Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B9: Superconducting Cuprates: Spectroscopy |
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Sponsoring Units: DCMP Chair: Pengcheng Dai, Rice University Room: 006D |
Monday, March 2, 2015 11:15AM - 11:27AM |
B9.00001: Evidence for phononic pairing in extremely overdoped ``pure'' d-wave superconductor Bi2212 Yu He, Makoto Hishimoto, Dongjoon Song, Hiroshi Eisaki, Zhi-Xun Shen Recent advancement in High Tc cuprate superconductor research has elucidated strong interaction between superconductivity and competing orders. Therefore, the mechanism behind the 'pure' d-wave superconducting behavior becomes the next stepping stone to further the understanding. We have performed photoemission study on extremely overdoped Bi2212 single crystal synthesized via high pressure method. In this regime, we demonstrate the much reduced superconducting gap and the absence of pseudogap. Clear gap shifted bosonic mode coupling is observed throughout the entire Brillouin zone. Via full Eliashberg treatment, we find the electron-phonon coupling strength capable of producing a transition temperature very close to Tc. This strongly implies bosonic contribution to cuprate superconductivity's pairing glue. [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B9.00002: Spectral moment sum rules for electron-phonon coupled superconductors in equilibrium and nonequilbrium Khadijeh Najafi, James Freericks Recent developments in high-resolution time- and angle-resolved photoemission spectroscopy (trARPES) has opened a new path to study the dynamics of quantum materials in nonequilibrium. Several experimental studies have used trARPES to characterize the dynamics of the energy gap in superconductors. One experiment from the Lanzara group indicates that the fluence dependence of the photoemission signal is consistent with a weakening of the electron-phonon coupling in the superconducting state that increases with increasing fluence. The normal state sum rule shows that the integrated spectral weight in the normal state is constant if the phonon fluctuations are unchanged. Here we discuss the extension of these sum rules to the superconducting state. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B9.00003: RIXS Study on the Doping Dependence of Elementary Excitations across AFM-SC Phase Boundary in Electron-doped Cuprates Wei-Sheng Lee, Simon Gerber, Y. B. Huang, Guichuan Yu, Brian Moritz, H. Y. Huang, R. P. Wang, W. B. Wu, V. N. Strocov, E. M. Motoyama, C. T. Chen, D. J. Huang, Martin Greven, Thorsten Schmitt, Z. X. Shen, T. P. Devereaux Tracking the doping dependence of elementary excitations in cuprates is an important approach to gain further insight into the mystery of high temperature superconductivity. Recently, RIXS measurements have revealed two surprising behaviors in the electron-doped cuprates: (i) the bandwidth of magnetic excitation increases, and (ii) an unexpected branch of collective modes emanating from the zone center was found in superconducting compounds, indicating the existence of a quantum phase distinct from superconductivity. Yet, a detailed doping dependence study of these two behaviors in the phase diagram, especially near the antiferromagnetic-superconductivity phase boundary, is still lacking. Here we report doping dependent RIXS measurements on electron-doped cuprates, Nd$_{\mathrm{2-x}}$Ce$_{\mathrm{x}}$CuO$_{\mathrm{4}}$. Doping dependence of magnetic and these zone-center excitations will be presented. [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B9.00004: Terahertz nano-spectroscopy and imaging of superfluid surface plasmons in conventional and anisotropic superconductors H. T. Stinson, J. S. Wu, B. Y. Jiang, Z. Fei, A. S. Rodin, B. Chapler, A. S. Mcleod, A. Castro Neto, Y. S. Lee, M. M. Fogler, D. N. Basov We numerically model near-field spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors in the infrared and terahertz regime. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting gap in Bardeen-Cooper-Schrieffer superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the $c$-axis plasma frequency, and thus the $c$-axis superfluid density, of layered unconventional superconductors such as cuprates and pnictides with identical spatial resolution. We discuss the development of a cryogenic terahertz near-field microscope designed to perform these proposed experiments. [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B9.00005: The fate of quasiparticles in the superconducting state S.V. Dordevic, D. van der Marel, C.C. Homes Quasiparticle properties in the superconducting state are masked by the superfluid and are not directly accessible to infrared spectroscopy. We show how one can use a Kramers-Kronig trans- formation to separate the quasiparticle from superfluid response and extract intrinsic quasiparticle properties in the superconducting state. We also address the issue of a narrow quasiparticle peak observed in microwave measurements, and demonstrate how it can be combined with infrared measurements to obtain unified picture of electrodynamic properties of cuprate superconductors. [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B9.00006: Broken time reversal symmetry states in superconductors using the ultrafast pump-probe method Chandan Setty, Jiangping Hu The excitation of vibrational modes by ultrafast optical pulses can be a useful probe of the electronic ground state in a solid through the electron-phonon interactions. In this work, we show that the phase of the oscillations of reflectivity/transmissivity as a function of the delay time can contain signatures of broken time reversal symmetry (BTRS) in the superconducting ground state. To illustrate this, we consider a simple Hamiltonian consisting of a two band electronic part and a phononic part; additionally, we include terms which couple electrons to phonons and light. In the absence of dissipation, we show that on entry into the BTRS superconducting state, the phase of the reflectivity oscillations deviates from the normal state values of $\pm$ $\pi $/2 in a continuous fashion. We will also comment on the effects of dissipation and the dependence of our result on the opacity of the superconductor. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B9.00007: Reduction of dissipative nonlinear conductivity of superconductors by static and microwave magnetic fields Alexander Gurevich A theory of dissipative nonlinear conductivity, $\sigma_1(\omega,H)$, of s-wave superconductors under strong electromagnetic fields at low temperatures and frequencies $\hbar\omega\ll k_BT$ is proposed. Closed-form expressions for $\sigma_1(H)$ and the surface resistance $R_s(\omega,H)$ are obtained in the nonequilibrium dirty limit for which $\sigma_1(H)$ has a significant minimum as a function of the amplitude of magnetic field $H$. The calculated microwave suppression of $R_s(H)$ is in good agreement with recent experiments on alloyed Nb resonator cavities. It is shown that superimposed dc and ac fields, $H=H_0+H_a\cos\omega t$, can be used to reduce ac dissipation in thin film nanostructures by tuning $\sigma_1(H_0)$ with the dc field, consistent with experiments performed in the sixties. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B9.00008: The non-linear response of a superconductor to a few-cycle THz pulse G.L. Carr, Xiaoxiang Xi We present a time-domain analysis of the response of a BCS superconductor (in the low temperature limit) to a few cycle THz pulse whose spectral content may span the absorption threshold for pair breaking. The analysis is based on the finite-difference time-domain (FDTD) approach, in combination with a model susceptibility for a superconductor that includes an explicit dependence on the energy gap[1]. The FDTD approach allows us to calculate the THz induced current density, from which we determine the modified energy gap at each instant of time during the THz wave's passage. The resulting non-linear susceptibility causes up-conversion of the incident THz wave into odd harmonics. The model results are compared with experiment for thin NbN films in both linear[2] and non-linear[3] regimes. [1] Xioaxiang Xi and G.L. Carr, \textit{Supercon. Sci. {\&} Technol.} \textbf{26}, 114001 (2013). [2] T. Hong et al, \textit{J. Appl. Phys.} \textbf{114}, 243905 (2013). [3] R. Matsunaga et al, \textit{Science} \textbf{345}, 1145 (2014). [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B9.00009: What does resonant inelastic x-ray scattering at the Cu L-edge measure? Chunjing Jia, Brian Moritz, Thomas Devereaux, Krzysztof Wohlfeld Recent resonant inelastic x-ray scattering (RIXS) experiments at the transition metal L-edge of copper oxides suggest that this technique can be regarded as one of the best momentum-resolved probes of low energy excitations. However, the theoretical understanding of this technique remains incomplete [1]. Here we show, using both numerical studies and analytical approaches, which low energy excitations are probed by RIXS in both undoped and doped cuprates, as modeled by the Hubbard Hamiltonian. We conclude on a qualitative level that (i) RIXS is sensitive to the spin dynamical structure factor in the cross-polarized geometry, whereas (ii) RIXS is sensitive primarily to the $A_{1g}$ projected charge dynamical structure factor, i.e. to both charge excitations and the two-spin excitations (including e.g. bimagnons) in the parallel scattering geometry. \\[4pt] [1] C. J. Jia {\it et al.}, Nature Communications 5, 3314 (2014). [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B9.00010: Terahertz transient photoconductivity of insulating cuprates J. Steven Dodge, Jesse Petersen, Amir Farahani, Derek Sahota, Ruixing Liang We establish a detailed phenomenology of photocarrier transport in the copper oxide plane by studying the terahertz transient photoconductivity of Sr$_2$CuO$_2$Cl$_2$ and YBa$_2$Cu$_3$O$_6$. We observe a common dependence on time, fluence, and temperature. We infer an intrinsic photocarrier mobility from the peak photoconductivity, and show that its temperature dependence can be associated with scattering from thermal excitations. The initial photoconductivity decay rate is independent of fluence, indicating a lack of interaction among photoexcitations. We observe a crossover with time, to a thermalized regime characterized by hopping conductivity with a low activation energy. [Preview Abstract] |
Monday, March 2, 2015 1:15PM - 1:27PM |
B9.00011: Pump-probe excitation spectroscopy of insulating cuprates Derek Sahota, Hanna Dabkowska, Graeme Luke, Ruixing Liang, J. Steven Dodge We examine the transient optical response of optically thick single crystals of the insulating cuprates La$_2$CuO$_4$, YBa$_2$Cu$_3$O$_6$, and Sr$_2$CuO$_2$Cl$_2$, as a function of probe wavelength, pump excitation wavelength, and pump fluence. At pump-probe time delay $t>1$ ps, the transient reflectance spectrum mimics a change in temperature, while for $t<1$ ps we observe a non-thermal response for which this description fails. The pump-probe signal saturates at a characteristic fluence that depends on pump wavelength. In all three materials, the saturation fluence reaches a minimum at a pump photon energy 0.6 eV above the optical absorption peak associated with the charge transfer gap. We associate both the pump-probe spectrum and its saturation behavior with the thermalization of the initial photoexcited state, and argue that the saturation spectrum indicates a relaxation bottleneck just above the charge transfer gap. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B9.00012: Effect of pressure on the Fermi-surface reconstruction in the cuprate superconductor YBa$_{2}$Cu$_{3}$O$_{y}$ Sven Badoux, Olivier Cyr-Choini\`ere, Sophie Dufour-Beaus\'ejour, Nicolas Doiron-Leyraud, Louis Taillefer, David Vignolles, Marc Nardone, Cyril Proust, Douglas Bonn, Walter Hardy, Ruixing Liang Quantum oscillations and transport measurements have shown that the Fermi surface of cuprate superconductors undergoes a reconstruction near optimal doping [1-5]. It has recently become clear that charge-density-wave order [6-8] causes this Fermi-surface reconstruction [9,10]. Here we report transport measurements in high magnetic fields under pressure that shed light on the pressure dependence of Fermi-surface reconstruction in YBa$_{2}$Cu$_{3}$O$_{y}$ at various dopings. [1] N. Doiron-Leyraud et al., Nature 447, 565 (2007). [2] D. LeBoeuf et al., Nature 450, 533 (2007). [3] B. Vignolle et al., Nature 455, 952 (2008). [4] D. LeBoeuf et al., Physical Review B 83, 054506 (2011). [5] N. Doiron-Leyraud et al., Physical Review X 3, 021019 (2013). [6] T. Wu et al., Nature 477, 191 (2011). [7] G. Ghiringhelli et al., Science 337, 821 (2012). [8] J. Chang et al., Nature Physics 8, 871 (2012). [9] F. Lalibert\'e et al., Nature Communications 2, 432 (2011). [10] G. Grissonnanche et al., Nature Communications 5, 3280 (2014). [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B9.00013: Magnetic excitations in the superconducting and pseudogap states of the slightly underdoped high-temperature superconductor HgBa$_{2}$CuO$_{4+\, \delta }$ Mun Chan, C .J. Dorow, Y. Tang, M. J. Veit, Y. Ge, M. Greven, L. Mangin-Thro, Y. Sidis, P. Bourges, X. Zhao, D. L. Abernathy We present an inelastic neutron scattering study of the dynamic magnetic susceptibility for slightly underdoped cuprate high-temperature superconductor HgBa$_{2}$CuO$_{4+\, \delta }$ (Hg1201, p$=$0.117, T$_{c}$ $=$ 88 K). Unlike more underdoped Hg1201, the magnetic spectrum exhibits an X - shaped hourglass dispersion with an incommensurate low energy response and a clear resonance mode in the superconducting state. At temperatures above T$_{c}$, the low energy incommensurate excitations disappear, replaced by a commensurate Y-shaped spectrum characteristic of the pseudogap state. The magnetic excitations become weaker with increasing temperature and are no longer discernable above the pseudogap temperature T*. The temperature evolution of the magnetic spectrum across T$_{c}$ is consistent with models based on excitations of itinerant spins with a d-wave superconducting order parameter. Our work suggests that itinerant carriers should play an integral part for the understanding of the pseudogap state as well. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B9.00014: Quasiparticle mass enhancement approaching optimal doping in YBa2Cu3O6$+$x Brad Ramshaw, Suchitra Sebastian, Ross McDonald, James Day, Beng Tan, Zengwei Zhu, Jon Betts, Ruixing Liang, Doug Bonn, Walter Hardy, Neil Harrison Unconventional superconductivity is almost always found in proximity to other broken-symmetry states. The high-Tc cuprates exhibit a rich phase diagram that includes both spin and charge order. Previous quantum oscillation studies on YBa2Cu3O6$+$x have addressed how broken symmetry reconstructs the Fermi surface, but the evolution of the Fermi surface toward optimal doping was missing due to the high upper-critical fields. We use magnetic fields approaching 100 tesla to measure quantum oscillations in YBa2Cu3O6$+$x at three new doping levels with Tcs of 75, 81, and 91 K. We find that the quasiparticle effective mass is strongly enhanced approaching a hole doping of p$=$0.18---the same doping where experimental signatures of broken symmetry terminate and superconducting properties are enhanced. This is suggestive of a quantum critical point underlying the superconducting dome near optimal doping. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B9.00015: Photo-induced Ultra-fast Carrier Dynamics in a Mott Insulator with Antiferromagnetic Long-range Order Sumio Ishihara, Eiki Iyoda We study transient dynamics of hole carriers injected into a Mott insulator with antiferromagnetic long-range order, motivated from the recent optical pump-probe experiments in high-Tc superconductors. This is termed ?dynamical hole doping? in contrast to the chemical hole doping. The theoretical framework for the transient carrier dynamics is presented based on the two-dimensional t-J model [1]. The time dependencies of the optical conductivity spectra, as well as the one-particle excitation spectra, are calculated based on the Keldysh Green's function formalism, associated with the self-consistent Born approximation. In the early stage, the Drude component only appears, and then incoherent components originating from hole-magnon scattering start to grow. Fast oscillatory behavior owing to coherent magnon and slow relaxation dynamics are confirmed in the spectra. The time profiles are interpreted as doped bare holes being dressed by magnon clouds and relaxed into spin polaron quasiparticle states.. Implications for recent pump-probe experiments are discussed. [1] E. Iyoda, and S. Ishihara, Phys. Rev. B 89, 125126 (2014). [Preview Abstract] |
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