Tuning low-energy scales in YbRh_{2}Si_{2} by non-isoelectronic substitution and pressure

Abstract

The heavy-fermion metal YbRh_{2}Si_{2} realizes a field-induced quantum critical point with multiple vanishing energy scales T_{N}(B) and T^{*}(B). We investigate their change with partial non-isoelectronic substitutions, chemical and hydrostatic pressure. Low-temperature electrical resistivity, specific heat, and magnetic susceptibility of Yb(Rh_{1−x}T_{x})_{2}Si_{2} with T=Fe or Ni for x≤0.1, magnetic fields B≤0.3T (applied perpendicular to the c axis), and hydrostatic pressure p≤1.5GPa are reported. The data allow us to disentangle the combined influences of hydrostatic and chemical pressure, as well as non-isoelectronic substitution. In contrast to Ni and Co substitution, which enhance magnetic order, Fe substitution acts oppositely. For x=0.1, it also completely suppresses the T^{*} crossover and eliminates ferromagnetic fluctuations. The pressure, magnetic field, and temperature dependences of T^{*} are incompatible with its interpretation as Kondo breakdown signature.