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
|
|
I05-ARPES
|
Kevin P.
Kramer
,
Rina
Tazai
,
Karin
Von Arx
,
Masafumi
Horio
,
Julia
Küspert
,
Qisi
Wang
,
Yasmine
Sassa
,
Timur K.
Kim
,
Cephise
Cacho
,
Julien E.
Rault
,
Patrick
Le Fèvre
,
François
Bertran
,
Marc
Janoschek
,
Nicolas
Gauthier
,
Daniel
Mazzone
,
Ramzy
Daou
,
Johan
Chang
Open Access
Abstract: We present a resonant angle-resolved photoemission spectroscopy (ARPES) study of the electronic band structure and heavy fermion quasiparticles in CeRu2Si2. Using light polarization analysis, considerations of the crystal field environment and hybridization between conduction and f electronic states, we identify the d-electronic orbital character of conduction bands crossing the Fermi level. Resonant ARPES spectra suggest that the localized Ce f states hybridize with eg and t2g states around the zone center. In this fashion, we reveal the orbital structure of the heavy fermion quasiparticles in CeRu2Si2 and discuss its implications for metamagnetism and superconductivity in the related compound CeCu2Si2.
|
Oct 2023
|
|
I11-High Resolution Powder Diffraction
|
Elisabetta
Nocerino
,
Shintaro
Kobayashi
,
Catherine
Witteveen
,
Ola K.
Forslund
,
Nami
Matsubara
,
Chiu
Tang
,
Takeshi
Matsukawa
,
Akinori
Hoshikawa
,
Akihiro
Koda
,
Kazuyoshi
Yoshimura
,
Izumi
Umegaki
,
Yasmine
Sassa
,
Fabian O.
Von Rohr
,
Vladimir
Pomjakushin
,
Jess H.
Brewer
,
Jun
Sugiyama
,
Martin
Mansson
Diamond Proposal Number(s):
[23840]
Open Access
Abstract: LiCrSe2 constitutes a recent valuable addition to the ensemble of two-dimensional triangular lattice antiferromagnets. In this work, we present a comprehensive study of the low temperature nuclear and magnetic structure established in this material. Being subject to a strong magnetoelastic coupling, LiCrSe2 was found to undergo a first order structural transition from a trigonal crystal system (P3¯m1
) to a monoclinic one (C2/m) at Ts = 30 K. Such restructuring of the lattice is accompanied by a magnetic transition at TN = 30 K. Refinement of the magnetic structure with neutron diffraction data and complementary muon spin rotation analysis reveal the presence of a complex incommensurate magnetic structure with a up-up-down-down arrangement of the chromium moments with ferromagnetic double chains coupled antiferromagnetically. The spin axial vector is also modulated both in direction and modulus, resulting in a spin density wave-like order with periodic suppression of the chromium moment along the chains. This behavior is believed to appear as a result of strong competition between direct exchange antiferromagnetic and superexchange ferromagnetic couplings established between both nearest neighbor and next nearest neighbor Cr3+ ions. We finally conjecture that the resulting magnetic order is stabilized via subtle vacancy/charge order within the lithium layers, potentially causing a mix of two co-existing magnetic phases within the sample.
|
Oct 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
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Qisi
Wang
,
Karin
Von Arx
,
Masafumi
Horio
,
Deepak John
Mukkattukavil
,
Julia
Kuespert
,
Yasmine
Sassa
,
Thorsten
Schmitt
,
Abhishek
Nag
,
Sunseng
Pyon
,
Tomohiro
Takayama
,
Hidenori
Takagi
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Johan
Chang
Diamond Proposal Number(s):
[24481]
Open Access
Abstract: Charge order is universal to all hole-doped cuprates. Yet, the driving interactions remain an unsolved problem. Electron-electron interaction is widely believed to be essential, whereas the role of electron-phonon interaction is unclear. We report an ultrahigh-resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bond-stretching phonon mode in stripe-ordered cuprate La1.675Eu0.2Sr0.125CuO4. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that, in addition to electronic correlations, electron-phonon coupling contributes substantially to the emergence of long-range charge-stripe order in cuprates.
|
Jun 2021
|
|
I05-ARPES
|
M.
Horio
,
Q.
Wang
,
V.
Granata
,
K. P.
Kramer
,
Y.
Sassa
,
S.
Jöhr
,
D.
Sutter
,
A.
Bold
,
L.
Das
,
Y.
Xu
,
R.
Frison
,
R.
Fittipaldi
,
T. K.
Kim
,
C.
Cacho
,
J. E.
Rault
,
P. Le
Fèvre
,
F.
Bertran
,
N. C.
Plumb
,
M.
Shi
,
A.
Vecchione
,
M. H.
Fischer
,
J.
Chang
Diamond Proposal Number(s):
[20259]
Open Access
Abstract: Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca3Ru2O7, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca3Ru2O7 a C2-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.
|
Mar 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Q.
Wang
,
M.
Horio
,
K.
Von Arx
,
Y.
Shen
,
D.
John Mukkattukavil
,
Y.
Sassa
,
O.
Ivashko
,
C. E.
Matt
,
S.
Pyon
,
T.
Takayama
,
H.
Takagi
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
T.
Adachi
,
S. M.
Haidar
,
Y.
Koike
,
Y.
Tseng
,
W.
Zhang
,
J.
Zhao
,
K.
Kummer
,
M.
Garcia-Fernandez
,
K.
Zhou
,
N. B.
Christensen
,
H. M.
Ronnow
,
T.
Schmitt
,
J.
Chang
Diamond Proposal Number(s):
[20828, 24481]
Abstract: We use resonant inelastic x-ray scattering to investigate charge-stripe correlations in
La
1.675
Eu
0.2
Sr
0.125
CuO
4
. By differentiating elastic from inelastic scattering, it is demonstrated that charge-stripe correlations precede both the structural low-temperature tetragonal phase and the transport-defined pseudogap onset. The scattering peak amplitude from charge stripes decays approximately as
T
−
2
towards our detection limit. The in-plane integrated intensity, however, remains roughly temperature independent. Therefore, although the incommensurability shows a remarkably large increase at high temperature, our results are interpreted via a single scattering constituent. In fact, direct comparison to other stripe-ordered compounds (
La
1.875
Ba
0.125
CuO
4
,
La
1.475
Nd
0.4
Sr
0.125
CuO
4
, and
La
1.875
Sr
0.125
CuO
4
) suggests a roughly constant integrated scattering intensity across all these compounds. Our results therefore provide a unifying picture for the charge-stripe ordering in La-based cuprates. As charge correlations in
La
1.675
Eu
0.2
Sr
0.125
CuO
4
extend beyond the low-temperature tetragonal and pseudogap phase, their emergence heralds a spontaneous symmetry breaking in this compound.
|
May 2020
|
|
I05-ARPES
|
D.
Sutter
,
M.
Kim
,
C. E.
Matt
,
M.
Horio
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
K.
Hauser
,
Y.
Sassa
,
G.
Gatti
,
M.
Grioni
,
M.
Hoesch
,
T. K.
Kim
,
E.
Rienks
,
N. C.
Plumb
,
M.
Shi
,
T.
Neupert
,
A.
Georges
,
J.
Chang
Diamond Proposal Number(s):
[15296]
Abstract: We present a comprehensive angle-resolved photoemission spectroscopy study of
Ca
1.8
Sr
0.2
RuO
4
. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to
d
x
z
,
d
y
z
orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions—associated with a predominantly
d
x
y
band character—are shown to display non-Fermi-liquid behavior. We thus demonstrate that
Ca
1.8
Sr
0.2
RuO
4
is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.
|
Mar 2019
|
|
I05-ARPES
|
C. E.
Matt
,
D.
Sutter
,
A. M.
Cook
,
Y.
Sassa
,
Martin
Mansson
,
O.
Tjernberg
,
L.
Das
,
M.
Horio
,
D.
Destraz
,
C. G.
Fatuzzo
,
K.
Hauser
,
M.
Shi
,
M.
Kobayashi
,
V. N.
Strocov
,
T.
Schmitt
,
P.
Dudin
,
M.
Hoesch
,
S.
Pyon
,
T.
Takayama
,
H.
Takagi
,
O. J.
Lipscombe
,
S. M.
Hayden
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[10550]
Open Access
Abstract: The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d x 2 −y 2
dx2-y2
and d z 2
dz2
) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.
|
Mar 2018
|
|
I05-ARPES
|
D.
Sutter
,
C. G.
Fatuzzo
,
S.
Moser
,
M.
Kim
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
Y.
Sassa
,
F.
Cossalter
,
G.
Gatti
,
M.
Grioni
,
H. M.
Rønnow
,
N. C.
Plumb
,
C. E.
Matt
,
M.
Shi
,
M.
Hoesch
,
T. K.
Kim
,
T.-R.
Chang
,
H.-T.
Jeng
,
C.
Jozwiak
,
A.
Bostwick
,
E.
Rotenberg
,
A.
Georges
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[14617, 12926]
Open Access
Abstract: A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund’s coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund’s coupling that together generate the Mott insulating state of Ca2RuO4.
|
May 2017
|
|
