YbRh2Si2:: Spin fluctuations in the vicinity of a quantum critical point at low magnetic field -: art. no. 107202

We report a Si-29 NMR study on aligned single crystals of YbRh2Si2 which shows behavior characteristic of a quantum critical point (QCP: T-N-->0). The Knight shift K and the nuclear spin-lattice relaxation rate 1/T-1 of Si show a strong dependence on the external field H, especially below 5 kOe. At the lowest H used in this measurement (Hsimilar to1.5 kOe), it was found that 1/T1T continues to increase down to 50 mK, whereas K stays constant with a large magnitude below 200 mK. This result strongly suggests the development of antiferromagnetic fluctuations with finite q vectors that compete with q=0 spin fluctuations in the vicinity of the QCP near H=0.5 kOe.