Muon spin rotation and relaxation experiments have been carried out in single crystals of YbRh 2 Si 2 , a compound that exhibits non-Fermi-liquid (NFL) behavior associated with a quantum critical point (QCP) at T=0. The zero-field muon relaxation rate is found to be independent of temperature down to 100 mK but to increase below ∼70 mK, which suggests magnetic order at low temperatures. From the relation between the internal field at the μ+ stopping site and the hyperfine coupling constant the ordered Yb 3+ moment is very small, ∼2×10− 3 μB. Muon spin rotation linewidths in a transverse field of 6 kOe indicate a homogeneous susceptibility down to 2 K, which is an order of magnitude lower than the characteristic (Kondo) temperature T K ≈25 K. This is evidence against the importance of disorder-driven NFL mechanisms in YbRh 2 Si 2 . In longitudinal magnetic fields the muon spin-lattice relaxation function G(t) is exponential, again indicative of a homogeneous system. The relaxation obeys the time-field scaling relation G(t, H)=G(t/H), which suggests long-lived spin correlations at low temperatures. The Yb 3+ spin dynamics derived from muon spin relaxation appear to be intimately related to critical magnetic fluctuations near the QCP.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 3 Nov 2003|