Devil's Staircase in Semimetals

点击翻译按钮获取中文摘要

Among the magnetic materials known so far, CeSb has the most complex phase diagram as a function of temperature and magnetic field. The complex magnetic phase diagram is know as the devil's staircase. Generally, the series of CeX (X=P,As, Bi, Sb) have complex magnetic phase diagrams in different degree, which suggeststhat there is a common mechanism for the devil's staircase observed in CeX.A characteristic feature of CeX is smallness of carriers. The carriers of CeX consist of holes at the GAMMA point and electrons at the X points. Under this situation, a new type of scattering processes from holes to electrons and vice versa accompanied by spin exchange with f-spins. This process may be calledoff-diagonal exchange in contrast to the usual exchanges where the scattering are within a band. The momentum transfer associated with his off-diagonal exchange corresponds to the antiferromagnetic wave vector, favoring antiferromagnetic RKKY interaction among the f spins. On the other hand, the ordinary exchanges favor ferromagnetic coupling in the low carrier limit. In this project, we have shown that the frustration between the RKKY interactions originated from these two types of exchange mechanisms is the basic mechanism for the devil's staircase in CeX by using a simple one-dimensional model.Since the origin of the RKKY interaction can be traced back to the Friedel oscillations, we have proceeded to study the spin and charge Friedel oscillations in the Kondo lattice model. By using thedensity matrix renormalization group method, we have observed spin and charge Friedel oscillations. From the period it is concluded that the Fermi volume is large in the sense that the Fermi wavevector isdetermined by the sum of densities of conduction electrons and localized spins.