Figure 5
(Color online) The transverse susceptibility and associated features in the Fermi surface and DoS of the next-nearest-neighbor tight-binding model discussed in the text. The first column shows transverse susceptibility,
evaluated for two situations, (a)
,
, and (b)
,
, chosen to illustrate various possible wave vectors of distortion. In both cases
is chosen such that the spin-splitting places one species’ Fermi surface at the van Hove singularity, in (a) this is the minority Fermi surface and in (b) the majority. The susceptibility shows peaks at both large and small
. In the second column, the spin-up and -down Fermi surfaces are shown for each case. Displacements of these Fermi surfaces corresponding to the wave vectors of the peaks in the susceptibility are indicated. These displacements show the origin of the peaks. Wave vectors
,
, and
are all nesting vectors, however,
is not, it corresponds to a different situation described below. Note that in (a), we have indicated the equivalent displacement of the hole rather than electron pocket for ease of visualization. The third column shows the Fermi surfaces after hybridization for the low
cases, these are the Fermi surfaces in the spiral state. The wave vector
corresponds to opening the neck of the Fermi surface across the van Hove singularity. The black dotted line shows the Fermi surface before hybridization. The rightmost column shows the densities of states for the two spin-species before (black dotted line) and after (solid lines) the spiral state forms. In (a), a new peak has appeared below the Fermi level. In (b), the peaks in the densities of states have split and moved below the Fermi level. The energetic origin of the nesting
and non-nesting (
) vectors is therefore similar, being associated with the appearance of new peaks in the DoS below the Fermi surface.
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