Single-crystal growth of YbRh2Si2 and YbIr2Si2

We report on the single-crystal growth of the heavy-fermion compounds YbRh2Si2 and YbIr2Si2 using a high-temperature indium-flux technique. The optimization of the initial composition and the temperature-time profile lead to large (up to 100 mg) and clean (rho(0) approximate to 0.5 mu Omega cm) single crystals of YbRh2Si2. Low-temperature resistivity measurements revealed a sample-dependent temperature exponent below 10 K, which for the samples with highest quality deviates from a linear-in-T behaviour. Furthermore, we grew single crystals of the alloy series Yb(Rh1-xIrx)(2)Si-2 with 0 <= x <= 0.23 and report the structural details. For pure YbIr2Si2, we establish the formation of two crystallographic modifications, where the magnetic 4f electrons have different physical ground states.