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Vaz da Cruz V, Ignatova N, Couto RC, Fedotov DA, Rehn DR, Savchenko V, Norman P, Ågren H, Polyutov S, Niskanen J, Eckert S, Jay RM, Fondell M, Schmitt T, Pietzsch A, Föhlisch A, Gel’mukhanov F, Odelius M, Kimberg V. Nuclear dynamics in resonant inelastic X-ray scattering and X-ray absorption of methanol. J Chem Phys 2019; 150:234301. [DOI: 10.1063/1.5092174] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Habel JC, Gossner MM, Schmitt T. What makes a species a priority for nature conservation? Anim Conserv 2019. [DOI: 10.1111/acv.12512] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Ivashko O, Horio M, Wan W, Christensen NB, McNally DE, Paris E, Tseng Y, Shaik NE, Rønnow HM, Wei HI, Adamo C, Lichtensteiger C, Gibert M, Beasley MR, Shen KM, Tomczak JM, Schmitt T, Chang J. Strain-engineering Mott-insulating La 2CuO 4. Nat Commun 2019; 10:786. [PMID: 30783084 PMCID: PMC6381167 DOI: 10.1038/s41467-019-08664-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 01/20/2019] [Indexed: 11/10/2022] Open
Abstract
The transition temperature Tc of unconventional superconductivity is often tunable. For a monolayer of FeSe, for example, the sweet spot is uniquely bound to titanium-oxide substrates. By contrast for La2-xSrxCuO4 thin films, such substrates are sub-optimal and the highest Tc is instead obtained using LaSrAlO4. An outstanding challenge is thus to understand the optimal conditions for superconductivity in thin films: which microscopic parameters drive the change in Tc and how can we tune them? Here we demonstrate, by a combination of x-ray absorption and resonant inelastic x-ray scattering spectroscopy, how the Coulomb and magnetic-exchange interaction of La2CuO4 thin films can be enhanced by compressive strain. Our experiments and theoretical calculations establish that the substrate producing the largest Tc under doping also generates the largest nearest neighbour hopping integral, Coulomb and magnetic-exchange interaction. We hence suggest optimising the parent Mott state as a strategy for enhancing the superconducting transition temperature in cuprates.
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Schlappa J, Kumar U, Zhou KJ, Singh S, Mourigal M, Strocov VN, Revcolevschi A, Patthey L, Rønnow HM, Johnston S, Schmitt T. Probing multi-spinon excitations outside of the two-spinon continuum in the antiferromagnetic spin chain cuprate Sr 2CuO 3. Nat Commun 2018; 9:5394. [PMID: 30568161 PMCID: PMC6300594 DOI: 10.1038/s41467-018-07838-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Accepted: 11/26/2018] [Indexed: 11/09/2022] Open
Abstract
One-dimensional (1D) magnetic insulators have attracted significant interest as a platform for studying quasiparticle fractionalization, quantum criticality, and emergent phenomena. The spin-1/2 Heisenberg chain with antiferromagnetic nearest neighbour interactions is an important reference system; its elementary magnetic excitations are spin-1/2 quasiparticles called spinons that are created in even numbers. However, while the excitation continuum associated with two-spinon states is routinely observed, the study of four-spinon and higher multi-spinon states is an open area of research. Here we show that four-spinon excitations can be accessed directly in Sr2CuO3 using resonant inelastic x-ray scattering (RIXS) in a region of phase space clearly separated from the two-spinon continuum. Our finding is made possible by the fundamental differences in the correlation function probed by RIXS in comparison to other probes. This advance holds promise as a tool in the search for novel quantum states and quantum spin liquids.
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Meyers D, Nakatsukasa K, Mu S, Hao L, Yang J, Cao Y, Fabbris G, Miao H, Pelliciari J, McNally D, Dantz M, Paris E, Karapetrova E, Choi Y, Haskel D, Shafer P, Arenholz E, Schmitt T, Berlijn T, Johnston S, Liu J, Dean MPM. Decoupling Carrier Concentration and Electron-Phonon Coupling in Oxide Heterostructures Observed with Resonant Inelastic X-Ray Scattering. PHYSICAL REVIEW LETTERS 2018; 121:236802. [PMID: 30576191 DOI: 10.1103/physrevlett.121.236802] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 10/15/2018] [Indexed: 06/09/2023]
Abstract
We report the observation of multiple phonon satellite features in ultrathin superlattices of the form nSrIrO_{3}/mSrTiO_{3} using resonant inelastic x-ray scattering (RIXS). As the values of n and m vary, the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the RIXS cross section, we extract the variation in the electron-phonon coupling strength as a function of n and m. Combined with the negligible carrier doping into the SrTiO_{3} layers, these results indicate that the tuning of the electron-phonon coupling can be effectively decoupled from doping. This work both showcases a feasible method to extract the electron-phonon coupling in superlattices and unveils a potential route for tuning this coupling, which is often associated with superconductivity in SrTiO_{3}-based systems.
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Chikina A, Lechermann F, Husanu MA, Caputo M, Cancellieri C, Wang X, Schmitt T, Radovic M, Strocov VN. Orbital Ordering of the Mobile and Localized Electrons at Oxygen-Deficient LaAlO 3/SrTiO 3 Interfaces. ACS NANO 2018; 12:7927-7935. [PMID: 29995384 DOI: 10.1021/acsnano.8b02335] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Interfacing different transition-metal oxides opens a route to functionalizing their rich interplay of electron, spin, orbital, and lattice degrees of freedom for electronic and spintronic devices. Electronic and magnetic properties of SrTiO3-based interfaces hosting a mobile two-dimensional electron system (2DES) are strongly influenced by oxygen vacancies, which form an electronic dichotomy, where strongly correlated localized electrons in the in-gap states (IGSs) coexist with noncorrelated delocalized 2DES. Here, we use resonant soft-X-ray photoelectron spectroscopy to prove the eg character of the IGSs, as opposed to the t2g character of the 2DES in the paradigmatic LaAlO3/SrTiO3 interface. We furthermore separate the d xy and d xz/d xz orbital contributions based on deeper consideration of the resonant photoexcitation process in terms of orbital and momentum selectivity. Supported by a self-consistent combination of density functional theory and dynamical mean field theory calculations, this experiment identifies local orbital reconstruction that goes beyond the conventional eg- vs-t2g band ordering. A hallmark of oxygen-deficient LaAlO3/SrTiO3 is a significant hybridization of the eg and t2g orbitals. Our findings provide routes for tuning the electronic and magnetic properties of oxide interfaces through "defect engineering" with oxygen vacancies.
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Horio M, Hauser K, Sassa Y, Mingazheva Z, Sutter D, Kramer K, Cook A, Nocerino E, Forslund OK, Tjernberg O, Kobayashi M, Chikina A, Schröter NBM, Krieger JA, Schmitt T, Strocov VN, Pyon S, Takayama T, Takagi H, Lipscombe OJ, Hayden SM, Ishikado M, Eisaki H, Neupert T, Månsson M, Matt CE, Chang J. Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates. PHYSICAL REVIEW LETTERS 2018; 121:077004. [PMID: 30169083 DOI: 10.1103/physrevlett.121.077004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Indexed: 06/08/2023]
Abstract
We present a soft x-ray angle-resolved photoemission spectroscopy study of overdoped high-temperature superconductors. In-plane and out-of-plane components of the Fermi surface are mapped by varying the photoemission angle and the incident photon energy. No k_{z} dispersion is observed along the nodal direction, whereas a significant antinodal k_{z} dispersion is identified for La-based cuprates. Based on a tight-binding parametrization, we discuss the implications for the density of states near the van Hove singularity. Our results suggest that the large electronic specific heat found in overdoped La_{2-x}Sr_{x}CuO_{4} cannot be assigned to the van Hove singularity alone. We therefore propose quantum criticality induced by a collapsing pseudogap phase as a plausible explanation for observed enhancement of electronic specific heat.
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Matt CE, Sutter D, Cook AM, Sassa Y, Månsson M, Tjernberg O, Das L, Horio M, Destraz D, Fatuzzo CG, Hauser K, Shi M, Kobayashi M, Strocov VN, Schmitt T, Dudin P, Hoesch M, Pyon S, Takayama T, Takagi H, Lipscombe OJ, Hayden SM, Kurosawa T, Momono N, Oda M, Neupert T, Chang J. Direct observation of orbital hybridisation in a cuprate superconductor. Nat Commun 2018; 9:972. [PMID: 29511188 PMCID: PMC5840306 DOI: 10.1038/s41467-018-03266-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 02/01/2018] [Indexed: 11/19/2022] Open
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 (\documentclass[12pt]{minimal}
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\begin{document}$$d_{z^2}$$\end{document}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. The essential physics of cuprate superconductors is often described by single-band models. Here, Matt et al. report direct observation of a two-band electronic structure in La-based cuprates.
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Habel JC, Seibold S, Ulrich W, Schmitt T. Seasonality overrides differences in butterfly species composition between natural and anthropogenic forest habitats. Anim Conserv 2018. [DOI: 10.1111/acv.12408] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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35
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Ertan E, Savchenko V, Ignatova N, Vaz da Cruz V, Couto RC, Eckert S, Fondell M, Dantz M, Kennedy B, Schmitt T, Pietzsch A, Föhlisch A, Gel'mukhanov F, Odelius M, Kimberg V. Ultrafast dissociation features in RIXS spectra of the water molecule. Phys Chem Chem Phys 2018; 20:14384-14397. [DOI: 10.1039/c8cp01807c] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The “pseudo-atomic” peak is formed significantly faster than the atomic-like peak in water RIXS.
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Wang RP, Liu B, Green RJ, Delgado-Jaime MU, Ghiasi M, Schmitt T, van Schooneveld MM, de Groot FMF. Charge-Transfer Analysis of 2p3d Resonant Inelastic X-ray Scattering of Cobalt Sulfide and Halides. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2017; 121:24919-24928. [PMID: 29170686 PMCID: PMC5694969 DOI: 10.1021/acs.jpcc.7b06882] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 10/27/2017] [Indexed: 05/19/2023]
Abstract
We show that with 2p3d resonant inelastic X-ray scattering (RIXS) we can accurately determine the charge-transfer parameters of CoF2, CoCl2, CoBr2, and CoS. The 160 meV resolution RIXS results are compared with charge-transfer multiplet calculations. The improved resolution and the direct observation of the crystal field and charge-transfer excitations allow the determination of more accurate parameters than could be derived from X-ray absorption and X-ray photoemission, both limited in resolution by their lifetime broadening. We derive the crystal field and charge-transfer parameters of the Co2+ ions, which provides the nature of the ground state of the Co2+ ions with respect to symmetry and hybridization. In addition, the increased spectral resolution allows the more accurate determination of the atomic Slater integrals. The results show that the crystal field energy decreases with increasing ligand covalency. The L2 edge RIXS spectra show that the intensity of the (Coster-Kronig induced) nonresonant X-ray emission is a measure of ligand covalency.
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Minola M, Lu Y, Peng YY, Dellea G, Gretarsson H, Haverkort MW, Ding Y, Sun X, Zhou XJ, Peets DC, Chauviere L, Dosanjh P, Bonn DA, Liang R, Damascelli A, Dantz M, Lu X, Schmitt T, Braicovich L, Ghiringhelli G, Keimer B, Le Tacon M. Crossover from Collective to Incoherent Spin Excitations in Superconducting Cuprates Probed by Detuned Resonant Inelastic X-Ray Scattering. PHYSICAL REVIEW LETTERS 2017; 119:097001. [PMID: 28949586 DOI: 10.1103/physrevlett.119.097001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Indexed: 06/07/2023]
Abstract
Spin excitations in the overdoped high temperature superconductors Tl_{2}Ba_{2}CuO_{6+δ} and (Bi,Pb)_{2}(Sr,La)_{2}CuO_{6+δ} were investigated by resonant inelastic x-ray scattering (RIXS) as functions of doping and detuning of the incoming photon energy above the Cu-L_{3} absorption peak. The RIXS spectra at optimal doping are dominated by a paramagnon feature with peak energy independent of photon energy, similar to prior results on underdoped cuprates. Beyond optimal doping, the RIXS data indicate a sharp crossover to a regime with a strong contribution from incoherent particle-hole excitations whose maximum shows a fluorescencelike shift upon detuning. The spectra of both compound families are closely similar, and their salient features are reproduced by exact-diagonalization calculations of the single-band Hubbard model on a finite cluster. The results are discussed in the light of recent transport experiments indicating a quantum phase transition near optimal doping.
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Di Sante D, Das PK, Bigi C, Ergönenc Z, Gürtler N, Krieger JA, Schmitt T, Ali MN, Rossi G, Thomale R, Franchini C, Picozzi S, Fujii J, Strocov VN, Sangiovanni G, Vobornik I, Cava RJ, Panaccione G. Three-Dimensional Electronic Structure of the Type-II Weyl Semimetal WTe_{2}. PHYSICAL REVIEW LETTERS 2017; 119:026403. [PMID: 28753342 DOI: 10.1103/physrevlett.119.026403] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Indexed: 06/07/2023]
Abstract
By combining bulk sensitive soft-x-ray angular-resolved photoemission spectroscopy and first-principles calculations we explored the bulk electron states of WTe_{2}, a candidate type-II Weyl semimetal featuring a large nonsaturating magnetoresistance. Despite the layered geometry suggesting a two-dimensional electronic structure, we directly observe a three-dimensional electronic dispersion. We report a band dispersion in the reciprocal direction perpendicular to the layers, implying that electrons can also travel coherently when crossing from one layer to the other. The measured Fermi surface is characterized by two well-separated electron and hole pockets at either side of the Γ point, differently from previous more surface sensitive angle-resolved photoemission spectroscopy experiments that additionally found a pronounced quasiparticle weight at the zone center. Moreover, we observe a significant sensitivity of the bulk electronic structure of WTe_{2} around the Fermi level to electronic correlations and renormalizations due to self-energy effects, previously neglected in first-principles descriptions.
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Marschall F, McNally D, Guzenko VA, Rösner B, Dantz M, Lu X, Nue L, Strocov V, Schmitt T, David C. Zone plates as imaging analyzers for resonant inelastic x-ray scattering. OPTICS EXPRESS 2017; 25:15624-15634. [PMID: 28789077 DOI: 10.1364/oe.25.015624] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 06/18/2017] [Indexed: 06/07/2023]
Abstract
We have implemented and successfully tested an off-axis transmission Fresnel zone plate as a novel type of analyzer optics for resonant inelastic x-ray scattering (RIXS). We achieved a spectral resolution of 64 meV at the nitrogen K-edge (E/dE = 6200), closely matching theoretical predictions. The fundamental advantage of transmission optics is the fact that it can provide stigmatic imaging properties. This opens up a variety of advanced RIXS configurations, such as efficient scanning RIXS, parallel detection for varying incident energy and time-resolved measurements.
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Menzel F, Schmitt T, Blaimer BB. The evolution of a complex trait: cuticular hydrocarbons in ants evolve independent from phylogenetic constraints. J Evol Biol 2017; 30:1372-1385. [PMID: 28485028 DOI: 10.1111/jeb.13115] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Revised: 04/29/2017] [Accepted: 05/03/2017] [Indexed: 12/31/2022]
Abstract
Cuticular hydrocarbons (CHCs) are ubiquitous and highly diverse in insects, serving as communication signal and waterproofing agent. Despite their vital function, the causes, mechanisms and constraints on CHC diversification are still poorly understood. Here, we investigated phylogenetic constraints on the evolution of CHC profiles, using a global data set of the species-rich and chemically diverse ant genus Crematogaster. We decomposed CHC profiles into quantitative (relative abundances, chain length) and qualitative traits (presence/absence of CHC classes). A species-level phylogeny was estimated using newly generated and previously published sequences from five nuclear markers. Moreover, we reconstructed a phylogeny for the chemically diverse Crematogaster levior species group using cytochrome oxidase I. Phylogenetic signal was measured for these traits on genus and clade level and within the chemically diverse C. levior group. For most quantitative CHC traits, phylogenetic signal was low and did not differ from random expectation. This was true on the level of genus, clade and species group, indicating that CHC traits are evolutionary labile. In contrast, the presence or absence of alkenes and alkadienes was highly conserved within the C. levior group. Hence, the presence or absence of biosynthetic pathways may be phylogenetically constrained, especially at lower taxonomic levels. Our study shows that CHC composition can evolve rapidly, allowing insects to quickly adapt their chemical profiles to external selection pressures, whereas the presence of biosynthetic pathways appears more constrained. However, our results stress the importance to consider the taxonomic level when investigating phylogenetic constraints.
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Schreck S, Pietzsch A, Kennedy B, Såthe C, Miedema PS, Techert S, Strocov VN, Schmitt T, Hennies F, Rubensson JE, Föhlisch A. Erratum: Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering. Sci Rep 2017; 7:46386. [PMID: 28664929 PMCID: PMC5492273 DOI: 10.1038/srep46386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Fabbris G, Meyers D, Xu L, Katukuri VM, Hozoi L, Liu X, Chen ZY, Okamoto J, Schmitt T, Uldry A, Delley B, Gu GD, Prabhakaran D, Boothroyd AT, van den Brink J, Huang DJ, Dean MPM. Doping Dependence of Collective Spin and Orbital Excitations in the Spin-1 Quantum Antiferromagnet La_{2-x}Sr_{x}NiO_{4} Observed by X Rays. PHYSICAL REVIEW LETTERS 2017; 118:156402. [PMID: 28452512 DOI: 10.1103/physrevlett.118.156402] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Indexed: 05/23/2023]
Abstract
We report the first empirical demonstration that resonant inelastic x-ray scattering (RIXS) is sensitive to collective magnetic excitations in S=1 systems by probing the Ni L_{3} edge of La_{2-x}Sr_{x}NiO_{4} (x=0, 0.33, 0.45). The magnetic excitation peak is asymmetric, indicating the presence of single and multi-spin-flip excitations. As the hole doping level is increased, the zone boundary magnon energy is suppressed at a much larger rate than that in hole doped cuprates. Based on the analysis of the orbital and charge excitations observed by RIXS, we argue that this difference is related to the orbital character of the doped holes in these two families. This work establishes RIXS as a probe of fundamental magnetic interactions in nickelates opening the way towards studies of heterostructures and ultrafast pump-probe experiments.
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Bogdanov NA, Bisogni V, Kraus R, Monney C, Zhou K, Schmitt T, Geck J, Mitrushchenkov AO, Stoll H, van den Brink J, Hozoi L. Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:035502. [PMID: 27869641 DOI: 10.1088/1361-648x/29/3/035502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In existing theoretical approaches to core-level excitations of transition-metal ions in solids relaxation and polarization effects due to the inner core hole are often ignored or described phenomenologically. Here we set up an ab initio computational scheme that explicitly accounts for such physics in the calculation of x-ray absorption and resonant inelastic x-ray scattering spectra. Good agreement is found with experimental transition-metal L-edge data for the strongly correlated d 9 cuprate Li2CuO2, for which we determine the absolute scattering intensities. The newly developed methodology opens the way for the investigation of even more complex d n electronic structures of group VI B to VIII B correlated oxide compounds.
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Couto RC, Cruz VV, Ertan E, Eckert S, Fondell M, Dantz M, Kennedy B, Schmitt T, Pietzsch A, Guimarães FF, Ågren H, Gel'mukhanov F, Odelius M, Kimberg V, Föhlisch A. Selective gating to vibrational modes through resonant X-ray scattering. Nat Commun 2017; 8:14165. [PMID: 28106058 PMCID: PMC5263870 DOI: 10.1038/ncomms14165] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2016] [Accepted: 11/30/2016] [Indexed: 12/02/2022] Open
Abstract
The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations. Investigating dynamics of polyatomic molecules is difficult as their potential energy surfaces are multidimensional due to coupled degrees of freedom. Here the authors demonstrate a spatial selective gating technique to probe the different vibrational modes of water upon core-level excitation with X-rays.
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Lu X, McNally DE, Moretti Sala M, Terzic J, Upton MH, Casa D, Ingold G, Cao G, Schmitt T. Doping Evolution of Magnetic Order and Magnetic Excitations in (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7}. PHYSICAL REVIEW LETTERS 2017; 118:027202. [PMID: 28128620 DOI: 10.1103/physrevlett.118.027202] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2016] [Indexed: 06/06/2023]
Abstract
We use resonant elastic and inelastic x-ray scattering at the Ir-L_{3} edge to study the doping-dependent magnetic order, magnetic excitations, and spin-orbit excitons in the electron-doped bilayer iridate (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} (0≤x≤0.065). With increasing doping x, the three-dimensional long range antiferromagnetic order is gradually suppressed and evolves into a three-dimensional short range order across the insulator-to-metal transition from x=0 to 0.05, followed by a transition to two-dimensional short range order between x=0.05 and 0.065. Because of the interactions between the J_{eff}=1/2 pseudospins and the emergent itinerant electrons, magnetic excitations undergo damping, anisotropic softening, and gap collapse, accompanied by weakly doping-dependent spin-orbit excitons. Therefore, we conclude that electron doping suppresses the magnetic anisotropy and interlayer couplings and drives (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} into a correlated metallic state with two-dimensional short range antiferromagnetic order. Strong antiferromagnetic fluctuations of the J_{eff}=1/2 moments persist deep in this correlated metallic state, with the magnon gap strongly suppressed.
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Vaz da Cruz V, Ertan E, Couto RC, Eckert S, Fondell M, Dantz M, Kennedy B, Schmitt T, Pietzsch A, Guimarães FF, Ågren H, Gel'mukhanov F, Odelius M, Föhlisch A, Kimberg V. A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering. Phys Chem Chem Phys 2017; 19:19573-19589. [DOI: 10.1039/c7cp01215b] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a full analysis of the resonant inelastic X-ray scattering spectra of H2O, D2O and HDO.
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Trottier-Lapointe W, Zabeida O, Schmitt T, Martinu L. Ultralow refractive index optical films with enhanced mechanical performance obtained by hybrid glancing angle deposition. APPLIED OPTICS 2016; 55:8796-8805. [PMID: 27828277 DOI: 10.1364/ao.55.008796] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Ultralow refractive index materials (n less than 1.38 at 550 nm) are of particular interest in the context of antireflective coatings, allowing one to enhance their overall optical performance. However, application of such materials is typically limited by their mechanical properties. In this study, we explore the characteristics of a new category of hybrid (organic/inorganic) SiOCH thin films prepared by glancing angle deposition (GLAD) using electron beam evaporation of SiO2 in the presence of an organosilicon precursor. The resulting layers exhibited n as low as 1.2, showed high elastic rebound, and generally better mechanical properties than their inorganic counterparts. In addition, hybrid GLAD films were found to be highly hydrophobic. The performance of the films is discussed in terms of their hybridicity (organic/inorganic) ratio determined by infrared spectroscopic ellipsometry as well as the presence of anisotropy assessed by the nanostructure-based spectroscopic ellipsometry model. Finally, we demonstrate successful implementation of the ultralow-index material in a complete antireflective stack.
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Bouravleuv AD, Lev LL, Piamonteze C, Wang X, Schmitt T, Khrebtov AI, Samsonenko YB, Kanski J, Cirlin GE, Strocov VN. Electronic structure of (In,Mn)As quantum dots buried in GaAs investigated by soft-x-ray ARPES. NANOTECHNOLOGY 2016; 27:425706. [PMID: 27631689 DOI: 10.1088/0957-4484/27/42/425706] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Electronic structure of a molecular beam epitaxy-grown system of (In,Mn)As quantum dots (QDs) buried in GaAs is explored with soft-x-ray angle-resolved photoelectron spectroscopy (ARPES) using photon energies around 1 keV. This technique, ideally suited for buried systems, extends the momentum-resolving capabilities of conventional ARPES with enhanced probing depth as well as elemental and chemical state specificity achieved with resonant photoexcitation. The experimental results resolve the dispersive energy bands of the GaAs substrate buried in ∼2 nm below the surface, and the impurity states (ISs) derived from the substitutional Mn atoms in the (In,Mn)As QDs and oxidized Mn atoms distributed near the surface. An energy shift of the Mn ISs in the QDs compared to (In,Mn)As DMS is attributed to the band offset and proximity effect at the interface with the surrounding GaAs. The absence of any ISs in the vicinity of the VBM relates the electron transport in (In,Mn)As QDs to the prototype (In,Mn)As diluted magnetic semiconductor. The SX-ARPES results are supported by measurements of the shallow core levels under variation of probing depth through photon energy. X-ray absorption measurements identify significant diffusion of interstitial Mn atoms out of the QDs towards the surface, and the role of magnetic circular dichroism is to block the ferromagnetic response of the (In,Mn)As QDs. Possible routes are drawn to tune the growth procedure aiming at practical applications of the (In,Mn)As based systems.
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Bisogni V, Catalano S, Green RJ, Gibert M, Scherwitzl R, Huang Y, Strocov VN, Zubko P, Balandeh S, Triscone JM, Sawatzky G, Schmitt T. Ground-state oxygen holes and the metal-insulator transition in the negative charge-transfer rare-earth nickelates. Nat Commun 2016; 7:13017. [PMID: 27725665 PMCID: PMC5062575 DOI: 10.1038/ncomms13017] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2016] [Accepted: 08/25/2016] [Indexed: 11/13/2022] Open
Abstract
The metal–insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal–insulator transition in terms of bond disproportionation. Rare-earth perovskite nickelates show intriguing metal–insulator transitions, whose mechanism remains elusive. Here, Bisogni et al. evidenced a 3d8 Ni configuration together with abundance of oxygen 2p holes in the ground state of a NdNiO3 thin film, suggesting a negative charge-transfer scenario.
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Fabbris G, Meyers D, Okamoto J, Pelliciari J, Disa AS, Huang Y, Chen ZY, Wu WB, Chen CT, Ismail-Beigi S, Ahn CH, Walker FJ, Huang DJ, Schmitt T, Dean MPM. Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels. PHYSICAL REVIEW LETTERS 2016; 117:147401. [PMID: 27740843 DOI: 10.1103/physrevlett.117.147401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Indexed: 06/06/2023]
Abstract
Resonant inelastic x-ray scattering is used to investigate the electronic origin of orbital polarization in nickelate heterostructures taking LaTiO_{3}-LaNiO_{3}-3×(LaAlO_{3}), a system with exceptionally large polarization, as a model system. We find that heterostructuring generates only minor changes in the Ni 3d orbital energy levels, contradicting the often-invoked picture in which changes in orbital energy levels generate orbital polarization. Instead, O K-edge x-ray absorption spectroscopy demonstrates that orbital polarization is caused by an anisotropic reconstruction of the oxygen ligand hole states. This provides an explanation for the limited success of theoretical predictions based on tuning orbital energy levels and implies that future theories should focus on anisotropic hybridization as the most effective means to drive large changes in electronic structure and realize novel emergent phenomena.
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