Kyu Ho Lee

All Publications

• A broken translational symmetry state in an infinite-layer nickelate NATURE PHYSICS Rossi, M., Osada, M., Choi, J., Agrestini, S., Jost, D., Lee, Y., Lu, H., Wang, B., Lee, K., Nag, A., Chuang, Y., Kuo, C., Lee, S., Moritz, B., Devereaux, T. P., Shen, Z., Lee, J., Zhou, K., Hwang, H. Y., Lee, W. 2022

  View details for DOI 10.1038/s41567-022-01660-6

  View details for Web of Science ID 000829739500004

• Electronic structure of superconducting nickelates probed by resonant photoemission spectroscopy MATTER Chen, Z., Osada, M., Li, D., Been, E. M., Chen, S., Hashimoto, M., Lu, D., Mo, S., Lee, K., Wang, B., Rodolakis, F., McChesney, J. L., Jia, C., Moritz, B., Devereaux, T. P., Hwang, H. Y., Shen, Z. 2022; 5 (6)

  View details for DOI 10.1016/j.matt.2022.01.020

  View details for Web of Science ID 000810939100001

• Insulator-to-metal crossover near the edge of the superconducting dome in Nd1-xSrxNiO2 PHYSICAL REVIEW RESEARCH Hsu, Y., Wang, B., Berben, M., Li, D., Lee, K., Duffy, C., Ottenbros, T., Kim, W., Osada, M., Wiedmann, S., Hwang, H. Y., Hussey, N. E. 2021; 3 (4)

  View details for DOI 10.1103/PhysRevResearch.3.L042015

  View details for Web of Science ID 000715926700001

• Nickelate Superconductivity without Rare-Earth Magnetism: (La,Sr)NiO2. Advanced materials (Deerfield Beach, Fla.) Osada, M., Wang, B. Y., Goodge, B. H., Harvey, S. P., Lee, K., Li, D., Kourkoutis, L. F., Hwang, H. Y. 2021: e2104083

  Abstract

  The occurrence of unconventional superconductivity in cuprates has long motivated the search for manifestations in other layered transition metal oxides. Recently, superconductivity is found in infinite-layer nickelate (Nd,Sr)NiO2 and (Pr,Sr)NiO2 thin films, formed by topotactic reduction from the perovskite precursor phase. A topic of much current interest is whether rare-earth moments are essential for superconductivity in this system. In this study, it is found that with significant materials optimization, substantial portions of the La1- x Srx NiO2 phase diagram can enter the regime of coherent low-temperature transport (x= 0.14 - 0.20), with subsequent superconducting transitions and a maximum onset of 9 K at x= 0.20. Additionally, the unexpected indication of a superconducting ground state in undoped LaNiO2 is observed, which likely reflects the self-doped nature of the electronic structure. Combining the results of (La/Pr/Nd)1- x Srx NiO2 reveals a generalized superconducting dome, characterized by systematic shifts in the unit cell volume and in the relative electron-hole populations across the lanthanides.

  View details for DOI 10.1002/adma.202104083

  View details for PubMedID 34536042

• Understanding Degradation Mechanisms in SrIrO3 Oxygen Evolution Electrocatalysts: Chemical and Structural Microscopy at the Nanoscale ADVANCED FUNCTIONAL MATERIALS Ben-Naim, M., Liu, Y., Stevens, M., Lee, K., Wette, M. R., Boubnov, A., Trofimov, A. A., Ievlev, A. V., Belianinov, A., Davis, R. C., Clemens, B. M., Bare, S. R., Hikita, Y., Hwang, H. Y., Higgins, D. C., Sinclair, R., Jaramillo, T. F. 2021

  View details for DOI 10.1002/adfm.202101542

  View details for Web of Science ID 000662722100001

• Epitaxial Stabilization and Oxygen Evolution Reaction Activity of Metastable Columbite Iridium Oxide ACS APPLIED ENERGY MATERIALS Lee, K., Flores, R. A., Liu, Y., Wang, B., Hikita, Y., Sinclair, R., Bajdich, M., Hwang, H. Y. 2021; 4 (4): 3074-3082

  View details for DOI 10.1021/acsaem.0c02788

  View details for Web of Science ID 000644737800012

• Highly Efficient Surface Charge Transfer in Fe2TiO5 Epitaxial Thin Film Photoanodes ACS APPLIED ENERGY MATERIALS Osada, M., Nishio, K., Lee, K., Colletta, M., Goodge, B. H., Kim, W., Kourkoutis, L. F., Hwang, H. Y., Hikita, Y. 2021; 4 (3): 2098-2106

  View details for DOI 10.1021/acsaem.0c02516

  View details for Web of Science ID 000636714000010

• 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

  View details for DOI 10.1038/s41567-020-01128-5

  View details for Web of Science ID 000604865700004

• 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)

  View details for DOI 10.1103/PhysRevMaterials.4.121801

  View details for Web of Science ID 000600662300001

• Superconducting Dome in Nd_{1-x}Sr_{x}NiO_{2} Infinite Layer Films. Physical review letters Li, D., Wang, B. Y., Lee, K., Harvey, S. P., Osada, M., 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

• 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)

  View details for DOI 10.1103/PhysRevLett.125.027001

  View details for Web of Science ID 000545870800006

• 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

• 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

• Large-Area Crystalline BaSnO3 Membranes with High Electron Mobilities ACS APPLIED ELECTRONIC MATERIALS Singh, P., Swartz, A., Lu, D., Hon, S., Lee, K., Marshall, A. F., Nishio, K., Hikita, Y., Hwang, H. Y. 2019; 1 (7): 1269–74

  View details for DOI 10.1021/acsaelm.9b00215

  View details for Web of Science ID 000496314700027

• Oxygen Evolution Reaction Activity in IrOx/SrIrO3 Catalysts: Correlations between Structural Parameters and the Catalytic Activity JOURNAL OF PHYSICAL CHEMISTRY LETTERS Lee, K., Osada, M., Hwang, H. Y., Hikita, Y. 2019; 10 (7): 1516-1522

  View details for DOI 10.1021/acs.jpclett.9b00173

  View details for Web of Science ID 000463960700014

• 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