UBC Theses and Dissertations
Holographic gauge/gravity duality and symmetry breaking in semimetals Kim, Namshik
We use the AdS/CFT correspondence (the holographic duality of gauge/gravity theory) to study exciton driven dynamical symmetry breaking in certain (2+1)-dimensional defect quantum field theories. These models can be argued to be analogs of the electrons with Coulomb interactions which occur in Dirac semimetals and the results our study of these model systems are indicative of behaviours that might be expected in semimetal systems such as monolayer and double monolayer graphene. The field theory models have simple holographic duals, the D3-probe-D5 brane system and the D3-probe-D7 brane system. Analysis of those systems yields information about the strong coupling planar limits of the defect quantum field theories. We study the possible occurrence of exciton condensates in the strong coupling limit of single-defect theories as well as double monolayer theories where we find a rich and interesting phase diagram. The phenomena which we study include the magnetic catalysis of chiral symmetry breaking in monolayers and inter-layer exciton condensation in double monolayers. In the latter case, we find a solvable model where the current-current correlations functions in the planar strongly coupled field theory can be computed explicitly and exhibit interesting behavior. Although the models that we analyze differ in detail from real condensed matter systems, we identify some phenomena which can occur at strong coupling in a generic system and which could well be relevant to the ongoing experiments on multi-monolayer Dirac semimetals. An example is the spontaneous nesting of Fermi surfaces in double monolayers. In particular, we suggest an easy to observe experimental signature of this phenomenon.
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