Quantum Materials Workgroup
Seminar Series
Seminar Series Abstracts
Pouyan Ghaemi
Assistant Professor of Physics
City College New York
Superconductivity in topological insulators: From topological phase transition to Neutrino Oscillations.
Abstract: The presence of helical surface states in topological insulators motivated many theoretical and experimental studies on the transport properties of such states. Unfortunately the bulk conducting bands have been shown to greatly challenge experimental observation of unique transport properties of the surface states, such as in absence of back scattering by non-magnetic impurities. In this talk I will show that in the presence of superconducting Cooper-paring, the signature of topological properties is apparent in the features of supercurrent transport through both surface and in the bulk of topological insulators. In particular by study of Josephson junctions made on the top of topological insulators, I will discuss the non-trivial temperature dependence of critical current as well as distribution of supercurrent in the junction which is controllable by external gating. I will show that puzzling recent experimental results are well consistent with our theoretical model of supercurrent transport in these materials and are indeed presenting signature of a topological phase transition in superconductor-topological insulator-superconductor Josephson junctions.
Phys. Rev. Lett. 116, 037001 (2016)
Phys. Rev. B 93, 035307 (2016)
Entanglement in large-scale light-matter systems
Speaker: Manas Kulkarni, CUNY-CityTech, USA
We propose [1, 2] and study the use of photon-mediated interactions for the generation of long-range steady-state entanglement between N atoms. Through the judicious use of coherent drives and the placement of the atoms in a network of cavity QED systems, a balance between their unitary and dissipative dynamics can be precisely engineered to stabilize a long-range correlated state of qubits in the steady state. We discuss the general theory behind such a scheme and present an example of how it can be used to drive a register of N atoms to a generalized W state and how the entanglement can be sustained indefinitely. The achievable steady-state fidelities for entanglement and its scaling with the number of qubits are discussed for presently existing superconducting quantum circuits. While the protocol is primarily discussed for a superconducting circuit architecture, it is ideally realized in any cavity QED platform that permits controllable delivery of coherent electromagnetic radiation to specified locations. The case of N=2 has been recently realized in collaboration with the experimental group at UC Berkeley [3]
[1] C. D. Aron, M. Kulkarni, H. E. Tureci, Phys. Rev. X 6, 011032 (2016)
[2] C. D. Aron, M. Kulkarni, H. E. Tureci, Phys. Rev. A 90, 062305 (2014)
[3] M.E. Schwartz, L. Martin, E. Flurin, C. Aron, M. Kulkarni, H.E. Tureci, I. Siddiqi (PRL, 2016)
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Prof. Javad Shabani
Title: "Two-dimensional epitaxial superconductor-semiconductor heterostructures: A platform for novel superconducting circuits"
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Theory suggests that the interface between a one-dimensional semiconductor (Sm) with strong spin-orbit coupling and a superconductor (S) hosts Majorana modes with nontrivial topological properties. A key challenge in fabrication of such hybrid devices is forming highly transparent contacts between the active electrons in the semiconductor and the superconducting metal. Recently, it has been shown that a near perfect interface and a highly transparent contact can be achieved using epitaxial growth of aluminum on InAs nanowires. In this work, we present the first two-dimensional epitaxial superconductor-semiconductor material system that can serve as a platform for topological superconductivity, and the search for quasiparticles such as Majorana zero modes that are predicted to obey non-abelian statistics. We show that our material system, Al-InAs, satisfies all the requirements necessary to reach into the topological superconducting regime by individual characterization of the semiconductor two dimensional electron system, superconductivity of Al and performance of S-Sm-S junctions. This exciting development might lead to a number of useful applications ranging from spintronics to quantum computing.”
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Nanoscale engineering of infrared plasmons in graphene
Speaker: Haiming Deng
Surface plasmons are collective oscillations of free charge carriers confined at the interface between two dielectrics, where the real part of the dielectric changes sign. The study of surface plasmons have become a popular research theme in recent years. Some of the potential applications include transfer of information in a frequency range of hundreds of terahertz instead of upper limit of gigahertz in traditional wires, photodetectors with frequency range from terahertz to mid-IR, and nano-imaging. In our experiments, we use an IR near-field microscopy with spatial resolution as high as 10 nm, however, with energy scale in the micron range. This is achieved by illuminating an AFM tip with an infrared laser on top of the sample and collecting the scattered light from the sample. The spatial resolution is proportional to the size of the tip and not the excitation wavelength, hence this technique beats the diffraction limit of near-IR (~10 mm) optical microscopy by a factor over 1000x. The wavelength and the amplitude damping of plasmons depends on the properties of free carriers in the material. While good metal films such as gold and silver had been widely studied and had shown promising results, a better platform with longer propagation length and shorter plasmon wavelength is needed for a number of applications. Graphene’s superb electronic transport (high mobility and low loss) makes it an excellent candidate material for plasmonic applications. In this talk, the original theory proposal of manipulating graphene plasmons with p-n junctions and our experimental data will be discussed, including oxygen doping via UV ozone which has shown to be promising for a graphene plasmon guide. We observe plasmon puddles developed in the interior of graphene after UV ozone treatment due to local surface doping by oxygen ions and localization of plasmons around the dopant. The UV ozone treatment can be fine-controlled to gently attach oxygen ions on graphene. Along with techniques such as lithography, one can, in principle, mask and selectively dope graphene and create a robust graphene plasmon circuit that is stable in room temperature.
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Guillermo Acuna
DNA Origami for plasmonics and fluorescence applications
TU Braunschweig, Institute of Physical and Theoretical Chemistry, Hans-Sommer-Str. 10, Braunschweig, Germany
This contribution will focus on different applications of the DNA-Origami technique [1] in the fields of plasmonics and fluorescence enhancement. In particular, we employ DNA-Origami as a platform where metallic nanoparticles as well as single organic fluorophores can be organized with nanometer precision in three dimensions. With these hybrid structures we initially study the nanoparticle-fluorophore interaction in terms of the distance-dependent fluorescence quenching [2] and angular dependence around the nanoparticle [3]. Based on these findings, we build highly efficient nano-antennas (figure a) based on 100 nm gold dimers [4-5] which are able to strongly focus light into the sub-wavelength region where the fluorophore is positioned and produce a fluorescence enhancement of more than three orders of magnitude. Using this highly confined excitation field we were able to perform single molecule measurements in solution at concentrations as high as 25 µM in the biologically relevant range (>1µM) [6]. Additionally, we report on a controlled increment of the radiative rate of organic dyes in the vicinity of gold nanoparticles with the consequent increment in the number of total emitted photons [6,7]. We also employ the nanoantennas to mediate the fluorophore emission and thus to shift the apparent emission origin: A single molecule mirage. Finally we will discuss how DNA-Origami can also improve the occupation of other photonic structures, the zeromode waveguides (ZMWs). These structures, which consist of small holes in aluminum films can serve as ultra-small observation volumes for single-molecule spectroscopy at high, biologically relevant concentrations and are commercially used for real-time DNA sequencing [8]. To benefit from the single-molecule approach, each ZMW should be filled with one target molecule which is not possible with stochastic immobilization schemes by adapting the concentration and incubation time. We present DNA origami nano-adapters that by size exclusion allow placing of exactly one molecule per ZMW (figure b). The DNA origami nano-adapters thus overcome Poissonian statistics of molecule positioning [9] and furthermore improve the photophysical homogeneity of the immobilized fluorescent dyes [10].
References
[1] P. W. Rothemund, Nature 440, (2006) 297.
[2] G. P. Acuna et al., ACS Nano 6, (2012) 3189.
[3] F. Möller, P. Holzmeister, T. Sen, G. P. Acuna and P. Tinnefeld, Nanophotonics 2, (2013) 167.
[4] G. P. Acuna et al., Science 338, (2012) 506.
[5] G. P. Acuna et al., Journal of Biomedical Optics 18, (2013) 065001.
[6] A. Puchkova et al., Nano Letters 15, (2015) 8354
[7] J. Pellegrotti et al., Nano Letters 14, (2014) 2831.
[8] P. Holzmeister, E. Pibiri, J.J. Schmied, T. Sen, G. P. Acuna and P. Tinnefeld, Nat. Comm. 5, (2014) 5356.
[9] Eid J et al., Science 323, (2009) 133.
[10] E. Pibiri, P. Holzmeister, B. Lalkens, G.P. Acuna and P. Tinnefeld, Nano Letters 14, (2014) 3499.
[11] S. Heucke et al., Nano Letters. 14, (2014) 391.
Elisa Riedo
Professor of Physics
ASRC and City College New York
Atomic Force Microscopy for nanomechanics and nanofabrication
Abstract: Understanding and manipulating solids and liquids at the nanoscale is a matter of continuously growing scientific and technological interest. The focus of my laboratory is to understand and design structure-function at the nanoscale. In the first part of my presentation I will discuss our recent studies on the inter-layer elasticity of 2D materials [1]. To study the elastic Van Der Waals coupling between layers in two-dimensional materials we have developed AFM modulated nano-indentation. Results and methods will be presented in this seminar. In the second part of my presentation I will discuss recent results on thermochemical nanolithography [2], TCNL, which was invented in my laboratory in 2007. TCNL uses a localized source of heat to activate a chemical reaction and fabricate micro- and nano-structures of a variety of materials and functionalizations. Here, I will discuss our new findings on the use of TCNL for 2D materials nanopatterning, and designing magnetic nanostructures for spin waves based devices [3].
1. Yang Gao, Si Zhou, Suenne Kim, Hsian-Chih Chiu, Daniel Nélias, Claire Berger, Walt de Heer, Laura Polloni, Roman Sordan, Angelo Bongiorno and Elisa Riedo, “Elastic coupling between layers in two-dimensional materials”, Nature Materials 14, 714–721 (2015), DOI: 10.1038/nmat4322
2. Ricardo Garcia, Armin Knoll, and Elisa Riedo “Advanced Scanning Probe Lithography, Nature Nanotechnology, 9, 577 (2014) DOI: 10.1038/NNANO.2014.157.
3. E. Albisetti, D. Petti, M. Pancaldi, M. Madami, S. Tacchi, J. Curtis, W.P. King, A. Papp, G. Csaba, W.Porod, P. Vavassori, E. Riedo, R. Bertacco, “Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography” Nature Nanotechnology, (2016) doi:10.1038/nnano.2016.25 (Cover article).
