Medium/high-field magnetoconductance in chaotic quantum dots

The magnetoconductance G in chaotic quantum dots at medium/high magnetic fl uxes Phi is calculated by means of a tight-binding Hamiltonian on a square lattice. Chaotic dots are simulated by introducing diagonal disorder on sur face sites of L x L clusters. It is shown that when the ratio W/L is suffic iently large, W being the width of the leads, G increases steadily (almost with no fluctuations) showing a maximum at a magnetic flux Phi (max) propor tional to L-2/W (a flux at which the cyclotron radius r(c) approximate to W /2). Neither regular nor bulk disordered ballistic cavities (with a content of impurities proportional to L) show this effect. On the other hand, for magnetic fluxes such that r(c) > L/2 and up to the aforementioned maximum, the average magnetoconductance increases almost linearly with the flux with a slope proportional to W-2. These results closely follow a theory propose d by Beenakker and van Houten to explain the magnetoconductance of two poin t contacts in series.