Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H38: Superconductivity-Disordered Thin Films and Quantum Phenomena |
Hide Abstracts |
Sponsoring Units: DCMP Chair: A. M. Goldman, University of Minnesota Room: Baltimore Convention Center 341 |
Tuesday, March 14, 2006 11:15AM - 11:27AM |
H38.00001: Quantum Superconductor-Insulator transition and Nernst effect in NbxSi1-x Herve Aubin, Alexandre Pourret, Kamran Behnia, Jerome Lesueur, Claire Marrache-Kikuchi, Laurent Berg\'{e}, Louis Dumoulin We show that the nature of magnetic-field tuned superconductor- insulator transitions in amorphous $Nb_{0.15}Si_{0.85}$ thin films depends on the orientation of the magnetic with respect to the film. In perperndicular magnetic field, the transition is driven by quantum fluctuations, characterized by an isobestic point (Bc,Rc) in the resistance measurements, and a kink in the temperature profile of the critical magnetic field -- that indicates a temperature scale below which quantum fluctuations control the dynamics of the system. The isobestic point and the kink are not found when the magnetic field is applied parallel to the films, where the transition is classical, driven by the breaking of Cooper pairs at the temperature dependent critical field $H_{c2}$. In addition, we will present the first study of Nernst coefficient in such a disordered superconductor. As previous studies on the cuprates have suggested, we show that the Nernst signal is particularly sensitive to superconducting fluctuations, where a sizable signal is observed in a large temperature(T>Tc) and magnetic field range. [Preview Abstract] |
Tuesday, March 14, 2006 11:27AM - 11:39AM |
H38.00002: The interplay between localization and superconductivity in ultrathin amorphous beryllium films Wenhao Wu, E. Bielejec Near the superconductor-insulator transition (SIT), quench-condensed ultrathin Be films show a highly anisotropic magnetoconductance (MC). The conductance can drop orders of magnitude in a weak perpendicular field ( $<$ 1 T). In the high field regime, 2 $\sim $ 10 T, the MC in a perpendicular field is positive and can vary orders of magnitude with increasing field. These features disappears when a small amount of Mn impurities are introduced. Our results indicate that superconductivity is the origin of the observed MC. We have carried out simultaneous electron transport and tunneling measurements across the SIT, which allow us to determine, \textit{independently} and up to a constant on the order of unity, the localization length, $\xi _{L}$, and the dielectric constant, $\kappa $, for the films. We have found that, as the normal-state sheet resistance of the films at 20 K is reduced with increasing film thickness, $\xi _{L}$ increases exponentially. The SIT occurs when $\xi _{L}$ crosses the Ginzburg-Landau coherence length, $\xi _{S}$. [Preview Abstract] |
Tuesday, March 14, 2006 11:39AM - 11:51AM |
H38.00003: Field-Induced Superconductor to Metal and Superconductor to Insulator Transitions in Thin Indium Oxide Films K. H. Sarwa B. Tan, Kevin A. Parendo, Allen M. Goldman, Z. Ovadyahu The application of magnetic fields to ultra-thin superconducting films is believed to bring about superconductor-insulator transitions which are quantum phase transitions. We will present measurements in perpendicular and parallel magnetic fields of R(T) of amorphous indium oxide films. In contrast with what has been reported for films with similar T$_{c}$'s, scaling, although successful for the superconducting curves, fails for the insulating ones. For a 150 Angstrom thick film with a zero-field T$_{c}$ = 2.8K, the high-field behavior is governed by a T$^{1/3}$ law suggestive of a 3D dirty metal. For a 100 Angstrom film with T$_{c}$ =1.8K the high-field regime is governed by Efros-Shklovskii hopping. This suggests that the former is superconductor-metal transition, whereas the latter is a superconductor-insulator transition. Further studies related to quantum corrections and film morphology are still in progress. This work was supported in part by the National Science Foundation under grant NSF/DMR-0455121. [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:03PM |
H38.00004: Vortices and quasiparticles near the ``superconductor-insulator'' transition in thin films. Victor Galitski, Gil Refael, Matthew P. A. Fisher, T. Senthil We consider the low temperature behavior of an amorphous superconducting film driven normal by a perpendicular magnetic field. We introduce a new two-fluid formulation consisting of fermionized field-induced vortices and electrically neutralized Bogoliubov quasiparticles interacting via a long-ranged statistical interaction. This approach allows us to access a novel non-Fermi liquid phase which naturally interpolates between the low field superconductor and the high field normal metal. We also discuss the transport, thermodynamics, and tunneling properties of the resulting ``vortex metal'' phase. [Preview Abstract] |
Tuesday, March 14, 2006 12:03PM - 12:15PM |
H38.00005: Anomalous Insulating State Induced by Application of Parallel Magnetic Fields to 2D Superconducting Films Kevin A. Parendo, K. H. Sarwa B. Tan, Allen M. Goldman Superconductor-insulator transitions in ultrathin films of amorphous Bi have been investigated by electrostatic electron doping, incrementing film thickness, and applying parallel magnetic fields. When superconductivity was induced in an insulating film by electrostatic tuning, a quantum phase transition was observed down to 60 mK. When superconductivity was quenched by parallel magnetic fields, above $\sim $ 150 mK, R(T) was best described by 2D Mott variable range hopping at the highest fields and scaling was successful. However, an anomalous insulating state was induced by the field below $\sim $ 150 mK in which the resistance becomes larger than expected from extrapolation of R(T) from higher temperatures, causing scaling to break down. This anomalous state has not been observed in zero field thickness- or electrostatic-tuned transitions in bismuth. It has also been observed in amorphous In$_{2}$O$_{3 }$films in parallel fields, but not in perpendicular fields. This work is supported in part by the National Science Foundation under grant NSF/DMR-0455121. [Preview Abstract] |
Tuesday, March 14, 2006 12:15PM - 12:27PM |
H38.00006: Insulating State of Granular Superconductors in a Strong Coupling Regime Igor Beloborodov, Yasha Fominov, Andrei Lopatin, Valerii Vinokur We analyze the possibly of the formation of a magnetic field induced insulating state in a two-dimensional granular superconductor with relatively strong intergranular coupling and show that such a state appears in a model with spatial variations of the single grain critical magnetic field. This model well describes realistic granular samples with the dispersion in grain sizes and explains qualitatively the recent experimental observation of a giant peak in the magnetoresistance of dirty superconducting films. [Preview Abstract] |
Tuesday, March 14, 2006 12:27PM - 12:39PM |
H38.00007: The effect of 3$d$ paramagnetic impurities on superconductivity in quench-condensed amorphous Pb films Ashwani Kumar, Dan E. Read, Jeffrey S. Parker, H Jeffrey Gardner, Peng Xiong A modified dilution refrigerator equipped with Sb, Pb and NiCr sources is used to carry out an \textit{in situ} study of the effect of magnetic impurities (\textit{MI}) on the \underline {same} quench-condensed Pb films. Si substrate with pre-deposited Au contacts is mounted in dilution unit and cool down to 5K. To ensure the electrical and possibly structural homogeneity down to monolayer thickness, we deposit a thin layer of Sb prior to the Pb evaporation. At a thickness above 8 ? the film exhibits superconductivity with well-defined resistive transition and $T_{c}$ controlled by the film thickness. When a film of desired $T_{c}$ is obtained we incrementally evaporate \textit{MI} onto the film by heating a NiCr wire at constant current and perform \textit{in situ} measurements. We observe that $T_{c}$ is continuously suppressed with increasing \textit{MI} density while the resistive transitions remain sharp, although the \textit{MI} induces significant filling of states inside the gap. The $T_{c}$ as a function of \textit{MI} density is well described by the Abrikosov-Gorkov theory regardless of the starting $T_{c}$ and the pair-breaking strength of the \textit{MI} appears to be independent of the degree of disorder. [Preview Abstract] |
Tuesday, March 14, 2006 12:39PM - 12:51PM |
H38.00008: Confirmation of the discrepancy between experiment and theory in the superconducting proximity effect Manjiang Zhang, Go Tateishi, Gerd Bergmann The transition temperature $T_{c}$ of a superconducting film S is reduced when it is covered with a normal metal N. Recently we investigated the superconducting proximity effect in double layers of Pb and alkali metals and found the initial slope $dT_ {c}/dd_{n}$ of $T_{c}$ as a function of the thickness of the normal metal $d_{n}$ was smaller than the theoretical value by a factor of 2 . The theory shows that the $\backslash$QTR normalized initial slope $S_{sn}=$ $(d_{s}/T_{s})|dT_{c}/dd_{n}|$ $=$ $\Gamma _{sn}\ast (N_{n}/N_{s})$ depends only on the density of states ratio of the two metals, $N_{n}/N_{s}$, but not on the mean free paths or the interface. A literature search showed that this initial slope is rarely measured. The few experiments in the literature where the initial slope can be derived yield the same disagreement with the theory. In the present work we investigated systematically the initial slope of S/N sandwiches (S for Pb and N for the normal conductor) and also extended the investigation to S$_{1}$/S$_{2}$ sandwiches (S$_{1}$=Pb, S$_{2} $= Cd, Zn, Al, In, Sn). The normalized initial slope $S_{sn}$ is confirmed to be independent of the Pb thickness. Again for S/N sandwiches the value of $\Gamma _{sn}$ is more than a factor 2 smaller than the theoretical value. For the S$_{1}$/S$_{2}$ sandwiches this discrepancy decreases with increasing $T_{c}$ of S$_{2}$. [Preview Abstract] |
Tuesday, March 14, 2006 12:51PM - 1:03PM |
H38.00009: Vortex Glass is a Metal Jiansheng Wu, Philip Phillips We consider the disordered quantum rotor model in the presence of a magnetic field. We analyze the transport properties in the vicinity of the multicritical point between the superconductor, phase glass and paramagnetic phases. We find that the magnetic field leaves metallic transport of bosons in the glassy phase in tact. In the vicinity of the superconductivity to the intervening metallic state transition, the resistivity turns on as $(H-H_c)^{2}$ with $H_c$. This functional form is in excellent agreement with the experimentally observed turn-on of the resistivity in the metallic state in MoGe, namely $R\approx R_c(H-H_c)^\mu$, $1<\mu<3$. The metallic state is also shown to presist in three spatial dimensions. As the phase glass in $d=3$ is identical to the vortex glass, we conclude that the vortex glass is, in actuality, a metal rather than a superconductor at $T=0$. [Preview Abstract] |
Tuesday, March 14, 2006 1:03PM - 1:15PM |
H38.00010: Quantum phase transition and possible phase separation in ultrathin doubly-connected superconducting cylinders of Al Haohua Wang, Neal Staley, Benjamin Clouser, Ying Liu Fluxoid quantization demands that the superfluid velocity, $v_s$, of a doubly-connected superconducting cylinder increase as its diameter, $d$, decreases, leading to a destructive regime and a quantum phase transition (QPT) in one dimension (1D) - Superconductivity is suppressed around half-integer flux quanta even at zero temperature for cylinders with a $d$ less than the zero-temperature superconducting coherence length, $\xi(0)$. We have fabricated ultrathin doubly-connected superconducting cylinders of Al over a wide range of $d/\xi (0)$ ratios, with the smallest cylinder down to 100 nm in diameter. Electrical transport measurements revealed the presence of robust step-like features in resistance $vs.$ temperature curves as the destructive regime is approached. These field-induced step-like features, present only in the smallest cylinders with $d/\xi (0) $ close to or less than 1, are unrelated to sample inhomogeneity or phase slip centers, and are most likely resulted from a phase separation close to the QPT. We have also found that the normal state in the destructive regime becomes less stable as the $d/\xi (0)$ ratio increases, with the resistances at the half-flux quantum suppressed continuously from its full normal-state value. Resistance $vs.$ magnetic field measurements show that the field tuned QPT is very sharp (less than 1G) with little evidence for hysteretic behavior. [Preview Abstract] |
Tuesday, March 14, 2006 1:15PM - 1:27PM |
H38.00011: Hysteresis and Noise from Electronic Nematicity Erica Carlson, Karin Dahmen, Eduardo Fradkin, Steven Kivelson An electron nematic is a translationally invariant state which spontaneously breaks the discrete rotational symmetry of a host crystal. In a clean square lattice, the electron nematic has two preferred orientations, while dopant disorder favors one or the other orientations locally. In this way, the electron nematic in a host crystal maps to the random field Ising model (RFIM). Since the electron nematic has anisotropic conductivity, we associate each Ising configuration with a resistor network, and use what is known about the RFIM to predict new ways to test for electron nematicity using noise and hysteresis. In particular, we have uncovered a remarkably robust linear relation between the orientational order and the resistance anisotropy which holds over a wide range of circumstances. We discuss the consequences of this for noise and hysteresis in transport anisotropy, as well as possible extensions to other experimental probes such as neutron scattering and STM. [Preview Abstract] |
Tuesday, March 14, 2006 1:27PM - 1:39PM |
H38.00012: Enhancement of superconductivity by local inhomogeneities Ivar Martin, Daniel Podolsky, Steven Kivelson We study the effect of inhomogeneity of the pairing interaction or the background potential on the superconducting transition temperature, $T_c$. In the weak coupling BCS regime, we find that inhomogeneity, which is incommensurate with the Fermi surface nesting vectors, enhances $T_c$ relative to its value for the uniform system. For a fixed modulation strength we find that the highest $T_c$ is reached when the characteristic modulation length scale is of the order of the superconducting coherence length. [Preview Abstract] |
Tuesday, March 14, 2006 1:39PM - 1:51PM |
H38.00013: Nanosecond, Transient Resistive State in Two-Dimensional Superconducting Stripes Jennifer Kitaygorsky, I. Komissarov, A. Jukna, Roman Sobolewski, O. Minaeva, N. Kaurova, A. Korneev, B. Voronov, I. Milostnaya, Gregory Gol'tsman We have observed, nanosecond-in-duration, transient voltage pulses, generated across two-dimensional (2-D) NbN stripes (width: 100--500 nm; thickness: 3.5--10 nm) of various lengths (1--500 $\mu $m), when the wires were completely isolated from the outside world, biased at currents close to the critical current, and kept at temperatures below the mean-field critical temperature T$_{co}$. In 2-D superconducting films, at temperatures below the Kosterlitz-Thouless transition, all vortices are bound and the resistance is zero. However, these vortices can get unbound when a large enough transport current is applied. The latter results in a transient resistive state, which manifests itself as spontaneous, 2.5--8-ns-long voltage pulses with the amplitude corresponding to the unbinding potential of a vortex pair. In our 100-nm-wide stripes, we have also observed the formation of phase slip centers (PSCs) at temperatures close to T$_{co}$, and a mixture of PSCs and unbound vortex-antivortex pairs at low temperatures. [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