Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y53: Superconductivity: Proximity Effects and SN Junctions III |
Hide Abstracts |
Sponsoring Units: DCMP Room: Hilton Baltimore Holiday Ballroom 4 |
Friday, March 18, 2016 11:15AM - 11:27AM |
Y53.00001: Scanning Tunneling Microscopy Study of Graphene/Cuprate Heterostructures. Minghao Cheng, Alexander Kerelsky, Xinjue Zhong, Da Wang, Yufeng Hao, James Hone, Xiaoyang Zhu, Ahbay Pasupathy We study the properties of single-layer graphene co-laminated to BSCCO-2212 single crystals using UHV-Low Temperature-STM. Samples were prepared by transferring large-area single layer graphene grown on copper substrate using the chemical vapor deposition to the freshly-cleaved surface of a BSCCO single crystal in an inert atmosphere. Under optimal conditions, the graphene acts as a protective film for the freshly-cleaved surface of BSCCO allowing for high-quality spectroscopic measurements to be performed subsequently. We will show evidence of this protection from topographic imaging of the BSCCO through the graphene monolayer. More interestingly, the d-wave superconductivity of BSCCO couples to the Dirac Fermions of graphene via the proximity effect. We will describe the signatures of this coupling as probed by point spectroscopy and spectroscopic imaging in the STM. [Preview Abstract] |
Friday, March 18, 2016 11:27AM - 11:39AM |
Y53.00002: Experimental study of electrical conduction across high-Tc superconductor-graphene interfaces David Perconte, Fabian Cuellar, Marie-Blandine Martin, Bruno Dlubak, Maelis Piquemal-Banci, Rozenn Bernard, Juan Trastoy, Constance Moreau-Luchaire, Pierre Seneor, Javier Villegas, Piran Kidambi, John Robertson, Stephan Hofmann Proximity-induced superconductivity presents unusual features in graphene (i.e. specular Andreev reflection [1]) due to its particular electronic structure. It has been theoretically discussed that, if a d-wave superconductor is put contact with graphene, the latter will sustain d-wave superconductivity, and further unusual features (such as oscillatory behavior) should be observed in the superconductor-graphene junction conductance [2]. Motivated by these prospects, we experimentally investigate YBCO-graphene junctions. We will show differential conductance measurements as a function of temperature, magnetic field, and graphene doping. The observed behavior will be discussed in the frame of the theory developed in [1,2,3]. [1] C.W.J. Beenakker, Phys. Rev. Lett. 97, 067007 (2006); [2] J. Linder et al., Phys. Rev. Lett. 99, 147001 (2007); [3] S. Kashiwaya et al., Phys. Rev. B 53, 2667 (1996). [Preview Abstract] |
Friday, March 18, 2016 11:39AM - 11:51AM |
Y53.00003: Proximity superconductivity in graphene Landau levels Gaurav Chaudhary, Xiao Li, Allan MacDonald We study monolayer graphene sheets in the quantum Hall regime that are proximity coupled to an $s$-wave superconducting thin film. At magnetic fields near $H_{c2}$ triangular vortex lattice states form in the superconductor and induce similar vortex lattice states in the graphene sheets. We use the Bogoliubov-de Gennes theory to study the properties of quasiparticle excitations in the graphene sheets, and find that the quantized Hall conductance survives even in such a vortex lattice state. We further explore the possibility of realizing topological superconductivity in such a system. In addition, we propose that under some circumstances the vortex cores may host zero-energy bound states which are Majorana fermions. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:03PM |
Y53.00004: ABSTRACT WITHDRAWN |
Friday, March 18, 2016 12:03PM - 12:15PM |
Y53.00005: Proximity Effect at Graphene - High Tc Superconductor Junctions Da Wang, En-Min Shih, Ghidewon Arefe, Youngduck Kim, Drew Edelberg, Erick Andrade, Dennis Wang, James Hone, Cory Dean, Abhay Pasupathy The proximity effect is a well-known mesoscopic phenomenon where Cooper pairs from a superconductor (S) enter into a normal metal (N) that is well coupled to it. Since graphene was discovered a decade ago, the proximity effect at superconductor-graphene junctions has been extensively studied and interesting phenomena such as specular Andreev reflection and ballistic transport at graphene Josephson junctions have been observed. However, superconductors used in these experiments to date are of conventional low Tc, such as aluminum(Tc=1.2K), NbSe2(Tc=7K), and MoRe(Tc=8K). Understanding how the proximity effect works between high-Tc superconductors (pnictides and cuprates) and the Dirac Fermions of graphene remains largely unexplored. The chief technical challenge here is to create high-quality junctions between high-Tc superconductors and graphene. In this work, we will introduce a home-made setup that allows us to exfoliate, transfer and encapsulate superconductor-graphene junctions in a well controlled inert atmosphere. Transport measurements of the proximity effect at graphene-iron pnictide(FeSe, FeTeSe) and graphene-cuprate(BSCCO) junctions will be described. [Preview Abstract] |
Friday, March 18, 2016 12:15PM - 12:27PM |
Y53.00006: Proximity superconductivity in ballistic graphene at high magnetic fields J. R. Prance, M. Ben Shalom, M. J. Zhu, V. I. Fal’ko, A. Mishchenko, A. V. Kretinin, K. S. Novoselov, C. R. Woods, K. Watanabe, T. Taniguchi, A. K. Geim We present measurements of the superconducting proximity effect in graphene-based Josephson junctions with a mean free path of several microns, which exceeds the junctions' length [1]. The junctions exhibit low contact resistance and large supercurrents. We observe Fabry-P\'{e}rot oscillations in the normal-state resistance and the critical current of the junctions. The proximity effect is mostly suppressed in magnetic fields of \textless 10 mT showing the conventional Fraunhofer interference pattern; however, unexpectedly, a weak proximity effect survives in magnetic fields as high as 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each exhibits a supercurrent carrying capacity close to the universal limit of e$\Delta $/h where $\Delta $ is the superconducting gap of the contacts. We attribute the high-field supercurrent to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion. [1] Ben Shalom et al., arXiv:1504.03286 (2015) [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 12:39PM |
Y53.00007: Proximity induced Superconductivity in Epitaxial Graphene Fabian D. Natterer, Jeonghoon Ha, Hongwoo Baek, Duming Zhang, William Cullen, Nikolai B. Zhitenev, Young Kuk, Joseph A. Stroscio The intimate electrical contact of a superconductor with a normal metal leads to an exchange of carriers through their boundary. Cooper pairs leak into the normal metal via Andreev reflection and enable the normal metal to acquire superconducting-like properties. The electron-hole conversion process in graphene is prominent due to relativistic quantum mechanics governing low energy chiral carriers in a multi-valley system. In the present experiment, we reveal spatial measurements of the proximity effect in graphene from a graphene-superconductor interface. Superconducting aluminum films were grown on epitaxial graphene on SiC. The aluminum films were discontinuous with networks of trenches in the film morphology reaching down to the substrate to exposed graphene terraces. Scanning tunneling spectra measured on the graphene terraces show a clear decay of the superconducting gap width with increasing separation from the graphene-aluminum edges. The decay length for the superconducting energy gap extends beyond 400 nm. Subtle deviations in the exponentially decaying energy gap were also observed on a much smaller length scale of tens of nanometers. [Preview Abstract] |
Friday, March 18, 2016 12:39PM - 12:51PM |
Y53.00008: Contact spectroscopy on S/TI/N devices: Induced pairing on the surface of a topological insulator Martin P. Stehno, Prosper Ngabonziza, Marieke Snelder, Hiroaki Myoren, Yu Pan, Anne de Visser, Y. Huang, Mark S. Golden, Alexander Brinkman Translating concepts of topological quantum computation into applications requires fine-tuning of parameters in the model Hamiltonians of candidate systems. Such level of control has proven difficult to achieve in devices where superconductors are used to induce pairing in topological insulator (TI) materials. While local probe experiments have indicated features of p-wave superconducting correlations in TIs (as suggested by theory), results on extended devices often remain ambiguous. We present contact spectroscopy data on superconductor/topological insulator/normal metal devices with bulk-insulating TI material and compare these with bulk conducting samples. We discuss the magnitude of the induced gap and unusual features in the conductance traces of the bulk-insulating samples that may suggest the presence of p-wave type correlations in the TI. [Preview Abstract] |
Friday, March 18, 2016 12:51PM - 1:03PM |
Y53.00009: Signatures of Induced Superconductivity in NbTi Contacted InAs Quantum Wells Anthony McFadden, Javad Shabani, Borzoyeh Shojaei, Joon Sue Lee, Chris Palmstrøm We have studied electrical transport through InAs quantum wells grown by MBE with unannealed superconducting NbTi contacts deposited \textit{ex-situ} and patterned by optical photolithography. Characterization of the InAs 2DEG's without superconducting contacts yields typical mobilities greater than 100,000 cm$^{\mathrm{2}}$/Vs at a density of 4e11 cm$^{\mathrm{-2}}$. NbTi-InAs-NbTi (SNS) and NbTi-InAs (SN) devices with dimensions greater than 1 \textmu m are fabricated using optical lithography. Although the dimensions of the fabricated SNS devices are too large to observe a supercurrent, signatures of superconductivity induced in the InAs are present. We observe two superconducting critical temperatures: one of the NbTi leads (T$_{\mathrm{c\thinspace }}$\textasciitilde 8K), and a second (T$_{\mathrm{c}}$ \textless 4.5K) attributed to superconductivity induced in the InAs channel. dI/dV vs V spectroscopy on SNS junctions below the second critical temperature shows a conductance maximum at zero applied voltage while conductance minima appear at finite bias voltage which is attributed to the presence of an induced superconducting gap in the InAs quantum well. [Preview Abstract] |
Friday, March 18, 2016 1:03PM - 1:15PM |
Y53.00010: Large superconducting double-gap, a pronounced pseudogap and evidence for proximity-induced topological superconductivity in the Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$/Fe$_{\mathrm{1+y}}$Te interfacial superconductor J. Y. Shen, M. Q. He, Q. L. He, K. T. Law, I. K. Sou, R. Lortz, A. P. Petrovic We investigate directional point-contact spectroscopy on a Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$/ Fe$_{\mathrm{1+y}}$Te heterostructure, fabricated via van der Waals epitaxy, which is interfacial superconducting with an onset T$_{\mathrm{C}}$ at 12K and zero resistance below 8K. A large superconducting twin-gap structure is seen down to 0.27K, together with a zero bias conductance peak. The anisotropic smaller gap ($\Delta _{\mathrm{1}}$) is around 5 meV at 0.27K and closes at 8K, while the other one ($\Delta_{\mathrm{2}}$), as large as 12 meV, is isotropic and eventually evolves into a pseudogap closing at 40K. Both, the two-gap BTK and Dynes models can well reproduce our data, demonstrating $\Delta _{\mathrm{1\thinspace }}$should be associated with the proximity-induced superconductivity in the topological Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ layer, while $\Delta_{\mathrm{2}}$ may be attributed to an intrinsically-doped FeTe thin film at the interface. [Preview Abstract] |
Friday, March 18, 2016 1:15PM - 1:27PM |
Y53.00011: Proximity-induced superconducting gap in low-dimensional materials Christopher Reeg, Dmitrii Maslov The ability to induce a sizable gap in the excitation spectrum of a metal placed in contact with a conventional superconductor has become increasingly important in recent years in the context of engineering a topological superconductor. Conventional studies of the proximity effect involving sufficiently bulky metals have shown that Andreev reflection processes at the superconductor/metal interface induce a nonzero pairing amplitude in the metal but do not endow it with a gap. Conversely, when the metal is an atomically thin layer, the tunneling of Cooper pairs can induce an excitation gap equal to the bulk gap of the superconductor (provided that the superconductor/metal interface is sufficiently transparent). We study how these two seemingly different views of the proximity effect evolve into one another as the thickness of the metal is changed. More specifically, we show that there is a thickness scale associated with the decrease of the induced gap, and that this scale is much larger than the Fermi wavelength. As a result, by proximity to most conventional superconductors, a sizable excitation gap can be induced in metals that are tens of atomic layers thick. [Preview Abstract] |
Friday, March 18, 2016 1:27PM - 1:39PM |
Y53.00012: General conditions for proximity induced odd-frequency superconductivity in two-dimensional electronic systems Enrico Rossi, Christopher Triola, Driss Badiane, Alexander V. Balatsky We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity-coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling will exhibit odd-frequency superconducting pairing. [Preview Abstract] |
Friday, March 18, 2016 1:39PM - 1:51PM |
Y53.00013: Growth and fabrication of proximity-coupled topological quantum wire circuits from thin InAs films Carolyn Kan, Chi Xue, Yang Bai, James Eckstein The realization of topological states in strongly spin orbit coupled semiconductors proximity-coupled to conventional superconductors requires delicate materials engineering. Key areas for improvement include the crystalline quality of the semiconductor itself, but a high-quality interface between the semiconductor and superconductor is essential. Recent results have demonstrated the necessity of forming an in situ interface to eliminate the “soft gap” observed in earlier experiments. While much work has focused on vertically grown nanowires, we take a lithographic approach to fabricating quantum wires out of MBE-grown thin films, which allow for increased flexibility and scalability of device structures. Notably, our films are grown entirely in situ in linked MBE systems, vastly improving interface transmission and cleanliness. Aspects of growth architecture aimed toward increasing the InAs mobility, such as substrate choice and layer structure, are also discussed. [Preview Abstract] |
Friday, March 18, 2016 1:51PM - 2:03PM |
Y53.00014: Superfluid density through 2D superconductor junctions. Hyoungdo Nam, Chih-Kang Shih As S. Qin et al. [1] reported, two monolayer (2 ML) lead film on a silicon (111) substrate has one of two different atomic structures on the silicon substrate: the unstrained 1x1 and the psedumorphically strained $\surd $3x$\surd $3 (i.e. the same lattice constant as the Si $\surd $3x$\surd $3 lattice). Most interestingly, although these two different regions show the same quantum well state features, they have different Tc's (5 K and 4 K). These two different regions of 2 ML film naturally form superconductor-superconductor (SS or SS') junctions along silicon step edges. Physical connection of the junction is only 1 ML thickness because of the step height difference of substrate. We will present this study of SS (or SS') junction system using scanning tunneling microscopy/spectroscopy and \textit{in-situ} double-coil mutual inductance measurement. The transition of superconducting gaps across either SS or SS' junctions should show how to locally affect each other. Double coil measurement show a global Tc close to the lower Tc region with sizable superfluid density. We will discuss the phase rigidity and its relationship to the superfluid density in this ultra-thin Pb film that is only 2 ML thick. [1] `Superconductivity at the two-dimensional limit' S. Qin, J. Kim, Q. Niu, and C. K. Shih, \textit{Science} \textbf{324}, 1314 (2009). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700