I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[32893]
Open Access
Abstract: The interplay between crystallographic symmetry, structural distortions, and the tolerance factor derived from the isotropic ionic radii of the constituent cations and anions of inorganic perovskites and related materials is a ubiquitous concept in solid-state and materials chemistry. Here we demonstrate a model for the phase transition temperatures associated with these structural distortions in layered perovskites by considering the anisotropy associated with cations, which are susceptible to first-order Jahn–Teller distortions. These symmetry-lowering phase transitions are known to have a significant interplay with superconductivity in the high-TC layered cuprates, and untangling the chemistry that can effectively control them is of the utmost relevance in the search for similar phenomena in the nickelates, the study of which has been greatly stimulated by recent reports of high-pressure superconductivity.
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Feb 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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I05-ARPES
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Chun
Lin
,
Armando
Consiglio
,
Ola Kenji
Forslund
,
Julia
Kuespert
,
M. Michael
Denner
,
Hechang
Lei
,
Alex
Louat
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Dina
Carbone
,
Mats
Leandersson
,
Craig
Polley
,
Thiagarajan
Balasubramanian
,
Domenico
Di Sante
,
Ronny
Thomale
,
Zurab
Guguchia
,
Giorgio
Sangiovanni
,
Titus
Neupert
,
Johan
Chang
Diamond Proposal Number(s):
[30650, 33528]
Open Access
Abstract: Tunable quantum materials hold great potential for applications. Of special interest are materials in which small lattice strain induces giant electronic responses. The kagome compounds AV3Sb5 (A = K, Rb, Cs) provide a testbed for electronic tunable states. In this study, through angle-resolved photoemission spectroscopy, we provide comprehensive spectroscopic measurements of the electronic responses induced by compressive and tensile strains on the charge-density-wave (CDW) and van Hove singularity (VHS) in CsV3Sb5. We observe a tripling of the CDW gap magnitudes with ~ 1% strain. Simultaneously, changes of both energy and mass of the VHS are observed. Combined, this reveals an anticorrelation between the unconventional CDW order parameter and the mass of the VHS, and highlight the role of the latter in the superconducting pairing. The substantial electronic responses uncover a rich strain tunability of the versatile kagome system in studying quantum interplays under lattice variations.
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Dec 2024
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I06-Nanoscience (XPEEM)
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O. J.
Amin
,
A.
Dal Din
,
E.
Golias
,
Y.
Niu
,
A.
Zakharov
,
S. C.
Fromage
,
C. J. B.
Fields
,
S. L.
Heywood
,
R. B.
Cousins
,
F.
Maccherozzi
,
J.
Krempasky
,
J. H.
Dil
,
D.
Kriegner
,
B.
Kiraly
,
R. P.
Campion
,
A. W.
Rushforth
,
K. W.
Edmonds
,
S. S.
Dhesi
,
L.
Šmejkal
,
T.
Jungwirth
,
P.
Wadley
Diamond Proposal Number(s):
[36317]
Open Access
Abstract: Nanoscale detection and control of the magnetic order underpins a spectrum of condensed-matter research and device functionalities involving magnetism. The key principle involved is the breaking of time-reversal symmetry, which in ferromagnets is generated by an internal magnetization. However, the presence of a net magnetization limits device scalability and compatibility with phases, such as superconductors and topological insulators. Recently, altermagnetism has been proposed as a solution to these restrictions, as it shares the enabling time-reversal-symmetry-breaking characteristic of ferromagnetism, combined with the antiferromagnetic-like vanishing net magnetization. So far, altermagnetic ordering has been inferred from spatially averaged probes. Here we demonstrate nanoscale imaging of altermagnetic states from 100-nanometre-scale vortices and domain walls to 10-micrometre-scale single-domain states in manganese telluride (MnTe). We combine the time-reversal-symmetry-breaking sensitivity of X-ray magnetic circular dichroism12 with magnetic linear dichroism and photoemission electron microscopy to achieve maps of the local altermagnetic ordering vector. A variety of spin configurations are imposed using microstructure patterning and thermal cycling in magnetic fields. The demonstrated detection and controlled formation of altermagnetic spin configurations paves the way for future experimental studies across the theoretically predicted research landscape of altermagnetism, including unconventional spin-polarization phenomena, the interplay of altermagnetism with superconducting and topological phases, and highly scalable digital and neuromorphic spintronic devices.
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Dec 2024
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I05-ARPES
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Abstract: Unconventional superconductors hold promise for high-temperature superconductivity, but their pairing mechanism remains uncertain. A key approach to understanding this is studying the normal state phases from which superconductivity emerges. In iron chalcogenide superconductors, this phase is the nematic electronic phase, and this thesis investigates its influence on the electronic structure using angle-resolved photoemission spectroscopy (ARPES). Using low-energy models I can quantify the experimental band dispersion and identify the orbital character. I further compliment these measurements with density functional theory calculations.
Initially, I examine the electronic structure of nematic FeSe1−xTex. From increasing the Te concentration, I find the effective masses of each hole band to reduce for x < 0.3. However, beyond this I observe significant variations in the hole band of dxy orbital character. As Te concentration increases, this band shifts towards the Fermi level, correlating with an increase in its effective mass and an enhanced superconductivity. To explore how strain couples to the nematic order, I apply uniaxial strain to FeSe1−xSx and track the electronic spectral function. I quantify momentum- dependent band splittings, orbital transmutation and an orbital dependent spectral weight transfer at hole pockets. These findings align well with other nematic systems, offering a comprehensive description of how the nematic phase distorts the electronic structure. Furthermore, I conduct temperature-dependent ARPES on three FeSe1−xSx systems under fixed symmetry-breaking strain. I observe significant temperature dependence within the spectral weight and band splittings at the hole pockets. In contrast, the band splittings at the electron pockets show a weaker temperature dependence, indicating they are driven predominantly by pure lattice distortion, rather than via the nematic order. Lastly, transport studies reveal no clear coupling between symmetry-breaking strain and superconductivity. Instead, I observe a linear strain dependence of the superconducting transition, where the trends agree with symmetry preserving pressure studies.
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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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I05-ARPES
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Diamond Proposal Number(s):
[26631]
Open Access
Abstract: Interaction between electrons and phonons in solids is a key effect defining the physical properties of materials, such as electrical and thermal conductivity. In transition metal dichalcogenides (TMDCs), the electron–phonon coupling results in the formation of polarons, quasiparticles that manifest themselves as discrete features in the electronic spectral function. In this study, we report the formation of polarons at the alkali-dosed MoSe2 surface, where Rashba-like spin splitting of the conduction band states is caused by an inversion-symmetry breaking electric field. In addition, we observed a crossover from phonon-like to plasmon-like polaronic spectral features at the MoSe2 surface with increasing doping. Our findings support the concept of electron–phonon coupling-mediated superconductivity in electron-doped layered TMDC materials, as observed using ionic liquid gating technology. Furthermore, the discovered spin-splitting at the Fermi level could offer crucial experimental validation for theoretical models of Ising-type superconductivity in these materials.
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Nov 2024
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[28846]
Open Access
Abstract: Understanding irradiation damage of REBCO is increasingly of interest for compact tokamak fusion reactor designs, as these materials are critical for the proposed magnetic plasma confinement systems. Here commercially sourced samples of REBCO coated conductor are irradiated with 300 keV He+ ions to a damage level of 169×10-3 displacements-per-atom, to the point where superconductivity is no longer detectable, meaning these samples correspond to a non-functional end-of-life component in a fusion reactor context. Subsequent analysis of the crystal structure through a combination of X-ray diffraction and X-ray absorption spectroscopy measurements reveals a complex variation away from the as-grown structure. The local structure probed by the spectroscopy measurements is further observed to change as a function of the relative polarisation of the incident X-ray beam, indicating that within this damage regime the structural anisotropy of the REBCO unit cell plays a determining role in where defects accumulate within the material. Here the local structure measurements probing the a-b plane of the system vary significantly less than those probing the c-axis direction following irradiation, mirroring the observed trend in the X-ray diffraction data that the a:b ratio is preserved upon irradiation whilst the absolute values increase, whereas the c-axis parameter expands. These observations highlight the role of oxygen defect formation in driving the degradation of superconductivity within irradiated REBCO. These changes are observed to preferentially accumulate along the c-axis of the material, indicating a possible mechanistic signature of the degradation of the superconducting properties within these systems that are evident using a local structure probe such as EXAFS.
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Nov 2024
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I15-Extreme Conditions
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Abstract: The presented thesis is focused on the investigation of magnetic properties among the family of tetragonal R2T2X intermetallics potentially hosting frustrated magnetism, especially with respect to the role of underlying structural details.
As a part of this work, several compounds were successfully prepared in the form of high-quality single-crystals (La2Pd2In, Ce2Pd2In, Dy2Cu2In, Yb2Pt2Pb), or eventually as polycrystals (R2Cu2In, R = La, Ce, Tm, Lu). Structural, magnetic, transport, and thermal properties of prepared samples were thoroughly studied by both bulk and microscopic methods under various external conditions with special emphasis on the pressure acting.
The performed experiments allow to state about the strong relation between structural aspects and magnetism within the R2T2X family. The importance of the mutual influence between the lattice and magnetic anisotropy is underlined by the comparison of magnetic systems and their non-magnetic analogs studied to provide the background information. In addition, superconductivity was revealed in La2T2In (T = Pd, Cu) compounds.
Magnetic anisotropy was found as an important ingredient in the magnetism of Dy2Cu2In. Determination of the magnetic structure by means of neutron diffraction together with the analysis of temperature dependence of the anisotropy constants clarified the uncertainties in the nature of its magnetic ordering. Another Cu-based system, Tm2Cu2In, was found to exhibit the pressure-enhanced spin dynamics.
The key material with a proven direct link between the structural changes and magnetic frustration is Ce2Pd2In exhibiting two distinct phases of pressure-driven destruction of magnetic order. Gradual buildup of Kondo interactions at pressures below 3 GPa is followed by the rapid loss of magnetism at higher pressures, placed into the context of pressure evolution of crystal lattice, in which all nearest neighbors in the basal plane converge to the same value, forming a triangular lattice with conditions for frustration.
Contrary to that, magnetism of Yb2Pt2Pb exhibiting frustration-related characteristics already at ambient pressure was found to be almost pressure-invariant and driven mainly by the anisotropy.
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Oct 2024
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