and magnetic REXS on the chiral structures.
|
Apr 2022
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[26148]
Open Access
Abstract: A major challenge in topological magnetism lies in the three-dimensional (3D) exploration of their magnetic textures. A recent focus has been the question of how 2D skyrmion sheets vertically stack to form distinct types of 3D topological strings. Being able to manipulate the vertical coupling should therefore provide a route to the engineering of topological states. Here, we present a new type of axially bound magnetic skyrmion string state in which the strings in two distinct materials are glued together across their interface. With quasi-tomographic resonant elastic X-ray scattering, the 3D skyrmion profiles before and after their binding across the interface were unambiguously determined and compared. Their attractive binding is accompanied by repulsive twisting; i.e., the coupled skyrmions mutually affect each other via a compensating twisting. This state exists in chiral magnet–magnetic thin film heterostructures, providing a new arena for the engineering of 3D topological phases.
|
Apr 2022
|
|
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
|
|
