Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session U41: Correlated Electrons: Superconductivity and Magnetism |
Hide Abstracts |
Sponsoring Units: GMAG Chair: Norman Birge, Michigan State Univ. Room: LACC 150A |
Thursday, March 24, 2005 8:00AM - 8:12AM |
U41.00001: Superconductivity and non-Fermi liquid behavior near antiferromagnetic quantum critical points in CeRh$_{1-x}$Co$_x$In$_5$ J.R. Jeffries, N.A. Frederick, E.D. Bauer, H. Kimura, V.S. Zapf, K.-D. Hof, T.A. Sayles, M.B. Maple Single crystals of CeRh$_{1-x}$Co$_x$In$_5$ have been investigated via measurements of specific heat, $C(x,T)$, and electrical resistivity under hydrostatic pressure, $\rho(x,P,T)$, up to $28$ kbar. Specific heat measurements for samples with cobalt concentrations of $x = 0.65, 0.71, 0.77, 0.87,$ and $0.93$ confirm the existence of antiferromagnetism (AFM) for $0\leq x \leq0.7$ and suggest the existence of a quantum critical point (QCP) at $x_c \sim 0.8$. Entropy vs $x$ isotherms below $\sim 5$ K and the normalized residual resistivity $\rho(0$ K$ )/\rho(290$ K) vs $x$ curve both display maxima near $x_c \sim 0.8$, suggesting further evidence for the existence and location of the QCP. Electrical resistivity measurements under pressure for samples with $x = 0.1, 0.2, 0.4$, and $0.6$ reveal AFM, pressure-induced superconductivity (SC), and the coexistence of AFM and SC. The $\rho(0$ K$ )/\rho(290$ K) vs $P$ curves favor the existence of QCP's at critical pressures $P_c \sim 24$ kbar for the $x = 0.1$, and $0.2$ samples and $P_c \sim 6$ kbar for the $x = 0.4$ sample. This research was supported by the U.S. DOE, NSF, and NNSA under the SSAA program. [Preview Abstract] |
Thursday, March 24, 2005 8:12AM - 8:24AM |
U41.00002: Field dependence of thermal conductivity in the superconducting state of M.A. Tanatar, J. Paglione, Louis Taillefer, C. Petrovic, P. Canfield The thermal conductivity of heavy-fermion superconductor CeCoIn5 reveals a notable hysteresis between up and down sweeps of magnetic field, observed at low temperatures, slightly below the upper critical field Hc2. We study systematically this effect as a function of temperature and magnetic history. A possible relation to a coexisting magnetic order is discussed. [Preview Abstract] |
Thursday, March 24, 2005 8:24AM - 8:36AM |
U41.00003: Low Temperature Susceptibility of the Noncentrosymmetric Superconductor Ce$_{1-x}$La$_{x}$Pt$_{3}$Si D.P. Young, M. Moldovan, X.S. Wu, P.W. Adams, J.Y. Chan We report ac susceptibility measurements of polycrystalline Ce$_{1-x}$La$_x$Pt$_3$Si down to 60 mK and in applied fields up to 9 T. In zero applied field, a full Meissner state emerges for pure CePt$_3$Si at temperatures $T/T_{c}$$<$ 0.3, where $T_{c}$ = 0.65 K is the onset transition temperature. Though transport measurements show a relatively high upper critical field $B_{c2}\sim$ 4 - 5 T, the low temperature susceptibility, $\chi \prime$, is quit fragile to applied field, with $\chi \prime$ diminishing rapidly in fields of a few kG. Interestingly, the field dependence of $\chi \prime$ is well described by the power law, 4$\pi$$\chi \prime$ + 1 = $(B/B_{c})^{1/2}$, where $B_{c}$ is the field at which the onset of resistance is observed in transport measurements. The effects of La doping on the superconductivity will also be presented. [Preview Abstract] |
Thursday, March 24, 2005 8:36AM - 8:48AM |
U41.00004: 2D fermionic systems near a magnetic $2k_F$ instability: application to electron-doped cuprates Pavel Krotkov, Andrey Chubukov We study spin-mediated pairing in 2D itinerant electron systems near antiferromagnetic instability in a situation when the antiferromagnetic vector $(\pi,\pi)$ connects nodal points on the Fermi surface. This scenario is related to the electron-doped high- $T_{c}$ materials where the variation of the Fermi surface with doping drives the hot spots towards zone diagonals. We obtain fermionic self-energy at strong coupling and analyze the $d-$wave pairing problem. [Preview Abstract] |
Thursday, March 24, 2005 8:48AM - 9:00AM |
U41.00005: Spin excitations in cuprates with fluctuating stripe order Ribhu Kaul, Matthias Vojta, Subir Sachdev We present a phenomenological Landau-Ginzburg-Wilson quantum lattice model with both anti-ferromagnetic and charge/bond order that is able to capture the physics of static stripes as well as fluctuating stripe order. We focus on the spin response of this model for the case of fluctuating stripe order and compare it with the results for the static case. We claim that our results are relevant to recent neutron scattering experiments in the cuprates. [Preview Abstract] |
Thursday, March 24, 2005 9:00AM - 9:12AM |
U41.00006: Quantum Monte Carlo Study of ``Fictive Impurity'' to Half-Filled Hubbard Model Andreas Fuhrmann, Satoshi Okamoto, Andrew Millis Quantum Monte Carlo (QMC) and analytical approximations are used to show that the two (and higher) impurity dynamical mean field approximation (both in the real space and DCA version) to the square lattice Hubbard model do not reproduce the paramagnetic Mott insulating phase at particle density n=1.Moreover the real space version strongly overestimates the Neel transition temperature at large U. Systematic comparison of QMC and semiclassical analytical approximation results are also presented. Research supported by DAAD, SFB 608, DFG-SPP 1073, JSPS, NSF DMR 0431350. [Preview Abstract] |
Thursday, March 24, 2005 9:12AM - 9:24AM |
U41.00007: Phonons in Hubbard Ladders Alexander Seidel, Dung-Hai Lee, Hsiu-Hau Lin The effects of phonons are studied in N-leg Hubbard ladders within the framework of one-loop renormalization group. In particular, we explicitly demonstrate that the role of phonons changes qualitatively even in the simplest two-leg ladder, as compared to the single-chain system. Our numerical results suggest that in the spin-gapped phase of the two-leg ladder, the opening of the spin gap by electron-electron interaction also drives the electron-phonon interaction to strong coupling in a subdominant fashion. Therefore, even though the inclusion of phonons does not alter the phase, their subdominant relevance renormalizes some physical properties strongly below the energy scale of the spin gap. This might shine some light on the recent experiments showing an anomalous isotope effect in high-temperature superconductors. [Preview Abstract] |
Thursday, March 24, 2005 9:24AM - 9:36AM |
U41.00008: Theoretical Evidence for the Equivalence between the Ground States of the Strong-Coupling BCS Hamiltonian and the Antiferromagnetic Heisenberg Model Kwon Park By explicitly computing wavefunction overlap via exact diagonalization, we show that, in the limit of strong coupling, the ground state of the Gutzwiller-projected BCS Hamiltonian (accompanied by proper particle-number projection) is identical to the exact ground state of the 2D antiferromagnetic Heisenberg model on the square lattice. This identity is adiabatically connected to a very high overlap between the ground states of the projected BCS Hamiltonian and the $t$-$J$ model at moderate doping. [Preview Abstract] |
Thursday, March 24, 2005 9:36AM - 9:48AM |
U41.00009: Possible Observation of a 'Zhang-RiceTriplet': RIXS Study of Li2CuO2 Timothy Learmonth, Cormac McGuinness, Per-Anders Glans, James E. Downes, Thorsten Schmitt, Laurent C. Duda, Jinghua Guo, Kevin E. Smith, Fangcheng Chou The electronic structure of cuprates has been of considerable interest since the discovery of high T$_{c}$ superconductivity in such materials. Li$_{2}$CuO$_{2}$ consists of edge-sharing Cu-O chains, with a quasi-one dimensional crystal structure. The electronic structure, however, is regarded as quasi-zero dimensional, since the resistivity is similar along all three crystal axes, and the insulating gap is estimated at 3.2eV. We have measured the O K edge and Cu L edge XAS, SXE, and RIXS spectra of Li$_{2}$CuO$_{2}$. The results indicate the presence of Cu d-d excitations, as well as a higher energy charge transfer excitation that is tentatively identified as a two hole final state ``Zhang-Rice Triplet.'' This identification is supported by energetic and magnetic arguments, as well as more general theoretical considerations. Supported in part by the U.S. DOE under DE-FG02-98ER45680. [Preview Abstract] |
Thursday, March 24, 2005 9:48AM - 10:00AM |
U41.00010: Pronounced enhancement of the lower critical field and critical current deep in the superconducting state of PrOs$_{4}$Sb$_{12}$ A.C. Mota, T. Cichorek, F. Steglich, N.A. Frederick, W.M. Yuhasz, M.B. Maple We have observed an unexpected enhancement of the lower critical field \textit{H}$_{c1}$(\textit{T}) and the critical current \textit{I}$_{c}$(\textit{T}) deep in the superconducting state below \textit{T}$\approx$0.6~K (\textit{T}/\textit{T}$_{c}$$\approx$0.3) in the filled skutterudite heavy fermion superconductor PrOs$_{4}$Sb$_{12}$. From a comparison of the behavior of \textit{H}$_{c1}$(\textit{T}) with that of the heavy fermion superconductors U$_{1-x}$Th$_{x}$Be$_{13}$ (\textit{x}=0.027) and UPt$_{3}$, we speculate that the enhancements in PrOs$_{4}$Sb$_{12}$ reflect a transition into another superconducting phase that occurs below \textit{T}/\textit{T}$_{c}$$\approx$0.3. An examination of the literature reveals unexplained anomalies in other physical properties of PrOs$_{4}$Sb$_{12}$ near \textit{T}/\textit{T}$_{c}$$\approx$0.3 that correlate with the features we have observed in \textit{H}$_{c1}$(\textit{T}) and \textit{I}$_{c}$(\textit{T}). On the other hand, the lack of obvious features in the heat capacity at \textit{T}/\textit{T}$_{c}$$\approx$0.3 is somewhat reminiscent of the transition between the A and B phases of superfluid $^{3}$He. Vortices in PrOs$_{4}$Sb$_{12}$ are very strongly pinned. They relax from a metastable state following a logarithmic law with decay rates smaller than 0.5\%. [Preview Abstract] |
Thursday, March 24, 2005 10:00AM - 10:12AM |
U41.00011: RPES of the Electron-Doped Cuprates Studied by the Variational Monte-Carlo Method Ting-kuo Lee, Chung-Pin Chou We use a variational approach to gain insight into low-energy states of extended $t-J$ model in the electron-doped regime. Compared with the recent results on $Nd_{1.87}Ce_{0.13}CuO_{4}$ obtained by ARPES, we show that strong correlations lead to qualitatively similar trends in ARPES spectra and Fermi surface topology. Additionally, the results about Fermi surface evolution as a function of doping density will be discussed. [Preview Abstract] |
Thursday, March 24, 2005 10:12AM - 10:24AM |
U41.00012: Enhancement of pairing in a boson-fermion model for coupled ladders Jose Riera Motivated by the presence of various charge inhomogeneities in strongly correlated systems of coupled ladders, a model of spatially separated bosonic and fermionic degrees of freedom is numerically studied. In this model, bosonic chains are connected to fermionic chains by two types of generalized Andreev couplings. It is shown that for both types of couplings the long-distance pairing correlations are enhanced. Near quarter filling, this effect is much larger for the splitting of a pair in electrons which go to the two neighboring fermionic chains than for a pair hopping process. It is argued that the pairing enhancement is a result of the nearest neighbor Coulomb repulsion which tunes the competition between pairing and charge ordering. [Preview Abstract] |
Thursday, March 24, 2005 10:24AM - 10:36AM |
U41.00013: Regular Perturbation Theory About Generalized Self-Consistent Field Hamiltonian Armen Kocharian, Chi Yang, You Ling Chiang, L.Y. Chen Strongly correlated electrons require non-traditional approaches to describe their unexpected properties. The perturbation theory about non-interacting electron gas first developed by Abrikosov and Khalatnikov has a zero convergence radius for the resulting perturbation series. The analytical theory of Gell-Mann and Bruckner, now known as random phase approximation (RPA), gives exact values for the correlation energy in the high density-weak coupling regime. However, this method also runs into difficulties due to the insufficient treatment of fluctuations. We give a formulation of a regular perturbation theory within the repulsive Hubbard model for interacting quasi-particles about exactly solvable generalized self-consistent field (GSCF) Hamiltonian for studying the intermediate range of interaction strength $U/t$, where there is no small parameter. Proposed perturbation series for interacting quasi-particles in entire parameter space of $U/t$ and electron concentration $n$ do not diverge. Performed analytical calculations of the ground state properties in extreme conditions of one dimensionality provide good numerical agreement with the Bethe-{\it ansatz} results and reasonable interpolation scheme for intermediate range of $U/t$ and $n$. The method can be used also for studies electron correlations in finite size clusters. [Preview Abstract] |
Thursday, March 24, 2005 10:36AM - 10:48AM |
U41.00014: Enhanced Superconductivity in Bilayered Systems Saurabh Basu We investigate superconducting correlations in bilayered systems. The planes are described by a two-dimensional $t_{\parallel} - J_{\parallel} - U$ with $t_{\perp}$ and $J_{\perp}$ denoting the interplanar parameters. These interplanar couplings when coupled with hopping anisotropies in the planes may account for a host of unusual superconducting properties. Our main focus is to calculate superconducting correlations (using BCS theory) for various regions of the parameter space formed by the interplanar variables. For $t_{\perp} = 0$ (confining the carriers in planes) and $J_{\perp} < J_{\parallel}$, the pairing correlations are found to be purely planar. Further we generalize to $t_{\perp} \ne 0$ and $J_{\perp}/J_{\parallel} = \left (t_{\perp}/t_{\parallel}\right )^{2}$ and find that pairing correlations are enhanced at lower densities with increasing $t_{\perp}$. The most dramatic effect sets in when, additionally the planar hopping frequencies are made highly anisotropic ($t_{y} \ll t_{x}$) and $J_{\perp} \sim J_{\parallel}$. A small $t_{\perp}$ increases $T_{c}$ as much as {\it {four}} times when compared with the calculations performed for a single layer (PRB, {\bf {66}}, 144507 (2002)). Straightforward generalizations to more number of layers is discussed with a goal to study crossover to the bulk 3D limit. [Preview Abstract] |
|
U41.00015: Nodal-antinodal dichotomy in doped Mott insulators Tiago C. Ribeiro The cuprate high-Tc superconductors are anisotropic in momentum space as observed by a variety of experiments. In hole underdoped samples the pseudogap regime becomes of preponderant importance and the excitations around the nodal points [$\vec{k}=(\pm \frac{\pi}{2},\pm \frac{\pi}{2})$] are well described as Landau's quasiparticles while those near the antinodal points [$\vec{k}=(\pi,0),\, (0,\pi)$] show no signs of quasiparticle-like behavior. We employ the exact diagonalization and the self-consistent Born approximation techniques to study the single hole $tt't''J$-model in order to address how excitations with different momentum can be so disparate. We find that the single hole states can be understood as the superposition of two distinct states, namely a state with hole-like quasiparticle features and a spin-charge separated state, and explain how the different properties of these states underlie the observed nodal-antinodal dichotomy in the pseudogap regime. [Preview Abstract] |
|
U41.00016: Higher order corrections to effective low-energy theories for strongly correlated electron systems Sasha Chernyshev, Dimitrios Galanakis, Philip Phillips, Alex Rozhkov, A.-M.S. Tremblay There is a significant recent interest in higher-order corrections to effective low-energy theories for a broad range of strongly-correlated electronic problems. We use the Hubbard model as an example to show how, to fourth order in hopping $t$, well-known perturbative approaches lead to the same effective theory, namely the $t$-$J$ model with ring exchange and various correlated hoppings. Several new issues appear in deriving higher-order low-energy effective theories. One may find amusing that the low-energy Hamiltonians obtained from different methods appear to be {\it different} in each case. However, we show that they are all connected by an additional unitary transformation that leaves the block-diagonal form invariant. We also emphasize the importance of transforming all the operators along with the Hamiltonian and demonstrate the equivalence of their transformed structure within the different approaches. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700