Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P39: Superconductivity: Mesoscopic & Related |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Barbara Jones, IBM Research Room: 386 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P39.00001: Phase slip dynamics in uniform mesoscopic superconducting rings Anthony Lollo, Ivana Petkovic, Jack Harris We study the dynamics of phase slips in uniform thin mesoscopic superconducting aluminum rings via cantilever torque magnetometry. In the full field range we measure the persistent current of a unique isolated flux-biased ring, which exibits a step at each phase slip. We then focus on a single transition and accumulate the statistics of the phase slip flux values. We find that as temperature is lowered the transition region becomes wider. This is in contrast with the thermally activated phase slip statistics usually observed in weak links, and contrary to the prediction of McCumber and Halperin for thermal activation in uniform rings. We fit the persistent current with Ginzburg-Landau theory in order to extract the relevant system parameters such as coherence length, and then use them to calculate the relevant free energy barrier between metastable states within the same formalism, which sets the phase slip dynamics. We discuss possible scenarios, including the role of temperature-dependent damping. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P39.00002: Electrostatically Tuned Superconductor-Insulator Transition in Indium Oxide Thin Films Qi Yang, Alexander Palevski, Aharon Kapitulnik Recently the ``standard paradigm" which assumes that in the presence of disorder, and in the limit of zero temperature, the two-dimensional (2D) electron may exhibit either an insulating or a superconducting ground state, has been challenged both, theoretically and experimentally. In this paper we study amorphous Indium Oxide (InO$_x$) thin films that are fabricated by electron beam evaporation on SrTiO$_3$. By annealing in vacuum, air or oxygen atmosphere the room temperature sheet resistance of the samples is varied. Applying an external electrostatic field (using back-gating) and magnetic fields at low temperatures, the samples are tuned, between a superconducting and an insulating states. Sheet resistance and Hall effect are measured at low temperatures gaining further insights into the superconductor-metal-insulator transitions (SIT) in this system. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P39.00003: Charge Density Waves in Single- and Bi-layer Bismuth Deposited on NbSe2 Carolina Adamo, Alan Fang, Robert Cava, Aharon Kapitulnik A connected low-temperature scanning tunneling (STM) and a molecular-beam epitaxy (MBE) chambers have been used to measure ultra thin films of bismuth (Bi) on NbSe2 single crystals. Due to large lattice mismatch between NbSe2 and Bi we observed two different lattice structures; when a single Ml of Bi is deposited a triangular lattice commensurate with the cleaved NbSe2 is seen and 1D charge density waves (CDW) patter is observed. Instead for thickness bigger than 1 Ml, the topography shows a structure corresponding to (110) Bi oriented film, which also exhibits both 2D and 1D CDW order. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P39.00004: Investigating Simultaneous Suppression of Superfluid and Resistivity in Ultrathin, Severely Underdoped YBCO Stanley Steers, Thomas Lemberger, Brian Baker Recent results in ultrathin, severely underdoped Y$_1$Ba$_2$Cu$_3$O$_{7-x}$ show an unusual offset between the low temperature scale at which the superfluid density vanishes and a higher temperature where resistivity vanishes, resulting in a simultaneous suppression of the superfluid density and the resistivity in a given temperature domain (Steers et. al, PRB 94, 094525 (2016)). This offset domain can be tens of kelvin in severely underdoped samples, and numerical studies rule out spatially random inhomogeneity as the sole cause of the offset. We present transport measurements in ultrathin YBCO and compare with thick film and bulk measurements from the literature to shed light on the offset. We also discuss the offset vis a vis the proposed pair density wave (PDW) state suggested for La$_{2-x}$Ba$_x$CuO$_4$ at $x=\frac{1}{8}$ doping. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P39.00005: Andreev Transport in InSb Nanowire Quantum Point Contacts Stephen Gill, Malcolm Durkin, John Jeffrey Damasco, Sasa Gazibegovic, Erik Bakkers, Nadya Mason Controlling mesoscopic and topological superconductivity in nanowires requires a nearly pristine superconductor-nanowire interface. We report on progress in controlling the proximity effect in InSb nanowires directly contacted with high quality Al. We discuss ballistic 1D transport in hybrid InSb nanowire-superconductor based quantum point contacts, which indicate a transparent Al-nanowire interface. We further discuss the how the conductance quantization in the normal state of InSb nanowires correlates to Andreev transport in the superconducting state. We find that Andreev conductance enhancements up to the theoretical limit of 2 can be observed. In addition, we explore the magnetic field and temperature dependence of the proximity superconductivity in ballistic InSb nanowire devices. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P39.00006: Magnetic properties of epitaxial $\beta $-Nb2N thin film on SiC substrate Zihao Yang, Roberto Myers, D. Scott Katzer, Neeraj Nepal, David J. Meyer Previously superconductivity in Nb$_{\mathrm{2}}$N was studied in thin films synthesized by reactive magnetron sputtering or pulsed laser deposition.[1][2] Recently, Nb$_{\mathrm{2}}$N was synthesized by molecular beam epitaxy (MBE).[3] Here, we report on the magnetic properties of MBE grown Nb$_{\mathrm{2}}$N measured by SQUID magnetometry. The single hexagonal $\beta $ phase Nb$_{\mathrm{2}}$N is grown on a semi-insulating Si-face 4H SiC (0001) substrate in nitrogen rich conditions at a substrate temperature of 850 ${^\circ}$C.[3] In-plane magnetization as a function of magnetic field measured at 5 K shows type-II superconductivity with critical fields H$_{\mathrm{c1}}$ and H$_{\mathrm{c2}}$ of 300 Oe and 10 kOe, respectively. In-plane field-cooled and zero-field-cooled a critical temperature (T$_{\mathrm{c}})$ of 11.5 K, higher than in sputtered Nb$_{\mathrm{2}}$N films. This work was supported by Army Research Office and the Office of Naval Research. [1] Treece et. al. Chem. Mater. 6, 2205 (1994) [2] Chockalingam et. al. PRB 77, 214503 (2008) [3] Katzer et. al. APEX 8, 085501 (2015) [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P39.00007: Enhanced superconductivity in atomically thin 2H-TaS$_{\mathrm{2}}$ down to the ultra-thin limit Yafang Yang, Efren Navarro-Moratalla, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero One attractive candidate for realizing superconductivity in the 2D limit is transitional metal dichalcogenides (TMDs). For example, studies of NbSe$_{\mathrm{2}}$ have verified superconductivity down to monolayer, with T$_{\mathrm{c}}$ reduced from 7 K (bulk) to 3 K (monolayer). Similar to NbSe$_{\mathrm{2}}$, 2H-TaS$_{\mathrm{2}}$ is another candidate, with very similar crystal structure yet T$_{\mathrm{c}}$ less than 1 K in bulk. Prior work attempting to access the 2D limit of 2H-TaS$_{\mathrm{2}}$ has found significant sample degradation after fabrication, and it turns to insulating behavior when thickness is less than 3.5 nm. We are able to overcome it by encapsulating TaS$_{\mathrm{2}}$ flake with hBN in a glove box while also using thin pre-evaporated metal contacts to maintain a good van der Waals `seal' to prevent air from reacting with the sample. With this method, we find that superconductivity persists down to the bilayer limit. More surprisingly, we observed pronounced increase in the T$_{\mathrm{c}}$ from around 0.7 K (bulk) to 3 K (bilayer) when the thickness of the flake is reduced, opposite to the trend observed in most superconducting films as well as recent studies on NbSe$_{\mathrm{2}}$. This provides interesting evidence that reducing the dimensionality can actually strengthen superconductivity as opposed to the weakening effect that has been reported in other 2D materials. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P39.00008: Detecting tip-induced superconductivity in topological materials Goutam Sheet It has been found that in certain topological materials, including the topological Dirac semimetal Cd$_3$As$_2$ and Weyl semimetal TaAs, a mesoscopic superconducting phase emerges at point contact junctions with elemental metals. For such superconducting phases, existing only at mesoscopic point contacts, the characterization tools like transport and magnetization measurements fail due to extremely small volume fraction of the superconducting phases. In such cases, however, it is possible to detect the local superconducting phases by performing point contact spectroscopy in different regimes of mesoscopic transport and studying the temperature and magnetic field evolution of the spectroscopic features. In this talk I will present how such experiments are performed to realize and detect tip-induced superconductivity (TISC) on topological materials. Experiments on certain new topological insulators will also be presented. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P39.00009: Electronic phase diagram of electron-doped cuprate La$_{2-}_{x}$Ce$_{x}$CuO$_{4}$ explored by electrolyte gating Hideki Matsuoka, Masaki Nakano, Masaki Uchida, Masashi Kawasaki, Yoshihiro Iwasa The electrolyte gating technique, which utilizes an electrolyte as a gate dielectric layer of the field-effect transistor, enables us to control a large number of carriers in materials by external voltages. Another advantage of this technique is that it enables stable and quasi-continuous tuning of carrier density in one sample without changing any other parameters, providing a very powerful tool for constructing an electronic phase diagram of a wide variety of materials. We applied this technique to La$_{2-}_{x}$Ce$_{x}$CuO$_{4}$, one of electron-doped cuprate superconductors, and realized gate-induced insulator-to-superconductor transitions. In the presentation, we will mainly discuss evolution of electronic states while changing carrier density, in particular by focusing in the underdoped regime. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P39.00010: Tuning phase transitions of FeSe thin flakes by field effect transistor with solid ion conductor as gate dielectric Xianhui Chen We develop a novel field effect transistor (FET) device using solid ion conductor (SIC) as a gate dielectric, and we can tune the carrier density of FeSe by driving lithium ions in and out of the FeSe thin flakes, and consequently control the material properties and its phase transitions. A dome-shaped superconducting phase diagram was mapped out with increasing Li content, with Tc \textasciitilde 46.6 K for the optimal doping, and an insulating phase was reached at the extremely overdoped regime. Our study suggests that, using solid ion conductor as a gate dielectric, the SIC-FET device can achieve much higher carrier doping in the bulk, and suit many surface sensitive experimental probes, and can stabilize novel structural phases that are inaccessible in ordinary conditions. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P39.00011: Probing and controlling fluxoid states in multiply-connected mesoscopic superconducting structures Hryhoriy Polshyn, Tyler Naibert, Raffi Budakian New ways to investigate and manipulate fluxoid and vortex states of mesoscopic superconducting structures are of great interest. The states with multiple vortices or winding numbers could be useful for the study of vortex interactions and interference effects, the braiding of Majorana bound states by winding vortices, and the development of novel superconducting devices. We demonstrate a methodology based on magnetic force microscopy that allows us to induce, probe and control fluxoid states in thin wall structures comprised of multiple loops. By using micro-magnet as a source of inhomogeneous magnetic field, we can efficiently explore the configuration space of fluxoid states. Scanning over the structure reveals the energy crossing points of the lowest laying fluxoid states. This is due the strong interaction of cantilever with thermally activated fluxoid transitions at points of degeneracy. We show that measured patterns of fluxoid transitions allow to identify the states, investigate their energetics, and manipulate them. Further, we show that the dynamics of driven fluxoid transitions can be described by stochastic resonance model, which provides a unique way of measuring fluxoid transition rate and related energy barrier for chosen transitions even in complicated structures. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P39.00012: Unconventional superconductivity in bilayer transition metal dichalcogenides Chaoxing Liu Two dimensional layered materials, such as graphene and transition metal dichalcogenides, have revealed rich physical phenomena due to the interplay between different degrees of freedom, including spin, valley and layer degrees. In this talk, we will discuss unconventional superconductivity in bilayer transition metal dichalcogenides and show how multiple degrees of freedom in this system can lead to unconventional superconductivity. We find that intra-layer singlet pairings (A1g and A1u pairing) and inter-layer triplet pairing (Eu pairing) are possible to be stable in the phase diagram, depending on the relative strength of intra-layer and inter-layer interactions. Furthermore, by applying an in-plane magnetic field, we predict that the superconducting state with intra-layer singlet pairing will evolve to an inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov phase due to the presence of a new linear gradient term, which also linearly depends on magnetic fields, in the Landau free energy. We also discuss the experimental relevance of our results and possible experimental signatures to identify the helical state. [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P39.00013: Shape dependence of occurrence conditions of spontaneous half-quantized vortices in d-dot Norio Fujita, Masaru Kato, Takekazu Ishida A d-dot is a nano-sized composite structure that consists of a d-wave superconductor (SC) embedded in an s-wave matrix. Since the phase of the superconducting order parameter in the d-wave SC depends on direction, phase difference appears at the corner junctions between d- and s-wave SCs in d-dot's. Due to quantization of fluxoids including this phase difference, spontaneous half-quantized vortices (SHQVs) appear at the each corner in d-dot's. [1]. We can use Pb as s-wave SCs and YBa2Cu3O7-$\delta $ (YBCO) as d-wave SCs. But it is pointed out that the SHQVs may not appear if there exist some defects, especially twin boundaries (TBs) in YBCO. In order to analyze effects of TBs on SHQVs, we introduce orthorhombic structure of YBCO into two-components Ginzburg-Landau(GL) equations [2] in terms of anisotropy of effective mass. Using the finite element method [1], we showed that fractional vortices appear on edges of TBs. In this study, we calculate magnetic field distribution in d-dot models with several TBs and investigate shape dependence of effects of TBs on SHQVs. [1] M. Kato, T. Ishida, T. Koyama, M. Machida, Superconductors -- Materials, Properties and Applications. (InTech 2012) Chap. 13. [2] N. Fujita, M. Kato, T. Ishida, Physica C, 518, (2015) 44. [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