Superconducting phase with fractional vortices in the frustrated kagome wire network at f=1/2 -: art. no. 134522

In classical XY kagome antiferromagnets, there can be a low-temperature phase where (3) = e(i3 theta) has quasi-long-range order but psi is disordered, as well as more conventional antiferromagnetic phases where psi is ordered in various possible patterns (theta is the angle of orientation of the spin). To investigate when these phases exist in a physical system. we study superconducting kagome wire networks in a transverse magnetic field when the magnetic flux through an elementary triangle is a half of a flux quantum. Within Ginzburg-Landau theory, we calculate the helicity moduli of each phase to estimate the Kosterlitz-Thouless (KT) transition temperatures. Then at the KT temperatures, we estimate the barriers to move vortices and the effects that lift the large degeneracy in the possible psi patterns, The effects we have considered are inductive couplings, nonzero wire width, and the order-by-disorder effect due to thermal fluctuations. The first two effects prefer q = 0 patterns, while the last one selects a root3 x root3 pattern of supercurrents. Using the parameters of recent experiments, we conclude that at the KT temperature, the nonzero wire width effect dominates, which stabilizes a conventional superconducting phase with a q = 0 current pattern. However, by adjusting the experimental parameters, for example by bending the wires a little, it appears that the psi (3) superconducting phase can instead be stabilized. The barriers to vortex motion are low enough that the system can equilibrate into this phase.