Victoria Mazo - Academia.edu (original) (raw)
Papers by Victoria Mazo
Physical Review B
We study the low energy edge states of bilayer graphene in a strong perpendicular magnetic field.... more We study the low energy edge states of bilayer graphene in a strong perpendicular magnetic field. Several possible simple boundaries geometries related to zigzag edges are considered. Tight-binding calculations reveal three types of edge state behaviors: weakly, strongly, and non-dispersive edge states. These three behaviors may all be understood within a continuum model, and related by nonlinear transformations to the spectra of quantum Hall edge-states in a conventional two-dimensional electron system. In all cases, the edge states closest to zero energy include a hole-like edge state of one valley and a particle-like state of the other on the same edge, which may or may not cross depending on the boundary condition. Edge states with the same spin generically have anticrossings that complicate the spectra, but which may be understood within degenerate perturbation theory. The results demonstrate that the number of edge states crossing the Fermi level in clean, undoped bilayer graphene depends both on boundary conditions and the energies of the bulk states.
We study the low energy edge states of bilayer graphene ribbons subject to a strong perpendicular... more We study the low energy edge states of bilayer graphene ribbons subject to a strong perpendicular magnetic field B, and show that they can be described within a continuum model (the Dirac equation). We are mainly interested in investigating the energy- band structure of ribbons with a zigzag termination. At the zero Landau Level there are eight degenerate bands, whose
Journal of High Energy Physics, 2008
We analyze the thermal phases of a non critical holographic model of QCD. The model is based on a... more We analyze the thermal phases of a non critical holographic model of QCD. The model is based on a six dimensional background of N c non extremal D4 branes wrapping a spacial circle of radius R and the compactified Euclidean time direction of radius β = 1/T. We place in this background stacks of N f D4 and anti-D4 flavor probe branes with a separation distance L at large radial direction. The analysis of the DBI effective action yields the following phase diagram: At low temperature the system is in a confining phase with broken chiral symmetry. In the high temperature deconfining phase chiral symmetry can be either restored for L > L c = 1.06R or broken for L < L c. All of these phase transitions are of first order. We analyze the spectrum of the low-spin and high-spin mesons. High spin mesons above certain critical angular momentum "melt". We detect (no) drag for (mesons) quarks moving in hot quark-gluon fluid. The results resemble the structure and properties of the thermal Sakai-Sugimoto model derived in hep-th/0604161.
Physical Review B, 2014
We consider the zero-filled quantum-Hall ferromagnetic state of bilayer graphene subject to a kin... more We consider the zero-filled quantum-Hall ferromagnetic state of bilayer graphene subject to a kink-like perpendicular electric field, which generates domain walls in the electronic state and lowenergy collective modes confined to move along them. In particular, it is shown that two pairs of collective helical modes are formed at opposite sides of the kink, each pair consisting of modes with identical helicities. We derive an effective field-theoretical model of these modes in terms of two weakly coupled anisotropic quantum spin-ladders, with parameters tunable through control of the electric and magnetic fields. This yields a rich phase diagram, where due to the helical nature of the modes, distinct phases possess very different charge conduction properties. Most notably, this system can potentially exhibit a transition from a superfluid to an insulating phase.
Physical review. B, Condensed matter
We derive an effective field-theoretical model for the one-dimensional collective mode associated... more We derive an effective field-theoretical model for the one-dimensional collective mode associated with a domain wall in a quantum Hall ferromagnetic state, as realized in confined graphene systems at zero filling. To this end, we consider the coupling of a quantum spin ladder forming near a kink in the Zeeman field to the spin fluctuations of a neighboring spin polarized two-dimensional environment. It is shown, in particular, that such coupling may induce anisotropy of the exchange coupling in the legs of the ladder. Furthermore, we demonstrate that the resulting ferromagnetic spin-1/2 ladder, subject to a kinked magnetic field, can be mapped to an antiferromagnetic spin chain at zero magnetic field.
Physical Review B
We study the low energy edge states of bilayer graphene in a strong perpendicular magnetic field.... more We study the low energy edge states of bilayer graphene in a strong perpendicular magnetic field. Several possible simple boundaries geometries related to zigzag edges are considered. Tight-binding calculations reveal three types of edge state behaviors: weakly, strongly, and non-dispersive edge states. These three behaviors may all be understood within a continuum model, and related by nonlinear transformations to the spectra of quantum Hall edge-states in a conventional two-dimensional electron system. In all cases, the edge states closest to zero energy include a hole-like edge state of one valley and a particle-like state of the other on the same edge, which may or may not cross depending on the boundary condition. Edge states with the same spin generically have anticrossings that complicate the spectra, but which may be understood within degenerate perturbation theory. The results demonstrate that the number of edge states crossing the Fermi level in clean, undoped bilayer graphene depends both on boundary conditions and the energies of the bulk states.
We study the low energy edge states of bilayer graphene ribbons subject to a strong perpendicular... more We study the low energy edge states of bilayer graphene ribbons subject to a strong perpendicular magnetic field B, and show that they can be described within a continuum model (the Dirac equation). We are mainly interested in investigating the energy- band structure of ribbons with a zigzag termination. At the zero Landau Level there are eight degenerate bands, whose
Journal of High Energy Physics, 2008
We analyze the thermal phases of a non critical holographic model of QCD. The model is based on a... more We analyze the thermal phases of a non critical holographic model of QCD. The model is based on a six dimensional background of N c non extremal D4 branes wrapping a spacial circle of radius R and the compactified Euclidean time direction of radius β = 1/T. We place in this background stacks of N f D4 and anti-D4 flavor probe branes with a separation distance L at large radial direction. The analysis of the DBI effective action yields the following phase diagram: At low temperature the system is in a confining phase with broken chiral symmetry. In the high temperature deconfining phase chiral symmetry can be either restored for L > L c = 1.06R or broken for L < L c. All of these phase transitions are of first order. We analyze the spectrum of the low-spin and high-spin mesons. High spin mesons above certain critical angular momentum "melt". We detect (no) drag for (mesons) quarks moving in hot quark-gluon fluid. The results resemble the structure and properties of the thermal Sakai-Sugimoto model derived in hep-th/0604161.
Physical Review B, 2014
We consider the zero-filled quantum-Hall ferromagnetic state of bilayer graphene subject to a kin... more We consider the zero-filled quantum-Hall ferromagnetic state of bilayer graphene subject to a kink-like perpendicular electric field, which generates domain walls in the electronic state and lowenergy collective modes confined to move along them. In particular, it is shown that two pairs of collective helical modes are formed at opposite sides of the kink, each pair consisting of modes with identical helicities. We derive an effective field-theoretical model of these modes in terms of two weakly coupled anisotropic quantum spin-ladders, with parameters tunable through control of the electric and magnetic fields. This yields a rich phase diagram, where due to the helical nature of the modes, distinct phases possess very different charge conduction properties. Most notably, this system can potentially exhibit a transition from a superfluid to an insulating phase.
Physical review. B, Condensed matter
We derive an effective field-theoretical model for the one-dimensional collective mode associated... more We derive an effective field-theoretical model for the one-dimensional collective mode associated with a domain wall in a quantum Hall ferromagnetic state, as realized in confined graphene systems at zero filling. To this end, we consider the coupling of a quantum spin ladder forming near a kink in the Zeeman field to the spin fluctuations of a neighboring spin polarized two-dimensional environment. It is shown, in particular, that such coupling may induce anisotropy of the exchange coupling in the legs of the ladder. Furthermore, we demonstrate that the resulting ferromagnetic spin-1/2 ladder, subject to a kinked magnetic field, can be mapped to an antiferromagnetic spin chain at zero magnetic field.