Jakson Fonseca | Universidade Federal de Viçosa (original) (raw)
Papers by Jakson Fonseca
We study the behavior of spin polarized current in stationary states inside the quantum well desc... more We study the behavior of spin polarized current in stationary states inside the quantum well described by 2-dimensional Bernevig-Hughes-Zhang model modified by a electric and magnetic barrier inside a non-completly insulating bulk. An attenuated quantum spin Hall effect occurs in the gaped region with a possible like-Klein paradox. Even more interesting, after colliding with the magnetic barrier the returning states eventually revert their spins due spin-momentum locking, giving rise to a spin polarized current in a channel distinct from that of incoming particles of the edge. Because of the time reversal symmetry broken inside the magnetic barrier another channels inside the barrier presents similar effects to a gaped region however preserving couterpropagation with oposite spins.
We study the scattering of graphene quasiparticles by topological defects, represented by holes, ... more We study the scattering of graphene quasiparticles by topological defects, represented by holes, pentagons and heptagons. For the case of holes, we obtain the phase shift and found that at low concentration they appear to be irrelevant for the electron transport, giving a negligible contribution to the resistivity. Whenever pentagons are introduced into the lattice and the fermionic current is constrained to move near one of them we realize that such a current is scattered with an angle that depends only on the number of pentagons and on the side the current taken. Such a deviation may be determined by means of a Young-type experiment, through the interference pattern between the two current branches scattered by a pentagon. In the case of a heptagon such a current is also scattered but it diverges from the defect, preventing a interference between two beams of current for the same heptagon. Comment: 7 pages, contribution to 4th International Conference on Fundamental Interactions A...
Journal of Applied Physics, 2015
Curvature effects are important for a proper description of the properties of magnetic systems. I... more Curvature effects are important for a proper description of the properties of magnetic systems. In this paper the exchange and dipolar energy of vortices on a paraboloidal shell is studied. Using analytical calculations it is shown that the in-plane component of vortices has larger energy on a paraboloidal shell than in a planar disk with same thickness. On the other hand, the dipolar energy associated to the vortex core diminishes if the vortex core is on a paraboloidal surface. This reduction in the dipolar energy may cause a vortex pinning mechanism by a paraboloidal shaped defect in a planar nanomagnet. Regarding skyrmions, by using an in-plane anisotropy approximation to the dipolar energy, it is shown that the skyrmion must have its width shrunk in order to diminishes the magnetostatic energy and satisfy geometrical constraints of the system.
Journal of Magnetism and Magnetic Materials, 2015
We study the stability and energetics associated to skyrmions appearing as excitations on curved ... more We study the stability and energetics associated to skyrmions appearing as excitations on curved surfaces. Using a continuum model we show that the presence of cylindrically radial and azimuthal fields destabilizes the skyrmions that appear in the absence of an external field. Weak fields generate fractional skyrmions while strong magnetic fields yield stable 2πskyrmions, which have their widths diminished by the magnetic field strength. Under azimuthal fields vortex appear as stable states on the curved surface.
Physics Letters A, 2015
We study the influence of curvature on the exchange energy of skyrmions and vortices on a parabol... more We study the influence of curvature on the exchange energy of skyrmions and vortices on a paraboloidal surface. It is shown that such structures appear as excitations of the Heisenberg model, presenting topological stability, unlike what happens on other simply-connected geometries such as pseudospheres. We also show that the skyrmion width depends on the geometrical parameters of the paraboloid. The presence of a magnetic field leads to the appearance of 2π-skyrmions, introducing a new characteristic length into the system. Regarding vortices, the geometrical parameters of the paraboloid play an important role in the exchange energy of this excitation.
ABSTRACT We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge r... more ABSTRACT We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge removed and edges identified, i.e., a graphitic cone. The angular defect gives rise to a mismatch of the components of the graphene's relativistic charged quasiparticle wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Such an effect should affect the basic electronic properties in "conical graphenes" as compared with their planar counterpart and it could be, in principle, detected experimentally. Measurements of the electronic transport in these graphitic materials and their relationships with the changes calculated in the quasiparticle wavefunctions could make available interesting probes to the Einstein theory of general relativity in two spatial dimensions. Therefore, we propose a way of verifying, in a microscopic scale, some predictions of a theory that is usually associated with incredible large objects such as planets, stars, black holes, galaxies and so on.
Physics Letters B, 2010
We investigate the breakdown of Lorentz symmetry in QED by a CPT violating interaction term consi... more We investigate the breakdown of Lorentz symmetry in QED by a CPT violating interaction term consisting of the coupling of an axial fermion current with a constant vector field b, in the framework of algebraic renormalization -a regularization-independent method. We show, to all orders in perturbation theory, that a CPT-odd and Lorentz violating Chern-Simons-like term, definitively, is not radiatively induced by the axial coupling of the fermions with the constant vector b. (O.M. Del Cima), jakson.fonseca@ufv.br (J.M. Fonseca), daniel.franco@ufv.br (D.H.T. Franco), opiguet@pq.cnpq.br (O. Piguet).
Journal of Applied Physics, 2014
We have studied ferromagnetic Permalloy clusters obtained by electrodeposition on n-type silicon.... more We have studied ferromagnetic Permalloy clusters obtained by electrodeposition on n-type silicon. Magnetization measurements reveal hysteresis loops almost independent on temperature and very similar in shape to those obtained in nanodisks with diameter bigger than 150nm. The spin configuration for the ground state, obtained by micromagnetic simulation, shows topological vortices with random chirality and polarization. This behavior in the small diameter clusters (∼80nm), is attributed to the Dzyaloshinskii-Moriya interaction that arises in its hemispherical geometries. This magnetization behavior can be utilized to explain the magnetoresistance measured with magnetic field in plane and out of sample plane.
Journal of High Energy Physics, 2010
We study CPT-and Lorentz-odd electrodynamics described by the Standard Model Extension.
Physics Letters B, 2009
We study a number of issues related to the emission and absorption radiation by nonrelativistic e... more We study a number of issues related to the emission and absorption radiation by nonrelativistic electrons within the framework of a Lorentz-breaking electrodynamics in (3+1) dimensions. Our main results concern how Planck-like spectrum law is sensitive to terms that violate Lorentz symmetry. We have realized that Planck law acquires extra terms proportional to the violating parameters: for the CPT-odd model, the leading extra terms appear to be linear or quadratic in these violating parameters according to the background vector is parallel or perpendicular to the photon wave-vector. In the CPT-even case a linear 'correction' shows up. Among other possible ways to probe for these violations, by means of the present results, we may quote the direct observation of the extra contributions or an unbalancing in the mean occupation number of photon modes in a given thermal bath. *
Physical Review D, 2007
We study magnetic monopoles in a Lorentz-and CPT-odd electrodynamical framework in (3+1) dimensio... more We study magnetic monopoles in a Lorentz-and CPT-odd electrodynamical framework in (3+1) dimensions. This is the standard Maxwell model extended by means of a Chern-Simons-like term, b µF µν A ν (b µ constant), which respects gauge invariance but violates both Lorentz and CPT symmetries (as a consequence, duality is also lost). Our main interest concerns the analysis of the model in the presence of Dirac monopoles, so that the Bianchi identity no longer holds, which naively yields the non-conservation of electric charge. Since gauge symmetry is respected, the issue of charge conservation is more involved. Actually, the inconsistency may be circumvented, if we assume that the appearance of a monopole induces an extra electric current. The reduction of the model to (2+1) dimensions in the presence of both the magnetic sources and Lorentz-violating terms is presented. There, a quantization condition involving the scalar remnant of b µ , say, the mass parameter, is obtained. We also point out that the breaking of duality may be associated with an asymmetry between electric and magnetic sources in this background, so that the electromagnetic force experienced by a magnetic pole is supplemented by an extra term proportional to b µ , whenever compared to the one acting on an electric charge. *
Journal of Applied Physics, 2012
We study the topological magnetoelectric effect on a conical topological insulator when a point c... more We study the topological magnetoelectric effect on a conical topological insulator when a point charge q is near the cone apex. The Hall current induced on the cone surface and the image charge configuration are determined. We also study a kind of gravitational Aharonov-Bohm effect in this geometry and realize a phase diference betwen the components of the wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Concretely, a net current flowing towards cone apex (or botton) shows up, yielding electric polarization of the conical topological insulator. Such an effect may be detected, for instance, by means of the net accumulated Hall charge near the apex. Once it depends only on the geometry of the material (essetially, the cone apperture angle) this may be faced as a microscopic scale realization of (2+1)-dimensional Einstein gravity.
The European Physical Journal B, 2013
ABSTRACT By coating a three-dimensional topological insulator (TI) with a ferromagnetic ?lm suppo... more ABSTRACT By coating a three-dimensional topological insulator (TI) with a ferromagnetic ?lm supporting an in-plane magnetic vortex, one breaks the time-reversal symmetry (TRS) without generating a mass gap. It rather yields electronic states bound to the vortex center which have di?erent probabilities associated with each spin mode. In addition, its associate current (around the vortex center) is partially polarized with an energy gap separating the most excited bound state from the scattered ones. Charged zero-modes also appear as fully polarized modes localized near the vortex center. From the magnetic point of view, the observation of such a special current in a TI-magnet sandwich comes about as an alternative technique for detecting magnetic vortices in magnetic thin ?lms.
We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge removed an... more We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge removed and edges identified, i.e., a graphitic cone. The angular defect gives rise to a mismatch of the components of the graphene's relativistic charged quasiparticle wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Such an effect should affect the basic electronic properties in "conical graphenes" as compared with their planar counterpart and it could be, in principle, detected experimentally. Measurements of the electronic transport in these graphitic materials and their relationships with the changes calculated in the quasiparticle wavefunctions could make available interesting probes to the Einstein theory of general relativity in two spatial dimensions. Therefore, we propose a way of verifying, in a microscopic scale, some predictions of a theory that is usually associated with incredible large objects such as planets, stars, black holes, galaxies and so on.
Physical Review D, 2012
Renormalizability of the (minimal) single-fermion QED extension is investigated at all orders of ... more Renormalizability of the (minimal) single-fermion QED extension is investigated at all orders of perturbation theory in the framework of algebraic renormalization, a regularization-independent method. Relative to the standard QED, new structures that could lead to gauge anomalies are identified. Nevertheless, even if the anomaly coefficients fail to vanish in the general case, they shall be absent provided we require invariance of the action under C and/or P T transformations. Stability is also verified in this case, hence full renormalizability is attained. An important result states that violations of CP T symmetry in a (local) quantum field theory [3] must be accompanied with the loss of Lorentz invariance, although the converse may not be true .
We study the behavior of spin polarized current in stationary states inside the quantum well desc... more We study the behavior of spin polarized current in stationary states inside the quantum well described by 2-dimensional Bernevig-Hughes-Zhang model modified by a electric and magnetic barrier inside a non-completly insulating bulk. An attenuated quantum spin Hall effect occurs in the gaped region with a possible like-Klein paradox. Even more interesting, after colliding with the magnetic barrier the returning states eventually revert their spins due spin-momentum locking, giving rise to a spin polarized current in a channel distinct from that of incoming particles of the edge. Because of the time reversal symmetry broken inside the magnetic barrier another channels inside the barrier presents similar effects to a gaped region however preserving couterpropagation with oposite spins.
We study the scattering of graphene quasiparticles by topological defects, represented by holes, ... more We study the scattering of graphene quasiparticles by topological defects, represented by holes, pentagons and heptagons. For the case of holes, we obtain the phase shift and found that at low concentration they appear to be irrelevant for the electron transport, giving a negligible contribution to the resistivity. Whenever pentagons are introduced into the lattice and the fermionic current is constrained to move near one of them we realize that such a current is scattered with an angle that depends only on the number of pentagons and on the side the current taken. Such a deviation may be determined by means of a Young-type experiment, through the interference pattern between the two current branches scattered by a pentagon. In the case of a heptagon such a current is also scattered but it diverges from the defect, preventing a interference between two beams of current for the same heptagon. Comment: 7 pages, contribution to 4th International Conference on Fundamental Interactions A...
Journal of Applied Physics, 2015
Curvature effects are important for a proper description of the properties of magnetic systems. I... more Curvature effects are important for a proper description of the properties of magnetic systems. In this paper the exchange and dipolar energy of vortices on a paraboloidal shell is studied. Using analytical calculations it is shown that the in-plane component of vortices has larger energy on a paraboloidal shell than in a planar disk with same thickness. On the other hand, the dipolar energy associated to the vortex core diminishes if the vortex core is on a paraboloidal surface. This reduction in the dipolar energy may cause a vortex pinning mechanism by a paraboloidal shaped defect in a planar nanomagnet. Regarding skyrmions, by using an in-plane anisotropy approximation to the dipolar energy, it is shown that the skyrmion must have its width shrunk in order to diminishes the magnetostatic energy and satisfy geometrical constraints of the system.
Journal of Magnetism and Magnetic Materials, 2015
We study the stability and energetics associated to skyrmions appearing as excitations on curved ... more We study the stability and energetics associated to skyrmions appearing as excitations on curved surfaces. Using a continuum model we show that the presence of cylindrically radial and azimuthal fields destabilizes the skyrmions that appear in the absence of an external field. Weak fields generate fractional skyrmions while strong magnetic fields yield stable 2πskyrmions, which have their widths diminished by the magnetic field strength. Under azimuthal fields vortex appear as stable states on the curved surface.
Physics Letters A, 2015
We study the influence of curvature on the exchange energy of skyrmions and vortices on a parabol... more We study the influence of curvature on the exchange energy of skyrmions and vortices on a paraboloidal surface. It is shown that such structures appear as excitations of the Heisenberg model, presenting topological stability, unlike what happens on other simply-connected geometries such as pseudospheres. We also show that the skyrmion width depends on the geometrical parameters of the paraboloid. The presence of a magnetic field leads to the appearance of 2π-skyrmions, introducing a new characteristic length into the system. Regarding vortices, the geometrical parameters of the paraboloid play an important role in the exchange energy of this excitation.
ABSTRACT We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge r... more ABSTRACT We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge removed and edges identified, i.e., a graphitic cone. The angular defect gives rise to a mismatch of the components of the graphene's relativistic charged quasiparticle wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Such an effect should affect the basic electronic properties in "conical graphenes" as compared with their planar counterpart and it could be, in principle, detected experimentally. Measurements of the electronic transport in these graphitic materials and their relationships with the changes calculated in the quasiparticle wavefunctions could make available interesting probes to the Einstein theory of general relativity in two spatial dimensions. Therefore, we propose a way of verifying, in a microscopic scale, some predictions of a theory that is usually associated with incredible large objects such as planets, stars, black holes, galaxies and so on.
Physics Letters B, 2010
We investigate the breakdown of Lorentz symmetry in QED by a CPT violating interaction term consi... more We investigate the breakdown of Lorentz symmetry in QED by a CPT violating interaction term consisting of the coupling of an axial fermion current with a constant vector field b, in the framework of algebraic renormalization -a regularization-independent method. We show, to all orders in perturbation theory, that a CPT-odd and Lorentz violating Chern-Simons-like term, definitively, is not radiatively induced by the axial coupling of the fermions with the constant vector b. (O.M. Del Cima), jakson.fonseca@ufv.br (J.M. Fonseca), daniel.franco@ufv.br (D.H.T. Franco), opiguet@pq.cnpq.br (O. Piguet).
Journal of Applied Physics, 2014
We have studied ferromagnetic Permalloy clusters obtained by electrodeposition on n-type silicon.... more We have studied ferromagnetic Permalloy clusters obtained by electrodeposition on n-type silicon. Magnetization measurements reveal hysteresis loops almost independent on temperature and very similar in shape to those obtained in nanodisks with diameter bigger than 150nm. The spin configuration for the ground state, obtained by micromagnetic simulation, shows topological vortices with random chirality and polarization. This behavior in the small diameter clusters (∼80nm), is attributed to the Dzyaloshinskii-Moriya interaction that arises in its hemispherical geometries. This magnetization behavior can be utilized to explain the magnetoresistance measured with magnetic field in plane and out of sample plane.
Journal of High Energy Physics, 2010
We study CPT-and Lorentz-odd electrodynamics described by the Standard Model Extension.
Physics Letters B, 2009
We study a number of issues related to the emission and absorption radiation by nonrelativistic e... more We study a number of issues related to the emission and absorption radiation by nonrelativistic electrons within the framework of a Lorentz-breaking electrodynamics in (3+1) dimensions. Our main results concern how Planck-like spectrum law is sensitive to terms that violate Lorentz symmetry. We have realized that Planck law acquires extra terms proportional to the violating parameters: for the CPT-odd model, the leading extra terms appear to be linear or quadratic in these violating parameters according to the background vector is parallel or perpendicular to the photon wave-vector. In the CPT-even case a linear 'correction' shows up. Among other possible ways to probe for these violations, by means of the present results, we may quote the direct observation of the extra contributions or an unbalancing in the mean occupation number of photon modes in a given thermal bath. *
Physical Review D, 2007
We study magnetic monopoles in a Lorentz-and CPT-odd electrodynamical framework in (3+1) dimensio... more We study magnetic monopoles in a Lorentz-and CPT-odd electrodynamical framework in (3+1) dimensions. This is the standard Maxwell model extended by means of a Chern-Simons-like term, b µF µν A ν (b µ constant), which respects gauge invariance but violates both Lorentz and CPT symmetries (as a consequence, duality is also lost). Our main interest concerns the analysis of the model in the presence of Dirac monopoles, so that the Bianchi identity no longer holds, which naively yields the non-conservation of electric charge. Since gauge symmetry is respected, the issue of charge conservation is more involved. Actually, the inconsistency may be circumvented, if we assume that the appearance of a monopole induces an extra electric current. The reduction of the model to (2+1) dimensions in the presence of both the magnetic sources and Lorentz-violating terms is presented. There, a quantization condition involving the scalar remnant of b µ , say, the mass parameter, is obtained. We also point out that the breaking of duality may be associated with an asymmetry between electric and magnetic sources in this background, so that the electromagnetic force experienced by a magnetic pole is supplemented by an extra term proportional to b µ , whenever compared to the one acting on an electric charge. *
Journal of Applied Physics, 2012
We study the topological magnetoelectric effect on a conical topological insulator when a point c... more We study the topological magnetoelectric effect on a conical topological insulator when a point charge q is near the cone apex. The Hall current induced on the cone surface and the image charge configuration are determined. We also study a kind of gravitational Aharonov-Bohm effect in this geometry and realize a phase diference betwen the components of the wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Concretely, a net current flowing towards cone apex (or botton) shows up, yielding electric polarization of the conical topological insulator. Such an effect may be detected, for instance, by means of the net accumulated Hall charge near the apex. Once it depends only on the geometry of the material (essetially, the cone apperture angle) this may be faced as a microscopic scale realization of (2+1)-dimensional Einstein gravity.
The European Physical Journal B, 2013
ABSTRACT By coating a three-dimensional topological insulator (TI) with a ferromagnetic ?lm suppo... more ABSTRACT By coating a three-dimensional topological insulator (TI) with a ferromagnetic ?lm supporting an in-plane magnetic vortex, one breaks the time-reversal symmetry (TRS) without generating a mass gap. It rather yields electronic states bound to the vortex center which have di?erent probabilities associated with each spin mode. In addition, its associate current (around the vortex center) is partially polarized with an energy gap separating the most excited bound state from the scattered ones. Charged zero-modes also appear as fully polarized modes localized near the vortex center. From the magnetic point of view, the observation of such a special current in a TI-magnet sandwich comes about as an alternative technique for detecting magnetic vortices in magnetic thin ?lms.
We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge removed an... more We study a kind of gravitational Aharonov-Bohm effect in a graphene sheet with a wedge removed and edges identified, i.e., a graphitic cone. The angular defect gives rise to a mismatch of the components of the graphene's relativistic charged quasiparticle wavefunctions (spinors) upon closed parallel transport around the (singular) cone tip. Such an effect should affect the basic electronic properties in "conical graphenes" as compared with their planar counterpart and it could be, in principle, detected experimentally. Measurements of the electronic transport in these graphitic materials and their relationships with the changes calculated in the quasiparticle wavefunctions could make available interesting probes to the Einstein theory of general relativity in two spatial dimensions. Therefore, we propose a way of verifying, in a microscopic scale, some predictions of a theory that is usually associated with incredible large objects such as planets, stars, black holes, galaxies and so on.
Physical Review D, 2012
Renormalizability of the (minimal) single-fermion QED extension is investigated at all orders of ... more Renormalizability of the (minimal) single-fermion QED extension is investigated at all orders of perturbation theory in the framework of algebraic renormalization, a regularization-independent method. Relative to the standard QED, new structures that could lead to gauge anomalies are identified. Nevertheless, even if the anomaly coefficients fail to vanish in the general case, they shall be absent provided we require invariance of the action under C and/or P T transformations. Stability is also verified in this case, hence full renormalizability is attained. An important result states that violations of CP T symmetry in a (local) quantum field theory [3] must be accompanied with the loss of Lorentz invariance, although the converse may not be true .