DOUBLE BUTTERFLY SPECTRUM FOR 2 INTERACTING PARTICLES IN THE HARPER MODEL

We study the effect of interparticle interaction U on the spectrum of the Harper model and show that it leads to a pure-point component aris ing from the multifractal spectrum of the noninteracting problem. Our numerical studies allow us to understand the global structure of the s pectrum. An analytical approach developed permits us to understand the origin of localized states in the limit of strong interaction U and f ine spectral structure for small U.