Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session V13: Infrared and Optical Spectroscopy of Superconductors |
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Sponsoring Units: DCMP Chair: Larry Carr, NSLS Room: LACC 402B |
Thursday, March 24, 2005 11:15AM - 11:27AM |
V13.00001: Optical signature of the Quantum Critical Point in electron doped cuprates R.P.S.M. Lobo, N. Bontemps, A. Zimmers, M.C. Barr, Y. Dagan, R.L. Greene, C.C. Homes, A.J. Millis We measured the temperature dependence of the optical conductivity of (Pr,Ce)$_2$CuO$_4$ films from the very underdoped to the overdoped regime between 4 meV and 3 eV. We observed a normal state gap but the presence of a Drude-like peak indicates that this gap is partial. The temperature at which the partial gap opens decreases with increasing Ce content and the gap disappears in the overdoped sample. Our data is consistent with a commensurate spin density wave with a $(\pi,\pi)$ wavevector. When the spin density wave is taken into account, the phase diagram of electron doped cuprates shows a quantum critical point inside the superconducting dome at a Ce concentration around 0.17 in agreement with evidence for a QCP from dc transport experiments [Dagan {\it et al.}, PRL {\bf 92}, 167001 (2004)]. [Preview Abstract] |
Thursday, March 24, 2005 11:27AM - 11:39AM |
V13.00002: The a-axis optical conductivity of detwinned Ortho-II YBa$_{2}$Cu$_{3}$O$_{6.50}$ Thomas Timusk, Jungseek Hwang, Jing Yang, Doug Bonn, Ruixing Liang, Walter Hardy The a-axis optical properties of a detwinned single crystal of YBa$_{2}$Cu$_{3}$O$_{6.50}$ in the Ortho II phase have been determined from reflectance data over wide frequency range (70 - 42 000 cm$^{-1}$). At high temperature the spectra are dominated by a broad background of scattering extending to 1 eV. Below 200 K a shoulder in the reflectance signals the opening of a scattering channel with an onset frequency of 400 cm. In this temperature range we also observe a peak in the optical conductivity at 177 cm. The shoulder spectrum is consistent with a scattering model with a bosonic mode at 33 meV whose amplitude {\it decreases} with temperature in parallel with the magnetic resonance measured on crystals from the same source by Stock {\it et al.} This temperature dependence enables us to set an upper limit to any phonon contribution to the scattering. Below $T_c=59$ K, the spectra change dramatically as the superconducting condensate appears. Its spectral weight is consistent, to within experimental error, with the FGT sum rule. [Preview Abstract] |
Thursday, March 24, 2005 11:39AM - 11:51AM |
V13.00003: Optical Properties of Nd$_{1-x}$TiO$_{3}$ Jing Yang, Jungseek Hwang, Thomas Timusk, Athena Safa-Sefat, John E. Greedan Infrared optical measurements were performed on the Nd$_{1-x}$TiO$_{3 }$ system of chemically doped transition-metal oxides. By introducing vacancies (x) on Nd sites, the degree of filling of the d-band on Ti can be controlled. For x=0.0, NdTiO$_{3}$, the compound is a Mott-Hubbard insulator, while for x=1/3, Nd$_{2/3}$TiO$_{3}$, there are no d electrons and the compound is a charge-transfer insulator. Two metal-insulator-transitions are expected at x$\sim $0.10 and 0.20. In this paper, we use the infrared spectroscopy to investigate the optical properties and the low-lying electronic structures of the titanium oxide system. The absolute reflectance of the single crystals was measured via an \textit{in situ} gold evaporation technique using a Bruker \textit{IFT 66v/s} spectrometer between 50 and 40 000 cm$^{-1}$. In the metallic phase (x=0.10), we observed an unusual temperature dependence of the Drude and midinfrared spectral weight. Temperature-dependent optical properties of the Nd$_{1-x}$TiO$_{3 }$ system at different doping levels will be presented. [Preview Abstract] |
Thursday, March 24, 2005 11:51AM - 12:03PM |
V13.00004: Far-Infrared Studies of the Development of the Electronic Lattices in La$_2$CuO$_{4+0.0315}$ Y.H. Kim, H.H. Hsieh, P.H. Hor La$_{2}$CuO$_{4+0.0315}$ undergoes a superconducting transition with an onset at T$_{c}$ = 30 K when it is slow-cooled at a rate of 1 K/min from the room temperature but it becomes a T$_{c}$ = 15 K superconductor when quenched down to 77 K in less than 1 minute. The corresponding far-infrared reflectivity measurements reveal that there exists only one collective mode at $\omega _{G1} \quad \sim $ 24 cm$^{-1}$ in the T$_{c}$ = 15 K phase [1]. However, when slow-cooled, there develop a series of collective modes at $\omega _{G1} \quad \sim $ 24 cm$^{-1}$, $\omega _{G2} \quad \sim $ 37 cm$^{-1}$, $\omega _{G3} \quad \sim $ 46 cm$^{-1}$ , and $\omega _{G4}$ $\sim $ 60 cm$^{-1}$ with a complex temperature dependences. Upon cooling, $\omega _{G1}$ and $\omega _{G3}$ show the similar behaviors as the Sr/O co-doped LSCO at the hole concentration p = 0.07 [1] while the $\omega _{G2}$ mode loses its oscillator strength for T $<$ 150 K and the $\omega _{G4}$ mode shows no change in its strength at all temperatures. We explain the implications of our findings within the 2D electronic lattice model [1, 2]. \begin{enumerate} \item Y. H. Kim and P.H. Hor, Mod. Phys. Lett. B\textbf{15}, 497 (2001). \item P.H. Hor and Y.H. Kim, J. Phys.: Condens. Matter \textbf{14}, 10377 (2002). \end{enumerate} [Preview Abstract] |
Thursday, March 24, 2005 12:03PM - 12:15PM |
V13.00005: Constant Effective Mass Across the Underdoped Region of the High Tc Cuprates Willie Padilla, Yunsang Lee, Michael Dumm, Girsh Blumberg, Shimpei Ono, Kouji Segawa, Seiki Komiya, Yoichi Ando, Dimitri Basov We investigate the hole dynamics in two prototypical high temperature superconducting systems: La$_{2-x}$Sr$_{x}$CuO$_{4}$ and YBa$_{2}$Cu$_{3}$O$_{y}$ using a combination of DC transport and infrared spectroscopy. By exploring the effective spectral weight obtained with optics in conjunction with DC Hall results we find a constant effective mass across the entire underdoped regime. The transition to the Mott insulating state in these systems is of the "vanishing carrier number" type as we observe no mass divergence as one proceeds to undoped phases. We discuss the implications of these results for the understanding of both transport phenomena and pairing mechanism in high-T$_{c}$ systems. [Preview Abstract] |
Thursday, March 24, 2005 12:15PM - 12:27PM |
V13.00006: In-plane optical response in underdoped YBCO Teruhisa Kakeshita, Takahiko Masui*, Setsuko Tajima* The recent STM experiments demonstrated that the electronic state in CuO$_{2}$ plane is inhomogeneous [1], which becomes conspicuous in the underdoped regime. In such an inhomogeneous state, it is not obvious whether a superfluid density is correctly estimated by a conventional way. We investigated the in-plane optical response for underdoped YBCO crystal to discuss the relation between inhomogeneity and superfluid density in the pseudo-gapped state. The a-axis optical spectrum shows a larger residual conductivity than that for the optimum doping. The superfluid density estimated from our optical spectrum at the lowest temperature is substantially smaller than that determined by $\mu $SR. We discuss this strongly suppressed superfluid density and the large residual conductivity in terms of the inhomogeneity in real- and k-space. This work was supported by the New Energy and Industrial Technology Development Organization(NEDO) through ISTEC as the Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications. [1]K.M.Lang et al., Nature 415, 412 (2002). *present address: Dept. of Physics, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan [Preview Abstract] |
Thursday, March 24, 2005 12:27PM - 12:39PM |
V13.00007: Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La$_{2-x}$Sr$_{x}$CuO$_4$ Paolo Calvani, Michele Ortolani, Stefano Lupi The infrared optical conductivity $\sigma_1^{ab} (\omega,T)$ of the $ab$-planes of La$_{2-x}$Sr$_x$CuO$_{4}$ (LSCO) has been measured for different temperatures and for $0.03 < x <0.26$. The spectral weight of the carriers $W = \int_0^\Omega {\sigma_1^{ab} (\omega,T) d\omega}$ fulfills the same law $W = W_0 - B(\Omega) T^2$ as in a conventional metal like gold, for any $\Omega$ up to the plasma edge. However in LSCO the thermal response $B(\Omega)$ points toward correlation effects and, unlike in gold, is related to an energy scale $t_T << t_0 \sim W_0$. This experimental result is in agreement with Dynamical mean Field Theory calculations. The Ferrell-Glover-Tinkham sum rule is fulfilled in LSCO superconductors for $\Omega \agt$ 2000 cm$^{-1}$, an energy much higher than predicted for conventional superconductors. [Preview Abstract] |
Thursday, March 24, 2005 12:39PM - 12:51PM |
V13.00008: Infrared Hall study of underdoped cuprate superconductor Pr$_{2-x}$Ce$_x$CuO$_4$ A. Zimmers, L. Shi, D.C. Schmadel, R.L. Greene, H.D. Drew The underdoped cuprate superconductor Pr$_{2-x}$Ce$_x$Cu$O_4$ exhibits a gap-like feature (cond-mat/0405284) in its optical conductivity that depends on electron doping and temperature. This feature suggests either the formation of a density wave state or the presence of hots spots on the Fermi surface. The magneto-optical properties of underdoped PCCO (x=0.13) thin film are investigated in the temperature range between 30K and 300K and in magnetic fields up to 8 Tesla by measuring the Faraday rotation and circular dichroism in the infrared region from 900 - 1100 cm$^{-1}$. A dramatic increase of the Hall frequency is observed as the temperature is lowered below $\sim$150K. These results together with the optical conductivity data, are consistent with a partial gapping of the Fermi surface and formation of a density wave state and not consistent with hot spots in the low temperature state. We will compare the IR Hall response of underdoped PCCO and overdoped PCCO where there is no evidence for gapping in the optical conductivity. Work supported by NSF grant DMR-0352735 and DMR-0303112. [Preview Abstract] |
Thursday, March 24, 2005 12:51PM - 1:03PM |
V13.00009: Probing strong coupling effects in high-$T_{c}$ superconductors using infrared spectroscopy in high magnetic field Yunsang Lee, Z.Q. Li, Willie J. Padilla, D.N. Basov, S.V. Dordevic, C.C. Homes, Kouji Segawa, Yoichi Ando Signatures of strong coupling effects in cuprate high-$T_{c}$ superconductors have been authenticated through a variety of spectroscopic probes. However, the microscopic nature of relevant excitations has not been agreed upon. Here we report on magneto-optical studies of the CuO$_{2}$ plane carrier dynamics in a prototypical high-$T_{c}$ superconductor YBa$_{2} $Cu$_{3}$O$_{y}$ (YBCO). Infrared data are directly compared with earlier inelastic neutron scattering results by Dai \textit {et al}. [Nature (London) \textbf{406}, 965 (2000)] revealing a characteristic depression of the magnetic resonance in H $\parallel $ \textit{c} field less than 7 T. This analysis has allowed us critically access the role of magnetic degrees of freedom in producing strong coupling effects for YBCO system. [Preview Abstract] |
Thursday, March 24, 2005 1:03PM - 1:15PM |
V13.00010: Hall scattering rates of doped GaAs and Bi$_2$Sr$_2$CaCu$_2$O$_{2+x}$ L. Shi, D.C Schmadel, H.D. Drew Magneto-optical measurement of infrared Hall effect provides important information about the Fermi surface topography and carrier scattering rates of metals. A recent study (Rigal et.al. Phys. Rev. Lett. vol 93, 137002 (2004)) of IR Hall effect of underdoped YBa$_2$Cu$_3$O$_{6+x}$ reveals a dramatic increase of the Hall frequency for underdoped samples, consistent with a partial gapping of the Fermi surface as predicted in density wave models. The scattering rates, or imaginary parts of self energies of quasiparticles of cuprate superconductors have been shown by various experimental techniques (transport, optical, APRES ) to have a linear dependence on frequencies. The scattering rates measured by IR Hall effect, however, have been found to be frequency independent. In this study, we compare the infrared Hall response of doped GaAs with that of underdoped Bi$_2$Sr$_2 $CaCu$_2$O$_{2+x}$ samples to investigate the origin of the apparent independence of Hall scattering rate of cuprate superconductors on frequency. The measurements are carried out from 900-1100 cm$^{-1}$ in fields to 8 T and temperatures from 10 K to 300 K. The GaAs sample is Si doped at 6x10$^{6}$ cm$^{- 3}$. The Faraday angle gives a measure of the carrier density and the circular dichroism measures the carrier scattering rates. (Work supported by NSF grant DMR-0303112). [Preview Abstract] |
Thursday, March 24, 2005 1:15PM - 1:27PM |
V13.00011: Time-resolved infrared spectroscopy of superconducting films in a magnetic field H. Zhang, H. Tashiro, J.M. Graybeal, D.H. Reitze, C.J. Stanton, D.B. Tanner, G.L. Carr We performed time-resolved, optical pump-probe measurements on thin NbTi and MoGe films in applied magnetic fields up to $H_{c2}$ /3 to study the recombination dynamics of excess quasiparticles. The films were pumped by a picosecond near-infrared Ti:sapphire laser and probed by time-synchronized far-infrared pulses from a synchrotron storage ring at the National Synchrotron Light Source. The photoexcited high energy quasiparticles (on the order of 1 eV) quickly relax to produce excess quasiparticles with energies $\sim \Delta $ (few meV) at the superconducting gap edge. Those excess quasiparticles recombine into Cooper pairs and produce phonons of energy 2$\Delta $. The resulting nonequilibrium phonon distribution slowly decays on a time scale of 1 ns by anharmonic effects or by escaping into the environment. When the shortest possible synchrotron pulses were used, we reached a temporal resolution of 300 ps. Despite the presence of the normal cores from vortices in the films, we find that the relaxation time does not decrease with magnetic field. The transmittance change in the far-infrared region due to the change of the applied magnetic field of the superconductor will also be discussed. [Preview Abstract] |
Thursday, March 24, 2005 1:27PM - 1:39PM |
V13.00012: Optical pump Terahertz probe transmission spectroscopy of YBCO thin films Anna Kristoffersen, John Nam, Robert Hughes, Henry Tiedje, Tom Timusk, John Preston Our facility uses optical pump THz probe transmission spectroscopy to study the quasiparticle dynamics in Yttrium Barium Copper Oxide (YBCO) thin films. The recovery of the film exhibits two components, a fast response on the order of several ps and a long tail that lasts nanoseconds. In this presentation, the behaviour of the film in both the fast and long components of the tail will be discussed. The frequency content of the transmitted THz pulse can determine whether the observed effect is largely due to normal state quasiparticles or the superconducting condensate. We interpret the data far into the tail in terms of an elevated temperature and use this to investigate the possibility of a phonon bottleneck associated with quasiparticle relaxation. [Preview Abstract] |
Thursday, March 24, 2005 1:39PM - 1:51PM |
V13.00013: Measurement of Localized Nonlinear Microwave Response of Superconductors Sheng-Chiang Lee, Dragos Mircea, Mathew Sullivan, Gregory Ruchti, Steven Anlage, Benjamin Palmer, B. Maiorov, E. Osquiguil We measure the local harmonic generation from superconducting thin films at microwave frequencies to investigate the intrinsic nonlinear Meissner effect near T{\_}c in zero magnetic field. Both second and third harmonic generation are measured to identify time-reversal symmetry breaking (TRSB) and time-reversal symmetric (TRS) nonlinearities. The microscope can measure the local nonlinear response of a bicrystal grain boundary [Sheng-Chiang Lee and Steven M. Anlage, Physica C 408-410, 324 (2004); cond-mat/0408170]. We also performed a systematic doping-dependent study of the nonlinear response and find that the TRS characteristic nonlinearity current density scale follows the doping dependence of the de-pairing critical current density [cond-mat/0405595]. We extract a spontaneous TRSB characteristic current density scale that onsets at T{\_}c, grows with decreasing temperature, and systematically decreases in magnitude (at fixed T/T{\_}c) with under-doping. The origin of this current scale could be Josephson circulating currents or the spontaneous magnetization associated with a TRSB order parameter. [Preview Abstract] |
Thursday, March 24, 2005 1:51PM - 2:03PM |
V13.00014: Infrared dynamics of Tl-doped PbTe Jason Hancock, Zack Schlesinger, Yana Matsushita, Theodore Geballe, Ian Fisher The rock-salt structure small-gap semiconductors PbTe exhibits highly unusual transport behavior when doped with thallium, including superconductivity and Kondo-like resistivity behavior at low temperature. Tl is a hole type dopant at low doping (up to about 0.3\%), but apparently aquires an amphoteric character higher doping which is associated with anomalous scattering and resonance formation at the Fermi level. It has been proposed that valence fluctuations at the Tl site cause it to act as a negative-U center. We use infrared and optical reflectivity measurements which encompass the region of the energy gap and the plasma edge as well as free-carrier response to study the nature of the charge dynamics in this system as a function of frequency, temperature and doping. [1] Y. Matsushita, H. Bluhm, T. H. Geballe, I. R. Fisher, cond-mat/0409174 [Preview Abstract] |
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V13.00015: The effect of magnetic field on electron-boson spectral function in the cuprates Sasa Dordevic, C.C. Homes, G. Gu, Qiang Li, Y.G. Wang We will report results of our infrared spectroscopy studies of high T$_c$ cuprates in high magnetic field. Several families of cuprates, such as YBCO, Bi2212, LBCO and NCCO have been studied using magneto-optical measurements, with magnetic field as high as 18 Tesla. From these measurements we extract the electron-boson spectral function $\alpha^2F(\omega)$ and estimate the effect magnetic field has on it. The results will be critically compared with the existing theoretical models. [Preview Abstract] |
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