I05-ARPES
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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.
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Oct 2022
|
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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.
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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.
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May 2022
|
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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.
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Jul 2021
|
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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.
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Jun 2021
|
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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.
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Jun 2021
|
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I16-Materials and Magnetism
|
Hiroki
Ueda
,
Michael
Porer
,
Jose R. L.
Mardegan
,
Sergii
Parchenko
,
Namrata
Gurung
,
Federica
Fabrizi
,
Mahesh
Ramakrishnan
,
Larissa
Boie
,
Martin Josef
Neugebauer
,
Bulat
Burganov
,
Max
Burian
,
Steven Lee
Johnson
,
Kai
Rossnagel
,
Urs
Staub
Diamond Proposal Number(s):
[15742]
Open Access
Abstract: The correlation between electronic and crystal structures of
1T − TiSe2
in the charge-density wave (CDW) state is studied by x-ray diffraction in order to clarify basic properties in the CDW state, transport properties, and chirality. Three families of reflections are used to probe atomic displacements and the orbital asymmetry in Se. Two distinct onset temperatures are found:
T
CDW
and a lower
T
∗
indicative for an onset of Se out-of-plane atomic displacements.
T
∗
coincides with a DC resistivity maximum and the onset of the proposed gyrotropic (chiral) electronic structure. However, no indication for chirality is found. The relation between the atomic displacements and the transport properties is discussed in terms of Ti
3
d
and Se
4
p
states that only weakly couple to the CDW order.
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Apr 2021
|
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I16-Materials and Magnetism
|
Max
Burian
,
Michael
Porer
,
Jose R. L.
Mardegan
,
Vincent
Esposito
,
Sergii
Parchenko
,
Bulat
Burganov
,
Namrata
Gurung
,
Mahesh
Ramakrishnan
,
Valerio
Scagnoli
,
Hiroki
Ueda
,
Sonia
Francoual
,
Federica
Fabrizi
,
Yoshikazu
Tanaka
,
Tadashi
Togashi
,
Yuya
Kubota
,
Makina
Yabashi
,
Kai
Rossnagel
,
Steven L.
Johnson
,
Urs
Staub
Diamond Proposal Number(s):
[15742]
Open Access
Abstract: In this work, we use ultrafast pump-probe nonresonant and resonant x-ray diffraction to track the periodic lattice distortion and the electronic charge density wave in
1
T
−
TiSe
2
upon optical excitation. We observe a fluence regime in which the periodic lattice deformation is strongly suppressed but the charge density wave related Se
4
p
orbital order remains mostly intact. Complete melting of both structural and electronic order occurs four to five times faster than expected from a purely electronic charge-screening process, strongly suggesting a structurally assisted weakening of excitonic correlations. Our experimental data provide insight on the intricate coupling between structural and electronic order in stabilizing the periodic-lattice-distortion/charge-density-wave state in
1
T
−
TiSe
2
. The results further show that electron-phonon coupling can lead to different, energy dependent phase-transition pathways in condensed matter systems, opening different possibilities in the conception of nonequilibrium phenomena at the ultrafast scale.
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Feb 2021
|
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I05-ARPES
|
Takafumi
Sato
,
Zhiwei
Wang
,
Daichi
Takane
,
Seigo
Souma
,
Chaoxi
Cui
,
Yongkai
Li
,
Kosuke
Nakayama
,
Tappei
Kawakami
,
Yuya
Kubota
,
Cephise
Cacho
,
Timur
Kim
,
Arian
Arab
,
Vladimir N.
Strocov
,
Yugui
Yao
,
Takashi
Takahashi
Diamond Proposal Number(s):
[23799]
Open Access
Abstract: We have performed angle-resolved photoemission spectroscopy on
EuIn
2
As
2
which is predicted to be an axion insulator in the antiferromagnetic state. By utilizing soft-x-ray and vacuum-ultraviolet photons, we revealed a three-dimensional hole pocket centered at the
Γ
point of the bulk Brillouin zone together with a heavily hole-doped surface state in the paramagnetic phase. Upon entering the antiferromagnetic phase, the band structure exhibits a marked reconstruction characterized by the emergence of an “M”-shaped bulk band near the Fermi level. The qualitative agreement with first-principles band-structure calculations suggests the occurrence of bulk-band inversion at the
Γ
point in the antiferromagnetic phase. We suggest that
EuIn
2
As
2
provides a good opportunity to study the exotic quantum phases associated with a possible axion-insulator phase.
|
Sep 2020
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[19421]
Open Access
Abstract: We report small-angle x-ray scattering measurements of the skyrmion lattice in two 200-nm-thick
Cu
2
OSeO
3
lamellae aligned with the applied magnetic field parallel to the out of plane [110] or [100] crystallographic directions. Our measurements show that the equilibrium skyrmion phase in both samples is expanded significantly compared to bulk crystals, existing between approximately 30 and 50 K over a wide region of magnetic field. This skyrmion state is elliptically distorted at low fields for the [110] sample, and symmetric for the [100] sample, possibly due to crystalline anisotropy becoming more important at this sample thickness than it is in bulk samples. Furthermore, we find that a metastable skyrmion state can be observed at low temperature by field cooling through the equilibrium skyrmion pocket in both samples. In contrast to the behavior in bulk samples, the volume fraction of metastable skyrmions does not significantly depend on cooling rate. We show that a possible explanation for this is the change in the lowest temperature of the skyrmion state in this lamellae compared to bulk, without requiring different energetics of the skyrmion state.
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Jan 2020
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