Evidence for power-law Griffiths singularities in a layered Heisenberg magnet

Quantum healing of classical singularities in power-law spacetimes

We study a broad class of spacetimes whose metric coefficients reduce to powers of a radius r in the limit of small r. Among these four-parameter “power-law” metrics we identify those parameters for which the spacetimes have classical singularities as r → 0. We show that a large set of such classically singular spacetimes is nevertheless nonsingular quantum mechanically, in that the Hamiltonian...

Griffiths Singularities in the Dynamics of Disordered Ising

We study the asymptotic behaviour of the correlation function q(t)= l N =-(Si(0) Si@>) for dilute, short-range Ising ferromagnets and spin glasses with single spin-N i-1 flip dynamics, Using an eigenfunction expansion for the time evolution operator and a variational estimate for the gap in the spectrum of this operator, we prove that, for a range of temperatures above the T, of the random syst...

Quantum Griffiths singularities in the transverse-field Ising spin glass.

We report a Monte Carlo study of the effects of fluctuations in the bond distribution of Ising spin glasses in a transverse magnetic field, in the paramagnetic phase in the T → 0 limit. Rare, strong fluctuations give rise to Griffiths singularities, which can dominate the zero-temperature behavior of these quantum systems, as originally demonstrated by McCoy for one-dimensional (d = 1) systems....

Griffiths-McCoy singularities in random quantum spin chains: Exact results

We consider random quantum (tight-binding, XX and Ising) spin chains in the off-critical region and study their Griffiths-McCoy singularities. These are obtained from the density of states of the low-energy excitations, which is calculated exactly by the Dyson-Schmidt method. In large finite systems the low-energy excitations are shown to follow the statistics of extremes and their distribution...

A Necessary Condition for Weyl-Heisenberg Frames