Thermal String Excitations in Artificial Spin-Ice Dipolar Arrays

We report on a theoretical investigation of artificial spin-ice dipolar arrays, using a nanoisland geometry adopted from recent experiments [A. Farhan $\mathit{\text{et}}\mathit{\text{al.}}$, Nature Phys.\ $\mathbf{\text{9}}$ (2013) 375]. The number of thermal magnetic string excitations in the square lattice is drastically increased by a vertical displacement of rows and columns. We find large increments especially for low temperatures and for string excitations with quasi-monopoles of charges $\pm 4$. By kinetic Monte Carlo simulations we address the thermal stability of such excitations, thereby providing time scales for their experimental observation.