CuCl 3 probed by muon-spin-relaxation method

The bond-randomness effect on the singlet ground state has been reported in the mixed system Tl1−xKxCuCl3 [1,2]. In zero field (ZF), the ground state has no gap (magnetic) in the mixed system, although both the parent materials have finite excitation gaps (nonmagnetic). Shindo et al. carried out specific heat measurements in magnetic fields, and discussed the obtained phase diagram in connection with the appearance of a new phase, the Bose glass phase, in lower magnetic fields at T = 0. We observed the slight increase and the saturation of the muon spin relaxation rate λ in Tl1−xKxCuCl3 with x = 0.20, and this result suggests the existence of the Bose glass phase [3]. Recently, ZF-μSR measurements for x = 0.44 were carried out, and the divergent increase of λ was observed, which suggests the critical slowing down of the frequency of the Cu-3d spin fluctuations toward a spin frozen state [4]. However, it is not yet known whether or not another ground state apart from the Bose-glass phase and the gapped state, for example, an ordered state, really appears when the randomness is enhanced with increasing the concentration of x in the system. In this study, in order to to investigate the ground state in highly random system and possibility of the existence of an ordered state, ZFand LF-field μSR measurements were carried out in single crystals Tl1−xKxCuCl3 with x = 0.58 at the Swiss Muon Source (SμS), Paul Scherrer Institut (PSI), Villigen, Switzerland. ZF-μSR results reveals that the rapid increase of λ with decreasing temperature and that the saturation of λ below 0.5 K, and the absolute value of λ is three times larger than that in the case of x = 0.44. From the LF-μSR measurements, the dynamical fluctuation, which can not be decoupled upto 4000 gauss, remains at 20 mK. These results suggest that there is a quite possibility of the existence of an ordered phase in a neighbouring concentration of x around 0.58.