The holographic Fermions over the ionic lattice with CDW

We study the holographic Fermion as a probe over the background with ionic lattice, which may undergo a phase transition with the development of charge density wave by the spontaneous breaking of the translational symmetry. We focus on the structure of the Fermi surface within different Brillouin zones and demonstrate how the presence of CDW in the background affects the formation of the band gap in the momentum space. Specifically, we find the formation of the CDW enhances the amplitude of spectral function as well as the momentum of the Fermi surface. Furthermore, we are concerned with the change of the Fermi surface with the doping parameter as well as the lattice amplitude. Interestingly, we find that the radius of the Fermi surface expands with the increase of the doping parameter and finally may cross the first Brillouin zone. Additionally, the width of band gap becomes larger with the increase of the lattice amplitude as well, which is consistent with the observation in condensed matter experiments.

💡 Research Summary

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The paper investigates fermionic response in a holographic setting where an ionic lattice coexists with a spontaneously generated charge‑density wave (CDW). The bulk theory consists of four‑dimensional Einstein gravity coupled to two U(1) gauge fields (A and B) and a scalar Φ. The first gauge field A encodes the doping level, while B plays the role of the electromagnetic field that couples to the probe fermion. The scalar Φ is the order parameter for the CDW and interacts non‑linearly with A through a coupling Z_A(Φ)=1−β²L²Φ² (β=−129), which triggers an instability at low temperature, leading to a spatially modulated Φ with wave‑vector p.

The ionic lattice is introduced via a spatially periodic chemical potential for B: \