Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y35: Low TC: 2-D Superconductor-insulator Transition |
Hide Abstracts |
Sponsoring Units: DMP Chair: Greg Boyd, Georgetown University Room: 343 |
Friday, March 22, 2013 8:00AM - 8:12AM |
Y35.00001: Strongly disordered s-wave superconductors probed by microwave electrodynamics E.F.C. Driessen, P.C.J.J. Coumou, R.R. Tromp, P.J. de Visser, T.M. Klapwijk In contrast to Anderson's theorem, recently evidence has emerged that superconductivity is susceptible to strong disorder and that there is a disorder-induced superconductor-to-insulator transition (SIT). We probe the effects of strong disorder ($8.6> k_Fl > 2.4$, approaching the SIT) in thin films of niobium titanium nitride and titanium nitride by measuring the microwave electrodynamics in coplanar waveguide resonators. The electromagnetic response gradually evolves with disorder, deviating from conventional Mattis-Bardeen theory, for both materials. The result is understood as due to changes in the quasiparticle density of states, as a consequence of the short elastic scattering length. Our observations are consistent with a model that uses an effective pair breaker, which is inversely proportional to the value of $k_Fl$. [Preview Abstract] |
Friday, March 22, 2013 8:12AM - 8:24AM |
Y35.00002: Berezinsky– Kosterlitz– Thouless transition in ultrathin NbN films near superconductor-insulator transition Jie Yong, K. Il'in, M. Siegel, Thomas Lemberger We report temperature dependent superfluid densities $\lambda$ $^{-2}$(T) in ultrathin NbN films near thickness-tuned superconductor-insulator transition (SIT). Superfluid densities in these films are measured by two-coil mutual inductance apparatus. For thick films, dirty limit BCS theory fits experimental data well and this verifies the correctness of this technique. As films get thinner and closer to SIT, sharp downturns near transition temperatures (T$_c$), signature of Berezinsky-Kosterlitz-Thouless transition, are observed. This downturn occurs much earlier than what 2-D XY theory predicts. This might due to smaller vortex core energy than expected in 2-D XY model. The superconducting gap, deduced from fitting low temperature $\lambda$ $^{-2}$(T), is linear with T$_c$ for most films but remain finite across SIT. This is consistent with the scenario that superconductivity is destroyed by phase fluctuations. Zero temperature sheet superfluid density also shows correlation with T$_c$, further proving the importance of fluctuations near SIT. [Preview Abstract] |
Friday, March 22, 2013 8:24AM - 8:36AM |
Y35.00003: Universal Scaling of the order parameter distribution in strongly disordered superconductors A. Kamlapure, S.C. Ganguli, G. Lemari\'e, D. Bucheli, L. Benfatto, J. Lorenzana, C. Castellani, G. Seibold, P. Raychaudhuri We present scanning tunneling spectroscopy measurements on strongly disordered s-wave superconductor, NbN, close to Anderson metal insulator transition. At low temperatures all our samples show superconducting spectra with dip close to zero bias and two coherence peaks after correcting with large V shaped background. Although spectra do not show significant variation in the superconducting energy gap but we see large distribution in the coherence peak heights characteristic to the strength of disorder. We take average value of the coherence peak heights on positive and negative bias as a measure of local order parameter $S$ [1]. We observe that maxima of order parameter distribution (OPD) steadily decrease with increasing disorder. On rescaling with the new scaling variable $R_{S}$ as logarithm of order parameter normalized to its variance, OPD for all the samples collapse into single curve showing universality of the OPD. In addition OPD is in good agreement with the universal Tracy-Widom distribution in finite dimension. We also identify similar scaling relation of the OPD within two prototype fermionic and bosonic models for disordered superconductors showing an excellent agreement between experiment and theory in the current field.\\[4pt][1]arXiv:1208.3336 [cond-mat.supr-con] [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y35.00004: The effects of disorder and temperature on the glassy dynamics of the first-order spin-paramagnetic transition in ultrathin granular Al films Joseph Prestigiacomo, Philip Adams We report an ongoing experimental study of the effects of disorder and temperature on the glassy dynamics of the first-order spin-paramagnetic transition in ultrathin granular Al films. The disorder of the films is gauged primarily by their proximity to the quantum sheet resistance $R_Q \approx$ 6.45 K$\Omega/$sq at temperatures slightly above $T_c$. In general, thicker films with $R \ll R_Q$ achieve equilibrium almost entirely through avalanches in resistance while thinner films with $R \sim R_Q$ exhibit slow stretched-exponential relaxation with very few detectable avalanches. Preliminary observations indicate that increasing measurement temperatures to near the tricritical point has the effect of speeding up the relaxations, thereby reducing the time constants involved. Similarities between this system and other glassy systems will be discussed. [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y35.00005: Transport Behavior of Ultrathin Films with NanoThickness Undulations in the Strongly Localized Regime J.C. Joy, S.M. Hollen, C. Zhao, G. Fernandes, J.M. Xu, J.M. Valles, Jr. Recent work on thin films of superconducting material grown on anodized aluminum oxide (AAO) has revealed the existence of a Cooper Pair Insulator (CPI), a state in which superconducting pair correlations survive, but with activated transport dominated by electron pairs. AFM data has revealed that the AAO substrates have a regular undulating structure, which causes films to grow with predictable variations in thickness. These thickness undulations, which have a spatial period greater than the superconducting coherence length, work to localize Cooper pairs in the insulating state. To gain insight into the properties of the normal state of the CPI, we are investigating the transport properties of Copper films grown on AAO substrates. Early data indicate activated transport with activation energies of approximately 20 K in the most insulating films. [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y35.00006: Superconductor-Metal-Insulator transition in two dimensional Ta thin Films Sun-gyu Park, Eunseong Kim Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y35.00007: Magneto-transport Measurements of Electrostatically Tuned Disordered In2O3 Films near the Superconductor-Insulator Transition Yeonbae Lee, Aviad Frydman, Allen Goldman We have used an electric double layer transistor configuration employing an ionic liquid to modify the carrier density and resultant properties of disordered In$_2$O$_3$ films near the superconductor-insulator (SI) transition. By carrier density modulation up to 7 X 10$^{14}$ carriers-cm$^{-2}$, we have been able to traverse the SI transition as well as significantly alter the strength and location of the large magnetoresistance peak found in the insulating regime. We have also been able to correlate the magnetic length associated with the largest magnetoresistance peak with a length scale for granularity of the film obtained from a spectral analysis of surface profile data obtained using atomic force microscopy. The latter suggests that film morphology may play an important role in the peak. [Preview Abstract] |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y35.00008: AC evidence of a field tuned 2D superconductor-metal transition in a low-disorder InO$_x$ film Wei Liu, LiDong Pan, Jiajia Wen, Minsoo Kim, Sambandamurthy Ganapathy, Peter Armitage Employing microwave spectroscopy, we investigated the field tuned quantum phase transition between the superconducting and the resistive states in a low-disorder amorphous InO$_x$ film in the frequency range of 0.05 to 16 GHz. Our AC measurements are explicitly sensitive to the critical slowing down of the characteristic frequency scales approaching a transition. The relevant frequency scale of superconducting fluctuations approaches zero at a field $B_{sm}$ far below the field $B_{cross}$ where different isotherms of resistance as a function of magnetic field cross each other. The phase stiffness at the lowest frequency vanishes from the superconducting side at B $\approx B_{sm}$, while the high frequency limit extrapolates to zero near $B_{cross}$. Our data are consistent with a scenario where $B_{sm}$ is the true quantum critical point for a transition from a superconductor to an anomalous metal, while $B_{cross}$ only signifies a crossover to a regime where superconducting correlations make a vanishing contribution to both AC and DC transport measurements in the low-disorder limit. [Preview Abstract] |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y35.00009: Observation of the Collapse of the Cooper Pair Phase Coherence Length at a Superconductor to Insulator Transition James Valles, Shawna Hollen, Gustavo Fernandes, Jimmy Xu Experiments on ultrathin amorphous Bi films provided one of the best known examples of a Superconductor to Insulator quantum phase transition (SIT). Nevertheless, controversy persists over whether this thickness tuned SIT is ``fermionic'' or ``bosonic''. Early data suggested fermionic with the suppression of the amplitude of the superconductor order parameter creating a weakly-localized, phase incoherent, single electron insulator. However, recent work on other uniformly disordered materials suggests that bosonic physics universally dominates at the SIT to produce insulators of locally phase coherent Cooper pair islands. To address this issue, we used a technique that previously revealed local Cooper pair phase coherence in insulating non-uniformly thick films. We measured the strength of flux periodic magneto-resistance oscillations of ultrathin a-Bi films patterned with a nano-array of holes. The data indicate that the Cooper pair phase coherence length collapses at this SIT. This collapse is inconsistent with the continuous decrease of the phase coherence length expected for a bosonic SIT. It is consistent with the order parameter amplitude disappearing at a fermionic SIT. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y35.00010: Transport of thin superconducting films and multilayer heterostructure made by Atomic layer deposition Thomas Proslier, Jeffrey Klug, Nickolas Groll, Nicholas Becker, Andreas Glatz, Valerii Vinokur, Michael Pellin, Tatyana Baturina, Jeffrey Elam, John Zasadzsinki We report the use of atomic layer deposition (ALD) to synthesize thin superconducting films and multilayer superconductor-insulator (S-I) heterostructures. The ALD technique applied to superconducting films opens the way for a variety of applications, including improving the performance and decreasing the cost of high energy particle accelerators, superconducting wires for energy storage, and bolometers for radiation detection. Furthermore, the atomic-scale thickness control afforded by ALD enables the study of superconductivity and associated phenomena in homogeneous layers in the ultra-thin film limit. In this respect, we will present results of ALD-grown transition metal-based superconductors, including nitrides, carbides, and silicides of niobium, nitrides of molybdenum and titanium, and Nb$_{\mathrm{1-x}}$Ti$_{\mathrm{x}}$N/AlN-based S-I heterostructures. Transport measurement for various composition and film thicknesses will be presented. [Preview Abstract] |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y35.00011: Dynamical conductivity across the superconductor-insulator transition Mason Swanson, Yen Lee Loh, Mohit Randeria, Nandini Trivedi Thin superconducting films can exhibit a quantum phase transition from a superconductor to an insulator with increasing disorder. While the exact mechanism of the transition is not completely understood, there is strong evidence that it is bosonic in nature in some models and materials, with disorder acting to localize the superconducting pairs [1]. Previous studies of bosonic models of the superconductor-insulator transition (SIT) have focused almost entirely on criticality and dc properties at the transition. We go beyond these studies by calculating the dynamical conductivity of a disordered (2$+$1)D XY model using quantum Monte Carlo simulations that capture the phase fluctuations driving the SIT. Our results obey standard sum rule constraints for the longitudinal and transverse current correlation functions and show a build-up of integrated spectral weight near the transition. We will discuss the low frequency spectral weight in terms of a possible intermediate bose-metal phase between the superconductor and insulator. [1] K. Bouadim, Y. L. Loh, M. Randeria, and N. Trivedi, \textit{Nat. Phys. }\textbf{7}, 884 -- 889 (2011). We acknowledge support from the NSF Graduate Research Fellowship Program (MS), NSF DMR-1006532 (MR), and DOE DE-FG02-07ER46423 (NT). [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y35.00012: Off-diagonal disorder in two-dimentional attractive Hubbard model: A Bogoliubov-deGennes study Sanjeev Kumar, Prabuddha Chakraborty We present a detailed computational study of the two-dimensional attractive Hubbard model on a square lattice in the presence of off-diagonal disorder. The focus is on the superconductor to insulator transition, and on the comparison between the effects of diagonal disorder and those of off-diagonal disorder. We decouple the attractive Hubbard model in the pairing channel and make use of the Bogoliubov deGennes methodology to study the resulting model numerically on finite lattices. The work is motivated by recent observation of Anderson localization in optical lattices, and the possibility of tuning the sign of interactions between the atoms [Rev. Mod. Phys. {\bf 80}, 885 (2008)]. We find very interesting qualitative differences between the models of diagonal and off-diagonal disorder. The average amplitude of superconducting order parameter and spectral gap are strongly suppressed with off-diagonal disorder. This is in contrast to the case of diagonal disorder, where the spectral gap has a minumum and the amplitude of superconducting order parameter remains finite. We also present systematic lattice-size dependence of results. In addition, we compare the results of binary (discrete), and box (continuous) distributions, for both diagonal and off-diagonal disorder models. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y35.00013: Random-Field Model of a Cooper Pair Insulator Thomas Proctor, Eugene Chudnovsky, Dmitry Garanin The model of a disordered superconducting film with quantum phase fluctuations is mapped on a random-field XY spin model in 2+1 dimensions. Analytical studies within continuum field theory, supported by our recent numerical calculations on discrete lattices, show the onset of the low-temperature Cooper pair insulator phase. The constant external field in the random-field spin model maps on the Josephson coupling between the disordered film and a bulk superconductor. Such a coupling, if sufficiently strong, restores superconductivity in the film. This provides an experimental test for the quantum fluctuation model of a superinsulator. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y35.00014: Collective effects in the two-dimensional Josephson junction array Valerii Vinokour, Ivan Sadovskyy, Alexey Galda We study collective quantum effects in the two-dimensional Josephson junction arrays (JJA) in the vicinity of the superconductor-insulator transition (SIT). We find the contribution of the quantum coherent phase slips (QCPS) into the formation of thermodynamic properties of the JJA, including critical current, as a function of the magnetic field. We investigate the response of the 2D JJA to the external bias and the contribution from QCPS to this response. [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