arXiv subjects

Andreas P. Schnyder

Publications and source records attributed to Andreas P. Schnyder.

112 records · Page 7Linked to original sources

arXiv2008

Spatially Anisotropic Heisenberg Kagome Antiferromagnet

We study the quasi-one-dimensional limit of the spin-1/2 quantum Heisenberg antiferromagnet on the kagome lattice. The lattice is divided into antiferromagnetic spin-chains (exchange J) that are weakly coupled via intermediate "dangling" spins (exchange J'). Using one-dimensional bosonization, renormalization group methods, and current algebra techniques the ground state is determined in the limit J'<<J. We find that the dangling spins and chain spins form a spiral with O(1) and O(J'/J) static moments, respectively, atop of which the chain spins exhibit a smaller O[(J'/J)^2] antiferromagnetically ordered component along the axis perpendicular to the spiral plane.

cond-mat.str-el↗

arXiv2008

Irrational vs. rational charge and statistics in two-dimensional quantum systems

We show that quasiparticle excitations with irrational charge and irrational exchange statistics exist in tight-biding systems described, in the continuum approximation, by the Dirac equation in (2+1)-dimensional space and time. These excitations can be deconfined at zero temperature, but when they are, the charge re-rationalizes to the value 1/2 and the exchange statistics to that of "quartons" (half-semions).

cond-mat.str-el↗

arXiv2007

Screening in (d+s)-wave superconductors: Application to Raman scattering

We study the polarization-dependent electronic Raman response of untwinned YBa$_2$Cu$_3$O$_{7-δ}$ superconductors employing a tight-binding band structure with anisotropic hopping matrix parameters and a superconducting gap with a mixing of $d$- and s-wave symmetry. Using general arguments we find screening terms in the $B^{\}_{1g}$ scattering channel which are required by gauge invariance. As a result, we obtain a small but measurable softening of the pair-breaking peak, whose position has been attributed for a long time to twice the superconducting gap maximum. Furthermore, we predict superconductivity-induced changes in the phonon line shapes that could provide a way to detect the isotropic s-wave admixture to the superconducting gap.

cond-mat.supr-con↗

arXiv2006

Theory for Inelastic Neutron Scattering in Orthorhombic High-Tc Superconductors

Using a Fermi-liquid-based theory we calculate the in-plane anisotropy of the spin susceptibility for hole-doped high-T_c cuprates. Employing the two-dimensional one-band Hubbard model and a generalized RPA-type theory we consider anisotropic hopping matrix elements ($t_x \neq t_y$) and a mixing of d- and s-wave symmetry of the superconducting order parameter in order to describe orthorhombic superconductors. We compare our calculations with available inelastic neutron scattering data on untwinned YBa{2}Cu{3}O{7-δ} and find good agreement. Furthermore, we predict a strongly anisotropic in-plane dispersion of the resonance peak.

cond-mat.supr-con↗