Emergence of charge order in a staggered loop-current phase of cuprate high-temperature superconductors

We study the emergence of charge ordered phases within a pi-loop current (piLC) model for the pseudogap based on a three-band model for underdoped cuprate superconductors. Loop currents and charge ordering are driven by distinct components of the short-range Coulomb interactions: loop currents result from the repulsion between nearest-neighbor copper and oxygen orbitals, while charge order results from repulsion between neighboring oxygen orbitals. We find that the leading piLC phase has an antiferromagnetic pattern similar to previously discovered staggered flux phases, and that it emerges abruptly at hole dopings p below the van Hove filling. Subsequent charge ordering tendencies in the piLC phase reveal that diagonal d-charge density waves (dCDW) are suppressed by the loop currents while axial order competes more weakly. In some cases we find a wide temperature range below the loop-current transition, over which the susceptibility towards an axial dCDW is large. In these cases, short-range axial charge order may be induced by doping-related disorder. A unique feature of the coexisting dCDW and piLC phases is the emergence of an incommensurate modulation of the loop currents. If the dCDW is biaxial (checkerboard) then the resulting incommensurate current pattern breaks all mirror and time-reversal symmetries, thereby allowing for a polar Kerr effect

Tunneling spectroscopy for probing orbital anisotropy in iron pnictides

Using realistic multi-orbital tight-binding Hamiltonians and the T-matrix formalism, we explore the effects of a non-magnetic impurity on the local density of states in Fe-based compounds. We show that scanning tunneling spectroscopy (STS) has very specific anisotropic signatures that track the evolution of orbital splitting (OS) and antiferromagnetic gaps. Both anisotropies exhibit two patterns that split in energy with decreasing temperature, but for OS these two patterns map onto each other under 90 degree rotation. STS experiments that observe these signatures should expose the underlying magnetic and orbital order as a function of temperature across various phase transitions.Comment: 12 pages, 9 figures, replacement with minor changes suggested by referee

Focussing quantum states

Does the size of atoms present a lower limit to the size of electronic structures that can be fabricated in solids? This limit can be overcome by using devices that exploit quantum mechanical scattering of electron waves at atoms arranged in focussing geometries on selected surfaces. Calculations reveal that features smaller than a hydrogen atom can be obtained. These structures are potentially useful for device applications and offer a route to the fabrication of ultrafine and well defined tips for scanning tunneling microscopy.Comment: 4 pages, 4 figure

Shadow features and shadow bands in the paramagnetic state of cuprate superconductors

The conditions for the precursors of antiferromagnetic bands in cuprate superconductors are studied using weak-to-intermediate coupling approach. It is shown that there are, in fact, three different precursor effects due to the proximity to antiferromagnetic instability: i) the shadow band which associated with new pole in the Green's function ii) the dispersive shadow feature due to the thermal enhancement of the scattering rate and iii) the non-dispersive shadow feature due to quantum spin fluctuation that exist only in $\vec{k}-$scan of the spectral function $A(\omega _{Fixed},\vec{k})$. I found that dispersive shadow peaks in $A(\omega,\vec{k})$ can exist at finite temperature T in the renormalized classical regime, when $T\gg \omega _{sf}$, $\xi_{AFM} >\xi_{th}=v_F/T$ ($\omega _{sf}$ is the characteristic energy of spin fluctuations, $\xi_{th}$ is the thermal wave length of electron). In contrast at zero temperature, only non-dispersive shadow feature in $A(\omega_{Fixed},\vec{k})$ has been found. I found, however, that the latter effect is always very small. The theory predict no shadow effects in the optimally doped materials. The conditions for which shadow peaks can be observed in photoemission are discussed.Comment: 6 pages, REVTEX, 2 ps figures, version to be published in PR

Structure of the Charge-Density Wave in Cuprate Superconductors: Lessons from NMR

Using a mix of numerical and analytic methods, we show that recent NMR $^{17}$O measurements provide detailed information about the structure of the charge-density wave (CDW) phase in underdoped YBa$_2$Cu$_3$O$_{6+x}$. We perform Bogoliubov-de Gennes (BdG) calculations of both the local density of states and the orbitally resolved charge density, which are closely related to the magnetic and electric quadrupole contributions to the NMR spectrum, using a microscopic model that was shown previously to agree closely with x-ray experiments. The BdG results reproduce qualitative features of the experimental spectrum extremely well. These results are interpreted in terms of a generic "hotspot" model that allows one to trace the origins of the NMR lineshapes. We find that four quantities---the orbital character of the Fermi surface at the hotspots, the Fermi surface curvature at the hotspots, the CDW correlation length, and the magnitude of the subdominant CDW component---are key in determining the lineshapes

Intrinsic Hallmarks of Phonon-Induced Charge Order in Cuprates

Charge-density wave (CDW) modulations in underdoped high-temperature cuprate superconductors remain a central puzzle in condensed matter physics. However, despite a substantial experimental verification of this ubiquitous phase in a large class of high $T_{\mathrm{c}}$ cuprates, a complete theoretical explanation of this phase is still missing. Here, we build upon our recent proposal that the CDW in underdoped cuprates (Y- and Bi- based compounds) emerges from a unique cooperation of the B$_{1g}$ bond-buckling phonon with strong electronic correlations. We assume a static mean-field lattice distortion with B$_{1g}$ symmetry, regardless of its origin, with a commensurate wave vector $\mathbf{q}^*=(2\pi/3,0)/(0,2\pi/3)$. We show that such a phonon-induced CDW (both uni- and biaxial) reconstructs the Fermi surface, leading to electron and hole pockets, with relevant quantum oscillation frequencies in close consistency with the experiments. Furthermore, a systematic analysis of the symmetry of the intra-unit-cell charge modulations on the copper-oxygen planes is provided. We find that the atomic charge modulation on the CuO$_2$ unit cell is predominantly of $s$-wave character -- in support of the recent experimental observation.Comment: 11 pages, 7 Figure

Competition between local and nonlocal dissipation effects in two-dimensional quantum Josephson junction arrays

We discuss the local and nonlocal dissipation effects on the existence of the global phase coherence transitions in two dimensional Josephson-coupled junctions. The quantum phase transitions are also examined for various lattice geometries: square, triangular and honeycomb. The T=0 superconductor-insulator phase transition is analyzed as a function of several control parameters which include self-capacitance and junction capacitance and both local and nonlocal dissipation effects. We found the critical value of the nonlocal dissipation parameter \alpha_{1} depends on a geometry of the lattice. The critical value of the normal state conductance seems to be difficult to obtain experimentally if we take into consideration different damping mechanisms which are presented in real physical systems.Comment: accepted to Physica C Ref. No.: PHYSC-D-06-00244R

Snow water equivalent modeling components in NewAge-JGrass

This paper presents a package of modified temperature-index-based snow water equivalent models as part of the hydrological modeling system NewAge-JGrass. Three temperature-based snow models are integrated into the NewAge-JGrass modeling system and use many of its components such as those for radiation balance (short wave radiation balance, SWRB), kriging (KRIGING), automatic calibration algorithms (particle swarm optimization) and tests of goodness of fit (NewAge-V), to build suitable modeling solutions (MS). Similarly to all the NewAge-JGrass components, the models can be executed both in raster and in vector mode. The simulation time step can be daily, hourly or sub-hourly, depending on user needs and availability of input data. The MS are applied on the Cache la Poudre River basin (CO, USA) using three test applications. First, daily snow water equivalent is simulated for three different measurement stations for two snow model formulations. Second, hourly snow water equivalent is simulated using all the three different snow model formulae. Finally, a raster mode application is performed to compute snow water equivalent maps for the whole Cache la Poudre Basin

The crystal structure of munakataite, Pb_2Cu_2(Se^(4+)O_3)(SO_4)(OH)_4, from Otto Mountain, San Bernardino County, California, USA

Munakataite, Pb_2Cu_2(Se^(4+)O_3)(SO_4)(OH)_4, has been found in association with a variety of rare secondary Te minerals at Otto Mountain, San Bernardino County, California, USA. It is very rare and occurs as subparallel bundles of blue needles up to 1 mm long. Electron microprobe analyses provided the empirical formula Pb_(1.96)Cu_(1.60)[(Se^(4+)_(0.89)S_(0.11)_(∑1)O_3](SO_4)[(OH)_(3.34)(H_2O)_(0.66)]_(∑4). Munakataite is monoclinic, space group P2_1/m, with cell parameters a = 9.8023(26), b = 5.6751(14), c = 9.2811(25) Å , β = 102.443(6), V = 504.2(2) Å^3 and Z = 2. The crystal structure, solved by direct methods and refined to R_1 = 0.0308 for 544 F_o > 4σF reflections, consists of Jahn-Teller-distorted Cu^(2+)O_6 square bipyramids, which form chains along b by sharing trans edges across their square planes. The chains are decorated by SO_4 tetrahedra and Se^4+O_3 pyramids, which bond to apical corners of adjacent bipyramids. The chains are linked to one another via bonds to two different PbO_9 polyhedra, only one of which exhibits one-sided coordination typical of Pb^(2+) with a stereochemically active 6s^2 lone-electron-pair. Munakataite is isostructural with schmiederite and the structure is closely related to that of linarite