Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P34: Superconductivity: STM |
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Sponsoring Units: DCMP Chair: Maria Iavarone Iavarone, Argonne National Laboratory Room: 404 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P34.00001: Heating Effects in Interlayer Tunneling Spectroscopy of Bi$_{2.1}$Sr$_{1.4}$Ca$_{1.5}$Cu$_{2}$O$_{8+\delta }$ as Inferred from Single Junction Methods C. Kurter, J.F. Zasadzinski, L. Ozyuzer, D.G. Hinks, K.E. Gray In order to study Joule-heating effects on small intrinsic Josephson junction (IJJ) stacks or mesas, we compare their current-voltage curves, I(V), with those of single junctions, both using Bi$_{2.1}$Sr$_{1.4}$Ca$_{1.5}$Cu$_{2}$O$_{8+\delta }$ (Ca-Bi2212) intercalated by HgBr$_{2}$. Even for small volume stacks with reduced dissipation by intercalation, there can be self-heating despite the absence of the commonly seen backbending of I(V). This conclusion is based on distinctive features of I(V) of intermediate size mesas which were absent in single junctions. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P34.00002: Development of a novel variable temperature scanning tunneling microscope and discovery of spectral weight shift between two bands across Tc in underdoped Bi2212. Jhinhwan Lee, K. Fujita, C.K. Kim, A. Schmidt, H. Eisaki, S. Uchida, J.C. Davis We investigated the quasiparticle interference as a function of temperature for underdoped Bi2212 with Tc=42K, using the newly developed variable temperature STM. Due to increased S/N and resolution, we could observe for the first time the dispersing octet peaks well above Tc. With novel high momentum resolution analysis we also found that each octet peak actually consists of two bands with distinct dispersions and observed clear spectral weight shift from one band, corresponding to the Bogoliubov quasiparticle whose dispersion depends sensitively on the temperature, to the other, with dispersion roughly following the normal state band structure with no significant temperature dependence, as we cross Tc from the superconducting state to the pseudogap state. This new discovery may shed new insight to our understanding of the pseudogap state of the underdoped cuprate superconductor. [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P34.00003: Imaging the Vortex Liquid State in Bi$_{2}$Sr$_{2}$CuO$_{6+\delta}$ T.L. Williams, M. Zech, Yi Yin, T. Kondo, T. Takeuchi, H. Ikuta, J.E. Hoffman We use a low temperature scanning tunneling microscope (STM) to study the vortex state of the high-T$_c$ superconductor Bi$_{2}$Sr$_{2}$CuO$_{6+\delta}$ in magnetic fields up to 9 T. At a temperature of 6 Kelvin, we find no localized vortices down to H = 0.25 T. However, the gap depth from the spatially averaged dI/dV spectrum decreases with increasing magnetic field, which indicates a vortex liquid state. By tracking atomically resolved locations at different magnetic fields, we apply a normalization technique to remove inhomogeneities in the underlying density of states, revealing a more homogeneous superconducting state. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P34.00004: Coexistence of competing orders with two energy gaps in real and momentum space in the High T$_{c}$ Superconductor Bi$_{2}$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta }$ Jihua Ma, Z.-H. Pan, F.C. Niestemski, M. Neupane, Y.-M. Xu, Zqiang Wang, Vidya Madhavan, P. Richard, K. Nakayama, T. Sato, T. Takahashi, H.-Q. Luo, L. Fang, H.-H. Wen, H. Ding We have performed scanning tunneling microscopy and angle-resolved photoemission spectroscopy on optimally doped and overdoped Bi$_{2}$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta }$. We observe two distinct energy gaps that coexist both in real space and in the antinodal region of momentum space below T$_{c. }$We find that the small gap is associated with superconductivity. The large gap persists above T$_{C}$ and seems to be linked to observed charge order. We also find a strong correlation between these two gaps suggesting they are affected by similar physical processes. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P34.00005: Coexistence of superconducting and pseudogap quasiparticles in underdoped Bi2212: Studies of STM/STS and ultra-fast optical spectroscopy Y. H. Liu, T. Kurosawa, Y. Toda, K. Shimatake, N. Momono, M. Oda, M. Ido At present, the relationship between superconducting (SC) gap and psuedogap (PG) of cuprate superconductors is still under intense debate. Here, we present our recent results of the electronic structure and quasiparticle dynamics measured by STM/STS and ultra-fast optical spectroscopy on underdoped Bi2212 crystals, which provide direct evidence that SC and PG quasiparticles coexist below Tc. We will also discuss the origins of the periodic charge order and the nano-scale electronic inhomogeneity. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P34.00006: Origin of electron-hole asymmetry in the scanning tunneling spectrum of $Bi_2Sr_2CaCu_2O_{8+\delta}$ A. Bansil, Jouko Nieminen, Hsin Lin, R. S. Markiewicz We have developed a material specific theoretical framework for modelling scanning tunneling spectroscopy (STS) of high temperature superconducting materials in the normal as well as the superconducting state. Results for $Bi_2Sr_2CaCu_2O_{8+\delta}$ (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states (LDOS) of the $d_{x^2-y^2}$ orbital of Cu. The dominant tunneling channel to the surface Bi involves the $d_{x^2-y^2}$ orbitals of the four neighbouring Cu atoms. In accord with experimental observations, the computed spectrum displays a remarkable asymmetry between the processes of electron injection and extraction, which arises from contributions of Cu $d_{z^2}$ and other orbitals to the tunneling current. Work supported in part by the USDOE. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P34.00007: The Impact of an Oxygen Dopant in an ideal Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ Crystal Steve Johnston, Francois Vernay, T. P. Devereaux Scanning tunneling microscopy studies have shown that local nanoscale pairing inhomogeneities are correlated with interstitial oxygen dopants in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. Combining electrostatic and cluster calculations, we examine the impact of a dopant on the local Madelung and charge transfer energies, magnetic exchange J , Zhang-Rice mobility, and interactions with the lattice. It is found that electrostatic modifications locally increases the charge transfer energy and slightly suppresses J. It is further shown that coupling to c-axis phonons is strongly modified near the dopant. The combined e?ects yield broadened spectral features, reduced charge gap energies, and a sizable local increase of J implying a strong local interplay between antiferromagnetism, polarons, and superconducting pairing. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P34.00008: Tunneling Spectral Dip Feature in High Tc Cuprates: Experiment and Analysis John Zasadzinski, Liam Coffey, Cihan Kurter, Ken Gray A fully self-consistent Eliashberg analysis is presented to analyze the spectral dip feature observed in tunnel junctions on Bi2212. Methods include SIS break junctions, intrinsic Josephson junctions in mesas and SIN junctions from STM. This analysis is presented for a variety of doping levels and the resulting electron-boson spectral function and self-energy is compared with other spectroscopic probes. Evidence of spectral dip features in other high Tc cuprates is presented including Tl2212 to demonstrate the universality of the spectral dip and its relation to the mechanism of pairing. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P34.00009: Phenomenological model of the bipartite electronic structure of Bi2Sr2CaCu2O8+d: Predicting bulk thermodynamic quantities from tunneling spectroscopy J.W. Alldredge, K. Fujita, Jinho Lee, M. Wang, H. Eisaki, S. Uchida, P.J. Hirschfeld, J.C. Davis, K. McElroy Using high quality local STM maps with corresponding quasiparticle interference data, we develop a complete phenomenological description of the density of states in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+d}$. This not only describes the local density of states but also consistently describes the spectral density of states derived from the QPI. The model consists of a d-wave gap structure at high energy. At low energies is has an additional higher harmonic term in the d-wave gap. Using this we capture not only the high energy gap signature but also the low energy features in the LDOS which accompany the termination of the QPI signal and this allows us to quantitatively measure the features across a wide series of dopings showing consistence between real and k-space. The use of this simple model allows us to successfully predict superfluid density, confirming that our model can successfully determine bulk physics from a local measurement. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P34.00010: Scanning tunneling spectroscopic evidence for a magnetic field-revealed microscopic order in the high-T$_{C}$ superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ A.D. Beyer, M.S. Grinolds, M.L. Teague, N.-C. Yeh, S. Tajima We present spatially resolved scanning tunneling spectroscopic measurements of YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ as a function of magnetic field and at T$<<$T$_{C}$. The observed \textit{intra}-vortex quasiparticle (QP) spectra appear pseudogap (PG)-like, with an energy gap of V$_{PG}\approx $32meV. The value of V$_{PG}$ is significantly larger than the observed \textit{inter}-vortex superconducting (SC) gap, $\Delta _{SC}$=20meV, and equal to the incommensurate spin fluctuation gap observed by neutron scattering. We also observe a secondary and less pronounced intra-vortex gap at $\Delta $'$\sim $7-10meV. Fourier transformation of QP spectra reveals two sets of non-dispersive, field-enhanced conductance modulations with periods of 3.4\underline {+}0.5 and 7.3\underline {+}0.5 lattice constants. Energy histograms of QP spectra show a significant shift from SC to primarily PG-like spectra and a growing enhancement of spectral weight at $\Delta $' as magnetic field increases, implying a significant interplay between SC and a field-enhanced microscopic order. Ref.: Beyer, \textit{et.al. }[arxiv:0808.3016]. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P34.00011: STM studies of Co$_{x}$NbSe$_{2}$ and Mn$_{x}$NbSe$_{2}$ Maria Iavarone, Goran Karapetrov, Roberto Di Capua, Alex Koshelev, Daniel Rosenmann, Terukazu Nishizaki, Norio Kobayashi The effect of the intercalation of Co and Mn into the 2H phase transition-metal dichalcogenide NbSe2 has been investigated with a low temperature scanning tunneling microscope (STM). The effect of individual atomic impurities on the superconduting state has been studied. Tunneling spectroscopy at 0.4 K reveals clear spectroscopic signature of the magnetic impurities at atomic scale. We find that Co is in the weak scattering limit and the tunneling spectra are homogeneous on the sample surface with sharp coherent superconducting peaks. Mn instead acts as a strong scatterer destroying superconductivity at atomic scale, even when the number of impurities is limited to just a few in a correlation volume. The effect of intercalation on the charge density waves will be discussed as well. This work was supported by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P34.00012: Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic (STS) studies of electron-doped cuprate superconductor La$_{0.1}$Sr $_{0.9}$CuO$_{2}$ (La-112) M.L. Teague, A.D. Beyer, N.-C. Yeh, S.-I. Lee We present STS studies on the electron-doped cuprate superconductor La-112 as a function of magnetic field (H). The spatially resolved spectra manifest vortices, and the average vortex lattice constant scales consistently with Abrikosov's theory. A hidden pseudogap (V$_{CO})$ smaller than the superconducting gap ($\Delta _{SC})$ is revealed inside the vortex core, and the core radius is comparable to the superconducting coherence length \textit{$\xi $}$_{ab}$ = 4$.$86 nm. Analysis of the energy histograms reveals that $\Delta _{eff}$, where $\Delta _{eff}$=[($\Delta _{SC})^{2 }$+ (V$_{CO})^{2}$]$^{1/2}$, shifts downward with increasing H from $\Delta _{eff}$= 12.2 $\pm $ 0.8 meV at H = 0 to a base value of V$_{CO}$=8.5 $\pm $0.6 meV at H $>$ 0. This finding differs from the behavior of conventional superconductors where the vortex-state spectral weight would shift continuously to lower energies with increasing H and show peaks at zero energy due to suppression of $\Delta _{SC}$ inside vortices. Finally, Fourier transformation of the vortex-state tunneling spectra will be reported and compared with results from other cuprates. Ref.: Teague et al., arxiv:0809.0541. Work supported by NSF Grant DMR-0405088. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P34.00013: Noise Predictions for STM in Systems with Local Electronic Nematic Order Erica Carlson, Yen Lee Loh, Karin Dahmen We propose that thermal noise in local stripe orientation should be readily detectable via STM on systems in which local stripe orientations are strongly affected by quenched disorder. Stripes, a unidirectional, nanoscale modulation of electronic charge, are strongly affected by quenched disorder in two-dimensional and quasi-two-dimensional systems. While stripe orientations tend to lock to major lattice directions, dopant disorder locally breaks rotational symmetry. In a host crystal with otherwise C4 rotational symmetry, stripe orientations in the presence of quenched disorder map to the random field Ising model. While the low temperature state of such a system is generally a stripe glass in two dimensional or strongly layered systems, as the temperature is raised, stripe orientational fluctuations become more prevalent. We propose that these thermally excited fluctuations should be readily detectable in scanning tunneling spetroscopy as telegraph noise in the high voltage part of the local I(V) curves. We predict the spatial, temporal, and thermal evolution of such noise, including the circumstances under which such noise is most likely to be observed. In addition, we propose an in-situ test for assessing whether such noise is due to correlated fluctuations rather than independent switchers. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P34.00014: STM Study of Bosonic Modes in the Cuprate Superconductor Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4}$ Vidya Madhavan, Francis Niestemski, Shiliang Li, Pengcheng Dai We use a low temperature (4 K) ultra-high vacuum scanning tunneling microscope (STM) to investigate the electron-doped high temperature superconductor Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4}$ (PLCCO). We examine the superconducting gap and the satellite features identified as bosonic modes. We investigate these modes with increasing oxygen reduction which represents the third dimension in the electron-doped superconducting phase diagram. We relate our findings to neutron scattering results performed on the same sample. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P34.00015: Collective action of nanopatterned pins: barrier towards creating interstitial vortices Gorky Shaw, Shyam Mohan, Jaivardhan Sinha, Satyajit Banerjee We show that by nano-patterning a superconductor (NbSe$_{2 }$single$_{ }$crystal) with an array of blind holes produces significant magnetic field sweep rate dependent metastable magnetization response[1]. Our results are explained on the basis of a unique collective action of the blind holes pins which creates a barrier against vortex redistribution inside the sample. We propose that this barrier leads to a phase separation creating distinct population of vortices viz., those pinned on blind holes and those confined in the interstitials between the holes [1]. We find that due to the barrier, there is a significant enhancement in the stability of vortices against thermal fluctuations. [1] Gorky Shaw, Shyam Mohan, Jaivardhan Sinha and S. S. Banerjee* (submitted; xxx.lanl.gov/abs/0811.1256) \textit{*satyajit@iitk.ac.in} [Preview Abstract] |
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