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624 results on '"Kourkoutis, Lena F."'

152. Disentangling types of lattice disorder impacting superconductivity in Sr2RuO4 by quantitative local probes.

Author

Goodge, Berit H., Nair, Hari P., Baek, David J., Schreiber, Nathaniel J., Miao, Ludi, Ruf, Jacob P., Waite, Emily N., Carubia, Philip M., Shen, Kyle M., Schlom, Darrell G., and Kourkoutis, Lena F.

Subjects
SUPERCONDUCTIVITY, SUPERCONDUCTING films, SCANNING transmission electron microscopy, THIN films
Abstract

The unconventional superconductivity in Sr2RuO4 is infamously susceptible to suppression by small levels of disorder such that it has been most commonly studied in extremely high-purity bulk crystals. Here, we harness local structural and spectroscopic scanning transmission electron microscopy measurements in epitaxial thin films of Sr2RuO4 to disentangle the impact of different types of crystalline disorder on superconductivity. We find that cation off-stoichiometry during growth gives rise to two distinct types of disorder: mixed-phase structural inclusions that accommodate excess ruthenium and ruthenium vacancies when the growth is ruthenium-deficient. Several superconducting films host mixed-phase intergrowths, suggesting this microstructural disorder has relatively little impact on superconductivity. In a non-superconducting film, on the other hand, we measure a high density of ruthenium-vacancies (∼ 14 %) with no significant reduction in the crystallinity of the film. The results suggest that ruthenium vacancy disorder, which is hidden to many structural probes, plays an important role in suppressing superconductivity. We discuss the broader implications of our findings to guide the future synthesis of this and other layered systems. [ABSTRACT FROM AUTHOR]

Published
2022
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155. Improved control of atomic layering in perovskite-related homologous series

Author

Barone, Matthew R., primary, Dawley, Natalie M., additional, Nair, Hari P., additional, Goodge, Berit H., additional, Holtz, Megan E., additional, Soukiassian, Arsen, additional, Fleck, Erin E., additional, Lee, Kiyoung, additional, Jia, Yunfa, additional, Heeg, Tassilo, additional, Gatt, Refael, additional, Nie, Yuefeng, additional, Muller, David A., additional, Kourkoutis, Lena F., additional, and Schlom, Darrell G., additional

Published
2021
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165. Strain relaxation induced transverse resistivity anomalies in SrRuO3 thin films

Author

Miao, Ludi, primary, Schreiber, Nathaniel J., additional, Nair, Hari P., additional, Goodge, Berit H., additional, Jiang, Shengwei, additional, Ruf, Jacob P., additional, Lee, Yonghun, additional, Fu, Matthew, additional, Tsang, Boris, additional, Li, Yingfei, additional, Zeledon, Cyrus, additional, Shan, Jie, additional, Mak, Kin Fai, additional, Kourkoutis, Lena F., additional, Schlom, Darrell G., additional, and Shen, Kyle M., additional

Published
2020
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176. Epitaxial growth and electronic properties of mixed valence YbAl3 thin films.

Author

Chatterjee, Shouvik, Suk Hyun Sung, Baek, David J., Kourkoutis, Lena F., Schlom, Darrell G., and Shen, Kyle M.

Subjects
MAGNESIUM oxide, ELECTRIC properties of thin films, MOLECULAR beam epitaxy, BUFFER layers, SURFACE roughness, X-ray diffraction
Abstract

We report the growth of thin films of the mixed valence compound YbAl3 on MgO using molecular-beam epitaxy. Employing an aluminum buffer layer, epitaxial (001) films can be grown with sub-nm surface roughness. Using x-ray diffraction, in situ low-energy electron diffraction, and aberration-corrected scanning transmission electron microscopy, we establish that the films are ordered in the bulk as well as at the surface. Our films show a coherence temperature of 37 K, comparable to that reported for bulk single crystals. Photoelectron spectroscopy reveals contributions from both f13 and f12 final states establishing that YbAl3 is a mixed valence compound and shows the presence of a Kondo Resonance peak near the Fermi-level. [ABSTRACT FROM AUTHOR]

Published
2016
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191. Physical Principles of Membrane Shape Regulation by the Glycocalyx

Author

Shurer, Carolyn R., primary, Kuo, Joe Chin-Hun, additional, Roberts, LaDeidra Monét, additional, Gandhi, Jay G., additional, Colville, Marshall J., additional, Enoki, Thais A., additional, Pan, Hao, additional, Su, Jin, additional, Noble, Jade M., additional, Hollander, Michael J., additional, O’Donnell, John P., additional, Yin, Rose, additional, Pedram, Kayvon, additional, Möckl, Leonhard, additional, Kourkoutis, Lena F., additional, Moerner, W.E., additional, Bertozzi, Carolyn R., additional, Feigenson, Gerald W., additional, Reesink, Heidi L., additional, and Paszek, Matthew J., additional

Published
2019
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196. Demystifying the growth of superconducting Sr2RuO4 thin films

Author

Nair, Hari P., primary, Ruf, Jacob P., additional, Schreiber, Nathaniel J., additional, Miao, Ludi, additional, Grandon, Morgan L., additional, Baek, David J., additional, Goodge, Berit H., additional, Ruff, Jacob P. C., additional, Kourkoutis, Lena F., additional, Shen, Kyle M., additional, and Schlom, Darrell G., additional

Published
2018
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197. Commensurate Stripes and Phase Coherence in Manganites Revealed with Cryogenic Scanning Transmission Electron Microscopy

Author

Baggari, Ismail El, Savitzky, Benjamin H, Admasu, Alemayehu S, Kim, Jaewook, Cheong, Sang-Wook, Hovden, Robert, and Kourkoutis, Lena F

Subjects
Condensed Matter::Materials Science, Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), FOS: Physical sciences, Condensed Matter::Strongly Correlated Electrons, cond-mat.str-el
Abstract

Incommensurate charge order in hole-doped oxides is intertwined with exotic phenomena such as colossal magnetoresistance, high-temperature superconductivity, and electronic nematicity. Here, we map at atomic resolution the nature of incommensurate order in a manganite using scanning transmission electron microscopy at room temperature and cryogenic temperature ($\sim$ 93K). In diffraction, the ordering wavevector changes upon cooling, a behavior typically associated with incommensurate order. However, using real space measurements, we discover that the underlying ordered state is lattice-commensurate at both temperatures. The cations undergo picometer-scale ($\sim $6-11 pm) transverse displacements, which suggests that charge-lattice coupling is strong and hence favors lattice-locked modulations. We further unearth phase inhomogeneity in the periodic lattice displacements at room temperature, and emergent phase coherence at 93K. Such local phase variations not only govern the long range correlations of the charge-ordered state, but also results in apparent shifts in the ordering wavevector. These atomically-resolved observations underscore the importance of lattice coupling and provide a microscopic explanation for putative "incommensurate" order in hole-doped oxides.

Published
2017

198. Enhancement of electron mobility at oxide interfaces induced by WO3 overlayers

Author

Mattoni, Giordano, Baek, David J., Manca, Nicola, Verhagen, Nils, Kourkoutis, Lena F., Filippetti, Alessio, and Caviglia, Andrea D.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

Interfaces between complex oxides constitute a unique playground for 2D electron systems (2DES), where superconductivity and magnetism can arise from combinations of bulk insulators. The 2DES at the LaAlO3/SrTiO3 interface is one of the most studied in this regard, and its origin is determined by both the presence of a polar field in LaAlO3 and the insurgence of point defects, such as oxygen vacancies and intermixed cations. These defects usually reside in the conduction channel and are responsible for a decreased electronic mobility. In this work we use an amorphous WO3 overlayer to control the defect formation and obtain an increased electron mobility and effective mass in WO3/LaAlO3/SrTiO3 heterostructures. The studied system shows a sharp insulator-to-metal transition as a function of both LaAlO3 and WO3 layer thickness. Low-temperature magnetotransport reveals a strong magnetoresistance reaching 900% at 10 T and 1.5 K, the presence of multiple conduction channels with carrier mobility up to 80 000 cm2/Vs and an unusually high effective mass of 5.6 me. The amorphous character of the WO3 overlayer makes this a versatile approach for defect control at oxide interfaces, which could be applied to other heterestrostures disregarding the constraints imposed by crystal symmetry.

Published
2017

199. Image registration of low signal-to-noise cryo-STEM data

Author

Savitzky, Benjamin H., Baggari, Ismail El, Clement, Colin, Waite, Emily, Sheckelton, John P., Pasco, Christopher, Admasu, Alemayehu S., Kim, Jaewook, Cheong, Sang-Wook, McQueen, Tyrel M., Hovden, Robert, and Kourkoutis, Lena F.

Subjects
Signal Processing (eess.SP), Physics - Data Analysis, Statistics and Probability, Computer Science::Computer Vision and Pattern Recognition, FOS: Electrical engineering, electronic engineering, information engineering, FOS: Physical sciences, Electrical Engineering and Systems Science - Signal Processing, Data Analysis, Statistics and Probability (physics.data-an)
Abstract

Combining multiple fast image acquisitions to mitigate scan noise and drift artifacts has proven essential for picometer precision, quantitative analysis of atomic resolution scanning transmission electron microscopy (STEM) data. For very low signal-to-noise ratio (SNR) image stacks - frequently required for undistorted imaging at liquid nitrogen temperatures - image registration is particularly delicate, and standard approaches may either fail, or produce subtly specious reconstructed lattice images. We present an approach which effectively registers and averages image stacks which are challenging due to their low-SNR and propensity for unit cell misalignments. Registering all possible image pairs in a multi-image stack leads to significant information surplus. In combination with a simple physical picture of stage drift, this enables identification of incorrect image registrations, and determination of the optimal image shifts from the complete set of relative shifts. We demonstrate the effectiveness of our approach on experimental, cryogenic STEM datasets, highlighting subtle artifacts endemic to low-SNR lattice images and how they can be avoided. High-SNR average images with information transfer out to 0.72 A are achieved at 300 kV and with the sample cooled to near liquid nitrogen temperature., Comment: 25 pages, 5 figures

Published
2017
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200. Isotropic Pauli-limited superconductivity in the infinite-layer nickelate Nd0.775Sr0.225NiO2

Author

Wang, Bai Yang, Li, Danfeng, Goodge, Berit H., Lee, Kyuho, Osada, Motoki, Harvey, Shannon P., Kourkoutis, Lena F., Beasley, Malcolm R., and Hwang, Harold Y.

Abstract

The recent observation of superconductivity in thin-film infinite-layer nickelates1–3offers a different angle from which to investigate superconductivity in layered oxides4. A wide range of candidate models have been proposed5–10, which emphasize single- or multi-orbital electronic structure, Kondo or Hund’s coupling and analogies to cuprates. Further experimental characterization of the superconducting state is needed to develop a full understanding of the nickelates. Here we use magnetotransport measurements to probe the superconducting anisotropy in Nd0.775Sr0.225NiO2. We find that the upper critical field is surprisingly isotropic at low temperatures despite the layered crystal structure. In a magnetic field, the superconductivity is strongly Pauli-limited, such that the paramagnetic effect dominates over orbital de-pairing. Underlying this isotropic response is a substantial anisotropy in the superconducting coherence length, which is at least four times longer in-plane than out-of-plane. A prominent low-temperature upturn in the upper critical field indicates the presence of an unconventional ground state.

Published
2021
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