Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session S6: Superfluid Density in Underdoped Cuprates |
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Sponsoring Units: DCMP Chair: Mohit Randeria, Ohio State University Room: Morial Convention Center RO4 |
Wednesday, March 12, 2008 2:30PM - 3:06PM |
S6.00001: Quantum critical behavior in the superfluid density of strongly underdoped ultrathin copper oxide films Invited Speaker: The relationship between transition temperatures T$_{C}$ and superfluid densities n$_{S}$(0) of cuprate superconductors has been a central issue in cuprate superconductivity from the beginning. When mobile holes are removed from optimally doped CuO$_{2}$ planes, T$_{C}$ and n$_{S}$(0) decrease in a surprisingly correlated fashion. Recent measurements of the superfluid density of strongly underdoped YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ films and crystals have found a square-root scaling, T$_{C} \propto$ n$_{S}$(0)$^{\alpha}$ where $\alpha \approx$ $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$}$, which supplants the approximately linear proportionality that had been deduced long ago from less underdoped samples by Uemura et al. and had been ascribed to the quasi-2D structure of cuprates. This situation leads back to a basic question -- what is the behavior of the fundamental structural unit, namely, a single CuO$_{2}$ layer or bilayer, which is truly two-dimensional by construction? To address this question, we studied 2D samples near the critical doping level where superconductivity disappears. We measured n$_{S}$(T) in films of Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ as thin as two CuO$_{2}$ bilayers. T$_{C}$'s were as low as 3 K. We observed the 2D Kosterlitz--Thouless--Berezinski drop in n$_{S}$ at T$_{C}$, and we recovered the linear scaling T$_{C} \propto $ n$_{S}$(0) expected in 2D due to fluctuations in the phase of the superconducting order parameter. Taken together, results on 3D and 2D samples suggest that the disappearance of superconductivity with underdoping is ultimately due to quantum fluctuations near a quantum critical point. [Preview Abstract] |
Wednesday, March 12, 2008 3:06PM - 3:42PM |
S6.00002: Superfluid density in the underdoped cuprates Invited Speaker: |
Wednesday, March 12, 2008 3:42PM - 4:18PM |
S6.00003: Two energy scales and the nodal-antinodal dichotomy in underdoped superconducting cuprates Invited Speaker: Recent electronic Raman scattering experiments on hole-doped cuprates in the underdoped regime reveal that nodal and antinodal regions behave in very different manners. I will present the conclusions of a theoretical analysis of these experiments, based on a new sum-rule, and on Fermi liquid and phenomenological considerations, which lead to the conclusion that the superconducting state involves a hitherto hidden energy scale, which has the same doping-dependence than the superconducting transition temperature, in contrast to the pseudogap energy scale. The low-frequency Raman response and the temperature-dependence of the superfluid density, both controlled by nodal excitations, are shown to behave in a qualitatively similar manner, which puts strong constraints on microscopic theories of the cuprates. For a reference and list of collaborators on this work, see: M. Le Tacon et al., Nature Physics, 2, 537 (2006). [Preview Abstract] |
Wednesday, March 12, 2008 4:18PM - 4:54PM |
S6.00004: Algebraic charge liquids and the underdoped cuprates Invited Speaker: We describe a possible theoretical route for the evolution with doping of an antiferromagnetic Mott insulator into a gapless d-wave superconductor. Central to this description are ``algebraic charge liquids'' with power law correlations of gapless, spinless, charge e fermions. Based on this understanding a specific theory of the underdoped cuprates that naturally explains a number of puzzling phenomena including the doping and temperature dependence of the superfluid density, the photoemission spectra, and Shubnikov-de Haas oscillations is proposed. Experiments to test the theory are suggested. [Preview Abstract] |
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