Magnetically induced suppression of phase breaking in ballistic mesoscopic billiards

The phase-breaking time of electrons (${\mathrm{\tau }}_{\mathrm{\phi }}$) trapped in a ballistic quantum dot is determined using two independent analyses of its low-temperature conductance fluctuations. In the first approach the amplitude of the fluctuations is analyzed in terms of random-matrix theory, while the second estimate is obtained from a study of the correlation field. Values of ${\mathrm{\tau }}_{\mathrm{\phi }}$ determined by these two techniques are found to differ by a factor of 6, and comparing with the results of previous experiments we suggest this discrepancy results from the random-matrix-theory-based analysis overestimating the phase-breaking rate. The correlation analysis is also found to be consistent with a sudden suppression of the phase-breaking rate, by more than an order of magnitude at high magnetic fields.