Zero field magnetoresistance peaks in open quantum dots: Weak localizationor a fundamental property?

We have performed numerical simulations of the magnetotransport of open qua ntum dots with contacts supporting several modes. We reproduce the zero fie ld resistance peaks seen in experiments performed on such structures, a phe nomenon previously attributed to weak localization. Our results, however, i ndicate that these peaks call have an entirely different origin. involving the zero field crossings of conductance resonance lines that reflect the un derlying dot spectrum. Even with significant,ll ensemble averaging, the nat ure of these crossings largely determines the shape and width of the resist ance peaks.