Bond-randomness effect on the quantum spin system Tl1-xKxCuCl3Tl1-xKxCuCl3 probed by muon-spin-relaxation method

Muon-spin-relaxation (μSRμSR) measurements were carried out on the randomness-introduced quantum spin system Tl1-xKxCuCl3Tl1-xKxCuCl3. Zero-field μSRμSR measurement results reveal that the rapid increase of the μSRμSR rate λλ with decreasing temperature in the case of x=0.58x=0.58. From the result of longitudinal-field μSRμSR measurements, a finite relaxation remains at 4000 G, which means that Cu-3dCu-3d spins fluctuate down to 20 mK although the slowing down of the frequency of the spin fluctuation occurs. These results suggest that there is a quite possibility of the existence of an ordered or spin frozen phase in a neighboring concentration of x around 0.58.