Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session L9: Superconducting Fluctuations |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Steven Anlage, University of Maryland Room: Colorado Convention Center Korbel 1D |
Tuesday, March 6, 2007 2:30PM - 2:42PM |
L9.00001: Direct test of pairing fluctuations in the pseudogap phase of an underdoped cuprate Jerome Lesueur, Nicolas Bergeal, Marco Aprili, Brigitte Leridon, Giancarlo Faini, Jean Pierre Contour In underdoped cuprates, many experiments have provided evidence for the presence of a gap-like structure in the electronic excitations spectrum, in a region above the critical temperature and below a characteristic temperature T*. The origin of this so-called pseudogap is still hardly debated and the answer to this question turns out to be essential for the understanding of high-T$_{c}$ superconductivity. One doesn't know if the pseudogap is related to superconductivity or to an order in competition. In the former case, it has been suggested that superconducting pairing fluctuations may be responsible for the partial suppression of electronic excitations. This remains to be tested experimentally, but most of the probes used to investigate the pseudogap are not sensitive to pairs and therefore cannot provide such a test. Here, we report for the first time on a direct test of pairing fluctuations in the pseudogap regime using a Josephson-like experiment. Our results shows that fluctuations survive only in a restricted range of temperature close to T$_{c}$ (T-T$_{c}<$15K), and therefore cannot be responsible for the opening of the pseudogap at high temperature. [Preview Abstract] |
Tuesday, March 6, 2007 2:42PM - 2:54PM |
L9.00002: Evidence for Quantum Criticality (QC) and Universal Field-Induced Quantum Fluctuations (QF) in Cuprate Superconductivity (SC) H. Yang, A.D. Beyer, V.S. Zapf, M.S. Park, K.H. Kim, S.-I. Lee, N.-C. Yeh We present experimental evidence for universal field-induced QF among cuprate superconductors as the result of their proximity to QC and the coexistence of SC and competing orders. We employ various experimental techniques to derive the in-plane magnetic irreversibility field in hole- and electron-type cuprate superconductors of varying doping levels and numbers of CuO$_{2}$ layers per unit cell, and we find strong suppression of the extrapolated zero-temperature in-plane irreversibility field relative to the paramagnetic field in all cuprates, suggesting universal field-induced QF. The irreversibility fields follow a universal dependence on a parameter that combines the effect of the doping level, electronic anisotropy, and charge imbalance in multi-layer samples. [Preview Abstract] |
Tuesday, March 6, 2007 2:54PM - 3:06PM |
L9.00003: Magnetic field effect on the superconducivity fluctuation of cuprates, LSCO and LCCO measured by microwave broadband technique A. Maeda, T. Ohashi, H. Kitano, L. Gomez, I. Tsukada, A. Tsukada, M. Naito Understanding of the electronic phase diagram is essential to clarify the mechanism of high-$T_c$ superconductivity (SC) of cuprates. Previously, we studied the SC fluctuation of hole doped LSCO by microwave broadband technique, and found that there was a sharp crossover from the 2D-XY (BKT) behavior to the 3D-XY behavior by changing the doping. However, behaviors in the overdoped region and the effect of disorder were remained to be seen as future issues. To answer these, we investigated the effect of magnetic field on the SC fluctuation on LSCO with various carrier concentrations. For underdoped samples, the BKT behavior observed in zero-field experiemnts sruvived. However, the divergence of correlation length was found to be supressed by the externally applied magnetic field. In contrast, for optimally doped samples, the range of the 3D-XY behavior became narrowed definitely under finite magnetic field. These provide strong support for our previous conclusion that there is a sharp change in the SC nature around at the optimum doping. The data in the overdoped LSCO and in electron doped cuprate LCCO will also be presented in a comparative manner. [Preview Abstract] |
Tuesday, March 6, 2007 3:06PM - 3:18PM |
L9.00004: Superconducting fluctuations in underdoped $La_{2-x}Sr_xCuO_4$ thin films Brigitte Leridon, Johan Vanacken, Tom Wambecq, Victor Moshchalkov Underdoped $La_{2-x}Sr_xCuO_4$ thin films resistivity was measured under high pulsed magnetic fields (50 T) in order to suppress superconductivity and extract the paraconductivity, or the conductivity due to superconducting fluctuations. Quite surprisingly, this paraconductivity is consistent \textit{without any adjustable parameter} with a Gaussian model for the fluctuations, where both amplitude and phase of the order parameter fluctuate, as calculated by Aslamazov and Larkin (AL). This tends to indicate that the pairs responsible for the transition at $T_C$ are not preformed, as that would rather lead to Kosterlitz-Thouless type fluctuations. At higher temperature, the paraconductivity departs from AL behavior and follows a power law in 1/T. At intermediate magnetic fields, the possibility of a quantum superconductor/insulator phase transition is investigated, as a plateau in the resistance versus temperature is observed under perpendicular magnetic field for all underdoped films. [Preview Abstract] |
Tuesday, March 6, 2007 3:18PM - 3:30PM |
L9.00005: Determination of the dynamical scaling exponent in the superconducting to normal metal phase transition Hua Xu, Su Li, Chris Lobb, Steven Anlage In the high Tc superconductors, measurements of fluctuation effects reveal interesting behavior. Thermodynamic measurements have been done to investigate scaling behavior, to obtain critical exponents and to test the universality of the transition and the 3D XY model. Transport measurements of critical fluctuations, such as the AC conductivity, are less explored, and a wide range of critical exponents have been reported. We have investigated critical fluctuations in the microwave conductivity of $\mathrm{YBa_{2}Cu_{3}O_{7-\delta}}$ films. Our improved temperature stability and conductivity calibration(10 MHz to 50 GHz) allow us to take high quality data at small temperature intervals(50mK). This improves the conventional data analysis method and allows a new method of extracting exponents to be developed. With these two methods, we determined consistent values of $T_c$ and the critical exponent using eight different samples. [Preview Abstract] |
Tuesday, March 6, 2007 3:30PM - 3:42PM |
L9.00006: Superconducting fluctuations and disorder in high-Tc cuprates Florence Rullier-Albenque, Henri Alloul, Cyril Proust The determination of critical fields and of the superconducting fluctuations in the cuprates are still highly debated questions, as both extremely high field and reduced $T_{c}$ cuprates are required to attempt to reach the normal state regime. We have studied in fields up to 60T the variation of the transverse magnetoresistance (MR) of underdoped YBCO$_{6.6}$ crystals either pure or with $T_{c}$ reduced down to 3.5K by electron irradiation [1]. We show that the normal state MR is restored above a threshold field $H_{c}^{\prime }(T)$, which is found to vanish at $T_{c}^{\prime}>>T_{c}$. This allows us to evidence a $(H,T)$ range where superconductivity survives at least as fluctuations. When $T_{c}$ is decreased by disorder, we found that the fluctuation range expands significantly as $T_{c}^{\prime}$ is slightly depressed. This $T_{c}^{\prime}$ behaves similarly versus defect content as the onset temperature $T_{\nu}$ of the Nernst signals measured on the same samples [2] which indicates that the $T_{c}$ decrease is partly due to the loss of the phase coherence. We found that $T_{c}^{\prime}$, $H_{c}^{\prime}(T)$ and $T_{\nu}$ which can be related to pair formation are depressed, although moderately, by the introduction of defects in contrast to the pseudogap temperature which is known to be insensitive to disorder, showing that these energy scales are not related. [1] F. Rullier-Albenque et al, cond-mat 0610838 [2] F. Rullier-Albenque et al., Phys. Rev. Lett. \textbf{96}, 067002 (2006) [Preview Abstract] |
Tuesday, March 6, 2007 3:42PM - 3:54PM |
L9.00007: Fluctuations and Glassy Behavior in the 2D Superconductor-Insulator Transition in Granular Bismuth Kevin Parendo, Sarwa Tan, Allen Goldman The superconductor-insulator transition has been investigated in granular, amorphous bismuth films. The system's dynamics have been investigated at various levels of disorder by incrementing film thickness and measuring voltage fluctuations. In insulating films in which local superconductivity was not evident, the first power spectra had 1/f$^{2}$ frequency dependences. In films that exhibited local superconductivity, the spectra had weaker frequency dependences. In a film with low enough disorder, the resistance had a very weak temperature dependence below 1.5 K and non-ergodic behavior and strong fluctuations were observed below 400 mK. The variations of the first and second power spectra with disorder and temperature will be discussed. [Preview Abstract] |
Tuesday, March 6, 2007 3:54PM - 4:06PM |
L9.00008: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 4:06PM - 4:18PM |
L9.00009: A Theory of the Quantum Metal to Superconductor Transition In Highly Conducting Films Paul Oreto, Steven Kivelson, Boris Spivak Treating the inhomogeneous solution of the BCS mean-field equations as the saddle point of an effective quantum action, we derive the theory of the superconductor to metal transition in films under the conditions in which the critical resistance is small compared to the quantum of resistance. The present results are applicable to the magnetic field driven transition in MoGe films. It is also applicable to the transition in zero field in a weakly coupled d-wave superconductor, which may in turn be a useful caricature of a cuprate high temperature superconductor. [Preview Abstract] |
Tuesday, March 6, 2007 4:18PM - 4:30PM |
L9.00010: The approach to a superconductor-to-Bose-insulator transition in disordered films Nicholas P. Breznay, M. A. Steiner, A. Kapitulnik We study the superconductor-insulator transition in the limit of strongly disordered films of indium oxide. It was observed previously that the insulating phase is strengthened as the disorder increases, creating a strong barrier to pair-breaking in the vicinity of the critical point. We find that for the strongest insulators, the critical resistance is approximately the universal resistance for pairs, RQ = h/4e2 and the scaling of both the linear and non-linear resistance is consistent with the quantum percolation solution to the dirty boson model. We combine these results with previous data and note separate branches corresponding to strong and weak disorder. The strong disorder branch suggests a true dirty boson superconductor-insulator transition. [Preview Abstract] |
Tuesday, March 6, 2007 4:30PM - 4:42PM |
L9.00011: Observation of Pairing Correlations in Strongly Localized Amorphous Films M.D. Stewart, Jr., J.M. Valles, Jr., Aijun Yin, J.M. Xu We have measured the Superconductor to Insulator Transition (SIT) as a function of thickness at dilution refrigerator temperatures in ultrathin Bi/Sb films perforated with a regular honeycomb array of holes separated by 100 nm. The presence of these perforations profoundly influences the character of the transition. In particular, on the insulating side of the SIT, the resistance as a function of temperature, R(T), rises monotonically and becomes activated below ~1K. Closer to the SIT, a minimum develops in the R(T) suggestive of strong superconducting fluctuations and the onset of Cooper pairing. Simultaneously, the perpendicular field magnetoresistance begins to oscillate with a period that corresponds to the superconducting flux quantum. Yet thicker films exhibit a relatively broad R(T) transition toward a zero resistance state. This behavior constitutes direct evidence that the superconducting ground state of this amorphous film system emerges from an insulating state containing localized Cooper pairs. This work has been supported by the NSF through DMR-0203608, and DMR-0605797, AFRL, and ONR. [Preview Abstract] |
Tuesday, March 6, 2007 4:42PM - 4:54PM |
L9.00012: Nonequilibrium Voltage Fluctuations in Aluminum Wires M. Reznikov, A. Frydman, M. Reese, D. Prober We present measurements of the nonequilibrium voltage fluctuations across current biased superconductive aluminum wires in the vicinity of $T_c$. Above $T_c$ these voltage fluctuations are due to superconductive fluctuations which persist on the time scale of the Ginzburg time. Below $T_c$ we believe they are due to the thermal activated phase slips. The frequency dependence of the fluctuations suggests the observation of the ac Josephson effect above $T_c$. [Preview Abstract] |
Tuesday, March 6, 2007 4:54PM - 5:06PM |
L9.00013: Fluctuations in Two-Dimensional Superconducting NbN Nanobridges and Nanostructures Meanders Jennifer Kitaygorsky, I. Komissarov, A. Jukna, O. Minaeva, N. Kaurova, A. Divochiy, A. Korneev, M. Tarkhov, B. Voronov, I. Milostnaya, G. Gol'tsman, R. Sobolewski We have observed fluctuations, manifested as sub-nanosecond to nanosecond transient, millivolt-amplitude voltage pulses, generated in two-dimensional NbN nanobridges, as well as in extended superconducting meander nanostructures, designed for single photon counting. Both nanobridges and nano-stripe meanders were biased at currents close to the critical current and measured in a range of temperatures from 1.5 to 8 K. During the tests, the devices were blocked from all incoming radiation by a metallic enclosure and shielded from any external magnetic fields. We attribute the observed spontaneous voltage pulses to the Kosterlitz-Thouless-type fluctuations, where the high enough applied bias current reduces the binding energy of vortex-antivortex pairs and, subsequently, thermal fluctuations break them apart causing the order parameter to momentarily reduce to zero, which in turn causes a transient voltage pulse. The duration of the voltage pulses depended on the device geometry (with the high-kinetic inductance meander structures having longer, nanosecond, pulses) while their rate was directly related to the biasing current as well as temperature. [Preview Abstract] |
Tuesday, March 6, 2007 5:06PM - 5:18PM |
L9.00014: Interaction of vortices in thin superconducting films and Berezinskii-Kosterlitz-Thouless transition Vladimir Kogan The precondition for the BKT transition in thin superconducting films, the logarithmic intervortex interaction, is satisfied at distances short relative to $\Lambda=2\lambda^2/d$, $\lambda$ is the London penetration depth of the bulk material and $d$ is the film thickness. For this reason, the search for the transition has been conducted in samples of the size $L<\Lambda$. It is argued below that film edges turn the interaction into near exponential (short-range) thus making the BKT transition impossible. If however the substrate is superconducting and separated from the film by an insulated layer, the logarithmic intervortex interaction is recovered and the BKT transition should be observable. [Preview Abstract] |
Tuesday, March 6, 2007 5:18PM - 5:30PM |
L9.00015: Density of States, Entropy, and the Superconducting Pomeranchuk Effect in Pauli-Limited Al Films Gianluigi Catelani, XiaoSong Wu, Philip Adams We present low temperature tunneling density of states measurements of Pauli-limited Al films in which the Zeeman and orbital contributions to the critical field are comparable. We show that films in the thickness range of 6-7 nm exhibit a reentrant parallel critical field transition which is associated with a high entropy superconducting phase, similar to the high entropy solid phase of $^3$He responsible for the Pomeranchuk effect. This phase is characterized by an excess of states near the Fermi energy so long as the parallel critical field transition remains second order. Theoretical fits to the zero bias tunneling conductance are in good agreement with the data well below the transition but theory deviates significantly near the transition. The discrepancy is a consequence of the emergence of $e$-$e$ interaction correlations as one enters the normal state. [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