Abstract
We describe a strongly coupled layered system in 3+1 dimensions by means of a top-down D-brane construction. Adjoint matter is encoded in a large-Nc stack of D3-branes, while fundamental matter is confined to (2 + 1)-dimensional defects introduced by a large-Nf stack of smeared D5-branes. To the anisotropic Lifshitz-like background geometry, we add a single flavor D7-brane treated in the probe limit. Such bulk setup corresponds to a partially quenched approximation for the dual field theory. The holographic model sheds light on the anisotropic physics induced by the layered structure, allowing one to disentangle flavor physics along and orthogonal to the layers as well as identifying distinct scaling laws for various dynamical quantities. We study the thermodynamics and the fluctuation spectrum with varying valence quark mass or baryon chemical potential. We also focus on the density wave propagation in both the hydrodynamic and collisionless regimes where analytic methods complement the numerics, while the latter provides the only resource to address the intermediate transition regime.
Highlights
The physics of (2 + 1)-dimensional layers is at the core of two active research fronts in condensed matter: graphene and layered hetero-structures
We describe a strongly coupled layered system in 3+1 dimensions by means of a top-down D-brane construction
Adjoint matter is encoded in a large-Nc stack of D3branes, while fundamental matter is confined to (2+1)-dimensional defects introduced by a large-Nf stack of smeared D5-branes
Summary
The physics of (2 + 1)-dimensional layers is at the core of two active research fronts in condensed matter: graphene and layered hetero-structures. The collective dynamics has to be directly addressed without any pre-established paradigm based on long-lived modes This constitutes a fundamental motivation to resort to holographic descriptions [2, 3] that, through the study of the small fluctuations of the gravity dual, provide explicit information on the low-energy collective behavior of the strongly-coupled boundary field theory. The study of the complete dynamical system is rather involved, we adopt an approximation in which the D7-brane is considered a probe in the geometry generated by the set of intersecting D3- and D5-branes. In appendix A we further show that this embedding is supersymmetric
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