I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[36775]
Abstract: Polar metals are an intriguing class of materials that feature a polar crystal structure while also exhibiting metallic conductivity. The unique properties of polar metals challenge expectations, making way for the exploration of exotic phenomena such as unconventional magnetism, hyperferroelectric multiferroicity, and the development of multifunctional devices that can leverage both the material's polar structure and its asymmetry in the spin conductivity, that arises due to the Rashba effect. Here, via a high-pressure single-crystal diffraction study, we report the pressure-induced enhancement of polar distortions in such a metal, Ca3Ru2O7. Our density functional theory calculations highlight that naive assumptions about the linear dependency between polar distortion amplitudes and the magnitude of the Rashba spin splitting may not be generally valid.
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May 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[31308]
Open Access
Abstract: Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement. A promising theoretical model of a QSL is the Kitaev model, composed of unusual bond-dependent exchange interactions, but experimentally, this model is challenging to realise. Here we show that the material requirements for the Kitaev QSL survive an extended pseudo-edge-sharing superexchange pathway of Ru3+ octahedra within the honeycomb layers of the inorganic framework solid, RuP3SiO11. We confirm the requisite state of Ru3+ in RuP3SiO11 and resolve the hierarchy of exchange interactions that provide experimental access to an unexplored region of the Kitaev model.
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Nov 2024
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I11-High Resolution Powder Diffraction
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H.
Lane
,
P. M.
Sarte
,
K.
Guratinder
,
A. M.
Arevalo-Lopez
,
R. S.
Perry
,
E. C.
Hunter
,
T.
Weber
,
B.
Roessli
,
A.
Stunault
,
Y.
Su
,
R. A.
Ewings
,
S. D.
Wilson
,
P.
Böni
,
J. P.
Attfield
,
C.
Stock
Open Access
Abstract: MgV
2
O
4
is a spinel based on magnetic
V
3
+
ions, which host both spin
(
S
=
1
)
and orbital
(
l
eff
=
1
)
moments. Owing to the underlying pyrochlore coordination of the magnetic sites, the spins in
MgV
2
O
4
only antiferromagnetically order once the frustrating interactions imposed by the
F
d
¯
3
m
lattice are broken through an orbitally-driven structural distortion at
T
S
≃
60
K. Consequently, a Néel transition occurs at
T
N
≃
40
K. Low-temperature spatial ordering of the electronic orbitals is fundamental to both the structural and magnetic properties; however, considerable discussion on whether it can be described by complex or real orbital ordering is ambiguous. We apply neutron spectroscopy to resolve the nature of the orbital ground state and characterize hysteretic spin-orbital correlations using x-ray and neutron diffraction. Neutron spectroscopy finds multiple excitation bands and we parametrize these in terms of a multilevel (or excitonic) theory based on the orbitally degenerate ground state. Meaningful for the orbital ground state, we report an “optical-like” mode at high energies that we attribute to a crystal-field-like excitation from the spin-orbital
j
eff
=
2
ground-state manifold to an excited
j
eff
=
1
energy level. We parametrize the magnetic excitations in terms of a Hamiltonian with spin-orbit coupling and local crystalline electric field distortions resulting from deviations from perfect octahedra surrounding the
V
3
+
ions. We suggest that this provides compelling evidence for complex orbital order in
MgV
2
O
4
. We then apply the consequences of this model to understand hysteretic effects in the magnetic diffuse scattering where we propose that
MgV
2
O
4
displays a high-temperature orbital memory of the low-temperature spin order.
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Nov 2023
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I16-Materials and Magnetism
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C. D.
Dashwood
,
A. H.
Walker
,
M. P.
Kwasigroch
,
L. S. I.
Veiga
,
Q.
Faure
,
J. G.
Vale
,
D. G.
Porter
,
P.
Manuel
,
D. D.
Khalyavin
,
F.
Orlandi
,
C. V.
Colin
,
O.
Fabelo
,
F.
Krüger
,
R. S.
Perry
,
R. D.
Johnson
,
A. G.
Green
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[23580, 25554]
Open Access
Abstract: The layered-ruthenate family of materials possess an intricate interplay of structural, electronic and magnetic degrees of freedom that yields a plethora of delicately balanced ground states. This is exemplified by Ca3Ru2O7, which hosts a coupled transition in which the lattice parameters jump, the Fermi surface partially gaps and the spins undergo a 90∘ in-plane reorientation. Here, we show how the transition is driven by a lattice strain that tunes the electronic bandwidth. We apply uniaxial stress to single crystals of Ca3Ru2O7, using neutron and resonant x-ray scattering to simultaneously probe the structural and magnetic responses. These measurements demonstrate that the transition can be driven by externally induced strain, stimulating the development of a theoretical model in which an internal strain is generated self-consistently to lower the electronic energy. We understand the strain to act by modifying tilts and rotations of the RuO6 octahedra, which directly influences the nearest-neighbour hopping. Our results offer a blueprint for uncovering the driving force behind coupled phase transitions, as well as a route to controlling them.
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Oct 2023
|
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I09-Surface and Interface Structural Analysis
|
Adam J.
Jackson
,
Benjamin J.
Parrett
,
Joe
Willis
,
Alex M.
Ganose
,
W. W. Winnie
Leung
,
Yuhan
Liu
,
Benjamin A. D.
Williamson
,
Timur K.
Kim
,
Moritz
Hoesch
,
Larissa S. I.
Veiga
,
Raman
Kalra
,
Jens
Neu
,
Charles A.
Schmuttenmaer
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Tung-Chun
Lee
,
Tim D.
Veal
,
Robert G.
Palgrave
,
Robin
Perry
,
David O.
Scanlon
Diamond Proposal Number(s):
[24449]
Open Access
Abstract: Transparent conducting oxides have become ubiquitous in modern optoelectronics. However, the number of oxides that are transparent to visible light and have the metallic-like conductivity necessary for applications is limited to a handful of systems that have been known for the past 40 years. In this work, we use hybrid density functional theory and defect chemistry analysis to demonstrate that tri-rutile zinc antimonate, ZnSb2O6, is an ideal transparent conducting oxide and to identify gallium as the optimal dopant to yield high conductivity and transparency. To validate our computational predictions, we have synthesized both powder samples and single crystals of Ga-doped ZnSb2O6 which conclusively show behavior consistent with a degenerate transparent conducting oxide. This study demonstrates the possibility of a family of Sb(V)-containing oxides for transparent conducting oxide and power electronics applications.
|
Oct 2022
|
|
I05-ARPES
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Diamond Proposal Number(s):
[13398, 5282]
Open Access
Abstract: Discrepancies in the low-energy quasiparticle dispersion extracted from angle-resolved photoemission, scanning tunneling spectroscopy, and quantum oscillation data are common and have long haunted the field of quantum matter physics. Here, we directly test the consistency of results from these three techniques by comparing data from the correlated metal Sr2RhO4. Using established schemes for the interpretation of the experimental data, we find good agreement for the Fermi surface topography and carrier effective masses. Hence, the apparent absence of such an agreement in other quantum materials, including the cuprates, suggests that the electronic states in these materials are of different, non-Fermi liquid-like nature. Finally, we discuss the potential and challenges in extracting carrier lifetimes from photoemission and quasiparticle interference data.
|
Dec 2020
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|
I16-Materials and Magnetism
|
C. D.
Dashwood
,
L. S. I.
Veiga
,
Q.
Faure
,
J. G.
Vale
,
D. G.
Porter
,
S. P.
Collins
,
P.
Manuel
,
D. D.
Khalyavin
,
F.
Orlandi
,
R. S.
Perry
,
R. D.
Johnson
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[23580]
Abstract: We show how complex modulated order can spontaneously emerge when magnetic interactions compete in a metal with polar lattice distortions. Combining neutron and resonant x-ray scattering with symmetry analysis, we reveal that the spin reorientation in
Ca
3
Ru
2
O
7
is mediated by a magnetic cycloid whose eccentricity evolves smoothly but rapidly with temperature. We find the cycloid to be highly sensitive to magnetic fields, which appear to continuously generate higher harmonic modulations. Our results provide a unified picture of the rich magnetic phases of this correlated, multiband polar metal.
|
Nov 2020
|
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I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[7798, 12911]
Open Access
Abstract: X-ray magnetic critical scattering measurements and specific heat measurements were performed on the perovskite iridate Sr3Ir2O7. We find that the magnetic interactions close to the Néel temperature Tn = 283.4(2) K are three-dimensional. This contrasts with previous studies which suggest two-dimensional behaviour like Sr2IrO4. Violation of the Harris criterion (dv > 2) means that weak disorder becomes relevant. This leads a rounding of the antiferromagnetic phase transition at Tn, and modifies the critical exponents relative to the clean system. Specifically, we determine that the critical behaviour of Sr2Ir2O7 is representative of the diluted 3D Ising universality class.
|
May 2019
|
|
I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[14024]
Open Access
Abstract: We study the magnetic structure of the “stuffed” (Tb-rich) pyrochlore iridate Tb2+xIr2−xO7−y, using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L3 and Tb M5 edges, which provide selective sensitivity to Ir 5d and Tb 4f magnetic moments, respectively. At the Ir L3 edge, we found the onset of long-range k = 0 magnetic order below TIr N ∼71K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS crosssections, we estimate an ordered magnetic moment of µIr 5d ≈ 0.34(3)µB at 5K. At the Tb M5 edge,long-range k = 0 magnetic order appeared below ∼ 40K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M5 edge in applied magnetic fields up to 6T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which TIr N = 130K and µIr 5d = 0.56µB, indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.
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May 2019
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I10-Beamline for Advanced Dichroism - scattering
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Abstract: The ground-state orbital occupancy of the Ru4+ ion in Ca2−xLaxRuO4[x=0, 0.05(1), 0.07(1), and 0.12(1)] was investigated by performing x-ray absorption spectroscopy (XAS) in the vicinity of the O K edge as a function of the angle between the incident beam and the surface of the single-crystal samples. A minimal model of the hybridization between the O 2p states probed at the K edge and the Ru 4d orbitals was used to analyze the XAS data, allowing the ratio of hole occupancies nxy/nyz,zx to be determined as a function of doping and temperature. For the samples displaying a low-temperature insulating ground state (x≤0.07), nxy/nyz,zx is found to increase significantly with increasing doping, with increasing temperature acting to further enhance nxy/nyz,zx. For the x=0.12 sample, which has a metallic ground state, the XAS spectra are found to be independent of temperature and not to be describable by the minimal hybridization model, while being qualitatively similar to the spectra displayed by the x≤0.07 samples above their insulating to metallic transitions. To understand the origin of the evolution of the electronic structure of Ca2−xLaxRuO4 across its phase diagram, we have performed theoretical calculations based on a model Hamiltonian, comprising electron-electron correlations, crystal field Δ, and spin-orbit coupling λ, of a Ru-O-Ru cluster, with realistic values used to parametrize the various interactions taken from the literature. Our calculations of the Ru hole occupancy as a function of Δ/λ provide an excellent description of the general trends displayed by the data. In particular they establish that the enhancement of nxy/nyz,zx is driven by significant modifications to the crystal field as the tetragonal distortion of the RuO6 octahedral changes from compressive to tensile with La doping. We have also used our model to show that the hole occupancy of the O 2p and Ru 4d orbitals displays the same general trend as a function of Δ/λ, thus validating the minimal hybridization model used to analyze the data. In essence, our results suggest that the predominant mechanism driving the emergence of the low-temperature metallic phase in La-doped Ca2RuO4 is the structurally induced redistribution of holes within the t2g orbitals, rather than the injection of free carriers.
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Feb 2019
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