Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session G2: Quantum Criticality in Cuprates |
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Sponsoring Units: DCMP Chair: Lia Krusin-Elbaum, IBM Room: Baltimore Convention Center Ballroom III |
Tuesday, March 14, 2006 8:00AM - 8:36AM |
G2.00001: Breakdown of One-Paramater Scaling in Quantum Critical Scenarios for the High-Temperature Copper-oxide Superconductors Invited Speaker: We show that if the excitations which become gapless at a quantum critical point also carry the electrical current, then a resistivity linear in temperature, as is observed in the copper-oxide high-temperature superconductors, obtains only if the dynamical exponent, z, satisfies the unphysical constraint, z<0. At fault here is the universal scaling hypothesis that, at a continuous phase transition, the only relevant length scale is the correlation length. Consequently, either the electrical current in the normal state of the cuprates is carried by degrees of freedom which do not undergo a quantum phase transition, or quantum critical scenarios must forgo this basic scaling hypothesis and demand that more than a single correlation length scale is necessary to model transport in the cuprates.\newline \newline In collaboration with Philip Phillips, Univ. of Illinois at Urbana-Champaign. [Preview Abstract] |
Tuesday, March 14, 2006 8:36AM - 9:12AM |
G2.00002: Evidence for a generic quantum transition in high-Tc cuprates. Invited Speaker: The progressive evolution of physical properties with doping in the high-Tc cuprates remains a puzzle, as does the origins of superconducting pairing. This talk will focus on a broad range of physical properties that all signal the presence of a generic quantum transition near optimal doping in these materials which helps explain this unusual evolution in properties. The data includes specific heat, NMR, transport, muon spin relaxation, inelastic neutron scattering, frequency dependent IR conductivity and magnetic properties. In spite of the weight of evidence, however, some key elements appear to be missing. Reasons for this will be surveyed. [Preview Abstract] |
Tuesday, March 14, 2006 9:12AM - 9:48AM |
G2.00003: Pseudogap scaling and quantum critical end point in electron- and hole-doped cuprates Invited Speaker: In spite of a large number of experiments on the anomalous pseudogap in cuprate superconductors, the real phase diagram of the pseudogap has not yet been established. We employ the interlayer tunneling transport to precisely detect the field dependence of low-energy density of states (DOS) in hole-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ and electron-doped Sm$_{2-x}$Ce$_x$CuO$_{4-\delta}$ crystals under high fields up to 60 T [1-4]. From a systematic analysis of negative interlayer magnetoresistance, we found a strong doping dependence of the pseudogap closing field whose Zeeman energy scales with the pseudogap energy scale, indicating a preeminent role of spin-singlet correlations in forming the pseudogap in cuprates. The results suggest no quantum critical point up to very overdoped side of the phase diagram. \newline \newline [1] T. Shibauchi {\it et al.}, Phys. Rev. Lett. {\bf 86}, 5763 (2001).\newline [2] T. Shibauchi {\it et al.}, Phys. Rev. B {\bf 67}, 064514 (2003).\newline [3] L. Krusin-Elbaum, T. Shibauchi, and C. H. Mielke, Phys. Rev. Lett. {\bf 92}, 097005 (2004).\newline [4] T. Kawakami {\it et al.}, Phys. Rev. Lett. {\bf 95}, 017001 (2005). [Preview Abstract] |
Tuesday, March 14, 2006 9:48AM - 10:24AM |
G2.00004: Field-induced magnetism in a high-temperature superconductor Invited Speaker: Many physical properties of the high-temperature (high-$T_{c}$) superconductors are two-dimensional phenomena derived from their square planar CuO$_{2}$ building blocks. This is especially true of the magnetism from the copper ions electronically connected to each other via the $p$-orbitals of intervening oxygen atoms. As mobile charge carriers enter these CuO$_{2}$ layers, the antiferromagnetism of the parent insulators, where each copper spin is antiparallel to its nearest neighbours, evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge carrier densities, the quantum fluctuations are sufficiently suppressed to yield static long-period order and external magnetic fields also induce such order. Here we show, using neutron scattering measurements, that in contrast to the chemically-controlled order in superconducting La$_{2-x}$Sr$_{x}$CuO$_{4}$, the field-induced order is actually three-dimensional, implying significant magnetic linkage between the CuO$_{2}$ planes. The results are important because they reveal the presence of three-dimensional magnetic couplings which survive into the superconducting state, and coexist with the crucial inter-layer couplings responsible for the three-dimensional superconductivity. [Preview Abstract] |
Tuesday, March 14, 2006 10:24AM - 11:00AM |
G2.00005: Superfluid density in strongly underdoped YBa$_2$Cu$_3$O$_{6.333}$ Invited Speaker: Current research in high temperature superconductivity focuses on the underdoped cuprates, in the region of the phase diagram where $d$-wave superconductivity gives way to antiferromagnetism. Important clues for connecting these two states can be found in the evolution of the superfluid density $\rho_s$ with doping. $ \rho_s$ is the most fundamental property of a superconductor, measuring its ability to resist perturbations to the phase of the superfluid wavefunction. In addition, the temperature dependence of $\rho_s$ provides a direct probe of the electrical current carried by the quasiparticle excitations. Here we report measurements of $ \rho_s$ in ultra-high purity YBa$_2$Cu$_3$O$_{6.333}$, over a range of dopings near the boundary of the superconducting phase. We have succeeded in producing samples with sharp superconducting transitions and have harnessed the process of CuO-chain ordering to fulfill a long-held ambition in strongly correlated electron materials --- continuous tunability of the carrier density in a {\em single sample}, with {\em no} change in cation disorder. We now have preliminary evidence for the production of so-called Ortho III$'$ oxygen order, in which every full CuO chain is separated by two empty chains. The superfluid density measurements are surprising and challenge current theoretical understanding of the underdoped cuprates. $\rho_s$ becomes anomalously small, but there is no vortex unbinding transition. The slope of $\rho_s(T)$ indicates that the current carried by the quasiparticles shrinks smoothly towards zero on approach to the Mott insulator. In addition, the correlation between $T_c$ and $\rho_s$ is sublinear, in disagreement with long-established phenomenology. In the same experiments, microwave spectroscopy of the quasiparticle conductivity has also been used to probe the evolution of the quasiparticle relaxation dynamics on the approach to the superconducting quantum critical point. [Preview Abstract] |
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