Holographic topological defects in a ring: role of diverse boundary conditions

We investigate the formation of topological defects in the course of a dynamical phase transition with different boundary conditions in a ring from AdS/CFT correspondence. According to the Kibble-Zurek mechanism, quenching the system across the critical point to symmetry-breaking phase will result in topological defects -- winding numbers -- in a compact ring. By setting two different boundary conditions, i.e., Dirichlet and Neumann boundary conditions for the spatial component of the gauge fields in the AdS boundary, we achieve the holographic superfluid and holographic superconductor models, respectively. In the final equilibrium state, different configurations of the order parameter phases for these two models indicate a persistent superflow in the holographic superfluid, however, the holographic superconductor lacks this superflow due to the existence of local gauge fields. The two-point correlation functions of the order parameter also behave differently. In particular, for holographic superfluid the correlation function is a cosine function depending on the winding number. The correlation function for the holographic superconductor, however, decays rapidly at short distances and vanishes at long distance, due to the random localities of the gauge fields. These results are consistent with our theoretical analysis.Comment: 15pages, 4 figures; Contexts improved and references added; Accepted by JHE

Parity Symmetry Breaking and Kink Hairy Black Hole

Motivated by the Kibble-Zurek mechanism and the Gubser's argument for the charged scalar hairs near the black hole horizon in a spacetime with negative cosmological constant, we realize the kink hairs in a planar Schwarzschild-AdS black hole. By increasing the chemical potential across the critical point of the dual boundary field theory, the former $Z_2$ symmetry of the real scalar fields spontaneously break and form kinks in the bulk. Correspondingly, in the AdS boundary it resembles the kinks in a one-dimensional chain. The relation between the kink numbers and the quench rate obeys a universal scaling law which satisfies the Kibble-Zurek's prediction.Comment: 10 pages; 3 figure

Electronic band gaps and transport in aperiodic graphene superlattices of Thue-Morse sequence

We have studied the electronic properties in aperiodic graphene superlattices of Thue-Morse sequence. Although the structure is aperiodic, an unusual Dirac point (DP) does exist and its location is exactly at the position of the zero-averaged wave number (zero-$\bar{k})$. Furthermore, the zero-$\bar{k}$ gap associated with the DP is robust against the lattice constants and the incident angles, and multi-DPs can appear under the suitable conditions. A resultant controllability of electron transport in Thue-Morse sequence is predicted, which may facilitate the development of many graphene-based electronics.Comment: Accepted for publication in Applied Physics Letters; 4 pagese, 5 figure