I05-ARPES
|
Y.
Alexanian
,
A.
De La Torre
,
S.
Mckeown Walker
,
M.
Straub
,
G.
Gatti
,
A.
Hunter
,
S.
Mandloi
,
E.
Cappelli
,
S.
Riccò
,
F. Y.
Bruno
,
M.
Radovic
,
N. C.
Plumb
,
M.
Shi
,
J.
Osiecki
,
C.
Polley
,
T. K.
Kim
,
P.
Dudin
,
M.
Hoesch
,
R. S.
Perry
,
A.
Tamai
,
F.
Baumberger
Diamond Proposal Number(s):
[10348, 12404, 17381]
Open Access
Abstract: The fate of the Fermi surface in bulk electron-doped Sr2IrO4 remains elusive, as does the origin and extension of its pseudogap phase. Here, we use high-resolution angle-resolved photoelectron spectroscopy (ARPES) to investigate the electronic structure of Sr2−xLaxIrO4 up to x = 0.2, a factor of two higher than in previous work. We find that the antinodal pseudogap persists up to the highest doping level, and thus beyond the sharp increase in Hall carrier density to ≃ 1 + x recently observed above x* ≃ 0.161. This suggests that doped iridates host a unique phase of matter in which a large Hall density coexists with an anisotropic pseudogap, breaking up the Fermi surface into disconnected arcs. The temperature boundary of the pseudogap is T* ≃ 200 K for x = 0.2, comparable to cuprates and to the energy scale of short range antiferromagnetic correlations in cuprates and iridates.
|
Oct 2025
|
|
Detectors
|
M.
Hajheidari
,
C. B.
Wunderer
,
J.
Correa
,
A.
Marras
,
S.
Lange
,
M.
Dahlgruen
,
J.
Gebert
,
F.
Krivan
,
I.
Shevyakov
,
V.
Vardanyan
,
Th.
Wendt
,
M.
Hoesch
,
K.
Bagschik
,
N.
Guerrini
,
B.
Marsh
,
I.
Sedgwick
,
T.
Nicholls
,
G.
Cautero
,
D.
Giuressi
,
R. H.
Menk
,
L.
Stebel
,
A.
Greer
,
W.
Nichols
,
M.
Nakhostin
,
H. J.
Hyun
,
K. S.
Kim
,
S. H.
Kim
,
S. Y.
Park
,
S. Y.
Rah
,
E.
Plönjes
,
G.
Brenner
,
K.
Kharitonov
,
F.
Goutierrez
,
T.
Hirono
,
M.
Ruiz-Lopez
,
R.
Pan
,
S.
Gang
,
B.
Keitel
,
S.
Jelinek
,
R.
Radloff
,
H.
Graafsma
Open Access
Abstract: Percival is a CMOS-based imager with 2 megapixels, also called P2M, designed for photon science experiments. The first generation of the P2M sensor showed some performance issues. Specifically, ADCs in full-speed operation mode are affected by crosstalk and show a non-linear and uncorrectable response. A firmware hack to the readout and data acquisition system has been introduced to partially overcome these effects, at the cost of limiting the frame rate to 83 Hz. Moreover, a non-uniform dark response of the sensor pixels is observed, explained by non-uniform bias currents across the chip: two opposite edges of the sensor cannot be digitized when applying biases that have the centre of the sensor operating normally. These issues are addressed in the re-submission of the chip. In this contribution, we present the current status of the detector and the first results from the re-designed sensor.
|
May 2025
|
|
I09-Surface and Interface Structural Analysis
|
H. J.
Elmers
,
O.
Tkach
,
Y.
Lytvynenko
,
P.
Yogi
,
M.
Schmitt
,
D.
Biswas
,
J.
Liu
,
S. V.
Chernov
,
Quynh
Nguyen
,
M.
Hoesch
,
D.
Kutnyakhov
,
N.
Wind
,
L.
Wenthaus
,
M.
Scholz
,
K.
Rossnagel
,
A.
Gloskovskii
,
C.
Schlueter
,
A.
Winkelmann
,
A. A.
Haghighirad
,
T.-L.
Lee
,
M.
Sing
,
R.
Claessen
,
M.
Le Tacon
,
J.
Demsar
,
G.
Schönhense
,
O.
Fedchenko
Diamond Proposal Number(s):
[33765]
Abstract: Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsV3Sb5 upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced nontrivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. In view of a negligible spontaneous Kerr signal in recent magneto-optical studies, the results suggest an antiferromagnetic coupling of the orbital magnetic moments along the 𝑐 axis. While the inherent structural chirality may also induce circular dichroism, the observed asymmetry values seem to be too large in the case of the weak structural distortions caused by the CDW.
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Mar 2025
|
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I05-ARPES
I10-Beamline for Advanced Dichroism - scattering
|
E. L.
Arnold
,
J. M.
Riley
,
L. B.
Duffy
,
A. I.
Figueroa
,
R.
Held
,
K. M.
Shen
,
D. G.
Schlom
,
P. D. C.
King
,
M.
Hoesch
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[16162, 15481]
Open Access
Abstract: We present a detailed x-ray magnetic circular dichroism (XMCD) study of the magnetic properties of Gd-doped EuO thin films, synthesized via molecular-beam epitaxy with Gd doping levels up to over 12%. The impact of Gd doping on the electronic and magnetic behavior of EuO is studied using XMCD and magnetometry. Gd doping significantly enhances the Curie temperature (𝑇C) from 69 K in undoped EuO to over 120 K, driven by increased carrier density, while preserving the high quality of the single-crystalline films. At higher doping levels, a plateau in 𝑇C is observed, which is attributed to the formation of Eu-Gd nearest-neighbor pairs that limit dopant activation. We also observe a distinctive “double-dome” structure in the temperature-dependent magnetization, which we attribute to both the ferromagnetic ordering of Eu 4𝑓 moments at lower temperatures and the influence of conduction electrons via 4𝑓−5𝑑 exchange interactions at higher temperatures. These findings provide key insights into the mechanisms of carrier-induced magnetic transitions.
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Feb 2025
|
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I05-ARPES
|
Masafumi
Horio
,
Filomena
Forte
,
Denys
Sutter
,
Minjae
Kim
,
Claudia G.
Fatuzzo
,
Christian E.
Matt
,
Simon
Moser
,
Tetsuya
Wada
,
Veronica
Granata
,
Rosalba
Fittipaldi
,
Yasmine
Sassa
,
Gianmarco
Gatti
,
Henrik M.
Ronnow
,
Moritz
Hoesch
,
Timur K.
Kim
,
Chris
Jozwiak
,
Aaron
Bostwick
,
Eli
Rotenberg
,
Iwao
Matsuda
,
Antoine
Georges
,
Giorgio
Sangiovanni
,
Antonio
Vecchione
,
Mario
Cuoco
,
Johan
Chang
Diamond Proposal Number(s):
[10550]
Open Access
Abstract: Doped Mott insulators are the starting point for interesting physics such as high temperature superconductivity and quantum spin liquids. For multi-band Mott insulators, orbital selective ground states have been envisioned. However, orbital selective metals and Mott insulators have been difficult to realize experimentally. Here we demonstrate by photoemission spectroscopy how Ca2RuO4, upon alkali-metal surface doping, develops a single-band metal skin. Our dynamical mean field theory calculations reveal that homogeneous electron doping of Ca2RuO4 results in a multi-band metal. All together, our results provide evidence for an orbital-selective Mott insulator breakdown, which is unachievable via simple electron doping. Supported by a cluster model and cluster perturbation theory calculations, we demonstrate a type of skin metal-insulator transition induced by surface dopants that orbital-selectively hybridize with the bulk Mott state and in turn produce coherent in-gap states.
|
Nov 2023
|
|
Detectors
|
J.
Correa
,
M.
Mehrjoo
,
R.
Battistelli
,
F.
Lehmkühler
,
A.
Marras
,
C. B.
Wunderer
,
T.
Hirono
,
V.
Felk
,
F.
Krivan
,
S.
Lange
,
I.
Shevyakov
,
V.
Vardanyan
,
M.
Zimmer
,
M.
Hoesch
,
K.
Bagschik
,
N.
Guerrini
,
B.
Marsh
,
I.
Sedgwick
,
G.
Cautero
,
L.
Stebel
,
D.
Giuressi
,
R. H.
Menk
,
A.
Greer
,
T.
Nicholls
,
W.
Nichols
,
U.
Pedersen
,
P.
Shikhaliev
,
N.
Tartoni
,
H. J.
Hyun
,
S. H.
Kim
,
S. Y.
Park
,
K. S.
Kim
,
F.
Orsini
,
F. J.
Iguaz
,
F.
Büttner
,
B.
Pfau
,
E.
Plönjes
,
K.
Kharitonov
,
M.
Ruiz-Lopez
,
R.
Pan
,
S.
Gang
,
B.
Keitel
,
H.
Graafsma
Open Access
Abstract: The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science.
|
Jan 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
|
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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
|
|
I05-ARPES
|
F.
Mazzola
,
C.-M.
Yim
,
V.
Sunko
,
S.
Khim
,
P.
Kushwaha
,
O. J.
Clark
,
L.
Bawden
,
I.
Markovic
,
D.
Chakraborti
,
T. K.
Kim
,
M.
Hoesch
,
A. P.
Mackenzie
,
P.
Wahl
,
P. D. C.
King
Diamond Proposal Number(s):
[12469, 14927, 1626]
Open Access
Abstract: Controlling spin wave excitations in magnetic materials underpins the burgeoning field of magnonics. Yet, little is known about how magnons interact with the conduction electrons of itinerant magnets, or how this interplay can be controlled. Via a surface-sensitive spectroscopic approach, we demonstrate a strong electron–magnon coupling at the Pd-terminated surface of the delafossite oxide PdCoO2, where a polar surface charge mediates a Stoner transition to itinerant surface ferromagnetism. We show how the coupling is enhanced sevenfold with increasing surface disorder, and concomitant charge carrier doping, becoming sufficiently strong to drive the system into a polaronic regime, accompanied by a significant quasiparticle mass enhancement. Our study thus sheds light on electron–magnon interactions in solid-state materials, and the ways in which these can be controlled.
|
Feb 2022
|
|
I05-ARPES
|
Y.
Falke
,
N.
Ehlen
,
G.
Marini
,
A. V.
Fedorov
,
V. Y.
Voroshnin
,
B. V.
Senkovskiy
,
K.
Nikonov
,
M.
Hoesch
,
T. K.
Kim
,
L.
Petaccia
,
G.
Di Santo
,
T.
Szkopek
,
G.
Profeta
,
A.
Gruneis
Diamond Proposal Number(s):
[17064]
Abstract: We investigate electron-phonon coupling (EPC) in the charge density wave (CDW) phase of
V
Se
2
by Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and ab initio calculations. Zone folding induced by the
4
×
4
in-plane CDW phase promotes the appearance of a Raman peak at
∼
170
cm
−
1
. The suppression of ARPES intensity in parts of the Fermi surface is also a result of CDW-induced zone folding and anticrossing of the electron energy bands. The appearance of the new Raman peak is in line with the ARPES observation of a kink feature in the spectral function at the same energy. A self-energy analysis yields an EPC constant of
λ
=
0.3
. Our calculations of the EPC are in excellent agreement and reveal that the kink is caused by several optical phonon branches close in energy. Our paper highlights the CDW phase as a means of inducing EPC pathways to optical phonons that directly affect its Raman spectrum.
|
Dec 2021
|
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