Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session C36: HTSC: Optical Probe of Competing Orders |
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Sponsoring Units: DCMP Chair: Xiao-Jia Chen, Carnegie Institution of Washington Room: 344 |
Monday, March 18, 2013 2:30PM - 2:42PM |
C36.00001: Pump-probe reflectivity study of competing orders in the electron doped cuprate superconductor Nd$_{2-x}$Ce$_{x}$CuO$_{4+?}$ J.P. Hinton, J.D. Koralek, G. Yu, E.M. Motoyama, Y.M. Lu, A. Vishwanath, M. Greven, J. Orenstein We study the electron doped cuprate superconductor Nd$_{2-x}$Ce$_{x}$CuO$_{4+?}$ using optical pump-probe spectroscopy over a range of dopings including both superconducting and underdoped antiferromagnetic samples. We focus on the pseudogap (PG) response, which is observed over the entire doping range, and its interaction with superconductivity (SC). The PG response onsets below values of $T^*$ consistent with other probes, and its time dependence exhibits scaling consistent with critical fluctuations in samples near optimal doping. Furthermore, we observe laser fluence-dependent interaction between the PG and SC responses below $T_c$, indicative of a repulsive interaction between superconductivity and another fluctuating order. [Preview Abstract] |
Monday, March 18, 2013 2:42PM - 2:54PM |
C36.00002: Fluctuating charge density waves in a cuprate superconductor Fahad Mahmood, Darius Torchinsky, Anthony Bollinger, Ivan Bozovic, Nuh Gedik Cuprate compounds that host high-temperature superconductivity also exhibit various forms of charge and/or spin ordering whose role in the complex cuprate phase diagram is not fully understood. Static charge-density wave (CDW) ordering has been detected so far by diffraction probes only for special doping or in an applied external field. However, dynamic (fluctuating) CDWs may also be present more broadly while being difficult to detect by conventional techniques. To observe and characterize fluctuating CDWs in cuprates, and determine whether they favor or compete with HTS, is thus an important open problem. Here, we present a new method, based on ultrafast spectroscopy, to detect the presence and measure the lifetime of CDW fluctuations in cuprates. In an underdoped La$_{1.9}$Sr$_{0.1}$CuO$_{4}$ film (Tc $=$ 26 K), we observe collective excitations of CDW that persist up to 100 K. This CDW is dynamic; it fluctuates with a characteristic lifetime of 2 ps at T $=$ 5 K which decreases to 0.5 ps at T $=$ 100 K. In contrast, in an optimally doped La$_{1.84}$Sr$_{0.16}$CuO$_{4}$ film (Tc $=$ 38.5 K), we see no signatures of fluctuating CDW at any temperature, favoring the competition scenario. This work opens a path towards a broad study of fluctuating order parameters in various superconductors and other materials. [Preview Abstract] |
Monday, March 18, 2013 2:54PM - 3:06PM |
C36.00003: Modified electron-boson coupling in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ nanocrystals Luke Sandilands, Zhijun Xu, Alina Yang, Genda Gu, Tor Pedersen, Ferenc Borondics, Kenneth Burch The coupling between electrons and bosons is thought to underlie a variety of unusual behavior in the cuprates. Here we present optical evidence that the electron-boson coupling is strongly modified in mechanically-exfoliated Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ nanocrystals. Through an extended Drude analysis of the mid-infrared optical conductivity, we demonstrate that the electron-boson spectral function is blue-shifted and enhanced in thin Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ nanocrystals. Taken together with complementary Raman and Laue diffraction data, our results provide further evidence that the bosons relevant to the electrodynamics of the normal state are magnetic. [Preview Abstract] |
Monday, March 18, 2013 3:06PM - 3:18PM |
C36.00004: Effect of out-of-plane disorder on electronic Raman spectra of Bi2212 single crystals Takahiko Masui, Naoki Murai, Motoyuki Ishikado, Shigeyuki Ishida, Hiroshi Eisaki, Shin-ichi Uchida, Setsuko Tajima Out-of plane disorder in cuprate superconductor is known to suppress Tc without serious increase of residual scattering of conduction carriers. This is quite advantageous for spectroscopic measurements. In this study we have measured electronic Raman spectra of optimally-doped Bi2212 single crystals with different degree of out-of plane disorders. In the superconducting state, the B1g electronic Raman spectra, which detect maximum of d-wave superconducting gap, show coherence peaks. Interestingly, the peak energies are independent of Tc for lower Tc samples. On the other hand, the peak position for a higher Tc sample shifts to higher energy. This is clear contrast with the B2g electronic Raman spectra, which detect nodal region of the superconducting gap. The strange polarization dependence of superconducting Raman spectra could be a clue to understand the doping dependence of the superconducting Raman responses in cuprates. [Preview Abstract] |
Monday, March 18, 2013 3:18PM - 3:30PM |
C36.00005: Optical scattering rate and effective mass throughout the phase diagram of Bi$_2$Sr$_{2-x}$La$_x$CuO$_6$ R.P.S.M. Lobo, Y.M. Dai, H.H. Wen, P. Cheng, H.Q. Luo, B. Xu, X.G. Qiu We determined the optical conductivity of Bi$_2$Sr$_{2-x}$La$_x$CuO$_6$ at dopings covering the phase diagram from the underdoped to the overdoped regimes. The frequency dependent scattering rate shows a pseudogap extending into the overdoped regime. We found that the effective mass enhancement calculated from the optical conductivity is constant throughout the phase diagram. Conversely, the effective optical charge density varies almost linearly with doping. Our results suggest that the low frequency electrodynamics of Bi$_2$Sr$_{2-x}$La$_x$CuO$_6$ is not strongly affected by the long range Mott transition. [Y.M. Dai \textit{et al.}, Phys. Rev. B \textbf{85}, 092504 (2012)]. [Preview Abstract] |
Monday, March 18, 2013 3:30PM - 3:42PM |
C36.00006: Microwave conductivity survey of YBa$_2$Cu$_3$O$_{6+x}$: from underdoped to overdoped Jordan Baglo, James Day, Pinder Dosanjh, Ruixing Liang, Walter Hardy, Doug Bonn Recent experimental results and theoretical proposals suggest significant changes in the electronic structure of the high-$T_c$ cuprate superconductors as one approaches optimal doping, including Fermi surface reconstruction associated with proposed electronic ordering transitions. As sensitive probes of the low-energy electrodynamics, microwave surface resistance and penetration depth measurements - from which the real and imaginary parts of the microwave conductivity may be extracted - are well-suited for investigating such changes in the electronic structure of the cuprates across their phase diagram. Here we present preliminary results of a detailed and systematic doping dependence study of the microwave conductivity of the cuprate superconductor YBa$_2$Cu$_3$O$_{6+x}$ from the underdoped to the overdoped regime. The implications of these results for various proposed scenarios will be discussed. [Preview Abstract] |
Monday, March 18, 2013 3:42PM - 3:54PM |
C36.00007: Disentangling the in- and out-of-plane components of the microwave surface resistance in Tl-2201 S. Mahyad Aghigh, James Day, Jordan Baglo, Darren Peets, Ludivine Chauviere, Pinder Dosanjh, Ruixing Liang, Walter Hardy, Doug Bonn Investigation of Tl$_{2}$Ba$_{2}$Cu$_{1}$O$_{x}$ (Tl-2201) properties is important as it provides access to the overdoped side of the superconducting dome. We are measuring the surface resistance of Tl-2201, R$_{s}$($\omega$,T), using a bolometric technique well established by our group. Experimentally separating the in- and out-of-plane components of R$_{s}$ for Tl-2201, however, is challenging due to demagnetization effects. To account for this complication, we are measuring R$_{s}$ of an isotropic replica sample of NbZr in two specific orientations where the field is parallel and perpendicular to the crystal plane. In this talk I will describe the modified bolometric technique, share the technical difficulties encountered in preparing the replica, and present the most up-to-date results. [Preview Abstract] |
Monday, March 18, 2013 3:54PM - 4:06PM |
C36.00008: Ion-size effects in HTS cuprates - superfluid density and energy gaps Benjamin Mallett, Christian Bernhard, Thomas Wolf, Edi Gilioli, Jeff Tallon The demonstrated central role that ion size plays in determining $T_c$ in the HTS cuprates needs to be further explored in order to determine whether the demonstrated systematic behaviour plays out in other superconducting properties. After all, $T_c$ can be diminished simply by disorder effects. What is the effect of systematic ion-size variation on the superfluid density and superconducting energy gap? And can these effects be used to infer details concerning the pairing mechanism? To address these issues we report the effect of changing ion size on muon spin relaxation measurements of the superfluid density and Raman measurements of the superconducting gap in the model system RA$_2$Cu$_3$O$_y$ (where R = La,..., Lu and A=Ba$_{2-x}$Sr$_x$). The electronic density of states is determined from the effect of Zn substitution in this system and we are able to discount disorder scattering as the source of the systematic changes in superconducting properties. Our results confirm a picture where the polarizability of the charge-reservoir layer plays a key role in setting the energy scale for pairing in this system. [Preview Abstract] |
Monday, March 18, 2013 4:06PM - 4:18PM |
C36.00009: New insights into the phase diagram of the copper oxide superconductors from electronic Raman scattering Alain Sacuto, Siham Benhabib, Yann Gallais, Maximilien cazayous, Marie-Aude Measson, Sebastien Blanc, Genda Gu, Dorothee Colson We explore the cuprate phase diagram by electronic Raman spectroscopy and shed light on the superconducting state in hole doped cuprates. Namely, how superconductivity is impacted by the pseudogap. [Preview Abstract] |
Monday, March 18, 2013 4:18PM - 4:30PM |
C36.00010: Ion-size effects in HTS cuprates -- dielectric versus magnetic pairing Jeffery Tallon, Ben Mallett, Neil Ashcroft We have been exploring the systematic effects of changing ion size on superconducting and normal-state properties of the HTS cuprates. In the model system RA$_{2}$Cu$_{3}$O$_{\mathrm{y}}$ (where R $=$ La,\textellipsis , Lu and A$=$Ba$_{\mathrm{2-x}}$Sr$_{\mathrm{x}})$ the maximum T$_{\mathrm{c}}$ in the dome-shaped phase curve can be shifted from 70 to 110 K in the model system. Surprisingly T$_{\mathrm{c}}$ correlates with the dielectric properties and not the magnetic properties. This highlights the fundamental importance of charge fluctuation and dielectric screening in the cuprates and may signal a novel pairing mechanism having its origin with quantized waves of electronic polarization. [Preview Abstract] |
Monday, March 18, 2013 4:30PM - 4:42PM |
C36.00011: Berry phase mechanism for polarization rotation in chiral metals Joseph Orenstein, Joel Moore There is currently considerable interest in inversion symmetry breaking in unconventional metals, particularly in chiral stacking of atomic layers with stripe-like charge density modulation in systems such as TiSe2 and the cuprate superconductor LBCO. A signature of broken chiral symmetry is optical gyrotropy, that is, different indices of refraction for left and right circular polarized light. In this talk we show that intraband gyrotropic response is a consequence of the anomalous velocity associated with the non-zero Berry curvature and we derive its strength for a model band structure as a function of the chiral order parameter. This work demonstrates that optical gyrotropy in chiral metals is the linear response counterpart to the anomalous Hall effect in time-reversal breaking metals. [Preview Abstract] |
Monday, March 18, 2013 4:42PM - 4:54PM |
C36.00012: Faraday and Kerr Effect Measurements of Cuprates in THz Regime Y. Lubashevsky, LiDong Pan, T. Kirzhner, G. Koren, N.P. Armitage Recent results using a laser-based zero-area loop Sagnac interferometer have found a small but significant spontaneous Kerr rotation [1] suggesting an emergent chiral or time-reversal broken character to the pseudogap regime in the cuprate superconductors. In this work, we have performed high resolution THz polarimetry to measure the low frequency Faraday and Kerr rotation in these compounds. The THz range gives an advantage for these studies as it presumably corresponds more closely to frequency scales relevant for the pseudogap (1 THz - 48 K). We have found that low frequencies enhances the signal into the tens of milli-radians range. Moreover, time-domain THz spectroscopy reveals more information about this phenomena as frequency dependent and birefringent effects among others can be measured. Results from YBCO and LBCO will be presented. \\[4pt] [1] J. Xia etal, Phys. Rev. Lett. 100, 127002 (2008). [Preview Abstract] |
Monday, March 18, 2013 4:54PM - 5:06PM |
C36.00013: Elastic moduli across the superconducting and pseudogap phase boundaries in four cuprate compounds Brad Ramshaw, Arkady Shekhter, Jon Betts, Albert Migliori A detailed understanding of the physics of the cuprate superconductors relies on an experimental determination of the thermodynamic phase diagram. Resonant ultrasound spectroscopy (RUS) is a unique thermodynamic probe, capable of measuring part per million changes in elastic moduli, and has access to symmetry information. Here we present a symmetry analysis of changes in the elastic moduli across the superconducting and psedogap phase boundaries in several classes of cuprates: YBCO, LSCO, Hg-1201, and Tl-2201. [Preview Abstract] |
Monday, March 18, 2013 5:06PM - 5:18PM |
C36.00014: Quantum Fluctuations of Superconductivity in Critically Underdoped La$_{2-x}$Sr$_x$CuO$_4$ N.P. Armitage, Y. Lubashevsky, L.S. Bilbro, R.V. Aguilar, G. Logvenov, I. Bozovic In the underdoped pseudogap regime of the high-temperature superconductors, one expects that due to low superfluid densities and short correlation lengths, superconducting fluctuations will be very significant for transport and thermodynamic properties. We have used THz time-domain spectroscopy (TTDS) to probe the fluctuations of superconductivity in extremely underdoped La$_{2-x}$Sr$_x$CuO$_4$ films close to and beyond the superconducting quantum critical point. On the approach to the transition from above, we find a significant range of quantum superconducting fluctuations that we quantify through a comparison of the low and high frequency phase stiffnesses. An explicit measure of these fluctuations through the quantity we propose as a ``quantum Debye-Waller factor'' shows that these fluctuations diverge and drive the transition. [Preview Abstract] |
Monday, March 18, 2013 5:18PM - 5:30PM |
C36.00015: Feedback effect on high-energy magnetic excitations in the model high-temperature superconductor {HgBa$_2$CuO$_{4+\delta}$} Yuan Li, M. Le Tacon, M. Bakr, D. Terrade, D. Manske, R. Hackl, L. Ji, M.K. Chan, N. Barisic, X. Zhao, M. Greven, B. Keimer Magnetic excitations might play an important role in the superconducting mechanism in the cuprates. Their contribution below $\sim$60 meV is manifested by the generic neutron ``resonance'' feature, which signifies a feedback effect of pairing on the magnetic excitations. However, the spectral weight of the resonance is insufficient to explain the high superconducting temperature ($T_c$). Recent research has demonstrated that intense magnetic excitations exist above 100 meV up to high doping, but it remains unknown whether and how these excitations participate in the pairing mechanism. Here we present a systematic electronic Raman scattering study of the model cuprate superconductor HgBa$_2$CuO$_{4+\delta}$. In an overdoped sample upon cooling below $T_c$, we observe a pronounced enhancement of a high-energy peak related to two-magnon excitations in insulating cuprates, which is accompanied by the opening of the superconducting gap and can be understood as a high-energy feedback effect that implies a direct involvement of high-energy magnetic excitations in the Cooper pairing. The effect occurs already above $T_c$ in two underdoped samples, demonstrating a related feedback mechanism associated with the pseudogap. [Preview Abstract] |
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