Band structure of Charge Ordered Doped Antiferromagnets

We study the distribution of electronic spectral weight in a doped antiferromagnet with various types of charge order and compare to angle resolved photoemission experiments on lightly doped La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) and electron doped Nd$_{2-x}$Ce$_x$CuO$_{4\pm\delta}$. Calculations on in-phase stripe and bubble phases for the electron doped system are both in good agreement with experiment including in particular the existence of in-gap spectral weight. In addition we find that for in-phase stripes, in contrast to anti-phase stripes, the chemical potential is likely to move with doping. For the hole doped system we find that ``staircase'' stripes which are globally diagonal but locally vertical or horizontal can reproduce the photoemission data whereas pure diagonal stripes cannot. We also calculate the magnetic structure factors of such staircase stripes and find that as the stripe separation is decreased with increased doping these evolve from diagonal to vertical separated by a coexistence region. The results suggest that the transition from horizontal to diagonal stripes seen in neutron scattering on underdoped LSCO may be a crossover between a regime where the typical length of straight stripe segments is longer than the inter-stripe spacing to one where it is shorter and that locally the stripes are always aligned with the Cu-O bonds.Comment: 13 pages, 16 figure

Infinitesimal Variations of Hodge Structure at Infinity

By analyzing the local and infinitesimal behavior of degenerating polarized variations of Hodge structure the notion of infinitesimal variation of Hodge structure at infinity is introduced. It is shown that all such structures can be integrated to polarized variations of Hodge structure and that, conversely, all are limits of infinitesimal variations of Hodge structure (IVHS) at finite points. As an illustration of the rich information encoded in this new structure, some instances of the maximal dimension problem for this type of infinitesimal variation are presented and contrasted with the "classical" case of IVHS at finite points

Nodal-antinodal dichotomy and magic doping fractions in a stripe ordered antiferromagnet

We study a model of a stripe ordered doped antiferromagnet consisting of coupled Hubbard ladders which can be tuned from quasi-one-dimensional to two-dimensional. We solve for the magnetization and charge density on the ladders by Hartree-Fock theory and find a set of solutions with lightly doped ``spin-stripes'' which are antiferromagnetic and more heavily doped anti-phase ``charge-stripes''. Both the spin- and charge-stripes have electronic spectral weight near the Fermi energy but in different regions of the Brillouin zone; the spin-stripes in the ``nodal'' region, near (\pi/2,\pi/2), and the charge-stripes in the ``antinodal'' region, near (\pi,0). We find a striking dichotomy between nodal and antinodal states in which the nodal states are essentially delocalized and two-dimensional whereas the antinodal states are quasi-one-dimensional, localized on individual charge-stripes. For bond-centered stripes we also find an even-odd effect of the charge periodicity which could explain the non-monotonous variations with doping of the low-temperature resistivity in LSCOComment: 6 pages, 6 figures, Expanded and improved, with additional reference

Electric arc device for heating gases Patent

Electric arc device for minimizing electrode ablation and heating gases to supersonic or hypersonic wind tunnel temperature

Monolayer charged quantum films: A quantum simulation study

We use path-integral Monte Carlo (PIMC) to study the effects of adding a long-range repulsive Coulomb interaction to the usual Van der Waals interaction between two atoms of a submonolayer quantum film such as helium on graphite or a pure two-dimensional superfluid. Such interactions frustrate or compete with the natural tendency of the system for phase separation namely to form a macroscopic liquid or solid phase. We find that as a function of the relative strength of the long-range repulsion, surface coverage and temperature, the system undergoes a series of transformations, including a triangular Wigner-like crystal of clusters, a charge stripe-ordered phase and a fluid phase. The goal of these studies is to understand the role of quantum fluctuations when such competing interactions appear together with formation of preexisting electron pairs as might be the case in cuprate superconductors.Comment: 10 pages, 7 figures to be published in International Journal of Modern Physics

"Exact" Algorithm for Random-Bond Ising Models in 2D

We present an efficient algorithm for calculating the properties of Ising models in two dimensions, directly in the spin basis, without the need for mapping to fermion or dimer models. The algorithm gives numerically exact results for the partition function and correlation functions at a single temperature on any planar network of N Ising spins in O(N^{3/2}) time or less. The method can handle continuous or discrete bond disorder and is especially efficient in the case of bond or site dilution, where it executes in O(L^2 ln L) time near the percolation threshold. We demonstrate its feasibility on the ferromagnetic Ising model and the +/- J random-bond Ising model (RBIM) and discuss the regime of applicability in cases of full frustration such as the Ising antiferromagnet on a triangular lattice.Comment: 4.2 pages, 5 figures, accepted for publication in Phys. Rev. Let