Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B42: Charge, Spin, and Superconductivity |
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Sponsoring Units: DCMP Chair: Andrei Bernevig, Princeton University Room: D138 |
Monday, March 15, 2010 11:15AM - 11:27AM |
B42.00001: Competition between spin density wave order and superconductivity in the underdoped cuprates Eun Gook Moon , Subir Sachdev We describe the interplay between $d$-wave superconductivity and spin density wave (SDW) order in a theory of the hole-doped cuprates at hole densities below optimal doping. We describe quantum and thermal fluctuations in the orientation of the local SDW order, which lead to $d$-wave superconductivity. We also describe the back-action of the superconductivity on the SDW order, showing that SDW order is more stable in the metal. Finally, we propose a finite temperature crossover phase diagram for the cuprates. In the metallic state, these are controlled by a `hidden' quantum critical point near optimal doping involving the onset of SDW order in a metal. However, the onset of superconductivity results in a decrease in stability of the SDW order, and consequently the actual SDW quantum critical point appears at a significantly lower doping. [Preview Abstract] |
Monday, March 15, 2010 11:27AM - 11:39AM |
B42.00002: Competition between ferromagnetism and superconductivity in hole and electron doped cuprates B. Barbiellini , T. Jarlborg , H. Lin , R. S. Markiewicz , A. Bansil Band calculations for supercells of La$_{2-x}$Ba$_x$CuO$_4$ beyond the rigid band model give support to the idea that weak ferromagnetism can be the cause of the destruction of superconductivity at high hole doping [1,2]. We are exploring similar mechanisms in the electron doped Nd$_{2-x}$Ce$_x$CuO$_4$. In this case, the treatment of the Nd and Ce f electrons presents new challenges. For this reason, we compare spin-polarized DFT results which include the Nd-f (and Ce-f) electron in the valence band with calculations in which the Nd-f electrons are forced to be core states. Our simulations use both the simple unit cell and $2 \times 2 \times 1$ supercells in various magnetic configurations (i.e. ferromagnetic, antiferromagnetic and ferrimagnetic). The results indicate that subtle charge transfers and screening occuring near the Ce impurity may give interesting Coulombic effects between the Nd/Ce and CuO planes [3]. Work supported in part by the US DOE.\\ \mbox{[1]} B. Barbiellini and T. Jarlborg, Phys. Rev. Lett. {\bf 101}, 157002 (2008).\\ \mbox{[2]} R.S. Markiewicz and A. Bansil, Phys. Rev. B {\bf 78}, 134513 (2008).\\ \mbox{[3]} H. Lin \textit{et al.} Phys. Rev. Lett. {\bf 96}, 097001 (2006).\\ [Preview Abstract] |
Monday, March 15, 2010 11:39AM - 11:51AM |
B42.00003: Charge and Superconducting Order in Stripe Phases Akbar Jaefari , Siddhartha Lal , Eduardo Fradkin We discuss the phases of striped superconductors with a spin gap. We will focus on the interplay between 2D superconducting charge-density-wave orders, and the possible existence of sliding phases. We use bosonization methods and dimensional crossovers to determine the phase diagram of this system, as a function of temperature and inter-stripe interactions, as well as the behavior of the superconducting and CDW correlation functions. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B42.00004: Competing orders and strong correlation in high temperature superconductors Rajdeep Sensarma , Victor Galitski We study competing antiferromagnetic and superconducting orders in the context of high temperature cuprate superconductors. Using a Gutzwiller projected variational wavefunction approach we look at different experimentally relevant quantities. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B42.00005: Impurity Influences on the Stripe Pattern Chung-Pin Chou , Ting-Kuo Lee Many experiments in high-Tc cuprates have clearly indicated the stripe order for decades ago. Recently the cluster glasses with randomly oriented domains of stripelike patterns have been observed by scanning tunneling spectroscopy[1]. However, it is still unclear whether or not the charge pattern is intimately related to disorder in real materials. Using a variational Monte-Carlo approach with a recently proposed cluster-glass stripe wave function in the t-t'-t"-J model[2], we will report the relation between the stripe configurations and impurities. [1]Y. Kohsaka, et al., Science 315, 1380 (2007). [2]C.-P. Chou, et al., Phys. Rev. B 78, 134530 (2008). [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B42.00006: Effect of Zn impurities on the superconducting state of high Tc cuprates. A. Garg , A. Kanigel , M. Randeria , N. Trivedi We study the effect of Zn impurities on the strongly correlated d-wave superconducting state. We solve the $t$-$t^{\prime}$-$J$ model in the presence of unitary scatterers, with the no-double-occupancy constraint imposed by Gutzwiller approximation and the disorder-induced inhomogeneity treated within the Bogoliubov-deGennes (BdG) approach. We study the effect of strong correlations on the quasibound states and its interplay with local moment formation. The density of mobile holes is reduced by the presence of unitary scatterers, resulting in a suppression of the superfluid density but a much weaker effect on the superconducting gap. We investigate the effect on spectral properties, such as the suppression of coherence peaks and low energy spectral weight in the density of states and contrast our results with our earlier study [1] that found protected low-energy excitations in the presence of Born scatterers. We compare our results with recent ARPES experiments [2] on Zn-doped Bi2212. [1] A. Garg, M. Randeria, and N. Trivedi, Nature Phys.~{\bf 4}, 762 (2008). [2] A. Kanigel {\it et al.}, (unpublished). [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 12:39PM |
B42.00007: Electrostatically induced phase transitions in superconducting complex oxides Li Han , Carlos S\'a de Melo We describe quantum phase transitions in superconducting complex oxides which could be tuned by electrostatic charge transfer. Using a simple model for the superconductivity of a thin film or surface of a bulk copper oxide, we show that tuning the carrier density may allow the visitation of spin-density-wave antiferromagnetic phase as well as several superconducting phases with different pairing symmetries such as extended $s$- ($se$), $d$- and $(se \pm id)$-wave. For a specific model with nearest neighbor attraction, we obtain the phase diagram in the interaction versus filling factor space showing the boundaries of the possible phases. Finally, we calculate the superfluid density and penetration depth as characteristic properties of the superconducting phases. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B42.00008: Theory of superconducting quantum liquid crystals Daniel Barci , Eduardo Fradkin A novel superconductor state, whose order parameter oscillates producing a {\em pair density wave} (PDW), in which charge, spin and superconducting orders are intertwined, was recently proposed\footnote{E. Berg, E. Fradkin, S.A. Kivelson, Phys.Rev. B79, 064515 (2009)}. The PDW necessarily has charge density wave(CDW) modulations with double period and a novel homogeneous superconducting order with $4e$ charged quasi-particles(4eSC)\footnote{E. Berg, E. Fradkin, S.A. Kivelson, Nature Phys. 5, 830 (2009)}. The PDW is an anisotropic quantum liquid with nematic symmetry. In this work, we present a theory of smectic and superconductor fluctuations, given by PDW, CDW and 4eSC order parameters, in a nematic background. Our theory closely resembles the description of the smectic-nematic phase transition in classical liquid crystals. We compute the effect of the director fluctuations on the correlations of each ordered phase. We also make contact with the theory of thermal melting. [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B42.00009: Charge $4e$ superconductivity from pair density wave order in high temperature superconductors Eduardo Fradkin , Erez Berg , Steven Kivelson Several spectacular experimental anomalies have recently been discovered in certain cuprates, notably LBCO and LNSCO, which exhibit unidirectional spin and charge order (known as ``stripe order''). These observations are evidence for a novel ``striped superconducting'' state, in which the superconducting order parameter is modulated in space, such that its average is precisely zero. We show[1] that thermal melting of the striped superconducting state can lead to a number of unusual phases, of which the most novel is a charge $4e$ superconducting state, with a corresponding fractional flux quantum $hc/4e$. These are never-before observed states of matter, that cannot arise from the conventional BCS mechanism. Direct confirmation of their existence, even in a subset of the cuprates, could have much broader implications for our understanding of high temperature superconductivity. We propose experiments to observe fractional flux quantization, which thereby could confirm the existence of these states. [1] E. Berg, E. Fradkin and S. A. Kivelson, Nature Physics 5, 830 (2009). [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:15PM |
B42.00010: Spin-density-wave fluctuations in underdoped cuprates: pseudogap and coherence Tigran Sedrakyan , Andrey Chubukov We study the form of the spectral function in a spin-density- wave (SDW) state of a quasi-2D syatem at a finite temperature and apply the results to underdoped cuprates. We explore the fact that dominant corrections to a mean-field SDW propagator come from near-divergent thermal fluctuations and use a nonperturbative eikonal-type approach in which we sum up infinite series of thermal self-energy corrections and solve integral equation for the fully dressed fermionic propagator. We use the results to study (i) the evolution of the Fermi- surface with increasing temperature and doping, (ii) the behavior of SDW order parameter as a function of temperature and doping, (iii) the transfer of spectral weight to higher energies, (iv) the temperature and doping dependence of optical conductivity. We show in particular that, when SDW order gets weaker, the spectral function in the antinode region splits into a running quasiparticle peak, whose residue and position scale with the magnitude of the SDW order, and a maximum (a pseudogap) which remains at about the same energy as at T=0. When SDW order disappears, only a pseudogap remains. We discuss the relation of our results to ARPES and optical conductivity data, and to the experiments on quantum oscillations. [Preview Abstract] |
Monday, March 15, 2010 1:15PM - 1:27PM |
B42.00011: Quantum Criticality in Electron-Doped La$_{2-x}$Ce$_{x}$CuO$_{4}$ Kui Jin , Nicholas Butch , Gabriel Droulers , Kevin Kirshenbaum , Xiaohang Zhang , Paul Bach , Johnpierre Paglione , Richard Greene We studied the in-plane resistivity of over-doped La$_{2-x}$Ce$_ {x}$CuO$_{4}$ thin films as a function of temperature (down to 20 mK) and in magnetic fields of up to 17 T. In zero field, we found a $\rho \sim T$ region above $T_{c}$ for superconducting films and a $\rho \sim T^{2}$ region for non-superconducting films as $T\rightarrow 0$. The boundaries of $\rho \sim T $ and $\rho \sim T^{2}$ regions merge at a critical doping $x=0.175\pm 0.005$, which is also the boundary of the superconducting dome. In magnetic fields, the $\rho \sim T$ to $\rho \sim T^{2}$ transition as $T\rightarrow 0$ is shifted to lower doping with increasing field. We compare these results to related behavior in hole-doped cuprates [1] and to a recent phase diagram proposed by Sachdev [2].\\[4pt] [1] R.A. Cooper \textit{et al.}, Science \textbf{323}, 603 (2009).\\[0pt] [2] S. Sachdev, http://arxiv.org/abs/0907.0008V7 (2009). [Preview Abstract] |
Monday, March 15, 2010 1:27PM - 1:39PM |
B42.00012: Effective theory of Fermi pockets in fluctuating antiferromagnets Yang Qi , Subir Sachdev Photo emission, STM, transport and other experiments in cuprate superconductors have revealed Fermi arc and Fermi pocket structures in underdoped regime. Here we present an analytical effective theory for the Fermi pocket structures appeared in electron excitation spectrum. The physics of Fermi pockets in the presence of fluctuating spin density wave order has been described by a U(1) gauge theory with charged fermions and bosonic spin fields, or the ``spin-fermion model''. We study a theory of bound states of spin and charge excitations in this model, and relate the bound state to physical electron excitations. We present a phenomenological effective Hamiltonian for the bound states, whose form is determined by symmetry and gauge invariance. The coupling constants of the theory will have to be determined by experiments. This effective model is used to calculate electron spectrum function across the entire Brillouin zone, and the result is compared to photo emission experiments. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B42.00013: Cuprate Superconductors with Applied Current, a Variational Study Lilach Goren , Ehud Altman We investigate the properties of cuprate superconductors subject to applied current, using modified Gutzwiller projected d-wave BCS states. The parent wave-functions include quasi-particle and quasi- hole pockets of variationally determined size, generated by the current. The pockets, growing with increasing current, contribute to the reduction of the superfluid stiffness and its eventual destruction. We identify two different mechanisms which determine the critical current: at high hole doping ($x > 0.15$) it occurs when the pockets completely destroy the gap, i.e. the standard BCS mechanism; at lower doping the critical current is set by a maximal phase twist, which destroys the superfluid stiffness with pairing still intact. The critical current follows a dome shaped curve, similar to the well known dependence of $T_c$ on doping. Finally we discuss how signatures of current induced Fermi pockets can be seen in ARPES measurements. [Preview Abstract] |
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