Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H25: Superconductivity: Tunneling Spectroscopy |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Jenny Hoffman, Harvard University Room: D166 |
Tuesday, March 22, 2011 8:00AM - 8:12AM |
H25.00001: Pairing Glue in High Tc Cuprates from Tunneling Spectroscopy John Zasadzinski, Omid Ahmadi, Liam Coffey, Lutfi Ozyuzer, Nobuaki Miyakawa Break junction tunneling spectroscopy data in Bi2212 over a wide range of doping are fit using a d-wave Eliashberg model. Self consistency is achieved as the electron-boson spectral function, $\alpha ^{2}$F($\omega )$, that fits the tunneling conductance dip feature also leads to the correct superconducting gap. The anomalous negative dI/dV observed in break junctions on optimal doped Bi2212 is also reproduced in the analysis. The diagonal and off-diagonal self energies, $\Sigma (\omega )$ and $\phi (\omega )$, respectively are generated in the analysis and they show trends with doping which are in agreement with numerical simulations of the Hubbard model. The peak in $\alpha ^{2}$F($\omega )$ is consistent with the resonance mode in the spin fluctuation spectrum. Tunneling data of other cuprates are also discussed. [Preview Abstract] |
Tuesday, March 22, 2011 8:12AM - 8:24AM |
H25.00002: How Topological Defects Couple the Smectic and Nematic Electronic Structure of the Cuprate Pseudogap States K. Fujita, A. Mesaros, H. Eisaki, S. Uchida, J. C. Davis, S. Sachdev, J. Zaanen, M. Lawler, Eun-Ah Kim We study the recently discovered coexisting smectic and nematic broken symmetries in the pseudogap-energy electronic structure of underdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$. By visualizing their spatial components separately, we discover 2$\pi $ topological defects throughout the phase-fluctuating smectic states. Imaging the locations of large numbers of these topological defects simultaneously with the fluctuations of the electronic nematicity about its average, reveals strong empirical evidence for a coupling between them. We also found the same phenomenology in a single layer compound of Bi$_{2}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+\delta }$. From these observations, we propose a Ginzburg-Landau free energy describing the quantum nematic/smectic coupling and demonstrate how it can explain the coexistence of these states and correctly predict their interplay at the atomic scale. This theoretical understanding of the coupling between the quantum nematic and smectic broken symmetries can lead to unraveling the complexities of the phase diagram of cuprate high-$T_{c}$ superconductors[1]. [1]A. Mesaros, K. Fujita, H. Eisaki, S. Uchida, J. C. Davis, S. Sachdev, J. Zaanen, M. J. Lawler, and Eun-Ah Kim, \textit{Submitted} (2010). [Preview Abstract] |
Tuesday, March 22, 2011 8:24AM - 8:36AM |
H25.00003: Universal properties of disordered electron nematics from surface probes Benjamin Phillabaum, Erica Carlson, Karin Dahmen When the electronic degrees of freedom break the rotational symmetry of the host crystal, i.e. from C$_4$ to C$_2$, the resulting state is an electronic Ising nematic. However the combination of reduced dimensionality and material disorder can forbid the formation of a long- range-ordered electron nematic, especially in strongly layered materials. Nevertheless, large domains are still possible. In this talk we will present results from a new kind of analysis for Scanning Tunneling Microscopy (STM) experiments as well as other surface probes. We map the locally broken C$_4$ to C$_2$ rotational symmetry of the electronic degrees of freedom to an Ising-type order parameter,use the local order parameter configuration to shed light on the universality class controlling the local pattern formation in cuprate superconductors. [Preview Abstract] |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H25.00004: Vacuum-aging effect on electronic structure of YBa$_{2}$Cu$_{3}$O$_{6+x}$ thin film: a STM/STS study Y.H. Liu, J. Xiong, D. Yarotski, Q. Jia, A.J. Taylor It is well known that oxygen plays a key role in the occurrence of superconductivity in high-temperature cuprate superconductors. Variation of oxygen content changes carrier concentration and directly affects electronic structure and superconducting properties of cuprate superconductors. Majority of previous studies relied on the intake process of oxygen to change the oxygen content in samples, while the reverse process, oxygen depletion, was rarely investigated. Nevertheless, the escape of oxygen from the surface of cuprate sample that was kept at room temperature under ultrahigh vacuum for extended period of time might lead to significant degradation of its superconducting properties due to the decrease of the carrier concentration. Here, we report this so-called vacuum-aging effect in YBa$_{2}$Cu$_{3}$O$_{6+x}$ thin films grown by laser-MBE technique. In particular, we use variable-temperature scanning tunneling microscopy/spectroscopy to follow the evolution of superconductivity and pseudogap states in this material as a function of aging time and tip position on the surface. [Preview Abstract] |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H25.00005: Influence of the tunneling property on the noise thermometry using a metal-insulator-metal tunnel junction Jung Hwan Park, Mushtaq Rehman, Zheong G. Khim, Sang-Wan Ryu, Woon Song, Yonuk Chong We are developing a noise thermometry setup based on precision RF measurement, where temperature can be inferred from the noise of a tunnel junction as a function of the bias voltage. We measure the electrical noise of an Al-AlOx-Al tunnel junction around 1 GHz with a bandwidth of a few hundred MHz. In this presentation, as an analysis on the source of error in thermometry, we studied the influence of the junction quality and the inelastic process on the temperature measurement. We compared the noise of an as-fabricated tunnel junction with that of a degraded tunnel junction after thermal cycling. Except for the junction degradation, all measurement environments were kept exactly same. We observed an apparently higher noise value near the zero-bias, which leads to an overestimation of temperature. We present a simple model to describe how the inelastic process in a tunnel junction affects the temperature measurement. [Preview Abstract] |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H25.00006: ABSTRACT WITHDRAWN |
Tuesday, March 22, 2011 9:12AM - 9:24AM |
H25.00007: Mapping the Pseudogap by Fourier Transform Scanning Tunneling Spectroscopy in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ E.W. Hudson, E Main, A.E. Pivonka, I. Zeljkovic, G. Gu, J.E. Hoffman The relationship between pseudogap and superconductivity in cuprate superconductors remains an important open question. To shed light on this issue, we have used Fourier-transform scanning tunneling microscopy to map quasiparticle interference (QPI) patterns as well as the ``checkerboard,'' a weak charge modulation associated with the pseudogap, as a function of doping and temperature in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ (Bi-2212). We can extract the doping dependence of the pseudogap transition temperature T* within the superconducting dome. Our results strongly suggest that the pseudogap is a competing order. [Preview Abstract] |
Tuesday, March 22, 2011 9:24AM - 9:36AM |
H25.00008: Phenomenological model for extracting local energy scales across dopings and temperatures in cuprates Kyle McElroy, Eduardo Calleja, Jixia Dai, Genda Gu, Jacob Alldredge One of the key questions that remains unanswered in the cuprate high temperature superconductors is the nature of the pesudogap phase that exists above the superconducting transition temperature in underdoped materials. In order to differentiate the different proposed origins of this phase, a detailed phenomenology of the different energy scales that characterize it and the superconducting phase is required. In addition, many of these materials (BSCCO-2212 in particular) have shown striking inhomogeneity that further complicates observations of these scales. Spectroscopic imaging scanning tunneling microscopy has the unique ability to resolve density of states features with the needed spatial resolution for seeing through this inhomogeneity. We will present a new phenomenological model for extracting three different energy scales that are present with atomic resolution across several dopings. In addition, preliminary data on the temperature dependence of these scales will be shown. Lastly, how these different scales relate to the different phases present in the underdoped cuprates will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 9:36AM - 9:48AM |
H25.00009: Understanding the Measurement of the K-Space Gap Using Spectroscopic Imaging Scanning Tunneling Microscopy Eduardo Calleja, Jixia Dai, Genda Gu, Kyle McElroy Two of the many tools used to probe the High Tc cuprates are Angle Resolved Photo Emission (ARPES) and Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM). While the two probes have had many qualitative agreements recently there has been a movement in the field to strive for quantitative agreement in order to better understand the phase diagram of the cuprates. When looking for quantitative agreement we are met with striking disagreements such as, the measurement of the super conducting gap by both probes and the observation of Fermi arcs. We have generated a preliminary simulation based on a superconducting tight binding model where we can tune different parameters in order to begin exploring some of these issues. With our STM just beginning to take data our simulation is allowing us to understand the type of data we need to shed some light on these issues. [Preview Abstract] |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H25.00010: a-axis NIS tunnel junctions using LaSrCuO4 Mao Zheng, Yize Li, James Eckstein Planar tunneling in NIS structures with crystalline order reveals the density of states largely focused in the tunneling direction. Earlier experiments with a-axis YBCO showed an unexpected strongly broken particle hole symmetry in the CuO bond direction. Here we report on work to make similar structures with a-axis LaSrCuO4. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H25.00011: Determining the pseudogap Dirac point in the underdoped cuprate superconductors using FT-STS and AC-ARPES E.J. Nicol, K.A.G. Fisher, J.P. Carbotte Prominent in the underdoped cuprate superconductors is the existence of a pseudogap in the excitation spectrum which opens above $T_c$ but below a temperature $T^*$. Whether this gap is the same as the superconducting energy gap or is a manifestation of a competing order independent of the superconductivity remains an open and central question. If there are two distinct gaps of $d$-wave symmetry, they each will exhibit a Dirac point at a different energy and momentum in the band structure. We demonstrate how to find the pseudogap Dirac point by using quasiparticle interference (QPI) measurements from Fourier transform scanning tunneling spectroscopy (FT-STS) or by extrapolating information from the autocorrelation function of angle-resolved photoemission spectroscopy (AC-ARPES) to positive energies. Current examination of photoemission data supports our proposal and suggests that a Dirac point exists at positive energy relative to the Fermi level. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H25.00012: Spatial Variations in the Fermi Surface of Bi-2212 Elizabeth Main, A.E. Pivonka, I. Zeljkovic, G. Gu, E.W. Hudson, J.E. Hoffman In cuprate superconductors, scanning tunneling microscopy can be used to see variations in the Fermi surface on a nanometer length scale caused by doping inhomogeneity. Prior STM studies show that the local wavelength of the checkerboard, a weak charge modulation ascribed to antinodal Fermi surface nesting, varies with the size of the pseudogap in Bi$_2$Sr$_2$CuO$_{6+\delta}$ (Bi-2201) [1]. Here we report similar STM measurements in Bi-2212. We therefore confirm the local relationship between pseudogap energy and charge ordering wavevector in a second high-Tc superconductor.\\[4pt] [1] W. D. Wise, et al. Nature Physics 5, 213 (2009). [Preview Abstract] |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H25.00013: Vortex-core structure in d-wave superconductors with weak triplet pairing attraction Mikael Fogelstr\"om, Annica Black-Schaffer The quasiparticle states found in the vortex core of an d-wave high-$T_c$ cuprate superconductor may be probed by STM experiments. Results of such experiments have revealed typical spectra that are quite different from what is seen in conventional low-$T_c$ superconductors. In particular the Caroli-deGennes-Matricon state at $E\sim 0$ in the core center is not seen. Instead, in a high-$T_c$ vortex core, quasiparticle states are found at energies that are at a sizable fraction of the gap energy. One explanation for this could be that a finite amplitude of a competing orderparameter stabilizes in the vortex-core center. We explore the possibility of nucleating a vortex-core state that locally breaks inversion symmetry. The vortex-core orderparameter is of mixed parity, in our case a (d + ip)-wave, and the quasiparticle spectra in the core center lacks the $E = 0$ states. We compare our results with available experimental data. [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H25.00014: Possible mechanism of enhanced pairing correlation near dopant oxygen in cuprate Michiyasu Mori, Giniyat Khaliullin, Takami Tohyama, Sadamichi Maekawa Recent experiments on Bi-based cuprate superconductors have revealed an unexpected enhancement of the pairing correlations near the interstitial dopant oxygens. We propose a mechanism by which the dopant oxygens strongly enhance the interaction $J$ locally [1]. We notice that there is a strong covalency between the dopant oxygen and closely located apical oxygens, forming a molecular orbital complex. By considering virtual $p$-$d$ and $d$-$d$ charge transitions within the Cu-O-Cu bond that lead to the spin exchange $J$, we will show that the corresponding excitation energies are screened by the polarization of molecular orbitals hence enhancing $J$. The effect is greatly amplified due to cooperative response of the spatially extended oxygens complex. We will also show, by an exact diagonalization of the $t$-$J$ model, that local enhancement of $J$ leads to the spatial variations in density of electronic states observed in STM experiments. Our findings suggest an interesting possibility of quantum-chemistry control of the key interaction $J$ in cuprates. \\[4pt] [1] G. Khaliullin, M. Mori, T. Tohyama, and S. Maekawa, arXiv:1008.0435 [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