Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F17: 2D Devices: Superconductors, Charge Density Waves, Phase TransitionsFocus
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Vincent Meunier, Rensselaer Polytechnic Institute Room: 316 |
Tuesday, March 15, 2016 11:15AM - 11:27AM |
F17.00001: hBN/graphene heterostructures for spectroscopy studies in normal and superconducting regime Riccardo Pisoni, Joel I-Jan Wang, Landry Bretheau, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero Tunneling spectroscopy is a powerful tool to study the electronic properties of materials, as it has the capability of probing the electronic density of states at energies away from the Fermi level. Though local probes, such as scanning tunneling spectroscopy (STS), are widely used to elucidate the novel electronic properties of graphene, planar (2-D to 2-D) tunneling is also desirable for its capability to probe the global behavior of a 2-D electronic system. To study the intrinsic properties of the material via tunneling, one must employ a proper tunneling barrier and minimize the local doping introduced by the tunneling. Here we present a fabrication technique involving ultra thin hexagonal Boron Nitride (hBN) as both a tunneling barrier and an encapsulation overlayer to protect the 2-D Van der Waals material under study. In particular we focus on the fabrication of ultra thin hBN/graphene/hBN Van der Waals heterostructures that allows us to perform tunneling spectroscopy in graphene in normal and superconducting regime. [Preview Abstract] |
Tuesday, March 15, 2016 11:27AM - 11:39AM |
F17.00002: New Method of fabricating high-mobility graphene/LaAlO$_3$/SrTiO$_3$ nanostructures shivendra Tripathi, Giriraj Jnawali, Lu Chen, Mengcheng Huang, Jen-feng Hsu, Brian D'Urso, Hyungwoo Lee, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Graphene and LaAlO$_3$/SrTiO$_3$ (LAO/STO) are both two-dimensional electronic systems with a fascinating range of properties. The coupling between these two 2DEG’s has the potential to produce various novel phenomena and create new functionalities. Successful integration of these two systems must overcome a number of technical challenges. Graphene-complex-oxide (GCO) heterostructures are created using Hyflon AD (2,2,4-trifluoro-5 trifluoromethoxy-1,3 dioxole) as a support layer for transferring and patterning CVD graphene on LAO/STO. This approach has advantages over more traditional methods that use Poly(Methyl Methacrylate) (PPMA) to transfer CVD graphene in that the Hyflon is easier to remove from the oxide surface after processing. To test the quality of GCO heterostructures, a graphene Hall bar structure is created. The quantum Hall regime can routinely be reached in the graphene layer, while preserving the ability of the LAO/STO to be patterned using AFM lithography. This approach opens up the possibility for the exploration of a wide range of GCO devices. [Preview Abstract] |
Tuesday, March 15, 2016 11:39AM - 11:51AM |
F17.00003: Tunneling Spectroscopy of Andreev states in Graphene Landry Bretheau, Joel I-Jan Wang, Riccardo Pisoni, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero Although not intrinsically superconducting, graphene (G) can inherit electronic properties of a superconductor (S) placed in good contact with it. This proximity effect originates from the formation in the graphene of entangled electron-hole states, the Andreev states. In an S-G-S geometry, the Andreev states’ energies depend on the difference between the order parameter phases of the two superconductors. Such a phenomenon is usually probed by measuring the dissipationless Josephson supercurrent carried by Andreev states. Here instead, we have performed a direct tunneling spectroscopy of graphene connected to two superconducting electrodes, in a SQUID geometry that enables us to vary the phase difference. The measured energy spectra are consistent with a continuum of Andreev bound states modulating with phase with energies smaller than the superconducting gap. Interestingly, out of gap modulation is also observed and can be interpreted as Andreev scattering states. Additionally, we discuss how these phenomena evolve as a function of graphene normal DOS, which is tuned by a back-gate electrode. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:03PM |
F17.00004: Specular Interband Andreev Reflections in Graphene Konstantin B. Efetov, Dmitri Efetov, Lei Wang, Gil-Ho Lee, Jia Shuang, Robert Cava, Takashi Taniguchi, Kenji Watanabe, James Hone, Cory Dean, Philip Kim Electrons incident from a normal metal onto a superconductor are reflected back as holes -- a process called Andreev reflection. In a normal metal where the Fermi energy is much larger than a typical superconducting gap, the reflected hole retraces the path taken by the incident electron. In graphene with ultra- low disorder, however, the Fermi energy can be tuned to be smaller than the superconducting gap. In this unusual limit, the holes are expected to be reflected specularly at the superconductor-graphene interface due to the onset of interband Andreev processes, where the effective mass of the reflected holes change sign. Here we present measurements of gate modulated Andreev reflections across the low disorder van der Waals interface formed between graphene and the superconducting NbSe$_{2}$. We find that the conductance across the graphene/superconductor interface exhibits a characteristic suppression when the Fermi energy is tuned to values smaller than the superconducting gap, a hallmark for the transition between intraband retro and interband specular- Andreev reflections. [Preview Abstract] |
Tuesday, March 15, 2016 12:03PM - 12:15PM |
F17.00005: Spin superconductivity and ac-Josephson effect in Graphene system under strong magnetic field Haiwen Liu, Hua Jiang, Qing-feng Sun, X. C. Xie We study the spin superconductivity in Graphene system under strong magnetic field. From the microscopically Gor'kov method combined with the Aharonov-Casher effect, we derive the effective Landau-Ginzburg free energy and analyze the time evolution of order parameter, which is confirmed to be the off-diagonal long range order. Meanwhile, we compare the ground state of spin superconductivity to the canted-antiferromagnetic state, and demonstrate the equivalence between these two states. Moreover, we give out the pseudo-field flux quantization condition of spin supercurrent, and propose an experimental measurable ac-Josephson effect of spin superconductivity in this system. [Preview Abstract] |
Tuesday, March 15, 2016 12:15PM - 12:27PM |
F17.00006: Ballistic and diffusive regimes in current-phase relations of graphene SNS heterojunctions Philip Kratz, Francois Amet, Christopher Watson, Kathryn Moler, Chung Ke, Ivan Borzenets, Kenji Watanabe, Takashi Taniguchi, Russell Deacon, Michihisa Yamamoto, Yuriy Bomze, Seigo Tarucha, Gleb Finkelstein Current-phase relations (CPRs) are an indirect measurement of the energy distribution of phase-coherent modes in Josephson junctions through the spectral supercurrent near equilibrium, probing low-energy excitations not accessible by transport. We report on planned experimental measurements of the CPRs of gated, high-mobility (~10$^5$ cm$^2$/Vs) single-layer graphene SNS heterojunctions in ring geometries with superconducting MoRe alloy contacts, inductively read out with a scanning superconducting quantum interference device (SQUID) magnetometer. The graphene layers are encapsulated on both sides with hexagonal-BN (h-BN). We will address the CPR dependence on experimentally tunable parameters (temperature, carrier density, and channel length), and possible crossovers between the ballistic and diffusive regimes. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 1:03PM |
F17.00007: The role of double TiO$_{2}$ layers at the interface of FeSe/SrTiO$_{3}$ superconductors Invited Speaker: Ke Zou The marked enhancement of the superconducting critical temperature for FeSe grown on SrTiO$_{3}$ (STO) is a notable recent discovery in the field of high temperature superconductivity. A complete understanding of the mechanism for this enhancement has not been elucidated and is thought to be due to how the electronic structure is modified by the interface. We determine the surface reconstruction of SrTiO$_{3}$ that is used to achieve superconducting FeSe films in experiments. In particular, we observe the existence of a double TiO$_{2}$ layer and identify the symmetry of the reconstruction at the FeSe/SrTiO$_{3}$ interface. The double TiO$_{2}$ layer plays two important roles. First, it facilitates epitaxial growth of FeSe films. Second, $\textit{ab initio}$ calculations reveal that electron transfer to the FeSe is enhanced by the double layer termination more strongly than by other surface structures of SrTiO$_{3}$. The enhanced electron transfer suppresses the hole pocket near the $\Gamma$ point, leading to a band structure characteristic of superconducting samples. The characterization of the interface structure presented here is a key step towards understanding the electronic properties of this novel superconductor. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:15PM |
F17.00008: Josephson Coupling in Nb/SmB$_{\mathrm{6}}$/Nb Junctions Xiaohang Zhang, Seunghun Lee, Jasper Drisko, John Cumings, Richard Greene, Ichiro Takeuchi Josephson coupling of superconductors through a topological surface has attracted considerable attention because it may provide device applications of topological insulators with implications for Majorana fermions. However, the results of previous Josephson junction studies on topological insulators have not been fully understood due to complications arising from the conducting bulk and the non-pristine nature of the surfaces/interfaces of the topological insulator materials used. In this work, SmB$_{\mathrm{6}}$ thin films with a highly insulating bulk were adopted to minimize the influence of the bulk carriers while in-situ deposition of Nb film on SmB$_{\mathrm{6}}$ surface was used to ensure the interface quality. The bilayer structure was then patterned into Nb/SmB$_{\mathrm{6}}$/Nb lateral junctions by e-beam lithography and ion milling. The Nb electrodes in our junctions had a typical width of \textasciitilde 1 $\mu $m and the gap between the two Nb electrodes was varied from 50 nm to 200 nm. A critical current up to 40 $\mu $A has been observed in junctions with a gap around 50 nm at 2.0 K. In this talk, I will discuss the implication of our results to the desired Josephson coupling through topological surface states. [Preview Abstract] |
Tuesday, March 15, 2016 1:15PM - 1:27PM |
F17.00009: Conductivity Modulation in a gated Normal-CDW-Normal configuration Saumya Biswas, Roger Lake There is considerable interest in switching by exploiting a voltage controlled phase transition, and one such phase is the charge density wave phase that occurs in a number of quasi one dimensional and two dimensional transition metal dichalcogenides. Voltage controlled switching of the charge density wave transition in 1T-TaS$_{\mathrm{2}}$ has recently been demonstrated. We consider a transistor geometry with normal metal contacts and a channel of CDW material. The interaction is modeled with a negative U Hubbard term. Normal-CDW-temperature-U phase diagrams show the regime of the CDW in the ideal lattice. The wavelength of the CDW in the transistor channel is determined by both the conditions of Fermi surface nesting and also the condition of commensurability with the channel length between the two normal leads. Moving the Fermi level of the channel first results in phase boundaries within the CDW as the conditions of commensurability and Fermi surface nesting become incompatible. Moving the Fermi level from half filling by few tens of meV causes a collapsing of the CDW gap and an effective CDW-normal transition, leaving vestiges of the CDW in the channel. The transition is accompanied by one to two orders of magnitude increase in the conductivity. [Preview Abstract] |
Tuesday, March 15, 2016 1:27PM - 1:39PM |
F17.00010: Probing the Interaction of Graphene and Correlated Electron Systems by STM and Magnetotransport Michael Altvater, Marc Reynaud, Aditya Sripal, Alice Huang, Guohong Li, Eva Y. Andrei, Rui Zhao, Joshua Robinson Since the discovery of 2D materials including graphene and TMDs, many have been shown to exhibit a wide variety of properties including correlated electronic phases, metal-insulator transi- tions, and highly tunable material properties leading to a rapid increase in research interest. Recent advances in nanostructure fabrication allow us to further study the interaction of these materials by creating heterostructures, layered devices made from low dimensional materials. In this work, we investigate the interaction of Dirac electrons in graphene with the charge density wave formed in 1T-TaS2, a van der Waals stacked TMD exhibiting a number of electronic phases including a high temperature metallic phase, several charge density wave phases, a Mott insulating phase, and superconductivity with the addition of pressure or dopants. Using STM, STS, and magnetotrans- port, we probe the effects of graphene on the phase transition properties of the CDW in TaS2 as well as the effect of the highly correlated substrate on the electronic spectrum in graphene. Our work will provide insight into the effects of correlated physics in heterostructures and how we might take advantage of these effects to produce novel devices and applications. [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 1:51PM |
F17.00011: Dimensionality effect on the charge density wave and superconductivity of molecular beam epitaxy grown monolayer NbSe$_{\mathrm{2}}$ Hyejin Ryu, Yi Zhang, Zahid Hussain, Sung-Kwan Mo, Z.-X. Shen, Miguel M. Ugeda, Aaron J. Bradley, Seita Onishi, Yi Chen, Wei Ruan, Claudia Ojeda-Aristizabal, Mark T. Edmonds, Hsin-Zon Tsai, Alexander Riss, Dunghai Lee, Alex Zettl, Michael F. Crommie Transition metal dichalcogenides are ideal compounds to investigate dimensionality effect since the weak coupling between layers enables to study single-layer material which removes interlayer interactions and introduces quantum confinement. We investigate dimensionality effect of NbSe$_{\mathrm{2}}$ in which the bulk phase shows charge density wave (CDW) (T$_{\mathrm{CDW}}=$33 K) and superconductivity (T$_{\mathrm{c}}=$7.2 K). We report electronic band structure of MBE grown monolayer NbSe$_{\mathrm{2}}$ measured by Angel-resolved photoemission spectroscopy compared with bulk. We find the number of bands crossing the Fermi energy reduces from three (bulk) to one (monolayer). Based on the significant suppression of superconducting T$_{\mathrm{c}}=$0.65 K with robust CDW in monolayer NbSe$_{\mathrm{2}}$, our results imply the band remained at the Fermi level in monolayer NbSe$_{\mathrm{2}}$ may play a crucial role in CDW formation and the disappeared bands are possibly in charge of superconductivity. [Preview Abstract] |
Tuesday, March 15, 2016 1:51PM - 2:03PM |
F17.00012: Reversible Semiconducting-to-Metallic Phase Transition in Chemical Vapor Deposition Grown Monolayer WSe$_{\mathrm{2}}$ and Applications for Devices Yuqiang Ma, Bilu Liu, Anyi Zhang, Liang Chen, Mohammad Fathi, Chenfei Shen, Ahmad Abbas, Mingyuan Ge, Matthew Mecklenburg, Chongwu Zhou Two-dimensional (2D) semiconducting monolayer transition metal dichalcogenides (TMDCs) have stimulated lots of interest because they are direct bandgap materials that have reasonably good mobility values. However, contact between most metals and semiconducting TMDCs like 2H phase WSe$_{\mathrm{2}}$ is highly resistive, thus degrading the performance of field effect transistors (FETs) fabricated with WSe$_{\mathrm{2}}$ as active channel materials. We applied a phase engineering method to chemical vapor deposition (CVD) grown monolayer 2H-WSe$_{\mathrm{2}}$ and demonstrated semiconducting-to-metallic phase transition in atomically thin WSe$_{\mathrm{2}}$. We have also shown that metallic phase WSe$_{\mathrm{2}}$ can be converted back to semiconducting phase, demonstrating the reversibility of this phase transition. In addition, we fabricated FETs based on these CVD-grown WSe$_{\mathrm{2}}$ flakes with phase-engineered metallic 1T-WSe$_{\mathrm{2}}$ as contact regions and intact semiconducting 2H-WSe$_{\mathrm{2}}$ as active channel materials. The device performance is substantially improved with metallic phase source/drain electrodes, showing on/off current ratios of 10$^{\mathrm{7}}$ and mobilities up to 66 cm$^{\mathrm{2}}$/V\textbullet s for monolayer WSe$_{\mathrm{2}}$. [Preview Abstract] |
Tuesday, March 15, 2016 2:03PM - 2:15PM |
F17.00013: \textbf{Metal to insulator quantum-phase transition in few-layered ReS}$_{\mathbf{2}}$. Nihar Pradhan, Amber MCCREARY, Daniel Rhodes, Zhenguang Lu, Dmitry Smirnov, EFSTRATIOS MANOUSAKIS, Simin Feng, Raju Namburu, Madan Dubey, Angela HIGHT WALKER, Humberto Terrones, Mauricio Terrones, VLADIMIR DOBROSAVLJEVIC, Luis Balicas ReS$_{2}$ a layer-independent direct band-gap semiconductor of 1.5 eV implies a potential for its use in optoelectronic applications. Here, we present an overall evaluation of transport and anisotropic Raman of few-layered ReS$_{2}$ FET. ReS$_{2}$ exfoliated on SiO$_{2}$ behaves as an $n$-type semiconductor with an intrinsic carrier mobility surpassing $\mu _{i}$ \textasciitilde 30 cm$^{2}$/Vs at $T =$ 300 K which increases up to \textasciitilde 350 cm$^{2}$/vs at 2 K. Semiconducting behavior is observed at low electron densities $n$, but at high values of $n $the resistivity decreases by a factor \textgreater 7 upon cooling to 2 K and displays a metallic$^{\, }T^{2}$-dependence. The electric-field induced metallic state observed in MoS$_{2}$ was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of $T $and $n$, we find that the metallic state of ReS$_{2}$ results from a second-order metal to insulator transition driven by electronic correlations. [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