I21-Resonant Inelastic X-ray Scattering (RIXS)
|
A.
Nag
,
L.
Zinni
,
J.
Choi
,
J.
Li
,
S.
Tu
,
A. C.
Walters
,
S.
Agrestini
,
S. M.
Hayden
,
Matías
Bejas
,
Z.
Lin
,
H.
Yamase
,
K.
Jin
,
M.
Garcia-Fernandez
,
J.
Fink
,
Andrés
Greco
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[27872]
Open Access
Abstract: Estimating many-body effects that deviate from an independent particle approach has long been a key research interest in condensed matter physics. Layered cuprates are prototypical systems, where electron-electron interactions are found to strongly affect the dynamics of single-particle excitations. It is, however, still unclear how the electron correlations influence charge excitations, such as plasmons, which have been variously treated with either weak or strong correlation models. In this work, we demonstrate the hybridized nature of collective valence charge fluctuations leading to dispersing acoustic-like plasmons in hole-doped La1.84Sr0.16CuO4 and electron-doped La1.84Ce0.16CuO4 using the two-particle probe, resonant inelastic x-ray scattering. We then describe the plasmon dispersions in both systems, within both the weak-coupling mean-field random phase approximation (RPA) and strong-coupling 𝑡−𝐽−𝑉 model in a large-𝑁 scheme. The 𝑡−𝐽−𝑉 model, which includes the correlation effects implicitly, accurately describes the plasmon dispersions as resonant excitations outside the single-particle intraband continuum. In comparison, a quantitative description of the plasmon dispersion in the RPA approach is obtained only upon explicit consideration of renormalized electronic band parameters. Our comparative analysis shows that electron correlations significantly impact the low-energy plasmon excitations across the cuprate doping phase diagram, even at long wavelengths. Thus, complementary information on the evolution of electron correlations, influenced by the rich electronic phases in condensed matter systems, can be extracted through the study of two-particle charge response.
|
Nov 2024
|
|
I10-Beamline for Advanced Dichroism - scattering
|
M. T.
Littlehales
,
S. H.
Moody
,
P. J.
Bereciartua
,
D. A.
Mayoh
,
Z. B.
Parkin
,
T. J.
Blundell
,
E.
Unsworth
,
S.
Francoual
,
G.
Balakrishnan
,
D.
Alba Venero
,
P. D.
Hatton
Diamond Proposal Number(s):
[34192]
Open Access
Abstract: The Eu(Ga1−𝑥Al𝑥)4 series is composed of centrosymmetric structures which exhibit a wide range of rich topological phenomena, including some members hosting magnetic skyrmions. In this letter, we investigate the previously unreported intermediate compound EuGa2.4Al1.6, which hosts two distinct phase transitions under zero applied magnetic field. We have used resonant elastic x-ray scattering with full linear polarization analysis to unambiguously determine the zero-field magnetic structures, which consist of a transition between a basal plane transverse spin density wave at higher temperatures into a noncollinear helical ground state. Furthermore, we demonstrate a phase coexistence regime below the transition and reveal an elliptically modulated helical magnetic structure emerging from wavevector splitting.
|
Jul 2024
|
|
I05-ARPES
|
Open Access
Abstract: We report on the interplay between a van Hove singularity and a charge density wave state in
2
H
−
TaSe
2
. We use angle-resolved photoemission spectroscopy to investigate changes in the Fermi surface of this material under surface doping with potassium. At high doping, we observe modifications which imply the disappearance of the
(
3
×
3
)
charge density wave and formation of a different correlated state. Using a tight-binding-based approach as well as an effective model, we explain our observations as a consequence of coupling between the single-particle Lifshitz transition during which the Fermi level passes a van Hove singularity and the charge density order. In this scenario, the high electronic density of states associated with the van Hove singularity induces a change in the periodicity of the charge density wave from the known
(
3
×
3
)
to a new
(
2
×
2
)
superlattice.
|
Jan 2024
|
|
I11-High Resolution Powder Diffraction
|
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.
|
Nov 2023
|
|
I05-ARPES
|
J.
Küspert
,
R.
Cohn Wagner
,
C.
Lin
,
K.
Von Arx
,
Q.
Wang
,
K.
Kramer
,
W. R.
Pudelko
,
N. C.
Plumb
,
C. E.
Matt
,
C. G.
Fatuzzo
,
D.
Sutter
,
Y.
Sassa
,
J.-Q.
Yan
,
J.-S.
Zhou
,
J. B.
Goodenough
,
S.
Pyon
,
T.
Takayama
,
H.
Takagi
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
M.
Hoesch
,
C.
Cacho
,
T. K.
Kim
,
M.
Horio
,
J.
Chang
Diamond Proposal Number(s):
[27768, 10550]
Open Access
Abstract: We carried out a comprehensive high-resolution angle-resolved photoemission spectroscopy (ARPES) study of the pseudogap interplay with superconductivity in La-based cuprates. The three systems
La
2
−
x
Sr
x
CuO
4
,
La
1.6
−
x
Nd
0.4
Sr
x
CuO
4
, and
La
1.8
−
x
Eu
0.2
Sr
x
CuO
4
display slightly different pseudogap critical points in the temperature versus doping phase diagram. We studied the pseudogap evolution into the superconducting state for doping concentrations just below the critical point. In this setting, near optimal doping for superconductivity and in the presence of the weakest possible pseudogap, we uncover how the pseudogap is partially suppressed inside the superconducting state. This conclusion is based on the direct observation of a reduced pseudogap energy scale and re-emergence of spectral weight suppressed by the pseudogap. Altogether these observations suggest that the pseudogap phenomenon in La-based cuprates is in competition with superconductivity for antinodal spectral weight.
|
Oct 2022
|
|
|
|
Sharon
Berkowicz
,
Sudipta
Das
,
Mario
Reiser
,
Mariia
Filianina
,
Maddalena
Bin
,
Giulio
Crevatin
,
Franz
Hennies
,
Clemens
Weninger
,
Alexander
Bjorling
,
Paul
Bell
,
Fivos
Perakis
Open Access
Abstract: Here, we demonstrate an experimental proof of concept for nanofocused x-ray photon correlation spectroscopy, a technique sensitive to nanoscale fluctuations present in a broad range of systems. The experiment, performed at the NanoMAX beamline at MAX IV, uses a novel event-based x-ray detector to capture nanoparticle structural dynamics with microsecond resolution. By varying the nanobeam size from
σ
=
88
nm to
σ
=
2.5
μ
m
, we quantify the effect of the nanofocus on the small-angle scattering lineshape and on the diffusion coefficients obtained from nano-XPCS. We observe that the use of nanobeams leads to a multifold increase in speckle contrast, which greatly improves the experimental signal-to-noise ratio, quantified from the two-time intensity correlation functions. We conclude that it is possible to account for influence of the high beam divergence on the lineshape and measured dynamics by including a convolution with the nanobeam profile in the model.
|
Jul 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
|
|
B16-Test Beamline
|
Diamond Proposal Number(s):
[21446]
Open Access
Abstract: It has long been believed that the core-hole lifetime (CHL) of an atom is an intrinsic physical property, and controlling it is significant yet is very hard. Here, the CHL of the
2
p
state of a W atom is manipulated experimentally by adjusting the emission rate of a resonant fluorescence channel with the assistance of an x-ray thin-film planar cavity. The enhanced emission rate is linearly accelerated by the photonic density of states inside the cavity, which can be directly controlled by adjusting the cavity field amplitude through choosing different cavity modes or changing the angle offset in experiment. This experimental observation is in good agreement with the prediction of a developed theoretical model. It is found that the manipulated resonant fluorescence channel can even dominate the CHL. The controllable CHL realized here will facilitate the nonlinear investigations and modern x-ray scattering techniques in the hard x-ray region.
|
Jul 2021
|
|
I05-ARPES
|
C. E.
Matt
,
O.
Ivashko
,
M.
Horio
,
J.
Choi
,
Q.
Wang
,
D.
Sutter
,
N.
Dennler
,
M. H.
Fischer
,
S.
Katrych
,
L.
Forro
,
J.
Ma
,
B.
Fu
,
B. Q.
Lv
,
M. V.
Zimmermann
,
T. K.
Kim
,
N. C.
Plumb
,
N.
Xu
,
M.
Shi
,
Johan
Chang
Diamond Proposal Number(s):
[16104]
Open Access
Abstract: The interplay between structural and electronic phases in iron-based superconductors is a central theme in the search for the superconducting pairing mechanism. While electronic nematicity is competing with superconductivity, the effect of purely structural orthorhombic order is unexplored. Here, using x-ray diffraction and angle-resolved photoemission spectroscopy, we reveal a structural orthorhombic phase in the electron-doped iron-pnictide superconductor
Pr
4
Fe
2
As
2
Te
0.88
O
4
(
T
c
=
25
K), which is distinct from orthorhombicity in the nematic phase in underdoped pnictides. Despite the high electron doping we find an exceptionally high orthorhombic onset temperature (
T
ort
∼
250
K), no signatures of phase competition with superconductivity, and absence of electronic nematic order as the driving mechanism for orthorhombicity. Combined, our results establish a high-temperature phase in the phase diagram of iron-pnictide superconductors and impose strong constraints for the modeling of their superconducting pairing mechanism.
|
Jun 2021
|
|
I16-Materials and Magnetism
|
Byungmin
Sohn
,
Bongju
Kim
,
Se Young
Park
,
Hwan Young
Choi
,
Jae Young
Moon
,
Taeyang
Choi
,
Young Jai
Choi
,
Hua
Zhou
,
Jun Woo
Choi
,
Alessandro
Bombardi
,
Dan. G.
Porter
,
Seo Hyoung
Chang
,
Jung Hoon
Han
,
Changyoung
Kim
Diamond Proposal Number(s):
[22181]
Open Access
Abstract: We observed a humplike feature in Hall effects of
SrRuO
3
ultrathin films, and systematically investigated it by controlling thicknesses, temperatures and magnetic fields. The humplike feature is extremely stable, even surviving as a magnetic field is tilted by as much as
85
∘
. Based on the atomic-level structural analysis of a
SrRuO
3
ultrathin film with a theoretical calculation, we reveal that atomic rumplings at the thin-film surface enhance Dzyaloshinskii-Moriya interaction, which can generate stable chiral spin textures and a humplike Hall effect. Moreover, temperature dependent resonant x-ray measurements at the Ru
L
edge under a magnetic field showed that the intensity modulation of unexpected peaks was correlated with the hump region in the Hall effect. We verify that the two-dimensional property of ultrathin films generates stable noncoplanar spin textures having a magnetic order in a ferromagnetic oxide material.
|
Jun 2021
|
|
