Anisotropic Hall effect in single-crystal heavy-fermion YbAgGe

Temperature- and field-dependent Hall effect measurements are reported for YbAgGe, a heavy-fermion compound exhibiting a field-induced quantum phase transition, and for two other closely related members of the RAgGe series: a nonmagnetic analog, LuAgGe and a representative, "good local moment," magnetic material, TmAgGe. Whereas the temperature-dependent Hall coefficient of YbAgGe shows behavior similar to what has been observed in a number of heavy-fermion compounds, the low temperature, field-dependent measurements reveal well-defined, sudden changes with applied field; in specific for H perpendicular to c a clear local maximum that sharpens as temperature is reduced below 2 K and that approaches a value of 45 kOe-a value that has been proposed as-the T=0 quantum critical point. Similar behavior was observed for H parallel to c where a clear minimum in the field-dependent Hall resistivity was observed at low temperatures. Although at our base temperatures it is difficult to distinguish between the field-dependent behavior predicted for (i) diffraction off a critical spin density wave or (ii) breakdown in the composite nature of the heavy electron, for both field directions there is a distinct temperature dependence of a feature that can clearly be associated with a field-induced quantum critical point at T=0 persisting up to at least 2 K.