Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X1: Complex Oxide Interaces at the Nanoscale: Electronic, Magnetic and Superconducting PropertiesInvited
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Sponsoring Units: DCMP GMAG Chair: Chang-Beom Eom, University of Wisconsin-Madison Room: Ballroom I |
Friday, March 18, 2016 8:00AM - 8:36AM |
X1.00001: Electron pairing without superconductivity Invited Speaker: Jeremy Levy Strontium titanate (SrTiO$_{\mathrm{3}})$ is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors---two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO$_{\mathrm{3}}$~has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO$_{\mathrm{3}}$~and a thin layer of lanthanum aluminate, LaAlO$_{\mathrm{3}}$. Electrostatic gating reveals a series of two-electron conductance resonances---paired electron states---that bifurcate above a critical pairing field~$B_{\mathrm{p}}$~of about 1--4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below~$B_{\mathrm{p}}$, these resonances are insensitive to the applied magnetic field; for fields in excess of~$B_{\mathrm{p}}$, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 9:12AM |
X1.00002: Magnetic coupling through lanthanum nickelate in non-metallic (111) LaMnO$_{\mathrm{3}}$/LaNiO$_{\mathrm{3}}$ superlattices Invited Speaker: Jean-Marc Triscone Perovskite nickelates (RNiO$_{\mathrm{3}}$, RE $=$ Rare Earth) are fascinating materials, well known for their metal to insulator transition (MIT) and unique antiferromagnetic (AFM) ground state [1]. In this presentation, I will first discuss how one can control the MIT and the magnetic properties of high quality epitaxial nickelate films through a variety of techniques [2-6]. I will then describe our work on heterostructures containing LaNiO$_{\mathrm{3}}$ -- the only member of the family that is metallic and paramagnetic in the bulk down to low temperature -- and ferromagnetic LaMnO$_{\mathrm{3}}$. In this system we observed an unusual exchange bias in [111] oriented (LaNiO$_{\mathrm{3}})$/(LaMnO$_{\mathrm{3}})$ superlattices [7] and an antiferromagnetic interlayer exchange coupling above the blocking temperature of the exchange biased state specifically in 7 unit cells LaNiO$_{\mathrm{3}}$/ 7 unit cells LaMnO$_{\mathrm{3}}$ superlattices. The antiferromagnetic coupling is attributed to the presence of a (1/4, 1/4, 1/4) wavelength AFM structure in LaNiO$_{\mathrm{3}}$. The complex exchange bias observed in this (LaNiO$_{\mathrm{3}})$/(LaMnO$_{\mathrm{3}})$ system is explained in this context also considering the presence of two types of interfaces [8]. [1] ML. Medarde, Journal of Physics: Condensed Matter, 9, 1679 (1997). [2] R. Scherwitzl et al., Advanced Materials 22, 5517 (2010). [3] S. Catalano et al., Appl. Phys. Lett. Mat. 2, 116110 (2014). [4] S. Catalano et al., Appl. Phys. Lett. Mat. 3, 062506 (2015). [5] A. Caviglia et al., Phys. Rev. Lett. 108, 136801 (2012). [6] M. F\"{o}rst et al., Nat. Mat. 14, 883 (2015). [7] M. Gibert et al., Nat. Mat. 11, 195 (2012). [8] M. Gibert et al., Nanoletters in press (2015). [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:48AM |
X1.00003: Emergent nanoscale superparamagnetism at oxide interfaces Invited Speaker: Eli Zeldov Atomically sharp oxide heterostructures exhibit a range of novel physical phenomena that do not occur in the parent bulk compounds. The most prominent example is the appearance of highly conducting and superconducting states at the interface between the band insulators LaAlO$_{3}$ and SrTiO$_{3}$. We present a new emergent phenomenon at the LaMnO$_{3}$/SrTiO$_{3}$ interface in which an antiferromagnetic insulator abruptly transforms into a superparamagnetic state. Above a critical thickness of LaMnO$_{3}$ of five unit cells, our scanning nanoSQUID-on-tip microscopy [1] shows spontaneous formation of isolated magnetic islands with in-plane moment of 10$^{4}$ to 10$^{5} \quad \mu_{B}$ with characteristic diameter of 10 to 50 nm [2]. The nanoscale islands display superparamagnetic dynamics of random moment reversals by thermal activation or in response to an in-plane magnetic field [1]. We propose a charge reconstruction model of the polar LaMnO$_{3}$/SrTiO$_{3}$ heterostructure which describes a sharp emergence of thermodynamic phase separation leading to nucleation of metallic ferromagnetic islands in an insulating antiferromagnetic matrix. The model suggests that a gate tunable superparamagnetic-ferromagnetic transition can be induced, holding potential for applications in magnetic storage and spintronics. [1] D. Vasyukov et al., Nature Nanotechnology 8, 639 (2013). [2] Y. Anahory, L. Embon, C. J. Li, S. Banerjee, A. Meltzer, H. R. Naren, A. Yakovenko, J. Cuppens, Y. Myasoedov, M. L. Rappaport, M. E. Huber, K. Michaeli, T. Venkatesan, and E. Zeldov, arXiv:1509.01895 [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:24AM |
X1.00004: Spatially resolved ultrafast magnetic dynamics initiated at a complex oxide heterointerface. Invited Speaker: Andrea Caviglia Static strain in complex oxide heterostructures has been extensively used to engineer electronic and magnetic properties at equilibrium. In the same spirit, deformations of the crystal lattice with light may be used to achieve functional control across heterointerfaces dynamically. Here, by exciting large-amplitude infrared-active vibrations in a LaAlO$_{3}$ substrate we induce magnetic order melting in a NdNiO$_{3}$ film across a heterointerface. Femtosecond resonant soft X-ray diffraction is used to determine the spatiotemporal evolution of the magnetic disordering. We observe a magnetic melt front that propagates from the substrate interface into the film, at a speed that suggests electronically driven motion. Light control and ultrafast phase front propagation at heterointerfaces may lead to new opportunities in optomagnetism. [Preview Abstract] |
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