Luis Palma-Chilla

A non-Hermitian LC quadrilayer metamaterial formed by alternating right-handed (RH) and left-handed (LH) circuit layers is investigated. The layers are connected through identical nearest-neighbor imaginary couplings, providing a minimal multilayer extension of the RH/LH bilayer. The quadrilayer connectivity generates two non-Hermitian spectral scales related by the golden ratio, giving rise to two exceptional families and up to four exceptional contours in the two-dimensional reciprocal space. The RH/LH circuit duality organizes the exceptional solutions into reciprocal pairs, while the golden-ratio structure determines the relative scale of the critical couplings. Increasing the coupling consequently changes the number of physically accessible exceptional contours from four to three and finally two. In the four-contour regime, the nested exceptional structure separates reciprocal-space regions containing zero, two, and four complex eigenfrequencies. These results show that the connectivity of an LC multilayer can generate multiple exceptional boundaries and golden-ratio spectral scaling using a single microscopic non-Hermitian coupling.

This study investigates the effect of incorporating heavy dopant atoms on the topological transitions in the energy spectrum of graphene, as well as on its thermodynamic properties. A tight-binding model is employed that incorporates a lattice composition parameter associated with the dopant’s effect to obtain the electronic spectrum of graphene. Thus, the substitutional atoms in the lattice impact the electronic structure of graphene by altering the connectivity of the Dirac cones and the symmetry of the energy surface in their spectrum. The Gibbs entropy is numerically calculated from the energy surface of the electronic spectrum, and other thermodynamic properties, such as temperature, specific heat, and Helmholtz free energy, are derived from theoretical principles. The results show that topological changes induced by the heavy dopant atoms in the graphene lattice significantly affect its electronic structure and thermodynamic properties, leading to observable changes in the distances between Dirac cones, the range of the energy spectrum, entropy, positive and negative temperatures, divergences in specific heat, and instabilities within the system.

This study explores the thermodynamic properties of doped graphene using an adapted electronic spectrum. We employed the one-electron tight-binding model to describe the hexagonal lattice structure. The dispersion relation for graphene is expressed in terms of the hopping energies using a compositional parameter that characterizes the different dopant atoms in the lattice. The focus of the investigation is on the impact of the compositions, specifically the presence of dopant atoms, on the energy spectrum, entropy, temperature, and specific heat of graphene. The numerical and analytical results reveal distinct thermodynamic behaviors influenced by the dopant composition, including topological transitions, inflection points in entropy, and specific heat divergences. In addition, the use of Boltzmann entropy and the revision of Nernst’s theorem for doped graphene are introduced as novel aspects.

In order to characterize seismically the Coquimbo Region, Chile, data from 1943 to 2020 were considered. The region was divided into 30 zones of 0.5 • latitude and 0.5 • longitude and the non-extensive statistical physics was used. Both, the Sotolongo-Costa-Posadas and Mathai models were proposed to analyze the magnitude-frequency distribution. The subdivision into cells of the catalog allowed to demonstrate that systems with value of q ∼ 1 present exponential behavior, while with the superposition of subsystems it was expected to obtain q > 1, supporting the su-perstatistical model. Thus, by subdividing the Coquimbo region into the South and North regions, we find that in both the entropic index is greater than one, q > 1, however , according to the value obtained, in the southern sector the long-range effects are greater than in the northern sector. This means that both sectors ae well described by the nonextensive statistical model, either by SCP model or Mathai model; the entropic index is q > 1 and in both cases R 2 > 0.99. As the Coquimbo region is considered as a all, the nonextensive statistical distribution is the more adequated. With respect to the probabilistic seismic hazard assessment, we showed that the Mathai’s model has the better fit. Thus, in the frequency-interevent time distribution was used for different limite magnitudes values. Our analysis shows that the probability occurrence of an seismic event in the northern sector of the region is lower than in the southern sector for the same period; in the former the behavior is of Poissonian type. Thus, the region’s northern and southern zones show different behaviors in terms of earthquake occurrence probability.

The total solar eclipse on July 2, 2019, has been studied by using data of the La Serena ground magnetic station in Chile located in the path of the totality (at geographic coordinates: 29.827° S, 71.261° W). The event reached 100% darkness and occurred from 1522:34 hr to 1746:36 hr LT. We monitored the X, Y, Z‑components of the geomagnetic field with a fluxgate magnetometer to investigate their variation caused by the passing of the Moon in front of the Sun. Our results show positive growth up to ∼12 nT for all components in the same time window during the eclipse and in total synchrony with its phases. Having to discard any effect on the observations such as magnetic and solar activities, seasonal and geographical conditions, and instrumental effects, we report a total increase of the geomagnetic field during this phenomenon.