Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H37b: Normal State Properties of Superconductors |
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Sponsoring Units: DCMP Chair: Andrew Wray, New York University Room: 384 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H37b.00001: Anomalous Thermal Diffusivity in Bad Metals Jiecheng Zhang, Eli M. Levenson-Falk, Brad J. Ramshaw, Douglas A. Bonn, Ruixing Liang, Walter N. Hardy, Sean A. Hartnoll, Aharon Kapitulnik Local measurements of thermal diffusivity are used to analyze the transport of heat in the bad metallic regime of several strongly correlated materials. In underdoped YBCO systems, we use the in-plane anisotropy to analyze transport in this system. Specifically, we find that the diffusivity anisotropy is comparable to reported values of the electrical resistivity anisotropy and drops sharply below the charge order transition, suggesting that both anisotropies have the same origin. We interpret our results through a strong electron-phonon scattering picture and find that both electronic and phononic contributions to the diffusivity exhibit a saturated scattering time of $\sim\hbar/k_BT$. Our results suggest that neither well-defined electron nor phonon quasiparticles are present in underdoped YBCO systems, and thermal transport exhibits a collective behavior of a "soup" of strongly coupled electrons and phonons which moves at a velocity that is smaller than the Fermi velocity, but larger than the speed of sound. We generalize this treatment to measurements of other bad metals and discuss its implications. [Preview Abstract] |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H37b.00002: The robustness of high-$T_{\rm c}$ superconductivity in underdoped YBa$_2$Cu$_3$O$_{6+x}$ investigated in under strong magnetic fields Neil Harrison, Y.-T. Hsu, M. Hartstein, M. Chan, J. Porras, T. Loew, M. Le Tacon, G. Lonzarich, B. Keimer, V. Flux, S. Sebastian A central unresolved mystery in high-$T_{\rm c}$ superconductivity is whether the pairing amplitude is small in the underdoped regime and relates to the superfluid density or whether it is large and relate to the intrinsic energy scales of the Mott insulating parent state. The magnetic field provides a sensitive probe of the pairing amplitude. However, experimental probes of the extent of the vortex state in temperature and magnetic field have thus far been indirect and hence subject to debate. Here we report measurements over a broad range of temperature and magnetic fields which we use to probe the extent of the vortex region in underdoped YBa$_2$Cu$_3$O$_{6+x}$. and its interplay with quantum oscillations. [Preview Abstract] |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H37b.00003: Quantum criticality in La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4\thinspace }}$cuprates probed with high magnetic fields. Arkady Shekhter, Paula Giraldo Gallo, Jose Augusto Galvis Echeverri, Zachary Stegen, Kimberly Modic, fedor Balakirev, Jonathan Betts, XiuJun Lian, camila Moir, Scott Riggs, Xi He, Jie Wu, Anthony Bollinger, Ivan Bozovic, Brad Ramshaw, Ross McDonald, Greg Boebinger We report magnetoresistance measurements at high magnetic fields, up to 80T, in thin-film La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4\thinspace }}$cuprates. At very high fields the resistivity is found to have a linear-in field behavior that mirrors the linear-in temperature behavior at high temperatures. We discuss the implications of linear-in-field magnetoresistance for energy scale competition near quantum critical point in high-temperature superconductors. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H37b.00004: Linear Magnetoresistance Near Critical Doping In $La_{2-x}Sr_xCuO_4$ Xiujun Lian, Brad Ramshaw, Jonathan Betts, Shimpei Ono, Ross McDonald, Gregory Boebinger, Arkady Shekhter The strange metallic state in high-temperature superconductors is characterized by anomalous transport behavior, such as linear-in-temperature resistivity over a broad temperature range. It has recently been shown that anomalous dynamics near critical doping can be probed by strong magnetic fields. We report resistivity measurements at high magnetic fields in micro-structured $La_{2-x}Sr_xCuO_4$ single crystals in the doping range near critical doping. In particular, we discuss the angular dependence of the magnetoresistance near quantum critical point. [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H37b.00005: Equilibrium States and Near-Equilibrium Transport of Holographic Fermions Garrett Vanacore, Philip Phillips Holographic duality enables non-perturbative study of strongly-interacting fermions, and has produced approximate models of non-Fermi liquid, pseudogapped, and Mott-gapped states. Using methods of numerical relativity, we construct fully-backreacted holographic models of charged and strongly-interacting fermions at finite density and at equilibrium, testing both the robustness of prior results as well as proposals relating the Mott transition to momentum-space deconfinement of charge. We further compute the near-equilibrium charge transport coefficients of these states and compare with optical conductivity measurements of the strange metal phase in cuprate superconductors. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H37b.00006: Bad metallic transport from fluctuating density waves Blaise Gouteraux, Luca Delacretaz, Sean Hartnoll, Anna Karlsson In many bad metals the Drude peak moves away from zero frequency as the resistivity becomes large at increasing temperatures. Bad metals likely have no long-lived quasiparticles and their late-time physics is thereby described by hydrodynamics. Within hydrodynamics a Drude peak is broadened by momentum relaxation, but can only move away from zero frequency if translations are spontaneously broken. We suggest that the hydrodynamics of density wave states is therefore the correct kinematic framework for discussing these materials. We show that the resistivity of general, non-Galilean invariant, density wave states is determined by universal diffusive processes that are independent of the rate of momentum relaxation and strength of pinning due to e.g. weak disorder. Weakly disordered, fluctuating density wave states can have large, finite resistivities. Fitting to available optical conductivity data for bad metals reveals that the energy scales controlling the dynamics are linear in temperature. The T-linearity of the resistivity follows from this observation. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H37b.00007: Charge dynamics near the onset of charge-density-wave (CDW) order in La-124 cuprates P. G. Baity, Dragana Popovi\'{c}, T. Sasagawa The dynamics of charge-ordered states is one of the central unresolved issues in underdoped cuprate high-temperature superconductors. By measuring nonequilibrium charge transport in La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$ across the CDW (and structural) transition, we have found evidence for collective dynamics of domains in the CDW-ordered phase: although they are strongly pinned by disorder, the domains are not static, but trapped in long-lived metastable states [1]. Nonequilibrium effects, such as nonexponential relaxations and avalanches in the resistance observed in response to a change in temperature $T$ or magnetic field $H$, are revealed only when the transition is approached from the charge-ordered phase. To isolate the effects of structure and charge order, we have performed similar measurements on La$_{1.7}$Eu$_{0.2}$Sr$_{0.1}$CuO$_{4}$, where CDW ordering at $T=T_{CO}$ does not coincide with the structural transition. We find that, in $H\parallel c$, both materials exhibit a similar onset of negative magnetoresistance near $T_{CO}$, thus attributing that behavior to the onset of charge order. Other similarities and differences in charge transport will also be discussed. [1] P.~G.~Baity \textit{et al.}, arXiv:1609.02591v2 [cond-mat] (2016). [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H37b.00008: Magnetic-field-induced normal state in a stripe-ordered cuprate La$_{1.7}$Eu$_{0.2}$Sr$_{0.1}$CuO$_{4}$ in the zero-temperature limit Zhenzhong Shi, P. G. Baity, Dragana Popovi\'{c}, T. Sasagawa Charge orders have been discovered in all hole-doped cuprates, but their precise interplay with the high-temperature superconductivity (SC), especially under extreme conditions of high magnetic fields ($H$), is not well understood. We have studied the magnetotransport properties of the stripe-ordered cuprate La$_{1.7}$Eu$_{0.2}$Sr$_{0.1}$CuO$_{4}$ [$T_{c}(H=0)=5.9$~K] at high fields ($H$ ${\le}$ 35 T) and very low temperatures ($T$ ${\ge}$ 16 mK). Our results reveal, for the first time in stripe-ordered cuprates, a full sequence of ground states as a function of $H$: a vortex solid [$T_c(H)\neq 0$], a vortex glass ($T_c=0$), a possible coexistence region of the vortex glass and the high-$H$ normal phase, and the high-$H$ normal phase in which SC is suppressed. The high-$H$ normal state is characterized by the negative magnetoresistance and a $\ln(1/T)$ dependence of the resistivity, which becomes weaker with increasing $H$ and disappears for $H >$ 55 T. Thus the results strongly suggest that the high-field ground ($T=0$) state in stripe-ordered cuprates is a metal. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H37b.00009: Electron Energy Dissipation in the Normal State of Optimally Doped BSCCO Jonathan Rameau, Simon Freutel, A.F. Kemper, M.A. Sentef, J.K. Freericks, I. Avigo, M. Ligges, L. Rettig, Y. Yoshida, H. Eisaki, J. Schneeloch, R.D. Zhong, G.D. Gu, P.D. Johnson, U. Bovensiepen New time-resolved ARPES (trARPES) results for the normal state of optimally doped Bi2212 will be discussed. These measurements reveal three intrinsic timescales for relaxation of hot carriers: an electron-electron timescale $\tau_{\mathrm{ee}}$ and two electron-phonon timescales, $\tau_{\mathrm{short}}(E)$ and $\tau_{\mathrm{long}}(E)$. While $\tau_{\mathrm{ee}}(E)$, appears to be energy- and pump fluence-independent, $\tau_{\mathrm{short}}(E)$ and $\tau_{\mathrm{long}}(E)$ are found to be energy-dependent, with $\tau_{\mathrm{short}}(E)$ also fluence dependent. Further, a distinct step in $\tau_{\mathrm{short}}(E)$ at $E \sim 75$ meV above the Fermi energy is fount to originate from coupling of hot electrons to an optical phonon mode. The implications of these findings will be addressed. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H37b.00010: Momentum scaling of the marginal Fermi liquid continuum in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ Matteo Mitrano, Ali Husain, Sean Vig, Melinda Rak, Anshul Kogar, Genda Gu, Chandra Varma, Peter Abbamonte High-temperature superconductivity in cuprates emerges from a metal whose temperature-dependent resistivity and NMR relaxation rate cannot be described in terms of a simple Fermi liquid. One of the main theoretical proposals to account for these normal state properties is the so-called marginal Fermi liquid (MFL) theory. A fundamental hypothesis of the MFL theory is the existence of a universal, momentum-independent form for the density fluctuation spectrum, $\chi(q,\omega)$. The most direct evidence supporting a MFL scenario is the observation of an energy-independent continuum at $q=0$ in Raman scattering experiments, but whether this exhibits the correct scaling form at $q\neq0$ has never been established. Here we present a meV-resolution electron energy-loss spectroscopy measurement of the MFL momentum-dependence in the cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ at optimal doping. We show that this continuum is present not only at q = 0, but rather extends throughout the entire Brillouin zone. Our study suggests that optimally-doped cuprates may be close to quantum criticality with strong, local normal-state fluctuations. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H37b.00011: Quasiparticle Interference and Strong Electron-Mode Coupling in the Quasi-One-Dimensional Bands of Sr$_2$RuO$_4$ Zhenyu Wang, Melinda Rak, Peter Abbamonte, Eduardo Fradkin, Vidya Madhavan, Daniel Walkup, Philip Derry, Yoshiteru Maeno Sr$_2$RuO$_4$ has attracted a great deal of interest as a spin-triplet superconductor with an order parameter that may potentially break time reversal invariance and host half-quantized vortices with Majorana zero modes. While the actual nature of the superconducting state is still a matter of controversy, it has long been believed that it condenses from a metallic state that is well described by a conventional Fermi liquid. In this talk we use a combination of Fourier transform scanning tunneling spectroscopy (FT-STS) and momentum resolved electron energy loss spectroscopy (M-EELS) to probe interaction effects in the normal state of Sr$_2$RuO$_4$. Our high-resolution FT-STS data show signatures of the $\beta$-band with a distinctly quasi-1D character. The band dispersion reveals surprisingly strong interaction effects that renormalize the Fermi velocity, suggesting the normal state is a `correlated metal` where correlations are strengthened by the quasi 1D nature of the bands. In addition, kinks at energies of approximately 10meV, 38meV and 70meV are observed. By comparison with M-EELS data we show that the two higher energy features arise from coupling with collective modes. This work opens up a unique approach to reveal the superconducting order parameter in this compound. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H37b.00012: Pairing of renormalized eigenstates of disordered superconductors with strong correlations Amit Ghosal, Debmalya Chakraborty, Nitin Kaushal Strongly correlated d-wave superconductors show amazing robustness to impurities up to moderate strengths within Hartree-Fock-Bogoliubov (HFB) calculations [1]. Motivated by this finding, we investigate the interplay of interactions and disorder in these systems using a simple pairing mechanism, similar to what leads to Anderson's theorem for s-wave superconductors. We first solve for the effective one-particle eigenstates in the presence of disorder, including the inherently strong electronic repulsions at the Hartree-Fock channels using Gutzwiller renormalization. These `normal-states' are then paired up keeping track of disorder induced inhomogeneities. Our results, matching with those in the literature [1], show that the inhomogeneities in the normal-states is qualitatively different from the eigenstates of noninteracting disordered Hamiltonian. The pairing, however, reflects strong insensitivity to inhomogeneities. Our results shed light on why d-wave superconductivity is robust to disorder in HFB formalism, compared to conventional Abrikosov Gorkov mechanism.\\ (1) D. Chakraborty and A. Ghosal, New J. Phys. 16, 103018 (2014) [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H37b.00013: Strongly Correlated Electron Systems: an operatorial perspective Andrea Di Ciolo, Adolfo Avella We show the potentialities of an operatorial approach based on the equations of motion and the Green's function formalisms to study strongly correlated systems. We give the general characterization of the exact solution of a generic interacting Hamiltonian and discuss how such an analysis performed on small clusters can suggest approximation schemes for the bulk. As a paradigmatic example, we consider the exact solution of the 2-site Hubbard model, identify the contributions of operators embodying charge, spin and pair degrees of freedom to the relevant physical quantities of the system and clarify the crucial role played by spin fluctuations. Correspondingly, according to the given general prescription, we devise a 3-pole approximation for the 2D Hubbard model in the framework of the Composite Operator Method (COM) with a basis given by the Hubbard operators plus an operator describing electronic transitions dressed by nearest-neighbor spin fluctuations. As well as the 3-pole approximate solution is in remarkable agreement with the exact one on the 2-site system, the one proposed for the 2D system performs very well once compared to advanced (semi-)numerical methods, being by far less computational-resource demanding and more accurate in frequency and momentum resolution. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H37b.00014: Diagrammatic Monte Carlo approach for diagrammatic extensions of dynamical mean-field theory -- convergence analysis of the dual fermion technique Jan Gukelberger, Evgeny Kozik, Hartmut Hafermann The dual-fermion approach provides a formally exact prescription for calculating properties of a correlated electron system in terms of a diagrammatic expansion around dynamical mean-field theory (DMFT). It can address the full range of interactions, the lowest order theory is asymptotically exact in both the weak- and strong-coupling limits, and the technique naturally incorporates long-range correlations beyond the reach of current cluster extensions to DMFT. Most practical implementations, however, neglect higher-order interaction vertices beyond two-particle scattering in the dual effective action and further truncate the diagrammatic expansion in the two-particle scattering vertex to a leading-order or ladder-type approximation. In this work we compute the dual-fermion expansion for the Hubbard model including all diagram topologies with two-particle interactions to high orders by means of a stochastic diagrammatic Monte Carlo algorithm. Benchmarking against numerically exact Diagrammatic Determinant Monte Carlo simulations allows us to systematically assess convergence of the dual-fermion series and the validity of these approximations. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H37b.00015: Hundness and Mottness in a Three-Band Hund Model with Relevance for Iron Pnictides Katharina Stadler, Zhiping Yin, Jan von Delft, Gabriel Kotliar, Andreas Weichselbaum The recently discovered iron pnictide superconductors (as well as chalcogenides, ruthenates, and other 4d transition metal oxides) show puzzling anomalous properties, like a coherence-incoherence crossover, also in the normal state. While there is consensus about strong correlation effects playing a key role in these materials, their precise origin (Coulomb repulsion or Hund’s rule coupling between electrons of different orbitals) has been under debate as one of the major open questions in the field many years. In a recent detailed study of the Hund metal problem [1] the coherence-incoherence crossover was shown to be connected to spin-orbital separation and to be clearly driven by Hund’s rule coupling. In order to better understand the differences between Mott insulators and Hund metals and to obtain a generic picture of the role of Hund’s rule coupling in both regimes, we explore the phase diagram for a channel-symmetric three-band model with Coulomb repulsion and Hund’s rule coupling on a Bethe lattice at and away from 1/3 filling using the numerical renormalization group to obtain a numerically exact dynamical mean-field theory solution. [1] K. M. Stadler et al., PRL 115, 136401 (2015) [Preview Abstract] |
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