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=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(Rh_(1-x)Ir_x)2Si2 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.