Enhanced thermoelectric power near the quantum phase transition in the itinerant-electron ferromagnet MnSi

The itinerant-electron ferromagnet MnSi is a well-known example that shows a transition from Fermi-liquid Δρ□ T2 to non-Fermi-liquid (NFL) Δρ□ T3⊃/2 behavior when the spiral ferromagnetic transition T_c≈29 K at ambient pressure is suppressed to zero by the application of hydrostatic pressures above P_c≈14.6 kbar. Several experimental probes have been employed to reveal the intriguing properties near P_c. In this paper, we report the temperature dependence of thermoelectric power S (T) under hydrostatic pressures up to 20 kbar on a single crystal of MnSi. At pressures close to P_c, we observed at low temperatures an unusual enhancement of S (T), which can be described well with the relationship S/T□ln (1/T), a formula that has been proposed to describe a system as a quantum critical point (QCP) is approached. The relationship has previously been observed in systems close to a magnetic QCP, for example, La_1.6-x Nd_0.4 Sr_x CuO₄ (x=0.24). The enhancement of thermoelectric power in MnSi occurs at a temperature above the NFL phase and over a broad pressure range around P_c.