arXiv subjects

L. F. Urrutia

Publications and source records attributed to L. F. Urrutia.

At least 19 recordsLinked to original sources

arXiv2026

A supersymmetric study of charge and spin transport in Weyl semimetals under axionic electrodynamic response

We investigate the charge and spin transport properties of a Weyl semimetal under an external magnetic field using a low-energy effective theory. By performing a chiral transformation, we remove the axial term from the fermionic Lagrangian, while its physical effects are retained through the system's electromagnetic response. This response, derived from integrating out the fermionic degrees of freedom, takes the form of axionic electrodynamics and enters the Dirac equation via minimal coupling. The resulting dynamics separate naturally into magnetic and electric components: the magnetic sector admits a supersymmetric factorization, while the electric part exhibits a PT-supersymmetric structure. Robin boundary conditions are applied to the spinor, setting the energy spectrum and defining exact spinor solutions. We obtain the chiral projections of probability and current densities, exhibiting a chiral imbalance in the material. We show that in the x-direction, only one chirality contributes to the chiral current ($j^x_l = 0$). Spin density and currents where also computed. Our results demonstrate how the interplay between axionic response and supersymmetry governs transport phenomena in our specific setup, offering novel insights into the effective field theory description of Weyl semimetals.

cond-mat.mes-hall↗

arXiv2022

Cherenkov radiation in chiral media

In the framework of Carrol-Field-Jackiw electrodynamics we calculate the spectral distribution of the Cherenkov radiation (CHR) produced by a charge moving at constant velocity in a chiral medium. We find zero, one or two Cherenkov angles according to the relation between the velocity of the particle and the refraction index of the medium.

hep-ph↗

arXiv2022

LIV in matter

We summarize recent work dealing with the characterization of effective actions giving the electromagnetic response of some topological materials, arising from their microscopic structure. The case of weakly tilted Weyl semimetals in the limit of zero temperature, but nonzero chemical potential, is presented as a subset of a specific choice of terms in the fermionic sector of the SME.

hep-ph↗

arXiv2022

Effective electromagnetic actions for Lorentz violating theories exhibiting the axial anomaly

The CPT odd contribution to the effective electromagnetic action deriving from the vacuum polarization tensor in a large class of fermionic systems exhibiting Lorentz invariance violation (LIV) is calculated using thermal field theory methods, focusing upon corrections depending on the chemical potential. The systems considered exhibit the axial anomaly and their effective actions are described by axion electrodynamics whereby all the LIV parameters enter in the coupling $Θ(x)$ to the unmodified Pontryagin density. A preliminary application to type-I tilted Weyl semimetals is briefly presented.

hep-th↗

arXiv2020

The magnetoelectric effect due to a semispherical capacitor surrounded by a spherical topologically insulating shell

We consider the magnetoelectric effect produced by a capacitor formed by two semispherical perfectly conducting plates subjected to a potential difference and surrounded by a spherical shell of a topologically insulating material. The modified Maxwell equations are solved in terms of coupled electric and magnetic scalar potentials using spherical coordinates and in the approximation where the effective magnetoelectric coupling is of the order of the fine structure constant. The emphasis is placed in the calculation of the magnetic field for several relevant configurations designed to enhance the possibility of measuring this field. The magnitudes we obtain fall within the sensitivities of magnetometers based upon nitrogen-vacancy centers in diamond as well as of devices using scanning SQUID magnetometry.

cond-mat.mes-hall↗

arXiv2019

Magnetoelectric effect of a conducting sphere near a planar topological insulator

When time-reversal symmetry is broken on its surface, topological insulators exhibit a magnetoelectric response which is described by axion electrodynamics. A direct consequence of this theory is the appearance of a magnetic field that resembles the one produced by a magnetic image monopole when a point-like electric charge is located near the surface of the material. In this paper we investigate the more realistic problem when the point-like charge is replaced by a finite size sphere at constant potential. We calculate the electromagnetic fields using the potential formulation in a particular bispherical coordinate system. We find that the electromagnetic fields can be interpreted in terms of point electric and image magnetic charges as if the medium were the vacuum. As a manifestation of the magnetoelectric effect, we highlight the resulting magnetic field, which we analyze in detail along the symmetry axis, since such estimates could be useful in evaluating the experimental possibility of its measurement via sensible magnetometers. Our numerical estimates show that the proposed setup provides a magnetic field strength in the range of 10-100 mG, which is attainable with present day sensitivities in NV center-diamond magnetometers, for example.

cond-mat.mes-hall↗

arXiv2019

Reversed electromagnetic Vavilov-Čerenkov radiation in naturally existing magnetoelectric media

We consider two semi-infinite magnetoelecteric media separated by a planar interface whose electromagnetic response is described by axion-electrodynamics. The time dependent Green's function characterizing this geometry is obtained by a method which can be directly generalized to cylindrical and spherical configurations of two magnetoelectrics separated by an interface. We establish the far-field approximation of the Green's function and apply these results to the case of a charged particle moving from one medium to the other at a high constant velocity perpendicular to the interface. From the resulting angular distribution of the radiated energy per unit frequency we provide theoretical evidence for the emergence of reversed Vavilov-Čerenkov radiation in naturally existing magnetoelectric media. In the case where one of the magnetolectrics is a 3D topological insulator, ${\rm TlBiSe}_2$ for example, located in front of a regular insulator, we estimate that an average forward Vavilov-Čerenkov radiation with frequency $\sim 2.5 \,\, {\rm eV}$ ($\sim 500\,\, {\rm nm}$) will produce a highly suppressed reversed Vavilov-Čerenkov radiation which can be characterized by an effective frequency in the range of $\sim (4\times 10^{-3}-0.5) \,\, {\rm meV}$. However, this value compares favorably with recent measurements in left-handed metamaterials yielding reversed Vavilov-Čerenkov radiation with frequencies of the order of $(1.2-3.9)\times 10^{-2}\,\, {\rm meV}$.

cond-mat.mes-hall↗

arXiv2019

Explicit spacetime symmetry breaking in matter: the reversed Vavilov-Čerenkov radiation

We show that reversed Vavilov-Čerenkov radiation occurs simultaneously with the forward output in naturally existing materials when an electric charge moves with a constant velocity perpendicular to the planar interface between two magnetoelectric media. Using the Green's function in the far-field approximation we calculate the angular distribution of the radiated energy per unit frequency obtaining a non-zero contribution in the backward direction.

hep-ph↗

arXiv2019

Electromagnetic fields induced by an electric charge near a Weyl semimetal

Weyl semimetals (WSM) are a new class of topological materials that exhibit a bulk Hall effect due to time-reversal symmetry breaking, as well as a chiral magnetic effect due to inversion symmetry breaking. These unusual electromagnetic responses can be characterized by an axion term $θ\textbf{E} \cdot \textbf{B}$ with space and time dependent axion angle $θ(\textbf{r} ,t)$. In this paper we compute the electromagnetic fields produced by an electric charge near to a topological Weyl semimetal with two Weyl nodes in the bulk Brillouin zone. We find that, as in ordinary metals and dielectrics, outside the WSM the electric field is mainly determined by the optical properties of the material. The magnetic field is, on the contrary, of topological origin in nature due to the magnetoelectric effect of topological phases. We show that the magnetic field exhibits a particularly interesting behavior above the WSM: the field lines begin at the surface and then end at the surface (but not at the same point). This behavior is quite different from that produced by an electric charge near the surface of a topological insulator, where the magnetic field above the surface is generated by an image magnetic monopole beneath the surface, in which case, the magnetic field lines are straight rays. The unconventional behavior of the magnetic field is an experimentally observable signature of the anomalous Hall effect in the bulk of the WSM. We discuss a simple candidate material for testing our predictions, as well as two experimental setups which must be sensitive to the effects of the induced magnetic field.

hep-th↗

arXiv2019

Exact solution of the Schrödinger equation for an hydrogen atom at the interface between the vacuum and a topologically insulating surface

When an hydrogen atom is brought near to the interface between $θ$-media, the quantum-mechanical motion of the electron will be affected by the electromagnetic interaction between the atomic charges and the $θ$-interface, which is described by an axionic extension of Maxwell electrodynamics in the presence of a boundary. In this paper we investigate the atom-surface interaction effects upon the energy levels and wave functions of an hydrogen atom placed at the interface between a $θ$-medium and the vacuum. In the approximation considered, the Schrödinger equation can be exactly solved by separation of variables in terms of hypergeometic functions for the angular part and hydrogenic functions for the radial part. In order to make such effects apparent we deal with unrealistic high values of the $θ$-parameter. We also compute the energy shifts using perturbation theory for a particular small value of $θ$ and we demonstrate that they are in a very good agreement with the ones obtained from the exact solution.

cond-mat.mes-hall↗

arXiv2018

The magnetoelectric coupling in Electrodynamics

We explore a model akin to axion electrodynamics in which the axion field $θ(t,\mathbf{x})$ rather than being dynamical is a piecewise constant effective parameter $θ$ encoding the microscopic properties of the medium inasmuch as its permittivity or permeability, defining what we call a $θ$-medium. This model describes a large class of phenomena, among which we highlight the electromagnetic response of materials with topological order, like topological insulators for example. We pursue a Green's function formulation of what amounts to typical boundary-value problems of $θ$-media, when external sources or boundary conditions are given. As an illustration of our methods, which we have also extended to ponderable media, we interpret the constant $θ$ as a novel topological property of vacuum, a so called $θ$-vacuum, and restrict our discussion to the cases where the permittivity and the permeability of the media is one. In this way we concentrate upon the effects of the additional $θ$ coupling which induce remarkable magnetoelectric effects. The issue of boundary conditions for electromagnetic radiation is crucial for the occurrence of the Casimir effect, therefore we apply the methods described above as an alternative way to approach the modifications to the Casimir effect by the inclusion of topological insulators.

hep-th↗

arXiv2018

Interaction of a hydrogenlike ion with a planar topological insulator

An electric charge near the surface of a topological insulator (TI) induces an image magnetic monopole. Here we study the spectra of hydrogenlike ions near the surface of a planar TI, taking into account the modifications which arise due to the presence of the image monopole magnetic fields. In fact, the atom-TI interaction provides additional contributions to the Casimir-Polder potential while the ion-TI interaction modifies the energy shifts in the spectrum, which now became distance dependent. We show that the hyperfine structure is sensitive to the image magnetic monopole fields in states with nonzero angular momentum, and that circular Rydberg ions can enhance the maximal energy shifts. We discuss in detail the energy splitting of the $n$P$_{1/2}$ and $n$P$_{3/2}$ states in hydrogen. We also analyze the Casimir-Polder potential and find that this magnetic interaction produces a large distance repulsive tail for some particular atomic states. A sizable value of the maximum of the potential requires TIs with very low values of the permittivity together with high values of the topological magnetoelectric polarization.

quant-ph↗

arXiv2017

Gravitational waves propagation in nondynamical Chern-Simons gravity

We investigate the propagation of gravitational waves in linearized Chern-Simons (CS) modified gravity by considering two nondynamical models for the coupling field $θ$: (i) a domain wall and (ii) a surface layer of $θ$, motivated by their relevance in condensed matter physics. We demonstrate that the metric and its first derivative become discontinuous for a domain wall of $θ$, and we determine the boundary conditions by realizing that the additional contribution to the wave equation corresponds to one of the self-adjoint extensions of the D'Alembert operator. Nevertheless, such discontinuous metric satisfies the area matching conditions introduced by Barrett. On the other hand, the propagation through a surface layer of $θ$ behaves similarly to the propagation of electromagnetic waves in CS extended electrodynamics. In both cases we calculate the corresponding reflection and transmission amplitudes. As a consequence of the distributional character of the additional terms in the equations that describe wave propagation, the results obtained for the domain wall are not reproduced when the thickness of the surface layer goes to zero, as one could naively expect.

gr-qc↗

arXiv2017

Extended Nambu Models: their relation to gauge theories

Yang-Mills theories supplemented by an additional coordinate constraint, which is solved and substituted in the original Lagrangian, provide examples of the so called Nambu models, in the case where such constraints arise from spontaneous Lorentz symmetry breaking. Some explicit calculations have shown that, after additional conditions are imposed, Nambu models are capable of reproducing the original gauge theories, thus making Lorentz violation unobservable and allowing the interpretation of the corresponding massless gauge bosons as the Goldstone bosons arising from the spontaneous symmetry breaking. A natural question posed by this approach in the realm of gauge theories is to determine under which conditions the recovery of an arbitrary gauge theory from the corresponding Nambu model, defined by a general constraint over the coordinates, becomes possible. We refer to these theories as extended Nambu models (ENM) and emphasize the fact that the {defining coordinate} constraint is not treated as a standard gauge fixing term. At this level, the mechanism for generating the constraint is irrelevant and the case of spontaneous Lorentz symmetry breaking is taken only as a motivation, which naturally bring this problem under consideration. Using a non-perturbative Hamiltonian analysis we prove that the ENM yields the original gauge theory after we demand current conservation for all time, together with the imposition of the Gauss laws constraints as initial conditions upon the dynamics of the ENM. The Nambu models yielding electrodynamics, Yang Mills theories and linearized gravity are particular examples of our general approach.

hep-th↗

arXiv2017

Unitarity and Lee-Wick prescription at one loop level in the effective Myers-Pospelov electrodynamics: the $e^++e^-$ annihilation

We study perturbative unitarity in a Lorentz-symmetry-violating QED model with higher-order derivative operators in the light of the results of Lee and Wick to preserve unitarity in indefinite metric theories. Specifically, we consider the fermionic sector of the Myers-Pospelov model, which includes dimension-five operators, coupled to standard photons. We canonically quantize the model, paying attention to its effective character, and show that its Hamiltonian is stable, emphasizing the exact stage at which the indefinite metric appears and decomposes into a positive-metric sector and a negative-metric sector. Finally, we verify the optical theorem at the one-loop level in the annihilation channel of the forward-scattering process $e^+(p_2, r) + e^-(p_1,s)$ by applying the Lee-Wick prescription in which the states associated with the negative metric are left out from the asymptotic Hilbert space, but nevertheless are considered in the loop integration via the propagator.

hep-th↗

arXiv2016

Emergence of Yang Mills theory from the Non-Abelian Nambu Model

The equivalence between the Non-Abelian Nambu model (NANM) and Yang Mills theory is proved, after demanding the Gauss laws at some initial time to the first one. Thereby, the Lorentz violation encoded into the constraint that defines the NANM is physically unobservable. As result, the Goldstone bosons in the NANM arising from the spontaneous symmetry breaking can be identified as the standard gauge fields.

hep-th↗

arXiv2016

Emergence of gauge invariance from Nambu models

In the framework of a hamiltonian nonperturbative approach we show that after demanding current conservation together with the Gauss constraints at some initial time in a nonabelian Nambu model, we recover the corresponding Yang-Mills theory. In this way, the spontaneous Lorentz symmetry breaking present in the Nambu model becomes unobservable and the Goldstone modes can be identified with the corresponding gauge bosons.

hep-ph↗

arXiv2016

A Green's function approach to the Casimir effect on topological insulators with planar symmetry

We investigate the Casimir stress on a topological insulator (TI) between two metallic plates. The TI is assumed to be joined to one of the plates and its surface in front of the other is covered by a thin magnetic layer, which turns the TI into a full insulator. We also analyze the limit where one of the plates is sent to infinity yielding the Casimir stress between a conducting plate and a TI. To this end we employ a local approach in terms of the stress-energy tensor of the system, its vacuum expectation value being subsequently evaluated in terms of the appropriate Green's function. Finally, the construction of the renormalised vacuum stress-energy tensor in the region between the plates yields the Casimir stress. Numerical results are also presented.

cond-mat.mes-hall↗