34 research outputs found

    Orbital-selective confinement effect of Ru 4d4d orbitals in SrRuO3_3 ultrathin film

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    The electronic structure of SrRuO3_3 thin film with thickness from 50 to 1 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O K-edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that orbital-selective quantum confinement effect (QCE) induces the splitting of Ru 4d4d orbitals. At the same time, we observed a clear suppression of the electron-hole continuum across the metal-to-insulator transition (MIT) occurring at the 4 u.c. sample. From these two clear observations we conclude that QCE gives rise to a Mott insulating phase in ultrathin SrRuO3_3 films. Our interpretation of the RIXS spectra is supported by the configuration interaction calculations of RuO6_6 clusters.Comment: 7 pages, 7 figure

    2\sqrt{2}×\times2R45\sqrt{2}R45^\circ surface reconstruction and electronic structure of BaSnO3_3 film

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    We studied surface and electronic structures of barium stannate (BaSnO3_3) thin-film by low energy electron diffraction (LEED), and angle-resolved photoemission spectroscopy (ARPES) techniques. BaSnO3_3/Ba0.96_{0.96}La0.04_{0.04}SnO3_3/SrTiO3_3 (10 nm/100 nm/0.5 mm) samples were grown using pulsed-laser deposition (PLD) method and were \emph{ex-situ} transferred from PLD chamber to ultra-high vacuum (UHV) chambers for annealing, LEED and ARPES studies. UHV annealing starting from 300^{\circ}C up to 550^{\circ}C, followed by LEED and ARPES measurements show 1×\times1 surfaces with non-dispersive energy-momentum bands. The 1×\times1 surface reconstructs into a 2\sqrt{2}×\times2R45\sqrt{2}R45^\circ one at the annealing temperature of 700^{\circ}C where the ARPES data shows clear dispersive bands with valence band maximum located around 3.3 eV below Fermi level. While the 2\sqrt{2}×\times2R45\sqrt{2}R45^\circ surface reconstruction is stable under further UHV annealing, it is reversed to 1×\times1 surface by annealing the sample in 400 mTorr oxygen at 600^{\circ}C. Another UHV annealing at 600^{\circ}C followed by LEED and ARPES measurements, suggests that LEED 2\sqrt{2}×\times2R45\sqrt{2}R45^\circ surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of electronic structure of BaSnO3_3 surface and are suggestive of role of oxygen vacancies in the reversible 2\sqrt{2}×\times2R45\sqrt{2}R45^\circ surface reconstruction.Comment: 7 pages, 4 figures, Journa

    Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer

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    Magnetic skyrmions have fast evolved from a novelty, as a realization of topologically protected structure with particle-like character, into a promising platform for new types of magnetic storage. Significant engineering progress was achieved with the synthesis of compounds hosting room-temperature skyrmions in magnetic heterostructures, with the interfacial Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation. Here we report findings of ultrathin skyrmion formation in a few layers of SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer. Measurement of the topological Hall effect (THE) reveals a robust stability of skyrmions in this platform, judging from the high value of the critical field 1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film proves the rumpling of the Ru-O plane to be the source of inversion symmetry breaking and DMI. First-principles calculations based on the structure obtained from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the main source of skyrmion robustness. These features promise a few-layer SRO to be an important new platform for skyrmionics, without the necessity of introducing the capping layer to boost the spin-orbit coupling strength artificially.Comment: Supplementary Information available upon reques

    Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer

    Get PDF
    Magnetic skyrmions have fast evolved from a novelty, as a realization of topologically protected structure with particle-like character, into a promising platform for new types of magnetic storage. Significant engineering progress was achieved with the synthesis of compounds hosting room-temperature skyrmions in magnetic heterostructures, with the interfacial Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation. Here we report findings of ultrathin skyrmion formation in a few layers of SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer. Measurement of the topological Hall effect (THE) reveals a robust stability of skyrmions in this platform, judging from the high value of the critical field 1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film proves the rumpling of the Ru-O plane to be the source of inversion symmetry breaking and DMI. First-principles calculations based on the structure obtained from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the main source of skyrmion robustness. These features promise a few-layer SRO to be an important new platform for skyrmionics, without the necessity of introducing the capping layer to boost the spin-orbit coupling strength artificially.Comment: Supplementary Information available upon reques

    Tuning orbital-selective phase transitions in a two-dimensional Hund's correlated system

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    Hund's rule coupling (J\textit{J}) has attracted much attention recently for its role in the description of the novel quantum phases of multi orbital materials. Depending on the orbital occupancy, J\textit{J} can lead to various intriguing phases. However, experimental confirmation of the orbital occupancy dependency has been difficult as controlling the orbital degrees of freedom normally accompanies chemical inhomogeneities. Here, we demonstrate a method to investigate the role of orbital occupancy in J\textit{J} related phenomena without inducing inhomogeneities. By growing SrRuO3_3 monolayers on various substrates with symmetry-preserving interlayers, we gradually tune the crystal field splitting and thus the orbital degeneracy of the Ru \textit{t_2_g$}$ orbitals. It effectively varies the orbital occupancies of two-dimensional (2D) ruthenates. Via in-situ angle-resolved photoemission spectroscopy, we observe a progressive metal-insulator transition (MIT). It is found that the MIT occurs with orbital differentiation: concurrent opening of a band insulating gap in the $\textit{d$_x_y} band and a Mott gap in the \textit{d_xz_z_/y_y_z} bands. Our study provides an effective experimental method for investigation of orbital-selective phenomena in multi-orbital materials

    Deep learning-based statistical noise reduction for multidimensional spectral data

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    In spectroscopic experiments, data acquisition in multi-dimensional phase space may require long acquisition time, owing to the large phase space volume to be covered. In such case, the limited time available for data acquisition can be a serious constraint for experiments in which multidimensional spectral data are acquired. Here, taking angle-resolved photoemission spectroscopy (ARPES) as an example, we demonstrate a denoising method that utilizes deep learning as an intelligent way to overcome the constraint. With readily available ARPES data and random generation of training data set, we successfully trained the denoising neural network without overfitting. The denoising neural network can remove the noise in the data while preserving its intrinsic information. We show that the denoising neural network allows us to perform similar level of second-derivative and line shape analysis on data taken with two orders of magnitude less acquisition time. The importance of our method lies in its applicability to any multidimensional spectral data that are susceptible to statistical noise.Comment: 8 pages, 8 figure

    Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite oxide thin films

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    Magnetism and spin-orbit coupling (SOC) are two quintessential ingredients underlying novel topological transport phenomena in itinerant ferromagnets. When spin-polarized bands support nodal points/lines with band degeneracy that can be lifted by SOC, the nodal structures become a source of Berry curvature; this leads to a large anomalous Hall effect (AHE). Contrary to three-dimensional systems that naturally host nodal points/lines, two-dimensional (2D) systems can possess stable nodal structures only when proper crystalline symmetry exists. Here we show that 2D spin-polarized band structures of perovskite oxides generally support symmetry-protected nodal lines and points that govern both the sign and the magnitude of the AHE. To demonstrate this, we performed angle-resolved photoemission studies of ultrathin films of SrRuO3_3, a representative metallic ferromagnet with SOC. We show that the sign-changing AHE upon variation in the film thickness, magnetization, and chemical potential can be well explained by theoretical models. Our study is the first to directly characterize the topological band structure of 2D spin-polarized bands and the corresponding AHE, which could facilitate new switchable devices based on ferromagnetic ultrathin films

    Electronic band structure of (111) SrRuO3SrRuO_{3} thin film-an angle-resolved photoemission spectroscopy study

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    We studied the electronic band structure of pulsed laser deposition (PLD) grown (111)-oriented SrRuO3_3 (SRO) thin films using \textit{in situ} angle-resolved photoemission spectroscopy (ARPES) technique. We observed previously unreported, light bands with a renormalized quasiparticle effective mass of about 0.8mem_{e}. The electron-phonon coupling underlying this mass renormalization yields a characteristic "kink" in the band dispersion. The self-energy analysis using the Einstein model suggests five optical phonon modes covering an energy range 44 to 90 meV contribute to the coupling. Besides, we show that the quasiparticle spectral intensity at the Fermi level is considerably suppressed, and two prominent peaks appear in the valance band spectrum at binding energies of 0.8 eV and 1.4 eV, respectively. We discuss the possible implications of these observations. Overall, our work demonstrates that high-quality thin films of oxides with large spin-orbit coupling can be grown along the polar (111) orientation by the PLD technique, enabling \textit{in situ} electronic band structure study. This could allow for characterizing the thickness-dependent evolution of band structure of (111) heterostructures-a prerequisite for exploring possible topological quantum states in the bilayer limit
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