Density of states in chromium alloys

Both the spin- and charge-density waves of Cr alloys have significant effects on the joint density-of-states rho(omega) of the nested electron and hole Fermi surfaces below the Neel temperature T-N. The random-phase approximation is used to evaluate rho(omega) within a three-band model of Cr alloys. In the commensurate phase of the spin-density wave, rho(omega) contains a single energy gap 2 Delta. At zero temperature, 2 Delta reaches a maximum value of about 370 meV and spans the Fermi energy, which is shifted upwards by the presence of a charge-density wave (CDW). In the incommensurate phase, rho(omega) contains two energy gaps Delta(1)' and Delta(1) above and below midgap states. If the CDW order parameter delta vanishes, then Delta(1)'=Delta(1) and both reach a maximum of about 130 meV at T=0; if delta is nonzero, then Delta(1)'<Delta(1). A third energy gap Delta(2) includes both the midgap states as well as the smaller gaps Delta(1) and Delta(1)'. For pure Cr, Delta(2) reaches a maximum value of about 450 meV at T=0. Unlike Delta(1) and Delta(1)', Delta(2) does not vanish at T-N but decreases to about 370 meV. Our results are compared with those obtained earlier from a two-band model in the absence of the CDW. This paper also clarifies the assumptions made by the three-band model and the role of the unpaired holes which reside on the larger of the two nested Fermi surfaces.