Oxide Molecular Beam Epitaxy Group

Group Members

Gennady Logvenov

Member of MBE Group from 2004 to 2009

Current Position

Senior Scientist and Group Leader
Max Planck Institute for Solid State Research

Publications in high-impact journals while in the MBE Group

J. Wu, O. Pelleg, G. Logvenov, A. T. Bollinger, Y. Sun, G. S. Boebinger, M. Vanevic, Z. Radovic and I. Bozovic. “Anomalous (in)dependence of interface superconductivity on carrier density.” Nature Materials (Submitted 2012). In press.

X. Shi, G. Logvenov, A. T. Bollinger, I. Bozovic, C. Panagopoulos and D. Popovic. “Emergence of superconductivity from the dynamically heterogeneous insulating state in La2-xSrxCuO4” Nature Materials 12, 47-51 (2013). Authors' version from arXiv (PDF) (may not exactly match published article) Article's page on arXiv Article's page on Nature Materials website DOI: 10.1038/nmat3487

L. S. Bilbro, R. V. Aguilar, G. Logvenov, O. Pelleg, I. Bozovic and N. P. Armitage. “Temporal correlations of superconductivity above the transition temperature in La2-xSrxCuO4 probed by terahertz spectroscopy.” Nature Physics 7, 298-302 (2011). Authors' version from arXiv (PDF) (may not exactly match published article) Article's page on arXiv Article's page on Nature Physics website DOI: 10.1038/nphys1912

E. Morenzoni, B. M. Wojek, A. Suter, T. Prokscha, G. Logvenov and I. Bozovic. “The Meissner effect in a strongly underdoped cuprate above its critical temperature.” Nature Communications 2, 272 (2011). Authors' version from arXiv (PDF) (may not exactly match published article) Article's page on arXiv Article's page on Nature Communications website DOI: 10.1038/ncomms1273

H. Zhou, Y. Yacoby, V. Y. Butko, G. Logvenov, I. Bozovic and R. Pindak. “Anomalous expansion of the copper-apical-oxygen distance in superconducting cuprate bilayers.” Proceedings of the National Academy of Sciences 107, 8103-8107 (2010). Authors' version from arXiv (PDF) (may not exactly match published article) Article's page on arXiv Article's page on Proceedings of the National Academy of Sciences website DOI: 10.1073/pnas.0914702107

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

I. Sochnikov, A. Shaulov, Y. Yeshurun, G. Logvenov and I. Bozovic. “Large oscillations of the magnetoresistance in nanopatterned high-temperature superconducting films.” Nature Nanotechnology 5, 516-519 (2010). Article's page on Nature Nanotechnology website DOI: 10.1038/nnano.2010.111

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

V. Y. Butko, G. Logvenov, N. Bozovic, Z. Radovic and I. Bozovic. “Madelung Strain in Cuprate Superconductors - A Route to Enhancement of the Critical Temperature.” Advanced Materials 21, 3644 (2009). Abstract "Madelung Strain" in cuprate films containing metal (M = La1.56Sr0.44CuO4) and insulator (I = La2CuO4) layers: X-ray diffraction shows that, unexpectedly, the volume of unit cell of the top layer adjusts to that of the bottom layer. The effect is due to long-range Coulomb forces; it affects interfacial superconductivity because the critical temperature scales with the unit-cell height. Authors' version (PDF) Supplemental materials (PDF) Article's page on Advanced Materials website DOI: 10.1002/adma.200803850

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

H. Shim, P. Chaudhari, G. Logvenov and I. Bozovic. “Electron-Phonon Interactions in Superconducting La1.84Sr0.16CuO4 Films.” Physical Review Letters 101, 247004 (2008). Abstract We have measured quasiparticle tunneling across a junction perpendicular to the superconducting copper oxide planes. The tunneling spectra show peaks in the density of states. There are 11 minima in the second derivative d(2)I/dV(2), where I is the current and V the voltage, suggesting multiple boson-quasiparticle interactions. These minima match precisely with the published Raman scattering data, leading us to conclude that the relevant bosons in superconducting La1.84Sr0.16CuO4 films are phonons. Full published article (PDF) Article's page on Physical Review Letters website DOI: 10.1103/PhysRevLett.101.247004

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

N. Gedik, D. S. Yang, G. Logvenov, I. Bozovic and A. H. Zewail. “Nonequilibrium phase transitions in cuprates observed by ultrafast electron crystallography.” Science 316, 425 (2007). Abstract Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Delta c) on fluence (F), with Delta c/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at similar to 0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity. Full published article (PDF) Article's page on Science website DOI: 10.1126/science.1138834

I. Bozovic, G. Logvenov, M. A. J. Verhoeven, P. Caputo, E. Goldobin and M. R. Beasley. “Giant proximity effect in cuprate superconductors.” Physical Review Letters 93, 157002 (2004). Abstract Using an advanced molecular beam epitaxy system, we have reproducibly synthesized atomically smooth films of high-temperature superconductors and uniform trilayer junctions with virtually perfect interfaces. We found that supercurrent runs through very thick barriers. We can rule out pinholes and microshorts; this "giant proximity effect" (GPE) is intrinsic. It defies the conventional explanation; it might originate in resonant tunneling through pair states in an almost-superconducting barrier. GPE may also be significant for superconducting electronics, since thick barriers are easier to fabricate. Full published article (PDF) Article's page on Physical Review Letters website DOI: 10.1103/PhysRevLett.93.157002

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Last Modified: July 1, 2013
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