Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X25: Superconductivity: Pseudogap and Related Phenomena |
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Sponsoring Units: DCMP Chair: Lex Kemper, North Carolina State University Room: 324 |
Friday, March 18, 2016 8:00AM - 8:12AM |
X25.00001: ABSTRACT WITHDRAWN |
Friday, March 18, 2016 8:12AM - 8:24AM |
X25.00002: Spin order, charge order, and spin liquid in spin-fermion model of cuprates. Kyungmin Lee, Oinam Ngamba Meetei, Steven White, Eun-Ah Kim Recent experimental observations that intra-unit-cell structures play crucial role in the detection of charge order motivates numerical studies that can include strong correlation effects as well as multi-site until cells. However, this costs precious Hilbert space. In this talk I will present our results using a minimal model for cuprates that can access intra-unit-cell information: multi-band spin-fermion model with spins on the copper sites and holes on oxygen sites. For this we used exact diagonalization as well as density matrix renormalization group. In addition to charge and spin order tendencies we test for evidence of the so-called FL* state. [Preview Abstract] |
Friday, March 18, 2016 8:24AM - 8:36AM |
X25.00003: Interplay of pair density wave and charge density wave order in the cuprate pseudogap phase Daniel Agterberg, Adil Amin Recent x-ray measurements in the cuprate YBCO suggest that the charge density wave (CDW) order seen at high-field has a different c-axis structure than that seen at zero-field and further suggests that CDW order breaks the c-axis mirror plane symmetry of the CuO$_2$ layers. We examine pair density wave order that induces CDW order consistent with these observations. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 8:48AM |
X25.00004: Hybridization of Higgs modes in a bond-density-wave state in cuprates Zachary Raines, Valentin Stanev, Victor Galitski Recently, several groups have reported observations of collective modes of the charge order present in underdoped cuprates. Motivated by these experiments, we study theoretically the oscillations of the order parameters, both in the case of pure charge order, and for charge order coexisting with superconductivity. We find in the coexistence regime two Higgs modes arising from hybridization of the amplitude oscillations of the different order parameters, one of which has a minimum frequency that is within the single particle energy gap and which is a non-monotonic function of temperature. Additionally, we explore an unusual low-energy damping channel for the collective modes, which relies on the band reconstruction caused by the coexistence of the two orders. [Preview Abstract] |
Friday, March 18, 2016 8:48AM - 9:00AM |
X25.00005: Thermodynamic properties of underdoped YBa$_2$Cu$_3$O$_{6+x}$ cuprates for doping values $x\in (0.5,0.9)$ P. SALAS, M. A. Solis, M. Fortes We extend the Boson-Fermion superconductivity model to include layered systems, such as underdoped cuprate superconductors YBa$_2$Cu$_3$O$_{6+x}$, with $x \in (0.5,0.9)$ ranging from underdoped to optimally doped. We model cuprates as a boson-fermion quantum gas mixture immersed in a layered structure, generated via a Dirac comb potential applied in one direction while the particles move freely in the other two directions. The optimum parameters of the system, which are the impenetrability of the planes and the paired fermion fraction, are obtained by minimizing the Helmholtz free energy and setting the experimental critical temperature $T_c$. Using this optimized scheme, we are able to predict the following thermodynamic properties of cuprates as a function of temperature: the entropy; the Helmholtz free energy; the electronic specific heat and the total specific heat for different doping values. Furthermore, we determinate the behavior of the jump height in the electronic specific heat, the normal electronic specific heat coefficient $\gamma (T_c)$, the quadratic $\alpha$ and cubic $\beta$ terms of the specific heat for low temperatures, the ground state energy and the mass anisotropy as a function of doping. Comparison to experimental values reported is analyzed. [Preview Abstract] |
Friday, March 18, 2016 9:00AM - 9:12AM |
X25.00006: The roles of antiferromagnetic and nematic fluctuations in cuprate superconductors: a sign-free quantum Monte-Carlo study Zixiang Li, Hong Yao, Fa Wang, Dung-Hai Lee Superconductivity is an emergent phenomena in the sense that the energy scale at which Cooper pairs form is generically much lower than the bare energy scale, namely the electron kinetic energy bandwidth. Addressing the mechanism of Cooper pairing amounts to finding out the effective interaction (or the renormalized interaction) that operates at the low energies. Finding such interaction from the bare microscopic Hamiltonian has not been possible for strong correlated superconductors such as the copper-oxide high temperature superconductor. In fact even one is given the effective interaction, determining its implied electronic instabilities without making any approximation has been a formidable task. Here, we perform sign-free quantum Monte-Carlo simulations to study the antiferromagnetic, superconducting, and the charge density wave instabilities which are ubiquitous in both electron and hole doped cuprates. Our result suggests only after including both the nematic and antiferromagnetic fluctuation, are the observed properties associated with these instabilities reproduced by the theory. [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X25.00007: Strong-coupling approach to nematicity in the cuprates Peter Philipp Orth, Bhilahari Jeevanesan, Joerg Schmalian, Rafael Fernandes The underdoped cuprate superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ is known to exhibit an electronic nematic phase in proximity to antiferromagnetism. While nematicity sets in at large temperatures of $T \approx 150$ K, static spin density wave order only emerges at much lower temperatures. The magnetic response shows a strong in-plane anisotropy, displaying incommensurate Bragg peaks along one of the crystalline directions and a commensurate peak along the other one. Such an anisotropy persists even in the absence of long-range magnetic order at higher temperatures, marking the onset of nematic order. Here we theoretically investigate this situation using a strong-coupling method that takes into account both the localized Cu spins and the holes doped into the oxygen orbitals. We derive an effective spin Hamiltonian and show that charge fluctuations promote an enhancement of the nematic susceptibility near the antiferromagnetic transition temperature. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X25.00008: Interplay between pair density waves and random field disorders in the pseudogap regime of cuprate superconductors Cheung Chan To capture various experimental results in the pseudogap regime, we propose a four-component pair density wave (PDW) state in which all components compete with each other. Without random field disorders (RFD), globally the PDW components are phase separated and only one of the component survives locally. If the RFD is included, this state becomes a phase separated state with short range PDW stripes, and induces charge density waves (CDW) and loop current order as secondary composite orders. We call this phase-separated pair nematic (PSPN) state. This state could capture a number of important experimental features in the pseudogap, in particular, the predominantly $d$-wave CDW with spatial dependent charge smecticity, the unusual ARPES quasiparticle spectrum, and the time reversal symmetry breaking order in polarized neutron diffraction and polar Kerr rotation. We also discuss how the various temperature scales arisen in the pseudogap can be understood in terms of the interplay with the RFD and fluctuating orders. [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X25.00009: Breakup of superconducting order parameter into 2 subbands of Cooper pairs increases temperature range of fluctuations in the pseudogap phase Fu-Chun Zhang, Ye-Hua Liu, Robert Konik, Thomas Maurice Rice The opening of the pseudogap in underdoped cuprates breaks up the Fermi surface, into 4 disconnected arcs centered on the nodal directions. In the superconducting phase, the d-wave order parameter breaks up into 2 subbands of Cooper pairs along (1,1) and (1,-1), with strong intra-subband and weak inter-subband couplings. This multiple-band superconductivity allows a low-energy Leggett mode to emerge due to phase fluctuations between the subbands. We propose that the overdamped Leggett mode is responsible for the highly unusual wide temperature range of superconducting fluctuations observed in the c-axis infrared conductivity in the pseudogap phase. [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X25.00010: Giant phonon anomaly associated with strong superconducting fluctuations in the pseudogap phase of underdoped cuprates Ye-Hua Liu, Robert Konik, Thomas Maurice Rice, Fu-Chun Zhang Phonons with wavevectors connecting Fermi-arc ends are strongly damped in the pseudogap phase as $T \rightarrow T_c$ from above. Below $T_c$ the anomaly abruptly switches to a dip in the phonon dispersions at the same wavevectors. Based on our proposed 2-subband model of superconductivity, we analyze the coupling between these phonons and the Leggett mode. We consider the phonon self energy arising from a forward scattering of the phonon accompanied by Cooper-pair transfers between the subbands. The intermediate state of this process involves 2 Leggett modes and a forward scattered phonon. Above $T_c$, the Leggett mode is overdamped giving rise to the giant phonon damping, while below $T_c$, the Leggett mode develops a finite energy turning the phonon anomaly into a dip in the energy dispersion. [Preview Abstract] |
Friday, March 18, 2016 10:00AM - 10:12AM |
X25.00011: Pairing in the presence of a pseudogap Douglas Scalapino, Thomas Maier, Peter Staar, Vivek Mishra After 30 years, the quest to experimentally identify the mechanism responsible for pairing in the high Tc superconductors continues. Here we discuss an approach in which angle resolved photoemission (ARPES)data for BSCCO 2212(Tc=89K) is used to extract the single particle spectral weight A(k,w). This spectral weight is then used to calculate the BCS kernel and estimate the RPA spin-fluctuation d-wave pairing strength. Previously A(k,w) results at T=140K, extrapolated to lower temperatures, found that the BSCCO pseudo gap suppressed the logarithmic singularity of the BCS kernel and the spin-fluctuation interaction was too weak to produce superconductivity [V.Mishra et al.,Nat.Phys.10,357]. Here using results for A(k,w) at T=40K for this same system, we find that while the BCS kernel is suppressed, there is a significant increase in the d-wave pairing strength for the spin-fluctuation interaction when the temperature drops from T=140K and 40K. These results are shown to be consistent with DCA calculations for a 2D Hubbard model of a BSCCO like system which has a pseudo gap. We conclude that in spite of the suppression of the usual BCS logarithmic instability by the pseudo gap, the increase in strength of the spin-fluctuation interaction is sufficient to lead to superconductivity. [Preview Abstract] |
Friday, March 18, 2016 10:12AM - 10:24AM |
X25.00012: Effect of Extended Saddle Point Singularities in Cuprates and Evidences Guang-Lin Zhao First-principles calculations and angle-resolved photoemission spectroscopy measurements showed extended saddle point singularities in the electron structures of some cuprates such as YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7}}$ (YBCO). The extended saddle point singularities in the electronic structures of the materials can lead to anomalous physical properties. In this work, a new methodology is implemented by integrating first-principles calculations of electronic structures of the materials into the theory of many-body physics for superconductivity. The aim is to seek a unified methodology to calculate the electronic and superconducting properties of the materials. It is demonstrated from first-principles that the extended saddle point singularities in the materials such as YBCO strongly correlate to the anomalous isotope effect in the superconductors. [Preview Abstract] |
Friday, March 18, 2016 10:24AM - 10:36AM |
X25.00013: Theory of Berry Phases in the Cuprate Pseudogap Phase Geremia Massarelli, Tamar Pereg-Barnea The geometric Berry phase is part of the phase accumulated by a quantum system undergoing adiabatic evolution around a closed loop in parameter space \footnote{Berry, M.~V. Quantal Phase Factors Accompanying Adiabatic Changes. \emph{Proceedings of the Royal Society of London.~A.~Mathematical and Physical Sciences} \textbf{392}, 45-57 (1984).}. Recently, data from quantum oscillations experiments, in which Berry's phase is accessible via its contribution to the phase offset, were used to determine Berry's phase in certain electron- and hole-doped cuprate superconductors in high-magnetic-field regimes \footnote{Doiron-Leyraud, N.,~et al. Berry Phase in Cuprate Superconductors. \emph{arXiv preprint arXiv:1407.1388} (2014).}. The data reveal a trivial Berry phase of $0$ in the hole-doped materials examined, while a phase of $\sim 1.4\pi$ was found in the electron-doped material. These findings set new, significant constraints on the possible descrpitions of the pseudogap phase of the cuprates. This is used as a test of validity for some proposed models of cuprate superconductors. Berry's phase is computed within the framework of these models in high-field regimes and compared to the experimental findings. [Preview Abstract] |
Friday, March 18, 2016 10:36AM - 10:48AM |
X25.00014: Interplay between uni-directional and bi-directional charge orders in underdoped cuprates Yuxuan Wang, Andrey Chubukov We analyze the interplay between charge-density-wave (CDW) orders with axial momenta $(Q,0)$ and $(0,Q)$ ($\Delta_x$ and $\Delta_y$ respectively), detected in the underdoped cuprates. The CDW order in real space can be uni-directional (either $\Delta_x$ or $\Delta_y$ is non-zero) or bi-directional (both $\Delta_x$ and $\Delta_y$ are non-zero). To understand which of the two orders develop, we adopt the magnetic scenario, in which the CDW order appears due to spin-fluctuation exchange. We derive the Ginzburg-Landau action to the sixth order in $\Delta_x$ and $\Delta_y$ and argue that the CDW order is bi-directional at the onset but changes to uni-directional inside the CDW phase. This implies that, at a given temperature, CDW order is uni-directional at smaller dopings, but becomes bi-directional at larger dopings. These results are consistent with recent x-ray data on YBCO, which detected tendency towards bi-directional order at larger dopings. We also discuss for completeness the effect of yet unobserved intertwined pair-density-wave (PDW) order, which may appear along with CDW. [Preview Abstract] |
Friday, March 18, 2016 10:48AM - 11:00AM |
X25.00015: Dipolon Theory of High Temperature Superconductors-- Prediction of the Existence of New Very Low Energy Excitations to be Observed in Photoemission Experiments Ram R Sharma The dipolon theory [1,2] first discovered [3,4] two high energy kinks in electron energy [5]. It [1-2] has also predicted two superconducting states, symmetric ("s") and anti-symmetric ("as"). Here we report the prediction of very low energy excitations due to transition from "as" state to "s" state ("ass") (or vice versa) which creates (annihilates) the quantum ("asson") of energy $ \hbar \omega_{a} (\vec{q}_a) = E^{s} (\vec{k'}) -E^{as} (\vec{k"})$; "a" is for "asson" and $E^{s} (\vec{k'}) $ and $E^{as} (\vec{k"}) $ are electron energies in "s" and "as" states, respectively ($E^i(\vec{k }) =\bar{E}^i_r(\vec{k }) $ [1-4]). Our theory [1-4] finds in BISCCO at M point on Fermi level at T=13 K asson energy about $14\pm 8 \ meV$. We predict that these assons create a new kink in electron energy at this energy. Also, a single pair transitions are possible which involve two assons. (1) R. R. Sharma, Phy. Rev. {\bf B 63}, 054506 (2001). (2) R. R. Sharma, Physica {\bf C 439}, 47 (2006). (3) R. R. Sharma, Physica {\bf C 468}, 190 (2008). (4) R. R. Sharma, "Dipolon Theory of Kink ...", in "Superconducting ...", Ed. K. N. Courtlandt, P. 81-100, Nova Sc, Pub., Inc., New York, 2009. (5) R. R. Sharma, http://meetings.aps.org/lnk/BAPS.2015.MAR.D9.15. [Preview Abstract] |
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