I15-Extreme Conditions
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A. L. J.
Pereira
,
J. A.
Sans
,
O.
Gomis
,
D.
Santamaria-Perez
,
S.
Ray
,
A.
Godoy
,
A. S.
Da Silva-Sobrinho
,
P.
Rodríguez-Hernández
,
A.
Muñoz
,
C.
Popescu
,
F. J.
Manjon
Diamond Proposal Number(s):
[6073]
Open Access
Abstract: We report a joint experimental and theoretical study of the structural and vibrational properties of C-type bulk Y2O3 under hydrostatic compression. The combination of high-pressure X-ray diffraction and Raman scattering experimental measurements with ab initio theoretical calculations on bulk Y2O3 allows us to confirm the cubic (C-type) - monoclinic (B-type) - trigonal (A-type) phase transition sequence on the upstroke and the trigonal-monoclinic phase transition on the downstroke. This result reconciles with the results already found in related rare-earth sesquioxides of cations with similar ionic radii as Y, such as Ho2O3 and Dy2O3, and ends with the controversy regarding the existence of the intermediate monoclinic phase between the cubic and trigonal phases in pure bulk Y2O3 on the upstroke. As a byproduct, the good agreement between experimental and calculated results allows us to use extensive theoretical data to discuss the structural and vibrational behavior of the three phases of Y2O3 under compression, thus allowing a more detailed understanding of the effect of pressure on rare-earth sesquioxides than previous studies.
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May 2023
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I05-ARPES
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Edgar
Abarca Morales
,
Gesa-R.
Siemann
,
Andela
Zivanovic
,
Philip A. E.
Murgatroyd
,
Igor
Markovic
,
Brendan
Edwards
,
Chris A.
Hooley
,
Dmitry A.
Sokolov
,
Naoki
Kikugawa
,
Cephise
Cacho
,
Matthew D.
Watson
,
Timur K.
Kim
,
Clifford W.
Hicks
,
Andrew P.
Mackenzie
,
Phil D. C.
King
Diamond Proposal Number(s):
[27471, 28412]
Abstract: We report the evolution of the electronic structure at the surface of the layered perovskite
Sr
2
RuO
4
under large in-plane uniaxial compression, leading to anisotropic
B
1
g
strains of
ϵ
x
x
−
ϵ
y
y
=
−
0.9
±
0.1
%
. From angle-resolved photoemission, we show how this drives a sequence of Lifshitz transitions, reshaping the low-energy electronic structure and the rich spectrum of van Hove singularities that the surface layer of
Sr
2
RuO
4
hosts. From comparison to tight-binding modeling, we find that the strain is accommodated predominantly by bond-length changes rather than modifications of octahedral tilt and rotation angles. Our study sheds new light on the nature of structural distortions at oxide surfaces, and how targeted control of these can be used to tune density of state singularities to the Fermi level, in turn paving the way to the possible realization of rich collective states at the
Sr
2
RuO
4
surface.
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Feb 2023
|
|
|
|
Abstract: Theories of the origin of superconductivity in cuprates depend on an understanding of their normal state, which exhibits various competing orders. Transport and thermodynamic measurements on La2 − xSrxCuO4 show signatures of a quantum critical point and the associated fluctuations, including a peak in the electronic specific heat versus doping, near the doping p* where the pseudogap collapses. The fundamental nature of these quantum fluctuations is unclear. Here we use inelastic neutron scattering to show that, close to the superconducting critical temperature and near p*, there are very-low-energy collective spin excitations with characteristic energies of ~5 meV. Cooling and applying a magnetic field creates a mixed state with a stronger magnetic response below 10 meV. We conclude that the low-energy spin fluctuations are due to the collapse of the pseudogap combined with an underlying tendency to magnetic order. We show that the large specific heat near p* can be understood in terms of collective spin fluctuations. The spin fluctuations we measure exist across the superconducting phase diagram and may be related to the strange metal behaviour observed in overdoped cuprates.
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Jan 2023
|
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I06-Nanoscience
|
Allan S.
Johnson
,
Daniel
Perez-Salinas
,
Khalid M.
Siddiqui
,
Sungwon
Kim
,
Sungwook
Choi
,
Klara
Volckaert
,
Paulina E.
Majchrzak
,
Soeren
Ulstrup
,
Naman
Agarwal
,
Kent
Hallman
,
Richard F.
Haglund
,
Christian M.
Günther
,
Bastian
Pfau
,
Stefan
Eisebitt
,
Dirk
Backes
,
Francesco
Maccherozzi
,
Ann
Fitzpatrick
,
Sarnjeet S.
Dhesi
,
Pierluigi
Gargiani
,
Manuel
Valvidares
,
Nongnuch
Artrith
,
Frank
De Groot
,
Hyeongi
Choi
,
Dogeun
Jang
,
Abhishek
Katoch
,
Soonnam
Kwon
,
Sang Han
Park
,
Hyunjung
Kim
,
Simon E.
Wall
Diamond Proposal Number(s):
[22048]
Open Access
Abstract: Using light to control transient phases in quantum materials is an emerging route to engineer new properties and functionality, with both thermal and non-thermal phases observed out of equilibrium. Transient phases are expected to be heterogeneous, either through photo-generated domain growth or by generating topological defects, and this impacts the dynamics of the system. However, this nanoscale heterogeneity has not been directly observed. Here we use time- and spectrally resolved coherent X-ray imaging to track the prototypical light-induced insulator-to-metal phase transition in vanadium dioxide on the nanoscale with femtosecond time resolution. We show that the early-time dynamics are independent of the initial spatial heterogeneity and observe a 200 fs switch to the metallic phase. A heterogeneous response emerges only after hundreds of picoseconds. Through spectroscopic imaging, we reveal that the transient metallic phase is a highly orthorhombically strained rutile metallic phase, an interpretation that is in contrast to those based on spatially averaged probes. Our results demonstrate the critical importance of spatially and spectrally resolved measurements for understanding and interpreting the transient phases of quantum materials.
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Dec 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[18398]
Abstract: Using the normal incidence x-ray standing-wave technique as well as low-energy electron microscopy we have investigated the structure of quasifreestanding monolayer graphene (QFMLG) obtained by intercalation of antimony under the
(
6
√
3
×
6
√
3
)
R
30
∘
reconstructed graphitized
6
H
-SiC(0001) surface, also known as zeroth-layer graphene. We found that Sb intercalation decouples the QFMLG well from the substrate. The distance from the QFMLG to the Sb layer almost equals the expected van der Waals bonding distance of C and Sb. The Sb intercalation layer itself is monoatomic, flat, and located much closer to the substrate, at almost the distance of a covalent Sb-Si bond length. All data is consistent with Sb located on top of the uppermost Si atoms of the SiC bulk.
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Oct 2022
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I09-Surface and Interface Structural Analysis
|
Johannes T.
Küchle
,
Aleksandr
Baklanov
,
Ari Paavo
Seitsonen
,
Paul
Ryan
,
Peter
Feulner
,
Prashanth
Pendem
,
Tien-Lin
Lee
,
Matthias
Muntwiler
,
Martin
Schwarz
,
Felix
Haag
,
Johannes V
Barth
,
Willi
Auwärter
,
David A.
Duncan
,
Francesco
Allegretti
Diamond Proposal Number(s):
[15804, 20771]
Open Access
Abstract: Silicene, the two-dimensional (2D) allotrope of silicon, is a promising material for electronics. So far, the most direct synthesis strategy has been to grow it epitaxially on metal surfaces; however, the effect of the strong silicon-metal interaction on the structure and electronic properties of the metal-supported silicene is generally poorly understood. In this work, we consider the 4×4-silicene monolayer grown on Ag(111), probably the most illustrious representative of the 2D silicon family, and show that our experimental results refute the common interpretation of this system as a simple buckled, honeycomb monolayer with a sharp interface to the Ag substrate. Instead, the presented analysis demonstrates the pervasive presence of a second silicon species, which we conclude to be a Si‑Ag alloy stacked between the 2D silicene and the silver substrate and scaffolding the 2D silicene layer. These findings question the current structural understanding of the silicene/Ag(111) interface and may raise expectations of analogous alloy systems in the stabilization of other 2D materials grown epitaxially on metal surfaces.
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Aug 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Charles C.
Tam
,
Jaewon
Choi
,
Xiang
Ding
,
Stefano
Agrestini
,
Abhishek
Nag
,
Mei
Wu
,
Bing
Huang
,
Huiqian
Luo
,
Peng
Gao
,
Mirian
Garcia-Fernandez
,
Liang
Qiao
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[30296]
Abstract: In materials science, much effort has been devoted to the reproduction of superconductivity in chemical compositions, analogous to cuprate superconductors since their discovery over 30 years ago. This approach was recently successful in realising superconductivity in infinite-layer nickelates1,2,3,4,5,6. Although differing from cuprates in electronic and magnetic properties, strong Coulomb interactions suggest that infinite-layer nickelates have a propensity towards various symmetry-breaking orders that populate cuprates7,8,9,10. Here we report the observation of charge density waves (CDWs) in infinite-layer NdNiO2 films using Ni L3 resonant X-ray scattering. Remarkably, CDWs form in Nd 5d and Ni 3d orbitals at the same commensurate wavevector (0.333, 0) reciprocal lattice units, with non-negligible out-of-plane dependence and an in-plane correlation length of up to ~60 Å. Spectroscopic studies reveal a strong connection between CDWs and Nd 5d–Ni 3d orbital hybridization. Upon entering the superconducting state at 20% Sr doping, the CDWs disappear. Our work demonstrates the existence of CDWs in infinite-layer nickelates with a multiorbital character distinct from cuprates, which establishes their low-energy physics.
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Aug 2022
|
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I06-Nanoscience
|
Andrea
Ronchi
,
Paolo
Franceschini
,
Andrea
De Poli
,
Pia
Homm
,
Ann
Fitzpatrick
,
Francesco
Maccherozzi
,
Gabriele
Ferrini
,
Francesco
Banfi
,
Sarnjeet S.
Dhesi
,
Mariela
Menghini
,
Michele
Fabrizio
,
Jean-Pierre
Locquet
,
Claudio
Giannetti
Diamond Proposal Number(s):
[18897, 21700]
Open Access
Abstract: Mott transitions in real materials are first order and almost always associated with lattice distortions, both features promoting the emergence of nanotextured phases. This nanoscale self-organization creates spatially inhomogeneous regions, which can host and protect transient non-thermal electronic and lattice states triggered by light excitation. Here, we combine time-resolved X-ray microscopy with a Landau-Ginzburg functional approach for calculating the strain and electronic real-space configurations. We investigate V2O3, the archetypal Mott insulator in which nanoscale self-organization already exists in the low-temperature monoclinic phase and strongly affects the transition towards the high-temperature corundum metallic phase. Our joint experimental-theoretical approach uncovers a remarkable out-of-equilibrium phenomenon: the photo-induced stabilisation of the long sought monoclinic metal phase, which is absent at equilibrium and in homogeneous materials, but emerges as a metastable state solely when light excitation is combined with the underlying nanotexture of the monoclinic lattice.
|
Jun 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[28680]
Open Access
Abstract: SrTiO3 (STO) is an incipient ferroelectric perovskite oxide for which the onset of ferroelectric order is suppressed by quantum fluctuations. This property results in a very large increase in static dielectric constant from ∼300 at room temperature to ∼20,000 at liquid He temperature in bulk single crystals. However, the low-temperature dielectric constant of epitaxial STO films is typically a few hundred to a few thousand. Here, we use all-epitaxial capacitors of the form n-STO/undoped STO/n-STO (001) prepared by hybrid molecular beam epitaxy, to demonstrate intrinsic dielectric constants of an unstrained STO (001) film exceeding 25,000. We show that the n-STO/undoped STO interface plays a critically important role not previously considered in determining the dielectric properties that must be properly accounted for to determine the intrinsic dielectric constant.
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Jun 2022
|
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I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[22052, 18967]
Open Access
Abstract: Understanding and controlling the transition between antiferromagnetic states having different symmetry content with respect to time-inversion and space-group operations are fundamental challenges for the design of magnetic phases with topologically nontrivial character. Here, we consider a paradigmatic antiferromagnetic oxide insulator, Ca2RuO4, with symmetrically distinct magnetic ground states and unveil a novel path to guide the transition between them. The magnetic changeover results from structural and orbital reconstruction at the transition metal site that in turn arise as a consequence of substitutional doping. By means of resonant X-ray diffraction we track the evolution of the structural, magnetic, and orbital degrees of freedom for Mn doped Ca2RuO4 to demonstrate the mechanisms which drive the antiferromagnetic transition. While our analysis focuses on a specific case of substitution, we show that any perturbation that can impact in a similar way on the crystal structure, by reconstructing the induced spin–orbital exchange, is able to drive the antiferromagnetic reorganization.
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Jun 2022
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