Field tuning of the electron and hole populations in the ruthenate Bi ₃Ru₃O₁₁

Experiments on the Hall coefficient R_H and heat capacity C reveal an unusual, compensated electronic ground state in the ruthenate Bi ₃Ru₃O₁₁. At low temperature T, R, R _H decreases linearly with magnetic field |H for fields larger than the field scale set by the Zeeman energy, The results suggest that the electron and hole populations are tuned by H in opposite directions via coupling of the spins to the field. As T is decreased below 5 K, the curve C(T)/T vs. T ² shows an anomalous flattening consistent with a rapidly growing Sommerfeld parameter γ(T). We discuss shifts of the electron and hole chemical potentials by H to interpret the observed behavior of R_H.