CHARGING SPECTRUM AND CONFIGURATIONS OF A WIGNER CRYSTAL ISLAND

Charging of a clean two-dimensional island is studied in the regime of small concentration of electrons when they form the Wigner crystal. T wo forms of electron-electron interaction potential are studied: the p ure Coulomb interaction and the exponential interaction corresponding to the screening by a pair of close metallic gates. The electrons are assumed to reside in a parabolic external confining potential. Due to the crystalline symmetry the center of the confinement can be situated at distinct positions with respect to the crystal. With the increasin g number of electrons N the center periodically hops from one such a l ocation to another providing the lowest total energy. These events occ ur with the period similar to N-1/2. At these moments in the case of t he pure Coulomb interaction the charging energy of the island has a ne gative correction approximate to 15%. For the case of the exponential interaction at the moments of switching the capacitance becomes negati ve and similar to N-1/4 new electrons enter the island simultaneously. The configurations of disclinations and dislocations in the island ar e also studied.