Stanford Advisors


All Publications


  • Doping evolution of the Mott-Hubbard landscape in infinite-layer nickelates. Proceedings of the National Academy of Sciences of the United States of America Goodge, B. H., Li, D., Lee, K., Osada, M., Wang, B. Y., Sawatzky, G. A., Hwang, H. Y., Kourkoutis, L. F. 2021; 118 (2)

    Abstract

    The recent observation of superconductivity in [Formula: see text] has raised fundamental questions about the hierarchy of the underlying electronic structure. Calculations suggest that this system falls in the Mott-Hubbard regime, rather than the charge-transfer configuration of other nickel oxides and the superconducting cuprates. Here, we use state-of-the-art, locally resolved electron energy-loss spectroscopy to directly probe the Mott-Hubbard character of [Formula: see text] Upon doping, we observe emergent hybridization reminiscent of the Zhang-Rice singlet via the oxygen-projected states, modification of the Nd 5d states, and the systematic evolution of Ni 3d hybridization and filling. These experimental data provide direct evidence for the multiband electronic structure of the superconducting infinite-layer nickelates, particularly via the effects of hole doping on not only the oxygen but also nickel and rare-earth bands.

    View details for DOI 10.1073/pnas.2007683118

    View details for PubMedID 33397720

  • Isotropic Pauli-limited superconductivity in the infinite-layer nickelate Nd0.775Sr0.225NiO2 NATURE PHYSICS Wang, B., Li, D., Goodge, B. H., Lee, K., Osada, M., Harvey, S. P., Kourkoutis, L. F., Beasley, M. R., Hwang, H. Y. 2021
  • Phase diagram of infinite layer praseodymium nickelate Pr1-xSrxNiO2 thin films PHYSICAL REVIEW MATERIALS Osada, M., Wang, B., Lee, K., Li, D., Hwang, H. Y. 2020; 4 (12)
  • Superconducting Dome in Nd1-xSrxNiO2 Infinite Layer Films PHYSICAL REVIEW LETTERS Li, D., Wang, B., Lee, K., Harvey, S. P., Osada, M., Goodge, B. H., Kourkoutis, L. F., Hwang, H. Y. 2020; 125 (2)
  • A Superconducting Praseodymium Nickelate with Infinite Layer Structure. Nano letters Osada, M., Wang, B. Y., Goodge, B. H., Lee, K., Yoon, H., Sakuma, K., Li, D., Miura, M., Kourkoutis, L. F., Hwang, H. Y. 2020

    Abstract

    A variety of nickel oxide compounds have long been studied for their manifestation of various correlated electron phenomena. Recently, superconductivity was observed in nanoscale infinite layer nickelate thin films of Nd0.8Sr0.2NiO2, epitaxially stabilized on SrTiO3 substrates via topotactic reduction from the perovskite precursor phase. Here, we present the synthesis and properties of PrNiO2 thin films on SrTiO3. Upon doping in Pr0.8Sr0.2NiO2, we observe superconductivity with a transition temperature of 7-12 K and robust critical current density at 2 K of 334 kA/cm2. These findings indicate that superconductivity in the infinite layer nickelates is relatively insensitive to the details of the rare earth 4f configuration. Furthermore, they motivate the exploration of a broader family of compounds based on two-dimensional NiO2 planes, which will enable systematic investigation of the superconducting and normal state properties and their underlying mechanisms.

    View details for DOI 10.1021/acs.nanolett.0c01392

    View details for PubMedID 32574061

  • Aspects of the synthesis of thin film superconducting infinite-layer nickelates APL MATERIALS Lee, K., Goodge, B. H., Li, D., Osada, M., Wang, B., Cui, Y., Kourkoutis, L. F., Hwang, H. Y. 2020; 8 (4)

    View details for DOI 10.1063/5.0005103

    View details for Web of Science ID 000526748400002

  • Electronic structure of the parent compound of superconducting infinite-layer nickelates. Nature materials Hepting, M., Li, D., Jia, C. J., Lu, H., Paris, E., Tseng, Y., Feng, X., Osada, M., Been, E., Hikita, Y., Chuang, Y., Hussain, Z., Zhou, K. J., Nag, A., Garcia-Fernandez, M., Rossi, M., Huang, H. Y., Huang, D. J., Shen, Z. X., Schmitt, T., Hwang, H. Y., Moritz, B., Zaanen, J., Devereaux, T. P., Lee, W. S. 2020

    Abstract

    The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors1-10. The recent discovery of superconductivity in the doped infinite-layer nickelate NdNiO2 (refs. 11,12) has strengthened these efforts. Here, we use X-ray spectroscopy and density functional theory to show that the electronic structure of LaNiO2 and NdNiO2, while similar to the cuprates, includes significant distinctions. Unlike cuprates, the rare-earth spacer layer in the infinite-layer nickelate supports a weakly interacting three-dimensional 5d metallic state, which hybridizes with a quasi-two-dimensional, strongly correlated state with [Formula: see text] symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics13-15, which are well known for heavy fermion behaviour, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy fermion compounds. This Kondo- or Anderson-lattice-like 'oxide-intermetallic' replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.

    View details for DOI 10.1038/s41563-019-0585-z

    View details for PubMedID 31959951

  • Superconducting Dome in Nd_{1-x}Sr_{x}NiO_{2} Infinite Layer Films. Physical review letters Li, D. n., Wang, B. Y., Lee, K. n., Harvey, S. P., Osada, M. n., Goodge, B. H., Kourkoutis, L. F., Hwang, H. Y. 2020; 125 (2): 027001

    Abstract

    We report the phase diagram of Nd_{1-x}Sr_{x}NiO_{2} infinite layer thin films grown on SrTiO_{3}. A superconducting dome spanning 0.125

    View details for DOI 10.1103/PhysRevLett.125.027001

    View details for PubMedID 32701320

  • Superconductivity in an infinite-layer nickelate. Nature Li, D., Lee, K., Wang, B. Y., Osada, M., Crossley, S., Lee, H. R., Cui, Y., Hikita, Y., Hwang, H. Y. 2019; 572 (7771): 624–27

    Abstract

    The discovery of unconventional superconductivity in (La,Ba)2CuO4 (ref. 1) has motivated the study of compounds with similar crystal and electronic structure, with the aim of finding additional superconductors and understanding the origins of copper oxide superconductivity. Isostructural examples include bulk superconducting Sr2RuO4 (ref. 2) and surface-electron-doped Sr2IrO4, which exhibits spectroscopic signatures consistent with a superconducting gap3,4, although a zero-resistance state has not yet been observed. This approach has also led to the theoretical investigation of nickelates5,6, as well as thin-film heterostructures designed to host superconductivity. One such structure is the LaAlO3/LaNiO3 superlattice7-9, which has been recently proposed for the creation of an artificially layered nickelate heterostructure with a singly occupied [Formula: see text] band. The absence of superconductivity observed in previous related experiments has been attributed, at least in part, to incomplete polarization of the eg orbitals10. Here we report the observation of superconductivity in an infinite-layer nickelate that is isostructural to infinite-layer copper oxides11-13. Using soft-chemistry topotactic reduction14-20, NdNiO2 and Nd0.8Sr0.2NiO2 single-crystal thin films are synthesized by reducing the perovskite precursor phase. Whereas NdNiO2 exhibits a resistive upturn at low temperature, measurements of the resistivity, critical current density and magnetic-field response of Nd0.8Sr0.2NiO2 indicate a superconducting transition temperature of about 9 to 15 kelvin. Because this compound is a member of a series of reduced layered nickelate crystal structures21-23, these results suggest the possibility of a family of nickelate superconductors analogous to copper oxides24 and pnictides25.

    View details for DOI 10.1038/s41586-019-1496-5

    View details for PubMedID 31462797

  • Oxygen Evolution Reaction Activity in IrO x/SrIrO3 Catalysts: Correlations between Structural Parameters and the Catalytic Activity. The journal of physical chemistry letters Lee, K., Osada, M., Hwang, H. Y., Hikita, Y. 2019: 1516–22

    Abstract

    Understanding how structural properties affect the oxygen evolution reaction (OER) of a catalyst can reveal important information not only on the catalytic mechanism but also on the general design strategy of OER catalysts. We report a variation of 0.15 V in the overpotential of the recently discovered IrO x/SrIrO3 OER catalysts, which directly correlates with the structural parameters of the as-synthesized SrIrO3 epitaxial films. This variation is caused by both extrinsic area enhancement and intrinsic electronic structure modification driven by defect formation. These correlations not only indicate that microscopic film defects play an important role in the activity of the IrO x/SrIrO3 catalyst but also provide readily accessible parameters predictive of the activity post-transformation to IrO x/SrIrO3. Establishing strong associations between the catalytic activity and key structural and electronic parameters, rather than synthetic variables, provides important guidance to control and study these complex catalysts independent of the synthetic technique.

    View details for PubMedID 30883127

  • Synthesis and electronic properties of Fe2TiO5 epitaxial thin films APL MATERIALS Osada, M., Nishio, K., Hwang, H. Y., Hikita, Y. 2018; 6 (5)

    View details for DOI 10.1063/1.5025569

    View details for Web of Science ID 000433944800001