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We study a holographic D3/probe-D5-brane model of a double monolayer Dirac semimetal in a magnetic field and in the presence of a nonzero temperature. Intra- and inter-layer exciton condensates can form by varying the balanced charge density on the layers, the spatial separation and the temperature. Constant temperature phase diagrams for a wide ra...
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Citations
... Holography, originated from string theory, is an efficient way to study strongly coupled many body systems [12,13]. Holographic models have been successfully used to describe superconductors [14], Dirac semimetals [15], Weyl semimetals [16,17], nodalline semimetals [18,19], Z 2 -Weyl semimetals [20], and others. Besides, transports [21][22][23][24] and the effect of disorders [25][26][27][28] also can be studied by holography. ...
A bstract
We introduce a holographic model that exhibits a coexistence state of the Weyl semimetal and the topological nodal line state, providing us with a valuable tool to investigate the system’s behavior in the strong coupling regime. Nine types of bulk solutions exhibiting different IR behaviors have been identified, corresponding to nine different types of boundary states. These nine states include four distinct phases, namely the Weyl-nodal phase, the gap-nodal phase, the Weyl gap phase and the gap-gap phase, four phase boundaries, which are the Weyl-Dirac phase, the gap-Dirac phase, the Dirac-gap phase and the Dirac-nodal phase, and finally a double critical point. A phase diagram is plotted that exhibits qualitative similarity to the one obtained in the weak coupling limit. The anomalous Hall conductivity, which serves as an order parameter, and the free energy are calculated, with the latter showing the continuity of the topological phase transitions within the system. Our study highlights the similarities and differences in such a topological system between the weak and strong coupling regimes, paving the way for further experimental observations.
... Various properties of the termodynamics of the D3/D5 system have been studied in refs. [11,12] and [14][15][16][17][18][19][20][21][22][23]. In ref. [12] a very general anstaz has been considered and the author has uncovered a number of interesting properties of the system. ...
A bstract
We study a holographic gauge theory dual to the D3/D5 intersection. We consider a pure gauge B-field flux through the internal two-sphere wrapped by the probe D5-brane, which corresponds to a non-commutative configuration of adjoint scalars. There is a domain wall separating the theory into regions with different ranks of the adjoint group. At zero temperature the theory is supersymmetric and at finite temperature there is a critical point of a second order phase transition. We study the corresponding critical exponents and find that the second derivatives of the free energy, with respect to the bare mass and the magnetic field, diverge with a critical exponent of − 2 / 3.
... The D3/probe-D5-brane setup was also used to model double monolayer semimetal systems formed by two parallel sheets of a semimetal separated by an insulator [17][18][19]. In this case one has to consider two stacks of probe branes (a stack of D5 and one of anti-D5) to represent holographically the two semimetal layers. ...
A bstract
We use the AdS/CFT correspondence to compute the AC conductivities for a (2+1)-dimensional system of massless fundamental fermions coupled to (3+1)-dimensional Super Yang-Mills theory at strong coupling. We consider the system at finite charge density, with a constant electric field along the defect and an orthogonal magnetic field. The holographic model we employ is the well studied D3/probe-D5-brane system. There are two competing phases in this model: a phase with broken chiral symmetry favored when the magnetic field dominates over the charge density and the electric field and a chirally symmetric phase in the opposite regime. The presence of the electric field induces Ohm and Hall currents, which can be straightforwardly computed by means of the Karch-O’Bannon technique. Studying the fluctuations around the stable configurations in linear response theory, we are able to derive the full frequency dependence of longitudinal and Hall conductivities in all the regions of the phase space.
... The D3/probe-D5-brane setup was also used to model double monolayer semimetal systems formed by two parallel sheets of a semimetal separated by an insulator [13,14,15]. In this case one has to consider two stacks of probe branes (a stack of D5 and one of anti-D5) to represent holographically the two semimetal layers. ...
We use the AdS/CFT correspondence to compute the AC conductivities for a (2+1)-dimensional system of massless fundamental fermions coupled to (3+1)-dimensional Super Yang-Mills theory at strong coupling. We consider the system at finite charge density, with a constant electric field along the defect and an orthogonal magnetic field. The holographic model we employ is the well studied D3/probe-D5-brane system. There are two competing phases in this model: a phase with broken chiral symmetry favored when the magnetic field dominates over the charge density and the electric field and a chirally symmetric phase in the opposite regime. The presence of the electric field induces Ohm and Hall currents, which can be straightforwardly computed by means of the Karch-O'Bannon technique.Studying the fluctuations around the stable configurations in linear response theory, we are able to derive the full frequency dependence of longitudinal and Hall conductivities in all the regions of the phase space.
... The only low energy modes of the open strings which connect the D7 and D3 branes are in the Ramond sector and they correspond to fermions which are two-component spinors of the SO(2,1) Lorentz group. For this reason, the D3-D7 system has been used to formulate holographic models of relativistic two dimensional electron gases [13][25]. The quantum field theory dual of this D3-D7 system is a defect field theory with fermions occupying an infinite planar 2+1-dimensional defect that is embedded in 3+1- dimensional spacetime. ...
... We shall nevertheless be able to extract some features of the field theory. Similar computations have been carried out in holographic constructions of double-monolayers of Weyl semimetals [23, 25]. The embedding of the D7 brane in the spacetime (1.6) is mostly dictated by symmetry. ...
The D3-probe-D7 brane system, oriented so as to have 2+1-dimensional Poincare symmetry, is argued to be the holographic representation of a strongly correlated fractional topological insulator which exhibits a zero-field quantized Hall effect with half-units of Hall conductivity. The phase diagram of the system with charge density and external magnetic field is found and, as well as charge gapped quantum Hall states, it exhibits metallic and semi-metallic phases with interesting behaviours. The relationship of this to other models of fractional topological insulators is discussed.
In this paper we consider holographic model of exciton condensation in double monolayer Dirac semimetal. Exciton is bound states of an electron and a hole. Being Bose particles, excitons can form a Bose—Einstein condensate. We study formation of two types of condensates. In first case both the electron and the hole forming the exciton are in the same layer (intralayer condensate), in the second case the electron and the hole are in different layers (interlayer condensate). We study how the condensates depend on the distance between layers and the mass of the quasiparticles in presence of a strong magnetic field. In order to take into account possible strong Coulomb interaction between electrons we use holographic appoach. The holographic model consists of two D5 branes embedded into anti de Sitter space. The condensates are described by geometric configuration of the branes. We show that the distance between layers at which interlayer condensate disappears decreases with quasiparticle mass.
