|
|
Daniel
Jost
,
Yonghao
Yuan
,
Ta
Tang
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Yonghun
Lee
,
Ke-Jin
Zhou
,
Brian
Moritz
,
Thomas
Devereaux
,
Wei-Sheng
Lee
,
Zhi-Xun
Shen
Abstract: The experimental investigation of one-dimensional spin chains is an important angle to benchmark theoretical frameworks tackling the physics of strongly correlated electron systems, such as the Hubbard model. Yet, relevant experimental studies are scarce due to the lack of dope-able 1D materials. Recently, thin films of the quasi-1D cuprate Ba2-xCuO3+d (BCO) were synthesized and successfully hole doped using molecular beam epitaxy (MBE). Here we present resonant inelastic x-ray scattering (RIXS) results on these quasi-1D spin chains. We identify dominant electronic and magnetic contributions to the RIXS cross section and the dependence of these spectral signatures as a function of doping. From these measurements, we find robust signatures of dispersive two-spinon and orbital excitations for doping concentrations exceeding 20%. Furthermore, we perform a comparison with numerical results invoking an extended 1D Hubbard model. The potential implications of our findings for higher dimensional cuprate systems will also be discussed.
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Mar 2023
|
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I05-ARPES
|
Z.
Wang
,
S.
Mckeown Walker
,
A.
Tamai
,
Y.
Wang
,
Z.
Ristic
,
F.
Bruno
,
A.
De La Torre
,
S.
Ricco
,
N. C.
Plumb
,
M.
Shi
,
P.
Hlawenka
,
J.
Sánchez-Barriga
,
A.
Varykhalov
,
Timur
Kim
,
Moritz
Hoesch
,
P. D. C.
King
,
Worawat
Meevasana
,
U.
Diebold
,
J.
Mesot
,
B.
Moritz
,
T. P.
Devereaux
,
M.
Radovic
,
F.
Baumberger
Diamond Proposal Number(s):
[11741]
Abstract: Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides1, 2, 3, 4. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface5, 6, 7 to reveal a remarkably complex evolution of electron–phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface8, 9, 10, 11, 12, 13, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron–phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.
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Apr 2016
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Hepting
,
D.
Li
,
C. J.
Jia
,
H.
Lu
,
E.
Paris
,
Y.
Tseng
,
X.
Feng
,
M.
Osada
,
E.
Been
,
Y.
Hikita
,
Y.-D.
Chuang
,
Z.
Hussain
,
K. J.
Zhou
,
A.
Nag
,
M.
Garcia-Fernandez
,
M.
Rossi
,
H. Y.
Huang
,
D. J.
Huang
,
Z. X.
Shen
,
T.
Schmitt
,
H. Y.
Hwang
,
B.
Moritz
,
J.
Zaanen
,
T. P.
Devereaux
,
W. S.
Lee
Diamond Proposal Number(s):
[22009]
Abstract: The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors. The recent discovery of superconductivity in the doped infinite-layer nickelate NdNiO2 has strengthened these efforts. Here, we use X-ray spectroscopy and density functional theory to show that the electronic structure of LaNiO2 and NdNiO2, while similar to the cuprates, includes significant distinctions. Unlike cuprates, the rare-earth spacer layer in the infinite-layer nickelate supports a weakly interacting three-dimensional 5d metallic state, which hybridizes with a quasi-two-dimensional, strongly correlated state with
3
d
x
2
−
y
2
3dx2−y2
symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics, which are well known for heavy fermion behaviour, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy fermion compounds. This Kondo- or Anderson-lattice-like ‘oxide-intermetallic’ replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.
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Jan 2020
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
W. S.
Lee
,
K.
Zhou
,
M.
Hepting
,
J.
Li
,
A.
Nag
,
A. C.
Walters
,
M.
Garcia-Fernandez
,
H. C.
Robarts
,
M.
Hashimoto
,
H.
Lu
,
B.
Nosarzewski
,
D.
Song
,
H.
Eisaki
,
Z. X.
Shen
,
B.
Moritz
,
J.
Zaanen
,
T. P.
Devereaux
Diamond Proposal Number(s):
[18462]
Abstract: Copper oxide high-TC superconductors possess a number of exotic orders that coexist with or are proximal to superconductivity. Quantum fluctuations associated with these orders may account for the unusual characteristics of the normal state, and possibly affect the superconductivity. Yet, spectroscopic evidence for such quantum fluctuations remains elusive. Here, we use resonant inelastic X-ray scattering to reveal spectroscopic evidence of fluctuations associated with a charge order in nearly optimally doped Bi2Sr2CaCu2O8+δ. In the superconducting state, while the quasielastic charge order signal decreases with temperature, the interplay between charge order fluctuations and bond-stretching phonons in the form of a Fano-like interference increases, an observation that is incompatible with expectations for competing orders. Invoking general principles, we argue that this behaviour reflects the properties of a dissipative system near an order–disorder quantum critical point, where the dissipation varies with the opening of the pseudogap and superconducting gap at low temperatures, leading to the proliferation of quantum critical fluctuations, which melt charge order.
|
Aug 2020
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
H.
Lu
,
M.
Rossi
,
A.
Nag
,
M.
Osada
,
D. F.
Li
,
K.
Lee
,
B. Y.
Wang
,
M.
Garcia-Fernandez
,
S.
Agrestini
,
Z. X.
Shen
,
E. M.
Been
,
B.
Moritz
,
T. P.
Devereaux
,
J.
Zaanen
,
H. Y.
Hwang
,
K.-J.
Zhou
,
W.-S.
Lee
Diamond Proposal Number(s):
[25165]
Abstract: The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a material class that mirrors the cuprate superconductors. We measured the magnetic excitations in these nickelates using resonant inelastic x-ray scattering at the Ni L3-edge. Undoped NdNiO2 possesses a branch of dispersive excitations with a bandwidth of approximately 200 milli–electron volts, which is reminiscent of the spin wave of strongly coupled, antiferromagnetically aligned spins on a square lattice. The substantial damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, whereas the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates.
|
Jul 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Haiyu
Lu
,
Matteo
Rossi
,
Jung-Ho
Kim
,
Hasan
Yavas
,
Ayman
Said
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Chunjing
Jia
,
Brian
Moritz
,
Thomas P.
Devereaux
,
Zhi-Xun
Shen
,
Wei-Sheng
Lee
Diamond Proposal Number(s):
[25165]
Abstract: We utilized high-energy-resolution resonant inelastic x-ray scattering (RIXS) at both the Ta and Ni
L
3
edges to map out element-specific particle-hole excitations in
Ta
2
Ni
Se
5
across the phase transition. Our results reveal a momentum-dependent gaplike feature in the low-energy spectrum, which agrees well with the band gap in element-specific joint density of states calculations based on ab initio estimates of the electronic structure in both the low-temperature monoclinic and high-temperature orthorhombic structures. Below
T
c
, the RIXS energy-momentum map shows a minimal gap at the Brillouin zone center
(
∼
0.16
eV
)
, confirming that
Ta
2
Ni
Se
5
possesses a direct band gap in its low-temperature ground state. However, inside the gap, no signature of anticipated collective modes with an energy scale comparable to the gap size can be identified. Upon increasing the temperature to above
T
c
, whereas the gap at the zone center closes, the RIXS map at finite momenta still possesses the gross features of the low-temperature map, suggesting a substantial mixing between the Ta and Ni orbits in the conduction and valence bands, which does not change substantially across the phase transition. Our experimental observations and comparison to the theoretical calculations lend further support to the phase transition and the corresponding gap opening in
Ta
2
Ni
Se
5
being largely structural by nature, with a possible minor contribution from the putative exciton condensate.
|
Jun 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Rossi
,
H.
Lu
,
A.
Nag
,
D.
Li
,
M.
Osada
,
K.
Lee
,
B. Y.
Wang
,
S.
Agrestini
,
Mirian
Garcia-Fernandez
,
J. J.
Kas
,
Y.-D.
Chuang
,
Z. X.
Shen
,
H. Y.
Hwang
,
B.
Moritz
,
Ke-Jin
Zhou
,
T. P.
Devereaux
,
W. S.
Lee
Diamond Proposal Number(s):
[25165]
Abstract: The recent discovery of superconductivity in Nd1−xSrxNiO2 has drawn significant attention in the field. A key open question regards the evolution of the electronic structure with respect to hole doping. Here we exploit x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the doping-dependent electronic structure of Nd1−xSrxNiO. Upon doping, a high-energy feature in Ni L3-edge XAS develops in addition to the main absorption peak, while XAS at the O K-, Nd M3- and Nd M5-edge exhibits a much weaker response. This implies that doped holes are mainly introduced into Ni 3 d states. By comparing our data to atomic multiplet calculations including D4h crystal field, the doping-induced feature in Ni L3-edge XAS is consistent with a d 8 spin-singlet state in which doped holes reside in the 3dx2−y2 orbitals. This is further supported by the softening of RIXS orbital excitations due to doping, corroborating with the Fermi level shift associated with increasing holes in the Ni 3dx2−y2 orbital.
|
Dec 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Matteo
Rossi
,
Motoki
Osada
,
Jaewon
Choi
,
Stefano
Agrestini
,
Daniel
Jost
,
Yonghun
Lee
,
Haiyu
Lu
,
Bai Yang
Wang
,
Kyuho
Lee
,
Abhishek
Nag
,
Yi-De
Chuang
,
Cheng-Tai
Kuo
,
Sang-Jun
Lee
,
Brian
Moritz
,
Thomas P.
Devereaux
,
Zhi-Xun
Shen
,
Jun-Sik
Lee
,
Ke-Jin
Zhou
,
Harold Y.
Hwang
,
Wei-Sheng
Lee
Diamond Proposal Number(s):
[25598, 27558]
Abstract: A defining signature of strongly correlated electronic systems is a rich phase diagram, which consists of multiple broken symmetries, such as magnetism, superconductivity and charge order1,2. In the recently discovered nickelate superconductors3,4,5,6,7,8,9,10, a large antiferromagnetic exchange energy has been reported, which implies the existence of strong electronic correlations11. However, signatures of a broken-symmetry state other than superconductivity have not yet been observed. Here we observe charge ordering in infinite-layer nickelates La1−xSrxNiO2 using resonant X-ray scattering. The parent compound orders along the Ni–O bond direction with an incommensurate wavevector, distinct from the stripe order observed in other nickelates12,13,14 that propagates along a direction 45° to the Ni–O bond. The resonance profile we measure indicates that ordering originates from the nickelate layers and induces a parasitic charge modulation of lanthanum electrons. Upon doping, the charge order diminishes and its wavevector shifts towards commensurate, hinting that strong electronic correlations are likely to be responsible for the ordered state. Our results suggest that the existence of charge order and its potential interplay with antiferromagnetic fluctuations and superconductivity are important themes in nickel-based superconductors.
|
Jul 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Haiyu
Lu
,
Makoto
Hashimoto
,
Su-Di
Chen
,
Shigeyuki
Ishida
,
Dongjoon
Song
,
Hiroshi
Eisaki
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Riccardo
Arpaia
,
Giacomo
Ghiringhelli
,
Lucio
Braicovich
,
Jan
Zaanen
,
Brian
Moritz
,
Kurt
Kummer
,
Nicholas B.
Brookes
,
Ke-Jin
Zhou
,
Zhi-Xun
Shen
,
Thomas P.
Devereaux
,
Wei-Sheng
Lee
Diamond Proposal Number(s):
[22009]
Abstract: Identifying quantum critical points (QCPs) and their associated fluctuations may hold the key to unraveling the unusual electronic phenomena observed in cuprate superconductors. Recently, signatures of quantum fluctuations associated with charge order (CO) have been inferred from the anomalous enhancement of CO excitations that accompany the reduction of the CO order parameter in the superconducting state. To gain more insight into the interplay between CO and superconductivity, here we investigate the doping dependence of this phenomenon throughout the Bi-2212 cuprate phase diagram using resonant inelastic x-ray scattering (RIXS) at the Cu
L
3
edge. As doping increases, the CO wave vector decreases, saturating near a commensurate value of 0.25 reciprocal lattice unit beyond a characteristic doping
p
c
, where the correlation length becomes shorter than the apparent periodicity (
4
a
0
). Such behavior is indicative of the fluctuating nature of the CO; the proliferation of CO excitations in the superconducting state also appears strongest at
p
c
, consistent with expected behavior at a CO QCP. Intriguingly,
p
c
appears to be near optimal doping, where the superconducting transition temperature
T
c
is maximal.
|
Oct 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Rossi
,
H.
Lu
,
K.
Lee
,
B. H.
Goodge
,
J.
Choi
,
M.
Osada
,
Y.
Lee
,
D.
Li
,
B. Y.
Wang
,
D.
Jost
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
Z. X.
Shen
,
Ke-Jin
Zhou
,
E.
Been
,
B.
Moritz
,
L. F.
Kourkoutis
,
T. P.
Devereaux
,
H. Y.
Hwang
,
W. S.
Lee
Diamond Proposal Number(s):
[25598]
Abstract: We conducted a comparative study of the rare-earth infinite-layer nickelate films,
R
NiO
2
(
R
= La, Pr, and Nd), using resonant inelastic x-ray scattering (RIXS). We found that the gross features of the orbital configurations are essentially the same, with minor variations in the detailed hybridization. For low-energy excitations, we unambiguously confirm the presence of damped magnetic excitations in all three compounds. By fitting to a linear spin-wave theory, comparable spin exchange coupling strengths and damping coefficients are extracted, indicating a universal magnetic structure in the infinite-layer nickelates. Interestingly, while signatures of a charge order are observed in
LaNiO
2
in the quasielastic region of the RIXS spectrum, it is absent in
NdNiO
2
and
PrNiO
2
. This prompts further investigation into the universality and the origins of charge order within the infinite-layer nickelates.
|
Jan 2024
|
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