Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session L13: Superconducting Nanostructures |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Michael Bleiweiss, Naval Academy Prep. Room: LACC 402B |
Tuesday, March 22, 2005 2:30PM - 2:42PM |
L13.00001: A Superconducting Phase Gradiometer Made Out of DNA-Templated Nanowires David Hopkins, Alexey Bezryadin, David Pekker, Paul Goldbart Continuous superconducting nanowires with diameters less than 10 nm can be fabricated by sputter-coating suspended DNA molecules. We have fabricated and measured pairs of such nanowires, using DNA as a mechanical template. It is found that a pair of nanowires connected in parallel between two superconducting thin-film electrodes acts as a phase gradiometer. We measure oscillations in the resistance and the critical current of the device with respect to magnetic field at various temperatures and bias currents. Surprisingly, the period of the magnetoresistance oscillations is not determined by the area of the loop formed by the pair of nanowires. Instead, it is determined by the phase difference along the edge of the leads created by screening currents. The results are in good quantitative agreement with our theoretical model, which predicts the phase gradients occurring in the system due to these currents and predicts the response of our double-wire device to such phase gradients. [Preview Abstract] |
Tuesday, March 22, 2005 2:42PM - 2:54PM |
L13.00002: Coupled Array of Superconducting Nanowires Andrei Ursache, James Goldbach, Thomas Russell, Mark Tuominen We present experiments that investigate the collective behavior of arrays of superconducting lead nanowires with diameters smaller than the coherence length. The ultrathin ($\sim$15nm) nanowires are grown by pulse electrodeposition into porous self-assembled P(S-b-MMA) diblock copolymer templates. The closely packed ($\sim$24 nm spacing) 1-D superconducting nanowires stand vertically upon a thin normal (Au or Pt) film in a brush-like geometry. Thereby, they are coupled to each other by Andreev reflection at the S-N (Pb-Au) point contact interfaces. Magnetization measurements reveal that the ZFC/FC magnetic response of the coupled array system can be irreversible or reversible, depending on the orientation, perpendicular or parallel, of the applied magnetic field with respect to the coupling plane. As found by electric transport measurements, the coupled array system undergoes an in plane superconducting resistive transition at a temperature smaller than the Tc of an individual nanowire. Current-voltage characteristics throughout the transition region are also discussed. This work was supported by NSF grant DMI-0103024 and DMR-0213695. [Preview Abstract] |
Tuesday, March 22, 2005 2:54PM - 3:06PM |
L13.00003: Superconductivity in one-dimensional nanowires isolated from environment by on-chip resistors Andrey Rogachev, Anthony T. Bollinger, Alexey Bezryadin To test the effects of dissipative environment on superconductivity in quasi-one-dimensional nanowires, we fabricated a series of samples in which the nanowire, connected to small-size thin-film superconducting electrodes, is isolated from the rest of the measurement circuit by means of on-chip Pt/C resistors. The resistors (about 50-100 k$\Omega )$ were made by focused-ion-beam-induced deposition of Pt. The nanowires were fabricated by deposition of MoGe on suspended carbon nanotube. Regardless the fact that nanowires are isolated from the environment, the temperature dependence of a wire resistance is similar to the one predicted by a theory of thermally activated phase slips. [Preview Abstract] |
Tuesday, March 22, 2005 3:06PM - 3:18PM |
L13.00004: Matching Effect in Superconducting Pb Inverse Opal. Ali Aliev, Sergey Lee, Anvar Zakhidov, Ray Baughman The type II superconductivity was observed in highly periodic three-dimensional lead inverse opal prepared by infiltration of a melted Pb in blue (D=160 nm), green (D=220 nm) and red (D=300 nm) opals and following extraction of SiO$_{2}$ spheres by chemical etching. The onset of a broad phase transition ($\Delta $T=0.3 K) measured by temperature dependence of magnetic moment and AC resistivity was shifted from T$_{c}$=7.196 K for bulk Pb to T$_{c}$=7.29 K. Upper critical field H$_{c2}$ (3150 Oe) measured from high-field hysteresis loops exceeds the critical field for bulk lead (803 Oe) four fold. Well distinguished matching affect in field dependence of magnetic moment confirmed by periodic pinning in magneto-resistivity measurements is complying with the lattice parameter of inverse opal structure. [Preview Abstract] |
Tuesday, March 22, 2005 3:18PM - 3:30PM |
L13.00005: Iso-Dissipative Measurements of Little-Parks Oscillations on Ultrathin, Superconducting Films Perforated with Nano-pores M. D. Stewart, Jr., Zhenyi Long, Niravun Pavenayotin, James M. Valles, Jr., Aijun Yin, J. M. Xu We have quench condensed ultra-thin Bi/Sb films on substrates with a regular (honeycomb) array of holes whose spacing is of the same order as the coherence length. The resulting films retain the same perforated structure as the substrate with a much longer penetration depth than previous studies [1]. Iso-dissipative measurments of magnetic field vs temperature have been made at several different fractions of the normal state resistance. The magnitude of the Little-Parks oscillations grows with decreased dissipation level, agreeing qualitatively with expectations for such a phase-coherent effect. In addition, the number of oscillations grow with hole size reflecting an increase in vortex pinning by the holes [2,3]. Our latest data will be presented and discussed within the context of the relative roles of amplitude and phase fluctuations for films near the Superconductor to Insulator Transition. We acknowledge the support of the NSF through DMR0203608 and an REU supplement. [1] U. Welp \textit{et al}., Phys. Rev. B, 66, 212507 (2002). [2] A. I. Buzdin, Phys. Rev. B, 47, 11416 (1993). [3] V. V. Metlushko \textit{et al}., Europhys Lett., 41 (3), 333 (1998). [Preview Abstract] |
Tuesday, March 22, 2005 3:30PM - 3:42PM |
L13.00006: Investigation of superconductivity in AuSn nanowires Nitesh Kumar, Mingliang Tian, Jinguo Wang, James Kurtz, Moses Chan We have fabricated superconducting AuSn nanowires by electrochemical deposition in porous polycarbonate membranes. The diameter of the wires is in the range of 40-100nm with length of 6$\mu$m. By carefully adjusting the deposition parameters, we can fabricate nanowires containing different phases of Au-Sn alloy. Electrical resistivity measurements were done on the array of nanowires still inside the membrane using a two-point probe technique. We observed two phases, AuSn and AuSn4, exhibiting different superconducting properties as observed in the transition temperature, critical field, etc. Currently, we are trying to conduct resistivity measurements on single AuSn nanowire in a four-point configuration, using an electrical field-assisted assembly technique to align the nanowires. This work was supported by Penn State MRSEC NSF grant DMR 0213623. [Preview Abstract] |
Tuesday, March 22, 2005 3:42PM - 3:54PM |
L13.00007: Superconducting wires of amorphous indium oxide Andreas Johansson, G. Sambandamurthy, Neta-Lee Jacobson, Ido Dolev, Dan Shahar, Reshef Tenne We present results of electronic transport measurements on disordered superconducting wires in the 1D limit. The wires are made of amorphous indium oxide (a:InO). They are templated on WS$_{2}$ nanotubes with a diameter between 20 and 120 nm, and stretching across an approximately 1 $\mu $m wide gap etched on the surface of a semiconductor. In earlier studies, a:InO was used extensively for studying the influence of disorder on superconductivity in 2D, including the interplay between disorder, superconductivity, and magnetic field. We have extended that work towards the 1D limit and see signatures of a 2D to 1D crossover in our measurements. The crossover is seen in resistance versus temperature data, as well as in magnetoresistance data. [Preview Abstract] |
Tuesday, March 22, 2005 3:54PM - 4:06PM |
L13.00008: Anomalous Current-Voltage Characteristics of Submicron High-$T_c$ Superconducting Wires P. Morales, M. DiCiano, J.Y.T. Wei We report anomalous non-linearities in the superconducting current-voltage characteristics of submicron YBa$_2$Cu$_3$O$_{7- \delta}$ wires. Submicron-wide and 100$\mu$m-long samples were fabricated using a chemical-free technique based on selective epitaxial growth. Both current-biased and voltage-biased measurements were made between 4.2 K and $T_c$, using pulsed signals to minimize Joule heating. $S$-shaped non-linearities were observed under voltage-biasing and sharp discontinuities were observed under current-biasing, in striking agreement with phase-slip phenomenology established for low-$T_c$ superconductors in quasi-1D geometries. For our quasi-2D high- $T_c$ wires, these observations indicate the formation of phase- slip lines transverse to the current. [Preview Abstract] |
Tuesday, March 22, 2005 4:06PM - 4:18PM |
L13.00009: Destructive regime and step features in ultrathin doubly-connected superconducting Al cylinders H. Wang, N. A. Kurz, M. M. Rosario, B. Rock, M. Tian, P. T. Carrigan, Y. Liu In doubly-connected superconductors, because of the fluxoid quantization, the supercurrent velocity, $v_s$, is modulated by the applied magnetic flux. The maximal $v_s$ is inversely proportional to the sample size, leading to a destructive regime in which superconductivity is lost around half-integer flux quanta even at the zero temperature limit, as the sample diameter, $d$, becomes less than the zero-temperature superconducting coherence length, $\xi (0)$. Our recent measurement shows that for ultrathin Al cylinders with $d<\xi (0)$, regular steps emerge in the resistance vs. temperature $R(T)$ curve as the destructive regime is approached. These resistance steps correspond to minima in $dR/dT$ and are approximately equally spaced in logarithmic scale. These features are not present for large cylinders. We also examined the effect of the size of the measurement currents and found that some steps disappeared at higher measurement currents. All these suggest that the regular step features observed in ultrathin cylinders are not due to the formation of phase slip centers. We will discuss the physical origin of these steps. [Preview Abstract] |
Tuesday, March 22, 2005 4:18PM - 4:30PM |
L13.00010: Suppression of superconductivity in nanowires by bulk superconductors Mingliang Tian, Nitesh Kumar, Shengyong Xu, Jinguo Wang, James Kurtz, Moses Chan Transport measurements were made on a system consisting of zinc nanowire array sandwiched between two bulk superconductors (Sn, In and Pb). It was found that the superconductivity of Zn nanowires could be unexpectedly suppressed by the existence of two mass superconducting reservoirs. The degree of suppression effect is found to closely depend on the diameter and length of the Zn nanowires, as well as the bulk materials (stronger with Sn and weaker with Pb). When a magnetic field (H) is applied and drives the bulk superconductors into the metallic state, the superconducting drop near T$_{c}$ of the Zn nanowires reappears or assumes its full magnitude, indicating the ZNWs have switched back to their superconducting state. Our systematic study demonstrates that this unexpected phenomenon is probably related to the one-dimensional character of zinc nanowires and the interaction of nanowires with the strong bulk superconducting reservoirs. [Preview Abstract] |
Tuesday, March 22, 2005 4:30PM - 4:42PM |
L13.00011: The superconductor-insulator transition in ultrathin Pb: the effects of disorder, magnetic field, and magnetic impurities Jeffrey Parker, Dan Read, Peng Xiong Using ultrathin quench-condensed Pb films we have performed a systematic comparative study of the superconductor-insulator transition (SIT) driven by disorder ($d)$, magnetic field ($B)$, and magnetic impurities (\textit{MI}). The Pb films were quench-condensed at low temperature onto an Sb buffer layer. The $d$-tuned transition was studied by increasing the thickness of the same film in small steps and performing \textit{in situ} transport measurements. The film was driven back into the insulating state by a perpendicular magnetic field and then later in zero field by magnetic impurities deposited in small increments. We observed that the $d$- and \textit{MI}-tuned transitions showed similar features across the SIT, while the $B$-tuned transition appeared qualitatively different. In particular, the $B$-field induced a quasi-reentrant behavior near the critical field and activated transport immediately on the insulating side, indicating possible $B$-induced mesoscale phase separation across the $B$-tuned SIT. These are distinguishing features for the SIT in granular films and were absent in the $d$- and \textit{MI}-tuned transitions which exhibited sharp well-defined phase boundaries. [Preview Abstract] |
Tuesday, March 22, 2005 4:42PM - 4:54PM |
L13.00012: Transport Properties of Superconducting Nanomeshes Fabricated Using Porous Aluminum Oxide Templates Joel Keay, P.R. Larson, K.L. Hobbs, S.Q. Murphy, M.B. Johnson, J.R. Kirtley It is known that critical superconducting phenomena in thin films are enhanced with the introduction of artificial pinning centers (APCs) into the films. Additionally, matching field anomalies in the film resistance and critical currents are observed. In this work, we have fabricated hexagonal arrays of holes in superconducting niobium thin films using porous anodic aluminum oxide templates. The hole diameters are 50 nm with an inner hole separation of 100 nm. Standard four-point measurements have been used to investigate the effect of the hole array on the longitudinal and transverse transport properties of the thin films. Results from these measurements will be presented. This work was supported by NSF grant nos. DMR-0080054 and NSF-0132534. [Preview Abstract] |
Tuesday, March 22, 2005 4:54PM - 5:06PM |
L13.00013: Superconductor-insulator transition in 1-D nanowires of different lengths Anthony Bollinger, Andrey Rogachev, Alexey Bezryadin It is unclear whether the superconductor-insulator transition (SIT) in thin superconducting wires is controlled by the wire's diameter, normal state resistance, or both. In order to distinguish between these possibilities we study the SIT in wires of different length. A well-defined SIT is only observed in homogeneous wires which are shorter than $\sim $200 nm. For these wires, the superconducting state is well described by the Langer-Ambegaokar-McCumber-Halperin theory of thermally activated phase slips whereas the insulating state can be explained by localization and electron-electron interactions in one dimension. Longer wires, though fabricated in the exact same manner, do not show a well-defined SIT and frequently display signs of non-uniformity such as double transition steps. Data obtained from resistance vs. temperature as well as differential resistance vs. bias current measurements will be presented which illustrate these observed traits. [Preview Abstract] |
Tuesday, March 22, 2005 5:06PM - 5:18PM |
L13.00014: Superconducting Properties of Amorphous Tantalum Thin Films Brian Gross, Yongguang Qin, Jongsoo Yoon We investigate superconducting properties of tantalum thin films. The films are deposited at a rate of 0.1nm/sec on quartz substrates by dc sputtering with an argon pressure of 4 mtorr. The samples are patterned to a Hall bar geometry with a shadow mask, and contacts are made with an indium press via gold pads that are pre-deposited on the substrates before the tantalum deposition. We found that with decreasing film thickness, the superconducting transition temperature ($T_c )$ of these films continuously decreases towards 0K. This is characteristic of the amorphous structure of the superconducting thin films, and in strong contrast to granular superconducting thin films where $T_c $ is nearly independent of film thickness. We also found that an exposure of these films to air at room temperature (at least for several months) does not cause any noticeable change in their superconducting properties. We present our results on superconducting properties measurements and structural studies on these amorphous tantalum films. [Preview Abstract] |
Tuesday, March 22, 2005 5:18PM - 5:30PM |
L13.00015: Observation of the quantum capacitance in a Cooper-pair transistor Tim Duty, Goeran Johansson, Kevin Bladh, David Gunnarsson, Chris Wilson, Per Delsing The effective capacitance of a single Cooper-pair box (SCB) can be defined as the second derivative of its energy with respect to gate voltage. This capacitance has two parts, the geometric capacitance, $C_{geom}$, and the quantum capacitance, $C_Q$. $C_Q$ is due to the anti-level crossing caused by the Josephson coupling energy $E_J$, and depends parametrically on the gate voltage. This capacitance, which is dual to the Josephson inductance, can be substantially larger than $C_{geom} $ as well as negative. To detect $C_Q$, we have measured the in- phase and out-of-phase rf-signal reflected from a Cooper-pair transistor (CPT), embedded in a resonant circuit. Under suitable biasing conditions the CPT acts as a SCB in series with a capacitance. It can be shown that the imaginary part of the reflected signal depends linearly on $C_Q$, and we can thus measure $C_Q$ directly from the reflected signal as a function of the gate voltage. The measured data agrees well with the theoretical prediction assuming that the system is in the ground state. We can extract the ratio $E_J/E_C$ for each of the two junctions in the CPT, where $E_C$ is the charging energy of the CPT. [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