Anomalous effect of hole-doping on YbRh2Si2

Substituting Fe at the Rh site in YbRh2Si2 causes both chemical pressure and hole doping. We have investigated single crystals of Yb(Rh1-xFex)2Si2 with x=0.05 by specific heat, magnetization, resistivity and magnetocaloric effect measurements down to ∝20 mK. The observed shift of the broad maximum in ρ(T) from 140 to 115 K and the reduction of the Kondo temperature from 25 to 15 K could be ascribed to the effect of an effective chemical pressure of ∝0.8 GPa. Without charge carrier doping, such pressure enhances TN from 0.07 to about 0.3 K. However, no magnetic order is found in Yb(Rh0.95Fe0.05)2Si2 which might be due to the hole-doping effect. The energy scale T*(H) that for undoped YbRh2Si2 collapses at a critical field of 0.05 T is moderately shifted and terminates at a slightly smaller field H*(T→ 0)=0.03 T. Divergent behavior of the Sommerfeld coefficient, γ∝(H-Hc)Gr, and the magnetic Grueneisen ratio, ΓH=-Gr/(H-Hc) with Gr=-0.18 and Hc=0.03 T, is found in the field-induced Landau Fermi liquid state at H>Hc and suggests a quantum critical point in the absence of antiferromagnetic ordering in this system.