Ferromagnetic Quantum Critical Fluctuations in YbRh_2(Si_(0.95)Ge_(0.05))_2

摘要

The bulk magnetic susceptibility χ(T, B) of YbRh_2(Si_(0.95)Ge_(0.05))_2 has been investigated close to the field-induced quantum critical point at B_c = 0.027 T. For B ≤ 0.05 T a Curie-Weiss law with a negative Weiss temperature is observed at temperatures below 0.3 K. Outside this region, the susceptibility indicates ferromagnetic quantum critical fluctuations, χ(T) ∝ T~(-0.6) above 0.3 K. At low temperatures the Pauli susceptibility follows χ_0 ∝ (B — B_C)~(0.6) and scales with the coefficient of the T~2 term in the electrical resistivity. The Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the critical field.