I21-Resonant Inelastic X-ray Scattering (RIXS)
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Sophia F. R.
Tenhuisen
,
Grace A.
Pan
,
Qi
Song
,
Denitsa R.
Baykusheva
,
Dan
Ferenc Segedin
,
Berit H.
Goodge
,
Hanjong
Paik
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Yanhong
Gu
,
Stefano
Agrestini
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Lena F.
Kourkoutis
,
Charles M.
Brooks
,
Julia E. A.
Mundy
,
Mark P. M.
Dean
,
Matteo
Mitrano
Diamond Proposal Number(s):
[27484]
Abstract: Magnetic interactions are thought to play a key role in the properties of many unconventional superconductors, including cuprates, iron pnictides, and square-planar nickelates. Superconductivity was also recently observed in the bilayer and trilayer Ruddlesden-Popper nickelates, the electronic structure of which is expected to differ from that of cuprates and square-planar nickelates. Here we study how electronic structure and magnetic interactions evolve with the number of layers, 𝑛, in thin film Ruddlesden-Popper nickelates Nd𝑛+1Ni𝑛O3𝑛+1 with 𝑛=1,3, and 5 using resonant inelastic x-ray scattering (RIXS). The RIXS spectra are consistent with a high-spin |3𝑑8
𝐿
̲
⟩ electronic configuration, resembling that of La2−𝑥Sr𝑥NiO4 and the parent perovskite, NdNiO3. The magnetic excitations soften to lower energy in the structurally self-doped, higher-𝑛 films. Our observations confirm that structural tuning is an effective route for altering electronic properties, such as magnetic superexchange, in this prominent family of materials.
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Apr 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Zhengang
Dong
,
Marios
Hadjimichael
,
Bernat
Mundet
,
Jaewon
Choi
,
Charles C.
Tam
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Claribel
Domínguez
,
Regan
Bhatta
,
Yue
Yu
,
Yufeng
Liang
,
Zhenping
Wu
,
Jean-Marc
Triscone
,
Chunjing
Jia
,
Ke-Jin
Zhou
,
Danfeng
Li
Diamond Proposal Number(s):
[32305]
Abstract: Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward to address these intricate questions is through the growth of high-crystallinity infinite-layer nickelates, including the “parent” phase. Here, we report the synthesis of a high-quality thin-film nickelate, NdNiO2. This is achieved through the growth of a perovskite precursor phase (NdNiO3) of superior crystallinity on the NdGaO3 substrate by off-axis RF magnetron sputtering and a low-temperature topochemical reduction using NaH. We observe a nonlinear Hall effect at low temperatures in this “non-doped” phase. We further study the electronic properties using advanced X-ray scattering and first-principles calculations. We observe spectroscopic indications of the enhanced two-dimensionality and a reduced hybridization of Nd 5d and Ni 3d orbitals. These findings unlock new pathways for preparing high-quality infinite-layer nickelates and provide new insights into the intrinsic features of these compounds.
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Jan 2025
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I09-Surface and Interface Structural Analysis
I15-1-X-ray Pair Distribution Function (XPDF)
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Liquan
Pi
,
Erik
Bjorklund
,
Gregory J.
Rees
,
Weixin
Song
,
Chen
Gong
,
John-Joseph
Marie
,
Xiangwen
Gao
,
Shengda D.
Pu
,
Mikkel
Juelsholt
,
Philip A.
Chater
,
Joohyuk
Park
,
Min Gyu
Kim
,
Jaewon
Choi
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Alex W.
Robertson
,
Robert S.
Weatherup
,
Robert A.
House
,
Peter G.
Bruce
Diamond Proposal Number(s):
[27336, 29028, 25807]
Abstract: Disordered rocksalt cathodes deliver high energy densities, but they suffer from pronounced capacity and voltage fade on cycling. Here, we investigate fade using two disordered rocksalt lithium manganese oxyfluorides: Li3Mn2O3F2 (Li1.2Mn0.8O1.2F0.8), which stores charge by Mn2+/Mn4+ redox, and Li2MnO2F, where charge storage involves both Mn3+/Mn4+ and oxygen redox (O-redox). Li3Mn2O3F2 is reported for the first time. We identify the growth of an electronically resistive surface layer with cycling that is present in both Li2MnO2F and Li3Mn2O3F2 but more pronounced in the presence of O-redox. This resistive surface inhibits electronic contact between particles, leading to the observed voltage polarization and capacity loss. By increasing carbon loading in the composite cathode, it is possible to substantially improve the cycling performance. These results help to disentangle O-redox from other leading causes of capacity fading in Mn oxyfluorides and highlight the importance of maintaining electronic conductivity in improving capacity and voltage retention.
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Dec 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Xiaoyang
Chen
,
Jaewon
Choi
,
Zhicheng
Jiang
,
Jiong
Mei
,
Kun
Jiang
,
Jie
Li
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Hualei
Sun
,
Xing
Huang
,
Dawei
Shen
,
Meng
Wang
,
Jiangping
Hu
,
Yi
Lu
,
Ke-Jin
Zhou
,
Donglai
Feng
Diamond Proposal Number(s):
[35805]
Open Access
Abstract: High-temperature superconductivity was discovered in the pressurized nickelate La3Ni2O7 which has a unique bilayer structure and mixed valence state of nickel. The properties at ambient pressure contain crucial information of the fundamental interactions and bosons mediating superconducting pairing. Here, using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we identified that Ni 3, Ni 3, and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Well-defined optical-like magnetic excitations soften into quasi-static spin-density-wave ordering, evidencing the strong electronic correlation and rich magnetic properties. Based on an effective Heisenberg spin model, we extract a much stronger inter-layer effective magnetic superexchange than the intra-layer ones and propose two viable magnetic structures. Our findings emphasize that the Ni 3 orbital bonding within the bilayer induces novel electronic and magnetic excitations, setting the stage for further exploration of La3Ni2O7 superconductor.
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Nov 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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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.
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Nov 2024
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B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Matthew J. W.
Ogley
,
Ashok S.
Menon
,
Gaurav C.
Pandey
,
Galo J.
Paez Fajardo
,
Beth J.
Johnston
,
Innes
Mcclelland
,
Veronika
Majherova
,
Steven
Huband
,
Debashis
Tripathy
,
Israel
Temprano
,
Stefano
Agrestini
,
Veronica
Celorrio
,
Gabriel E.
Perez
,
Samuel G.
Booth
,
Clare P.
Grey
,
Serena A.
Cussen
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33292, 33173]
Open Access
Abstract: This study refutes the commonly used ionic-bonding model that demarcates transition metal (TM) and oxygen redox using an archetypal Ni-rich layered oxide cathode, LiNi0.8Mn0.1Co0.1O2. Here, charge compensation during delithiation occurs without formal (ionic) Ni oxidation. Instead, oxygen-dominated states control the redox process, facilitated by strong TM-O hybridization, forming bulk-stable 3d8L and 3d8L2 electronic states, where L is a ligand hole. Bulk O–O dimers are observed with O K-edge resonant inelastic X-ray scattering but, critically, without the long-range TM migration or void formation observed in Li-rich layered oxides. Above 4.34 V vs. Li+/Li, the cathode loses O, forming a resistive surface rock-salt layer that causes capacity fade. This highlights the importance of cathode engineering when attempting to achieve higher energy densities with layered oxide cathodes, especially in those where O dominates the charge compensation mechanism.
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Oct 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Changwei
Zou
,
Jaewon
Choi
,
Qizhi
Li
,
Shusen
Ye
,
Chaohui
Yin
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Qingzheng
Qiu
,
Xinqiang
Cai
,
Qian
Xiao
,
Xingjiang
Zhou
,
Ke-Jin
Zhou
,
Yayu
Wang
,
Yingying
Peng
Diamond Proposal Number(s):
[28855]
Open Access
Abstract: How Cooper pairs form and condense has been the main challenge in the physics of copper-oxide high-temperature superconductors. Great efforts have been made in the ‘underdoped’ region of the phase diagram, through doping a Mott insulator or cooling a strange metal. However, there is still no consensus on how superconductivity emerges when electron-electron correlations dominate and the Fermi surface is missing. To address this issue, here we carry out high-resolution resonant inelastic X-ray scattering and scanning tunneling microscopy studies on prototype cuprates Bi2Sr2Ca0.6Dy0.4Cu2O8+δ near the onset of superconductivity, combining bulk and surface, momentum- and real-space information. We show that an incipient charge order exists in the antiferromagnetic regime down to 0.04 holes per CuO2 unit, entangled with a particle-hole asymmetric pseudogap. The charge order induces an intensity anomaly in the bond-buckling phonon branch, which exhibits an abrupt increase once the system enters the superconducting dome. Our results suggest that the Cooper pairs grow out of a charge-ordered insulating state, and then condense accompanied by an enhanced interplay between charge excitations and electron-phonon coupling.
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Sep 2024
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Xiao
Wang
,
Jie
Zhang
,
Zhao
Pan
,
Dabiao
Lu
,
Maocai
Pi
,
Xubin
Ye
,
Cheng
Dong
,
Jie
Chen
,
Kai
Chen
,
Florin
Radu
,
Sonia
Francoual
,
Stefano
Agrestini
,
Zhiwei
Hu
,
Chun-Fu
Chang
,
Arata
Tanaka
,
Kazunari
Yamaura
,
Yao
Shen
,
Youwen
Long
Abstract: By means of X-ray absorption spectroscopic studies, both experimentally and theoretically, we investigated the magnetic properties of the transition-metal-only double perovskite oxide Mn2CoReO6, which experiences an antiferromagnetic transition at TN = 93 K, whereas it holds a considerable net moment at low temperature. Internal exchange fields against the applied magnetic field for all the transition metal ions were identified, providing a microscopic insight into the intrasite antiferromagnetic couplings. Nevertheless, parallelly oriented canted spins of the Mn, Co, and Re cations were observed. In particularly, the Mn and Co cations hold considerable canting moments, which can be ascribed to the competition between the ferromagnetic intersite and antiferromagnetic intrasite magnetic interactions. Moreover, a spin-valve-type magnetoresistance was observed below the TN. The concurrence of the magnetoresistance effect and the antiferromagnetic semiconductive nature make Mn2CoReO6 a promising candidate for high-speed and energy-saving spintronics applications.
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Sep 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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S.
Agrestini
,
F.
Borgatti
,
P.
Florio
,
J.
Frassineti
,
D.
Fiore Mosca
,
Q.
Faure
,
B.
Detlefs
,
C. j.
Sahle
,
S.
Francoual
,
J.
Choi
,
Mirian
Garcia-Fernandez
,
K.-J.
Zhou
,
V. f.
Mitrović
,
P. m.
Woodward
,
G.
Ghiringhelli
,
C.
Franchini
,
F.
Boscherini
,
S.
Sanna
,
M.
Moretti Sala
Open Access
Abstract: A supposedly nonmagnetic 5𝑑1 double perovskite oxide is investigated by a combination of spectroscopic and theoretical methods, namely, resonant inelastic x-ray scattering, x-ray absorption spectroscopy, magnetic circular dichroism, and multiplet ligand-field calculations. We found that the large spin-orbit coupling admixes the 5𝑑 𝑡2𝑔 and 𝑒𝑔 orbitals, covalency raises the 5𝑑 population well above the nominal value, and the local symmetry is lower than 𝑂ℎ. The obtained electronic interactions account for the finite magnetic moment of Os in this compound and, in general, of 5𝑑1 ions. Our results provide direct evidence of elusive Jahn-Teller distortions, hinting at a strong electron-lattice coupling.
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Aug 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Teguh Citra
Asmara
,
Robert J.
Green
,
Andreas
Suter
,
Yuan
Wei
,
Wenliang
Zhang
,
Daniel
Knez
,
Grant
Harris
,
Yi
Tseng
,
Tianlun
Yu
,
Davide
Betto
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Yannick Maximilian
Klein
,
Neeraj
Kumar
,
Carlos W.
Galdino
,
Zaher
Salman
,
Thomas
Prokscha
,
Marisa
Medarde
,
Elisabeth
Müller
,
Yona
Soh
,
Nicholas B.
Brookes
,
Ke-Jin
Zhou
,
Milan
Radovic
,
Thorsten
Schmitt
Diamond Proposal Number(s):
[28665]
Open Access
Abstract: Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO3, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phenomena. An important example is the LaNiO3/LaTiO3 superlattice, where an interlayer electron transfer has been observed from LaTiO3 into LaNiO3 leading to a high-spin state. However, macroscopic emergence of magnetic order associated with this high-spin state has so far not been observed. Here, by using muon spin rotation, x-ray absorption, and resonant inelastic x-ray scattering, direct evidence of an emergent antiferromagnetic order with high magnon energy and exchange interactions at the LaNiO3/LaTiO3 interface is presented. As the magnetism is purely interfacial, a single LaNiO3/LaTiO3 interface can essentially behave as an atomically thin strongly-correlated quasi-2D antiferromagnet, potentially allowing its technological utilization in advanced spintronic devices. Furthermore, its strong quasi-2D magnetic correlations, orbitally-polarized planar ligand holes, and layered superlattice design make its electronic, magnetic, and lattice configurations resemble the precursor states of superconducting cuprates and nickelates, but with an S→1 spin state instead.
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Aug 2024
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