Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B11: Cuprate Superconductivity: Pseudogap |
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Sponsoring Units: DCMP Chair: Mike Osofsky, Naval Research Laboratory Room: 007B |
Monday, March 2, 2015 11:15AM - 11:27AM |
B11.00001: Intra unit cell electronic structure of the d-symmetry form factor density wave in the underdoped cuprates -- Part I Kazuhiro Fujita, Mohammad Hamidian, Stephen Edkins, Chung Koo Kim, Andy Mackenzie, Hiroshi Eisaki, Shin-ichi Uchida, Michael Lawler, Eun-Ah Kim, Subir Sachdev, J.C. Davis A central issue of cuprate superconductivity research is to understand the nature of the unknown phase called the \textit{pseudogap} and its relationship to the $d$-wave superconductivity. To approach this we use spectroscopic imaging STM to study the electronic structure of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$. Using our recently developed technique of sub-lattice phase-resolved electronic structure visualization within each CuO$_{2}$ unit-cell, we discovered a $d$-symmetry form factor density wave within the cuprate pseudogap state. In this talk, part I, we demonstrate that $d$-symmetry is the predominant form factor in the density wave within pseudogap states and show how this situation evolves upon doping. [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B11.00002: Intra unit cell electronic structure of the d-symmetry form factor density wave in the underdoped cuprates -- Part II Stephen Edkins, Kazuhiro Fujita, Mohammad Hamidian, Chung Koo Kim, Andrew Mackenzie, Hiroshi Eisaki, Shinichi Uchida, Michael Lawler, Eun-Ah Kim, Subir Sachdev, Seamus Davis A central issue of cuprate superconductivity research is to understand the nature of the unknown phase called the \textit{pseudogap} and its relationship to the $d$-wave superconductivity. To approach this we use spectroscopic imaging STM to study the electronic structure of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$. Using our recently developed technique of sub-lattice phase-resolved electronic structure visualization within each CuO$_{2}$ unit-cell, we discovered a $d$-symmetry form factor density wave within the cuprate pseudogap state. In this talk, part II, we report on the electronic structure of the density wave and its interplay with superconductivity. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B11.00003: Decoding Spatial Complexity of Local Charge Modulations in Superconducting Pb-Bi-2201 Erica Carlson, Can-Li Song, Elizabeth Main, Shuo Liu, Benjamin Phillabaum, Karin Dahmen, Eric Hudson, Jennifer Hoffman In unconventional superconductors, real-space orders such as charge density modulations can coexist with superconductivity. In the cuprate superconductors, it has recently been recognized that local charge modulations are a ubiquitous feature and likely important for understanding the superconductivity in these materials. However, there are still open issues surrounding the dimensional profile of these charge modulations, including whether the modulation wavevector is unidirectional or bidirectional, and also whether the charge modulations extend beyond the surface of the material into the bulk. In bismuth-based cuprates, material disorder is a severe enough effect so as to preclude understanding the charge modulations through bulk scattering techniques. In order to resolve these issues, we use a local technique, scanning tunneling microscopy, to image the static charge modulations in Pb-Bi-2201. We find that the charge modulations are more consistent with an underlying tendency to a unidirectional charge density wave than a bidirectional charge density wave. Using recently developed cluster analysis technques, we show that these locally 1D structures are more than surface deep, extending into the bulk of the material throughout the doping range. [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B11.00004: Resonant x-ray scattering study of charge order in the electron-doped cuprate Nd$_{\mathrm{2-x}}$Ce$_{\mathrm{x}}$CuO$_{4}$ Eduardo da Silva Neto, Riccardo Comin, Feizhou He, Ronny Sutarto, Yeping Jiang, Richard Greene, George Sawatzky, Andrea Damascelli In cuprate high-temperature superconductors, an antiferromagnetic Mott insulating state can be destabilized toward unconventional superconductivity by either hole- or electron-doping. In hole-doped (p-type) cuprates a charge ordering (CO) instability competes with superconductivity inside the pseudogap state. In this talk we report resonant x-ray scattering measurements that demonstrate the presence of charge ordering in the n-type cuprate Nd$_{\mathrm{2-x}}$Ce$_{\mathrm{x}}$CuO$_{4}$ (NCCO) near optimal doping. We find that the CO in NCCO occurs with similar periodicity, and along the same direction as in p-type cuprates. However, in contrast to the latter, the CO onset in NCCO is higher than the pseudogap temperature, and is in the temperature range where antiferromagnetic fluctuations are first detected. Our discovery opens a parallel path to the study of CO and its relationship to antiferromagnetism and superconductivity. E.H. da Silva Neto, R.C. Comin et al. arXiv 1410.2253 (2014). [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B11.00005: Mapping the Striped Phase Diagram of La$_{2-x}$Ba$_x$CuO$_4$ with Resistance Fluctuation Spectroscopy Adam Weis, Azton Wells, Justin Lane, So Ra Chung, Pathikumar Sellappan, Waltraud Kriven, Dale Van Harlingen La$_{2-x}$Ba$_x$CuO$_4$ (LBCO) is an exceptional high-temperature superconductor in which, near x=1/8 doping, superconductivity is suppressed and `striped' charge order emerges. The charge stripes cause short-range conductance anisotropy that may be observed as fluctuations in resistance. In thin film LBCO devices grown by pulsed laser deposition, we measure time-resolved resistance as a function of bias current, temperature, and doping. As is consistent with charge stripes, the resistance noise exhibits a critical onset temperature and suppression at high currents. Combining resistance fluctuation spectroscopy with combinatorial laser deposition techniques, we are able to tune the doping of of LBCO and map its phase diagram. [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B11.00006: Magnetic-field-driven superconductor-insulator transition in stripe-ordered La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$ Paul Baity, Zhenzhong Shi, Dragana Popovi\'{c}, T. Sasagawa The effects of the magnetic field ($H$) in underdoped cuprates, the nature of the $H$-driven superconductor-insulator transition (SIT), and the interplay with charge ordering are some of the key questions in high-temperature superconductivity. A recent study of the $H$-driven SIT in highly underdoped ($T_c\sim 4$~K) La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) revealed an intermediate phase, with two quantum critical points separating the superconductor and the insulator. While charge distribution in highly underdoped LSCO seems to be inhomogeneous, its sister compound La$_{2-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ (LNSCO) with $x=0.12$ is known to have a charge-stripe order already in $H=0$ at low enough temperatures ($T$). In order to address the above issues, we carry out detailed measurements of the in-plane and out-of-plane magnetoresistance with different $H$ orientations and over a wide range of $T$ on LNSCO single crystals with $x=0.12$ and $T_c\sim 4$~K. The results will provide insight into the universality of the $H$-driven SIT in cuprates with different types or, at least, varying degrees of charge order. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B11.00007: Pairing interaction near a nematic QCP of a 3-band CuO$_2$ model Thomas Maier, Douglas Scalapino We calculate the pairing interaction and the k-dependence of the gap function associated with the nematic charge fluctuations of a CuO$_2$ model. We find that the nematic pairing interaction is attractive for small momentum transfer and that it gives rise to $d$-wave pairing. As the doping $p$ approaches a quantum critical point, the strength of this pairing increases and higher $d$-wave harmonics contribute to the $k$-dependence of the superconducting gap function, reflecting the longer range nature of the nematic fluctuations. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B11.00008: Doping dependence of fluctuation diamganetism in High Tc superconductors Subroto Mukerjee, Kingshuk Sarkar, Sumilan Banerjee, T. V. Ramakrishnan Using a recently proposed Ginzburg-Landau-like energy functional due to Banerjee et. al. Phys. Rev. B 83, 024510 (2011), we calculate the fluctuation diamagnetism of high-Tc su- perconductors as a function of doping $x$ in addition to the magnetic field $H$ and temperature $T$ by employing classical Monte-Carlo simulations. We explicitly show that the doping dependence of our diamagnetism results are in good qualitative agreement and reasonable quantitative agreement with experimental data. Our calculations show that a model where the pairing scale increases and superfluid density decreases with underdoping produces features of the observed magnetization in the pseudogap region. In particular we show that the magnetization tracks the superconducting dome instead of the pseudogap temperature as seen in experiment and also comment on the determination of doping dependence of the upper-critical field. [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B11.00009: Fermi Arc Evolution and Doping Mechanism in High-Temperature Superconductors Denis K. Sunko, Damjan Pelc, Miroslav Po\v{z}ek, Vito Despoja, Predrag Lazic We calculate realistic Fermi surface (FS) evolution of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) with Sr doping within an extensive ab-initio framework including advanced band-unfolding techniques. We show that ordinary Kohn-Sham DFT+U can reproduce the observed metal-insulator transition and arc growth, when not restricted to the paramagnetic solution space. We elucidate both arc protection and the inadequacy of the rigid-band picture as consequences of a rapid change in orbital symmetry at the Fermi energy: the material undergoes a dimensional crossover along the Fermi surface, between the nodal (2D) and antinodal (3D) regions. In LSCO, this crossover accounts for FS arcs and the antinodal pseudogap, otherwise ubiquitous phenomena in high-Tc cuprates. The orbital transition is experimentally confirmed by replacing 4\% of planar Cu in nearly optimally doped YBa$_2$Cu$_{2.97}$Zn$_{0.03}$O$_{6.92}$ powder with $^{67}$Zn isotope, lowering T$_c$ to 57 K. The NQR spectrum of $^{67}$Zn, measured for the first time, shows that each Zn dopand surrounds itself with an insulating cluster. Zn destroys the SC metal by a Coulomb ``domino effect'' which reverts the orbital transition locally and pushes a significant number of surrounding sites back towards the parent-compound configuration. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B11.00010: Andreev-Bragg reflection from an Amperian superconductor Paul Baireuther, Timo Hyart, Brian Tarasinski, Carlo Beenakker We show how an electrical measurement can detect the pairing of electrons on the same side of the Fermi surface (Amperian pairing), recently proposed by Patrick Lee for the pseudogap phase of high-$T_c$ cuprate superconductors. Bragg scattering from the pair-density wave introduces odd multiples of $2k_{\rm F}$ momentum shifts when an electron incident from a normal metal is Andreev-reflected as a hole. These Andreev-Bragg reflections can be detected in a three-terminal device, containing a ballistic Y-junction between normal leads $(1,2)$ and the superconductor. The cross-conductance $dI_1/dV_2$ has the opposite sign for Amperian pairing than it has either in the normal state or for the usual BCS pairing. [Preview Abstract] |
Monday, March 2, 2015 1:15PM - 1:27PM |
B11.00011: Shearconductivity as evidence for broken mirror symmetries Patrik Hlobil, Srinivas Raghu, Akash Maharaj, Pavan Hosur We propose the possible detection of broken mirror symmetries in highly correlated two-dimensional materials by elastotransport measurements. Using linear response theory we calculate the shearconductance $\Gamma_{xx,xy}=\partial \sigma_{xx}/ \partial \epsilon_{xy}$, the linear change of the longitudinal conductivity $\sigma_{xx}$ due to a shear strain $\epsilon_{xy}$. This quantity can only be non-vanishing if the in-plane mirror symmetries are broken and we show that a square lattice with checkerboard charge and bond density wave shows a finite shearconductivity. This implies that a measurement of $\Gamma_{xx,xy}$ opens the possibility to verify broken mirror symmetry in the pseudogap regime of high-$T_c$ superconductors. Experimental setups to detect shearconductance are presented. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B11.00012: Nanoscale phase separation in deep underdoped Bi$_{2}$Sr$_{2}$CuO$_{6+\delta}$ and Ca$_2$CuO$_2$Cl$_2$ Peter Mistark, Robert Markiewicz, Arun Bansil We demonstrate that the tunneling spectra from deeply underdoped Bi$_{2}$Sr$_{2}$CuO$_{6+\delta}$ (Bi2201) and Ca$_2$CuO$_2$Cl$_2$ (CCOC) provide clear evidence for a nanoscale phase separation (NPS), which causes the gap to fill rather than close with doping. The phase separation extends from half-filling to a doping of $x\sim 0.09$. Assuming that the NPS is in the form of stripes, the nodal gap, which we model as a Coulomb gap, arises from impurity pinning of the charged stripes, and ultimately drives a metal-insulator transition. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B11.00013: Closing the pseudogap quietly James Storey The physical properties of hole-doped cuprate high-temperature superconductors are heavily influenced by an energy gap known as the pseudogap whose origin remains a mystery second only to that of superconductivity itself. A key question is whether or not the pseudogap closes at a temperature $T^*$. The absence of a specific heat anomaly, together with persistent entropy losses up to 300K, have long suggested that the pseudogap does not vanish at $T^*$. However, amid a growing body of evidence from other techniques pointing to the contrary we revisit this question. Here we investigate if, by adding a temperature dependence to the pseudogap energy and quasiparticle lifetime in the resonating-valence-bond spin-liquid model of Yang Rice and Zhang, we can close the pseudogap quietly in the specific heat. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B11.00014: The insulator and pseudogap states coalescence beneath the superconductor dome Alejandro Cabo Montes De Oca, Alejandro Cabo-Bizet, Victor Martinez, Yoandri Vielza The pseudogap effects and the expected quantum phase transitions (QPT) in cuprate materials are yet unclear in nature. A single band Tight-Binding (TB) model for the CuO planes of these materials had predicted the existence of definite pseudogap states at half-filling, after considering that a crystal symmetry breaking and non-collinear spin orientations of the single particle states are allowed. Here we show that after including hole doping in the model, a QPT which lies beneath the superconducting dome exists and is a second order one. In it, an insulator ground state (AFI), showing strong spin fluctuations at low doping, coalesce with an excited paramagnetic pseudogap (PPG) state, exhibiting a broken lattice symmetry at the critical hole density $x_{c} =$ 0$.$2. Above this value the system becomes a paramagnetic metal. The band structures and Fermi surfaces with doping are evaluated and their evolution show a close resemblance with the experimental observations, including the topological change in structure for varying hole density. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B11.00015: Charge Order in the Three-Band Model of Cuprate Superconductors Bill Atkinson, Arno Kampf, Sinan Bulut Numerous experiments have pointed to the widespread occurrence in underdoped high temperature superconductors of charge order with a strong intra-unit cell component. Motivated by this, we have performed theoretical calculations of charge instabilities in cuprate superconductors. First, we discuss a persistent discrepancy between theoretical predictions and experimental observations of the ordering wavevector ${\bf q}^\ast$. We show that the correct direction and magnitude for ${\bf q}^\ast$ can be obtained under the assumption that the charge order emerges from a pre-formed pseudogap. Second, we show that this type of long-range charge order reacts sensitively to dilute concentrations of strongly scattering impurities such as zinc, unlike the pseudogap which has been found to be robust against zinc doping. Taken together, these suggest that the pseudogap is a distinct phenomenon from charge order. [Preview Abstract] |
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