Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session B10: Gaps, Pseudogaps and Fermi Surfaces in Cuprates |
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Sponsoring Units: DCMP Chair: Laura Greene, University of Illinois at Urbana Champaign Room: Morial Convention Center RO8 |
Monday, March 10, 2008 11:15AM - 11:27AM |
B10.00001: Revealing pseudogap physics using lanthanide substituted Bi$_{2}$Sr$_{1.6}$Ln$_{0.4}$CuO$_{6+\delta}$ Daniel Garcia, Jeff Graf, Chris Jozwiak, Shuyun Zhou, Hiroshi Eisaki, Alessandra Lanzara Towards understanding the physics of the high-temperature superconducting cuprates, there has been growing interest in the role lattice strain plays between the copper oxide planes. We have examined Bi$_{2}$Sr$_{1.6}$Ln$_{0.4}$CuO$_{6+\delta}$ (Ln=La, Nd, Eu, Bi) near optimal doping using angle resolved photoemission spectroscopy. The increasing radius mismatch of the substituted lanthanide, which monotonically decreases the superconducting Tc, appears to also affect the electronic properties of these system. The effect of strain on Fermi arcs, superconducting gap and pseudogap physics will be discussed. [Preview Abstract] |
Monday, March 10, 2008 11:27AM - 11:39AM |
B10.00002: A Laser Based ARPES Study of the Nodal Region of the Cuprates J.D. Rameau, H.-B. Yang, G.D. Gu, P.D. Johnson A new laser based facility has been constructed at the NSLS for studies of strongly correlated electron systems. While recent studies of the nodal and near-nodal spectrum of the cuprates with low energy lasers appear to show good agreement with higher energy, synchrotron based ARPES, several adverse effects of performing ARPES with lasers remain to be explored. Using the new facility we show that the combination of high emission angles and low electron kinetic energies has many implications for the accurate measurement of any linewidth or band dispersion. We show that this is particularly so for the nodal and near-nodal single particle spectrum of the cuprates. The results and implications of our studies for future laser based ARPES are analyzed and discussed. [Preview Abstract] |
Monday, March 10, 2008 11:39AM - 11:51AM |
B10.00003: Evidence for pairing above Tc from the electronic dispersion in the pseudogap phase of cuprates A. Kanigel, U. Chatterjee, M. Randeria, M.R. Norman, J.C. Campuzano In the BCS paradigm for the superconducting state, electrons close to the Fermi level $E_{F}$ form Cooper pairs which condense into a zero center of mass momentum state. This results in a gap in the electronic excitation spectrum which is symmetrically centered about $E_{F}$. Above $T_{c}$ where the condensate is lost, the pairs dissociate, the energy gap collapses, and the the normal state Fermi surface appears. On the other hand, in the underdoped high temperature superconductors, instead of a complete Fermi surface above $T_{c}$, only disconnected Fermi arcs appear, separated by regions that still exhibit an energy (pseudo)gap. We show that in this pseudogap phase, the energy-momentum relation of electronic excitations near $E_{F}$ behaves like the dispersion of a normal metal on the Fermi arcs, but like that of a superconductor in the gapped regions. We argue that this dichotomy in the dispersion is hard to reconcile with a competing order parameter, but is consistent with pairing without condensation. Below $T_{c}$ the pairs condense and the electronic excitations, that were short-lived above $T_{c}$, become long-lived and exhibit a d-wave energy gap. [Preview Abstract] |
Monday, March 10, 2008 11:51AM - 12:03PM |
B10.00004: Possible Explanation of the Fermi Arcs in Cuprates, based on a clustered superconducting state above Tc Gonzalo Alvarez, Elbio Dagotto A previously introduced Landau-Ginzburg model [1] to describe the competition between antiferromagnetism and d-wave superconductivity in the cuprates is here further investigated. The state above the critical temperature Tc is made of superconducting (SC) clusters, with a nonzero amplitude of the SC order parameter but random phase factors, coexisting with antiferromagnetic(AF) regions. This state disappears above a higher temperature scale T*. The LDOS of this state is in good agreement with recent STM experiments [2]. Our main result is that the angle-resolved photoemission spectrum of this SC-AF clustered state contains Fermi surface arcs in the region Tc$<$T$<$T*, very similar to those observed experimentally [3]. Low energy states created at the interface between clusters are responsible for the arcs. [1] G. Alvarez et al., Phys. Rev. B 71, 014514 (2005). [2] K. K. Gomes et al., Nature 447, 569 (2007). [3] A. Kanigel et al., cond-mat/0708.4099 (2007). [Preview Abstract] |
Monday, March 10, 2008 12:03PM - 12:15PM |
B10.00005: Understanding the Protected Nodes and the Fermi Arcs in the Cuprate Superconductors Qijin Chen, K. Levin We address a recent analysis of photoemission data which elucidates the superconducting phase of the underdoped cuprates. We first present a simple phenomenological approach to the spectral function which shows how the $d$-wave order parameter symmetry results in protected nodes, which, above $T_c$ broaden into Fermi arcs; this ``protection'' is associated with superconducting coherence rather than reduced thermal broadening. A microscopic theory, consistent with this phenomenology, is presented. It reconciles the observations that the excitation gap below $T_c$ is temperature independent while the superfluid density necessarily vanishes at $T_c$. \\ Reference: Q.J. Chen, K. Levin, and I. Kosztin, Phys. Rev. B \textbf{63}, 184519 (2001). [Preview Abstract] |
Monday, March 10, 2008 12:15PM - 12:27PM |
B10.00006: Pseudogap correlations inside the superconducting dome Elena Bascones, Belen Valenzuela Recent experiments[1,2] have uncovered, two energy scales, an antinodal energy scale and a nodal one in the superconducting phase of underdoped hole doped cuprates. This finding reminds the nodal-antinodal dichotomy seen in the pseudogap state. The competing Yang-Rice-Zhang[3] scenario for the pseudogap has shown to be useful to understand these experiments[4]. Here we explore the effect of the competition between pseudogap and superconductivity on the condensation energy and superfluid density which show deviations from the standard BCS behavior. We compare the theoretical results with experiments. \newline [1] M. Le Tacon et al., Natur. Phys. 2, 537 (2006). [2] J. Mesot et al., Phys. Rev. Lett. 83, 840 (1999) K. Tanaka et al. Science 314, 1910 (2006); T. Kondo et al. Phys. Rev. Lett. {\bf 98}, 297004 (2007). [3] K-Y Yang, T.M. Rice and F-C Zhang, Phys. Rev. B 73, 174501 (2006). [4] B. Valenzuela and E. Bascones, Phys. Rev. Lett {\bf 98}, 227002 (2007). [Preview Abstract] |
Monday, March 10, 2008 12:27PM - 12:39PM |
B10.00007: Pseudogap and Superconducting Gap - Same or Different? W.S. Lee, I.M. Vishik, K. Tanaka, R. Moore, D.H. Lu, T. Sasagawa, N. Nagaosa, T.P. Devereaux, Z. Hussain, Z.X. Shen The pseudogap state in underdoped cuprates has been one of the central questions in high-$T_{C}$ research. Recently, whether pseudogap and supercondicting gap are same energy gap or two different energy scales is strongly debated in data interpretation of single-particle spectrum, such as ARPES and STM. To gain further insight into this issue, detailed doping dependence and temperature dependence of the gap were studied using ARPES. In contrast to the behavior of the well-known pseudogap in the antinodal region, we found that the behavior of the gap is qualitatively different near the nodal region, a momentum space region overlooked in the previous measurements. This gap seems closely related to the superconductivity; it opens up at $T_{C}$ and reduces with decreasing doping in the deeply underdoped region following the trend of the superconducting dome in the heavily underdoped region of the phase diagram. The emerging two-gap phenomenon points to a picture of richer quantum configurations in high-$T_{C}$ superconductors. [Preview Abstract] |
Monday, March 10, 2008 12:39PM - 12:51PM |
B10.00008: Different temperature evolution of electronic states in superconducting state and normal state in underdoped Bi2212 high-Tc superconductor Kiyoshisa Tanaka, W.S. Lee, D.H. Lu, R. Moore, T. Sasagawa, Z. Hussain, Z.-X. Shen One of the most mysterious issues in high-Tc superconductor is an energy gap called ``pseudogap'' well above Tc, which exists over a wide region of compositions and temperatures. The origin of this pseudogap and its relation to the superconducting gap are believed to hold the key for understanding the mechanism of high-Tc superconductivity. Recent angle-resolved photoemission spectroscopy (ARPES) revealed the coexistence of two distinct energy gaps in heavily underdoped samples which have opposite doping dependence [1]. One gap can be assigned as pseudogap and the other gap as superconducting gap because of the positive correlation between the gap magnitude and Tc. This result suggests that pseudogap arises from another mechanism and gives profound implications on the mechanism of high-Tc superconductivity. More recently, this two gap feature has been observed in the temperature dependence even in near optimally doped samples [2]. Detailed temperature dependence of ARPES spectra will be shown and the special character of pseudogap state will be discussed. [1] K. Tanaka et al., Science, 314, 1910 (2006). [2] W.S. Lee et al., Nature, 450, 81 (2007). [Preview Abstract] |
Monday, March 10, 2008 12:51PM - 1:03PM |
B10.00009: Temperature and doping dependent ARPES study of the gaps in Bi2212 H.-B. Yang, J.D. Rameau, P.D. Johnson, T. Valla, G.D. Gu, A.T. Tsvelik High-resolution angle-resolved photoemission (ARPES) is used to probe the development of the gaps around the Fermi surface in Bi2212. A new method of data analysis is presented to remove the complications associated with the experimental resolution. Normalizing by the Fermi function then allows the observation of both the occupied and unoccupied states. The results on the temperature and doping dependence of the gap show that the underdoped system in the normal state behaves differently from all region of the phase diagram in the superconducting state, and point to potentially different origins for the pseudogap. [Preview Abstract] |
Monday, March 10, 2008 1:03PM - 1:15PM |
B10.00010: Fermi arcs and phase diagram of the high-T$_{c}$ cuprates: Insights from Raman and angle resolved photoemission spectroscopies. James Storey, Jeffery Tallon, Grant Williams We calculate the B$_{1g}$ and B$_{2g}$ Raman responses of Bi-2212 from an ARPES-derived energy momentum dispersion and a model for the normal-state pseudogap. In light of these calculations, the Raman data demonstrates that the Fermi arc length remains finite in the pseudogap ground state. A re-examination of recent ARPES results is found to confirm this result. In addition, the presence of a van Hove singularity in the overdoped regime, as revealed by ARPES, allows us to propose a universal pairing potential that reproduces both the doping dependence of T$_{c}$, as well as the variation in T$_{c,max}$ between different species of cuprate superconductors. [Preview Abstract] |
Monday, March 10, 2008 1:15PM - 1:27PM |
B10.00011: Hall Effect Signature of Fermi Surface Reconstruction in High-$T_{c}$ Superconductors F.F. Balakirev, J.B. Betts, A. Migliori, I. Tsukada, Yoichi Ando, G.S. Boebinger The doping dependence of the Hall number in the normal state of two different HTS systems, La$_{2-x}$Sr$_{x}$CuO$_{4}$ and Bi$_{2}$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta }$, exhibits an anomalous peak at optimum doping that emerges only at low temperatures. With increasing hole doping, as the pseudogap energy scale decreases, the peak onset is ascribed to the emergence of electron-like Fermi pockets in the Brillouin zone. The destruction of the peak beyond optimum doping suggests the destruction of the electron pockets and emergence of a large hole pocket, two phenomena that would result simultaneously with the loss of the Brillouin zone folding associated with the pseudogap state. The low temperature Hall resistance thus elucidates the Fermi surface evolution in the HTS cuprates, characterized by a zero temperature phase transition upon collapse of the pseudogap near optimum doping. [Preview Abstract] |
Monday, March 10, 2008 1:27PM - 1:39PM |
B10.00012: Energy gaps in failed superconductor La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ R.-H. He, K. Tanaka, S.-K. Mo, T. Sasagawa, M. Fujita, N. Mannella, K. Yamada, Z. Hussain, Z.-X. Shen By angle-resolved photoemission spectroscopy with improved energy and momentum resolution, we find in the normal state of La$_{2-x}$Ba$_{x}$CuO$_{4}$ x = 1/8 a strong existence of the nodal quasi-particle together with a $d$-wave energy gap along the underlying Fermi surface extending over a significant range in the momentum space before an abrupt take-off of the gap close to the antinodal region. This suggests the presence of a novel nodal metal state, which is different from the one proposed that assumes a single $d$-wave extension of the pseudogap from the antinode toward the node along the whole underlying Fermi surface. This state is compatible with the static stripe ordering but only involves a precursor pairing of the electrons away from the antinodal region. We argue that the traditional pseudogap defined exclusively for the antinodal states has a distinct origin than its new nodal counterpart, i.e., a $d$-wave gap above T$_{c}$. Moreover, this normal state gap function is found to be quantitatively very similar with those of La$_{2-x}$Sr$_{x}$CuO$_{4}$ x$\sim $1/8 (T$_{c}<<$4K) in the superconducting state, pointing to a universal doping dependence of the pairing strength for La-based cuprates, which also highlights the inherent lack of a global phase coherence in La$_{2-x}$Ba$_{x}$CuO$_{4}$ x = 1/8 that makes it a failed superconductor. [Preview Abstract] |
Monday, March 10, 2008 1:39PM - 1:51PM |
B10.00013: Quantum Oscillations in the mixed state of d-wave superconductors Ashot Melikyan, Oskar Vafek We show that the low-energy density of quasiparticle states in the mixed state of ultra-clean $d$-wave superconductors is characterized by pronounced quantum oscillations in the regime where the cyclotron frequency $\hbar\omega_c\ll \Delta_0$, the $d-$wave pairing gap. Such oscillations as a function of magnetic field $B$ are argued to be due to the internodal scattering of the $d$-wave quasiparticles near wavevectors $(\pm k_D,\pm k_D)$ by the vortex lattice as well as their Zeeman coupling. The periodicity of the oscillations is set by the condition $k_D [hc/(eB)]^{1/2} \equiv k_D' [hc/(eB')]^{1/2}\pmod {2\pi}$. We find that there is additional structure within each period which grows in complexity as the Dirac node anisotropy increases. [Preview Abstract] |
Monday, March 10, 2008 1:51PM - 2:03PM |
B10.00014: Quantum Oscillations in the Underdoped Cuprate YBa$_{2}$Cu$_{4}$O$_{8}$ Edward Yelland, John Singleton, Chuck Mielke, Neil Harrison, Fedor Balakirev, Bogdan Dabrowski, Marcin Matusiak, John Cooper The quantum oscillations (QOs) seen in the underdoped cuprate superconductor YBa$_{2}$Cu$_{4}$O$_{8}$ (Y124) in magnetic fields up to $B$=85T [1] are strong evidence for a well-defined Fermi surface (FS) in Y124 at low temperature $T$ and high $B$. The QO frequency $F$=660$\pm $15T, implies a FS pocket with 2.4{\%} of the full Brillouin zone (BZ) area. Taken with earlier work [2], our data suggest FS pockets are generic to underdoped CuO$_{2}$ planes and give the first hint of doping dependence of the FS. We discuss the carrier concentration implied by the QOs within various models. Comparison of the T-linear specific heat $\gamma $ (from QO quasiparticle mass m*) to $\gamma $ estimated from zero-field specific heat measurements constrains the number of FS pockets present in the BZ and supports a reduced BZ due e.g. to a charge/spin density wave or ordered orbital currents. [1] E. A. Yelland et al, arXiv:0707.0057. [2] N. Doiron-Leyraud et al, Nature 446, 565 (2007) [Preview Abstract] |
Monday, March 10, 2008 2:03PM - 2:15PM |
B10.00015: Fermi surface pockets in the underdoped cuprate YBa$_{2}$Cu$_{4}$O$_{8}$, - are they present in low magnetic fields? J. R. Cooper, M. Matusiak, J. W. Loram, E. A. Yelland, B. Dabrowski The observations of quantum oscillations in the underdoped cuprate superconductors, ortho-II YBa$_{2}$Cu$_{3}$O$_{6.5}$ [1] and YBa$_{2}$Cu$_{4}$O$_{8}$ (Y124) [2] at very high magnetic fields and low temperatures could lead to improved understanding of cuprate superconductivity. This will be especially true if the small Fermi surface (FS) pockets are still present at higher temperatures and lower magnetic fields. As pointed out in ref. [2] the pockets appear to have low Fermi energies $\sim $ 300 K, and could therefore give rise to T-dependent magnetic anisotropy in the normal state associated with Landau-Peierls diamagnetism. We report susceptibility anisotropy data for Y124 crystals up to 300 K, and discuss whether these data and zero field heat capacity data, are consistent with the properties of the FS pockets obtained from high field measurements. [1] N. Doiron-Leyraud, et al., Nature 447,565 (2007) [2] E.A. Yelland et al. arXiv:cond-mat/07070057. [Preview Abstract] |
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