Lifshitz transition in a holographic finite density flavor brane Weyl semimetal

We extend a top-down holographic model of a Weyl semimetal to finite charge density and compute the fermionic spectral function by introducing two probe fermions of opposite chirality. The model is controlled by the boundary fermion mass <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>M</a:mi> </a:mrow> </a:math> and the chemical potential <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>μ</c:mi> </c:math> . In the zero density, small- <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>M</e:mi> </e:math> limit, we recover four energy bands, two Weyl points, and linear dispersion in their vicinity, the hallmarks of a Weyl semimetal. As <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>M</g:mi> </g:math> increases, the bands between the Weyl points become progressively compressed and the spectral weight associated with those bands is smeared out. At finite charge density, we map the Fermi surface in momentum space and identify a Lifshitz transition: two distinct Fermi pockets, each enclosing a different Weyl point, merge into a single large Fermi surface that encloses both. This transition can be induced by either control parameter. Varying <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>M</i:mi> </i:math> alters the band structure and thus the band shape, which drives the Lifshitz transition, whereas changing <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>μ</k:mi> </k:math> shifts the bands relative to the Fermi level without qualitatively changing the band structure, producing the Lifshitz transition by moving the band positions.