Ground state properties of a Zeeman-split heavy metal
  A Zeeman field affects the metallic heavy fermion ground state in two ways: (i) it splits the spin-degerenate conduction sea, leaving spin up and spin down Fermi surfaces with different band curvature; (ii) it competes with the Kondo effect and thus suppresses the mass enhancement. Taking these two effects into account, we compute the quasiparticle effective mass as a function of applied field strength within hybridization mean field theory. We also derive an expression for the optical conductivity, which is relevant to infrared spectroscopy measurements. 
K. S. D. Beach