Oxide Molecular Beam Epitaxy Group

Group Members

Adrian Gozar

Member of MBE Group from 2005 to 2009

Current Position

Associate Scientist and Principal Investigator
Brookhaven National Laboratory

Publications in high-impact journals while in the MBE Group

A. Suter, E. Morenzoni, T. Prokscha, B. M. Wojek, H. Luetkens, G. Nieuwenhuys, A. Gozar, G. Logvenov and I. Bozovic. “Two-Dimensional Magnetic and Superconducting Phases in Metal-Insulator La2-xSrxCuO4 Superlattices Measured by Muon-Spin Rotation.” Physical Review Letters 106 (2011). Authors' version from arXiv (PDF) (may not exactly match published article) Article's page on arXiv Article's page on Physical Review Letters website DOI: 10.1103/PhysRevLett.106.237003

G. Logvenov, A. Gozar and I. Bozovic. “High-Temperature Superconductivity in a Single Copper-Oxygen Plane.” Science 326, 699 (2009). Abstract The question of how thin cuprate layers can be while still retaining high-temperature superconductivity (HTS) has been challenging to address, in part because experimental studies require the synthesis of near-perfect ultrathin HTS layers and ways to profile the superconducting properties such as the critical temperature and the superfluid density across interfaces with atomic resolution. We used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal (La1.65Sr0.45CuO4) and a cuprate insulator (La2CuO4) in which each layer is just three unit cells thick. We selectively doped layers with isovalent Zn atoms, which suppress superconductivity and act as markers, to show that this interface HTS occurs within a single CuO2 plane. This approach may also be useful in fabricating HTS devices. Full published article (PDF) Article's page on Science website DOI: 10.1126/science.1178863

S. Smadici, J. C. T. Lee, S. Wang, P. Abbamonte, G. Logvenov, A. Gozar, C. D. Cavellin and I. Bozovic. “Superconducting Transition at 38 K in Insulating-Overdoped La2CuO4-La1.64Sr0.36CuO4 Superlattices: Evidence for Interface Electronic Redistribution from Resonant Soft X-Ray Scattering.” Physical Review Letters 102, 107004 (2009). Abstract We use resonant soft x-ray scattering (RSXS) to quantify the hole distribution in a superlattice of insulating La2CuO4 (LCO) and overdoped La2-xSrxCuO4 (LSCO). Despite its nonsuperconducting constituents, this structure is superconducting with Tc=38 K. We found that the conducting holes redistribute electronically from LSCO to the LCO layers. The LCO layers were found to be optimally doped, suggesting they are the main drivers of superconductivity. Our results demonstrate the utility of RSXS for separating electronic from structural effects at oxide interfaces. Full published article (PDF) Article's page on Physical Review Letters website DOI: 10.1103/PhysRevLett.102.107004

A. Gozar, G. Logvenov, L. F. Kourkoutis, A. T. Bollinger, L. A. Giannuzzi, D. A. Muller and I. Bozovic. “High-temperature interface superconductivity between metallic and insulating copper oxides.” Nature 455, 782 (2008). Abstract The realization of high- transition- temperature (high-Tc) superconductivity confined to nanometre-sized interfaces has been a long- standing goal because of potential applications(1,2) and the opportunity to study quantum phenomena in reduced dimensions(3,4). This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas Tc is high and the coherence length very short, which provides an opportunity - but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation. In these bilayers, Tc is either similar to 15 K or similar to 30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2 - 3nm of the interface. If such a bilayer is exposed to ozone, Tc exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1 - 2 unit cells thick. Enhancement of Tc in bilayer systems was observed previously(5) but the essential role of the interface was not recognized at the time. Authors' version (PDF) Supplemental materials (PDF) Article's page on Nature website DOI: 10.1038/nature07293

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Last Modified: July 1, 2013
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