arXiv subjects

Yonatan Betancur-Ocampo

Publications and source records attributed to Yonatan Betancur-Ocampo.

18 recordsLinked to original sources

arXiv2026

Antiresonances of Wannier-Stark ladders in Su-Schrieffer-Heeger lattices

We demonstrate that Wannier-Stark ladders (WSLs) in one-dimensional Su-Schrieffer-Heeger (SSH) chains manifest as antiresonance signatures in the electron transmission. We study the quantum transport in the SSH chain in the presence of a periodic potential profile plus a uniform electric field. By employing the global matrix method with non-trivial matching conditions, we find that these WSL antiresonances correspond to states that are exponentially localized at the potential's incident boundary. These findings provide a robust, unified framework for identifying WSLs across diverse scales, ranging from electronic transport in trans-polyacetylene to classical-wave analogs in phononic crystals and surface water waves.

cond-mat.mes-hall↗

arXiv2026

Topical Review: The rise of Klein tunneling in low-dimensional materials and superlattices

We review recent advances in Klein and anti-Klein tunneling in one- and two-dimensional materials. Using a general tight-binding framework applied to multiple periodic systems, we establish the criteria for the emergence of Klein tunneling based on the conservation of an effective reduced pseudospin. The inclusion of higher-order terms in the wave vector leads to nontrivial matching conditions for wave scattering at interfaces. We further examine the emergence of multiple types of Klein tunneling in two-dimensional materials beyond graphene, including phosphorene and borophene, as well as in one-dimensional systems such as Su-Schrieffer-Heeger lattices. Finally, we discuss how these tunneling phenomena can be tested in both synthesized and artificial lattices, including elastic metamaterials, optical, photonic, phononic, and superconducting platforms, demonstrating the universality of Klein tunneling across different wave natures and length scales.

cond-mat.mtrl-sci↗

arXiv2026

Anomalous Klein tunnelling with magnetic barriers in strained graphene

We study electron transport in a strained graphene sheet subjected to a sequence of $N$ electrostatic and magnetic barriers. Employing a modified and improved transfer-matrix framework, we examine how the transmission and reflection coefficients evolve with variations in uniaxial strain and in the number of barriers. The interplay of mechanical deformation and external magnetic fields is found to generate an anomalous Klein tunnelling, allowing the conductance to be effectively modulated through strain and barrier configurations. These findings highlight the role of strain engineering and magnetic field modulation as powerful tools for tailoring charge transport in two-dimensional materials. More broadly, they underscore how mechanical and electromagnetic control can be used to design next-generation solid-state devices with tunable electronic properties.

cond-mat.mes-hall↗

arXiv2026

Dual energy-differentiated topological transition in artificial red phosphorus chains

We investigate the spectral and transport properties of an atomic chain of red phosphorus. We reveal the separation of flat-band states from the rest of the system and calculate its energy bands analytically. The topological properties of the system are established through the evaluation of the Berry (Zak) phase of the energy bands, revealing nontrivial topology. The Berry phase depends on the relative strength of the hopping parameters and exhibits dual energy-dependent topological phase transitions. Remarkably, the emergence of inert band edges provides a direct spectral signature of these transitions, acting as energy-resolved indicators of the redistribution of topological charge between bands. The existence of the associated edge states is proved numerically for finite lattices. The theoretical predictions, particularly the band structure and the existence of edge states, are further confirmed by numerical simulations of red phosphorus through a phononic lattice in the form of a highly structured aluminum plate.

cond-mat.mtrl-sci↗

arXiv2025

Electronic transport and anti-super-Klein tunneling in few-layer black phosphorous

The electronic transport in few-layer black phosphorus (FLBP) nanoribbons is studied theoretically. The system is modeled on the basis of band-structures, which have been measured recently by $μ$-ARPES experiments. We show that the anisotropic bands of FLBP leads to highly anisotropic transport properties; while the current in one direction can be rather focused, it can be strongly disperse in the orthogonal direction. The low-energy current is carried mainly in the central layer due to the vertical confinement of the electrons. In FLBP pn junctions, generated by the electrostatic potential of a gate contact in a certain region of the system, the electrons pass through the interface of the junction, if it is oriented along the zigzag direction of FLBP. If the junction is rotated by 90 degree and oriented along the armchair direction, the current is reflected completely for all angles of incidence and for a wide range of electron energies. This omni-directional total reflection is named anti-super-Klein tunneling as it is due to opposite pseudo-spins of the electrons in the two region of the pn junction. The effect of oxidation of the top layer of FLBP pn junctions is investigated and it is found that, while the current flow in the top layers is strongly suppressed, the anti-super-Klein tunneling persists.

cond-mat.mes-hall↗

arXiv2024

Kekulé distortions in graphene on cadmium sulfide

The deposition of a two-dimensional material on the surface of a three-dimensional crystal can generate superlattices with electronic properties modified through the proximity spin-orbit effect. In this study, we found that Kekulé graphene superlattices are obtained by placing graphene on Cd-terminated (001)-(1$\times$1) cadmium sulfide (CdS) surface. From an effective model of Kekulé superlattices, which is corroborated by Density Functional Theory (DFT) calculations, we identified that the puckered surfqace of CdS modifies the on-site energies (staggered potential) and C-C bonds, giving rise to two possible $\sqrt{3} \times \sqrt{3}$ hexagonal superlattices, which are known as Kekulé-O graphene and Kekulé-Y with a quadratic band crossing point. Both Kekulé superlattices present spin-orbit coupling due to the interaction of graphene with the CdS surface. To guide the experimental realization of Kekulé superlattices based on graphene/CdS heterostructures, we simulate electron diffraction patterns, as well as images from High-Resolution Transmission Electron Microscopy (HRTEM), and Scanning Transmission Electron Microscopy in the mode of High Angle Annular Dark Field (STEM-HAADF).

cond-mat.mtrl-sci↗

arXiv2024

Twofold topological phase transitions induced by third-nearest-neighbor interactions in 1D chains

Strong long-range hoppings up to third nearest neighbors may induce a topological phase transition in one-dimensional chains. Unlike the Su-Schrieffer-Heeger model, this transition from trivial to topological phase occurs with the emergence of a pseudospin valley structure and a twofold nontrivial topological phase. Within a tight-binding approach, these topological phases are analyzed in detail and it is shown that the low-energy excitations follow a modified Dirac equation, in which the dynamics of particles with positive and negative mass occur differently. An experimental realization in a one-dimensional elastic chain, where it is feasible to tune directly the third-nearest-neighbor hoppings, is proposed.

cond-mat.mtrl-sci↗

arXiv2023

Identifying Klein tunneling signatures in bearded SSH lattices from bent flat bands

Su-Schrieffer-Heeger (SSH) lattices have helped to understand key concepts of topological insulators. In this paper, we study the transmission properties of $pn$ junctions of bearded SSH lattices forming a bipartite structure. From a tight-binding approach, a Bloch Hamiltonian depicts the electron behavior as a massive pseudo-spin one particle in quasi-one-dimensional systems. It is possible to design the band structure of these lattices by tuning the on-site energy and hopping parameters. The characteristic flat band of pseudo-spin one systems can be bent by the staggered potential of the bottom atom in the bearded edge. We explore interband transmissions from the bent flat band to the valence one of a bipartite structure, where Klein tunneling can be obtained depending on the hopping parameter associated with the bearded edge. The identification of Klein tunneling signatures is feasible in artificial lattices such as photonic lattices, elastic resonators, topolectric circuits, or quantum dot arrangements. On the other hand, the study of Klein tunneling in polyatomic molecules may contribute to advance in one-dimensional transistors.

cond-mat.mes-hall↗

arXiv2023

Atomically thin current pathways in graphene through Kekulé-O engineering

We demonstrate that the current flow in graphene can be guided on atomically thin current pathways by means of the engineering of Kekulé-O distortions. A grain boundary in these distortions separates the system into topological distinct regions and induces a ballistic domain-wall state. The state does not depend on the precise orientation of the grain boundary with respect to the graphene sublattice and therefore, permits to guide the current on arbitrary paths through the system. As the state is gapped, the current flow can be switched by electrostatic gates. Our findings can be explained by a generalization of the Jackiw-Rebbi model, where the electrons behave in one region of the system as fermions with an effective complex mass, making the device not only promising for technological applications but also a test-ground for concepts from high-energy physics. An atomic model supported by DFT calculations demonstrates that the proposed system can be realized by decorating graphene with Ti atoms.

cond-mat.mes-hall↗

arXiv2022

Extended transfer matrix method for electron transmission in anisotropic 2D materials: Interplay of strain and (a)periodicity of potentials

We extend the conventional transfer matrix method to include anisotropic features for electron transmission in two-dimensional materials, such as breaking reflection law in pseudo-spin phases and wave vectors. This method allows to study transmission properties of anisotropic and stratified electrostatic potential media from a wide range of tunable parameters, which include strain tensor and gating. We apply the extended matrix method to obtain the electron transmission, conductance, and Fano factor for the interplay of an uniaxially strained graphene sheet with external one-dimensional aperiodic potentials. Our results suggest the possibility of visualizing this interplay from conductance measurements.

cond-mat.mtrl-sci↗

arXiv2022

Valley-dependent time evolution of coherent electron states in tilted anisotropic Dirac materials

The effect of the Dirac cone tilt of anisotropic two-dimensional materials on the time evolution of coherent electron states in the presence of electric and magnetic fields is studied. We propose a canonical transformation that maps the anisotropic Dirac-Weyl Hamiltonian with tilted Dirac cones to an effective and isotropic Dirac Hamiltonian under these fields. In this way, the well-known Landau-level spectra and wave functions allow calculating the Wigner matrix representation of Landau and coherent states. We found a valley dependency in the behavior of the Wigner function for both Landau and coherent electron states. The time evolution shows that the interplay of the Dirac cone tilt and the electric field keeps the uncertainties of both position and momentum in one valley significantly lower than in the other valley. The increment of quantum noise correlates with the emergence of negative values in the Wigner function. These results may help us to understand the generation of coherent electron states under the interaction with electromagnetic fields. The reported valley-dependent signatures in the Wigner function of materials with tilted Dirac cones may be revealed by quantum tomography experiments, even in the absence of electric fields.

cond-mat.mes-hall↗

arXiv2021

Generalized Hamiltonian for Kekulé graphene and the emergence of valley-cooperative Klein tunneling

We introduce a generalized Hamiltonian describing not only all topological phases observed experimentally in Kekulé graphene (KekGr) but predicting also new ones. These phases show features like a quadratic band crossing point, valley splitting, or the crossing of conduction bands, typically induced by Rashba spin-orbit interactions or Zeeman fields. The electrons in KekGr behave as Dirac fermions and follow pseudo-relativistic dispersion relations with Fermi velocities, rest masses, and valley-dependent self-gating. Transitions between the topological phases can be induced by tuning these parameters. The model is applied to study the current flow in KekGr $pn$ junctions evidencing a novel cooperative transport phenomenon, where Klein tunneling goes along with a valley flip. These junctions act as perfect filters and polarizers of massive Dirac fermions, which are the essential devices for valleytronics. The plethora of different topological phases in KekGr may also help to establish phenomena from spintronics.

cond-mat.mes-hall↗

arXiv2021

Phosphorene pnp junctions as perfect electron waveguides

The current flow in phosphorene pnp junctions is studied. At the interfaces of the junction, omni-directional total reflection takes place, named anti-super-Klein tunneling, as this effect is not due to an energetically forbidden region but due to pseudo-spin blocking. The anti-super-Klein tunneling confines electrons within the junction, which thus represents a perfect lossless electron waveguide. Calculating the current flow by applying the Green's function method onto a tight-binding model of phosphorene, it is observed that narrow electron beams propagate in these waveguides like light beams in optical fibers. The perfect guiding is found for all steering angles of the electron beam as the total reflection does not rely on the existence of a critical angle. For low electron energies and narrow junctions, the guided modes of the waveguide are observed. The waveguide operates without any loss only for a specific orientation of the junction. For arbitrary orientations, minor leakage currents are found, which however decay for low electron energies and grazing incidence angles. It is shown that a crossroad shaped pnp junction can be used to split and direct the current flow in phosphorene. The proposed device, a phosphorene pnp junction as a lossless electron waveguide, may not only find applications in nanoelectronics but also in quantum information technology.

cond-mat.mes-hall↗

arXiv2021

Steering the current flow in twisted bilayer graphene

A nanoelectronic device made of twisted bilayer graphene (TBLG) is proposed to steer the direction of the current flow. The ballistic electron current, injected at one edge of the bottom layer, can be guided predominantly to one of the lateral edges of the top layer. The current is steered to the opposite lateral edge, if either the twist angle is reversed or the electrons are injected in the valence band instead of the conduction band, making it possible to control the current flow by electric gates. When both graphene layers are aligned, the current passes straight through the system without changing its initial direction. The observed steering angle exceeds well the twist angle and emerges for a broad range of experimentally accessible parameters. It is explained by the trigonal shape of the energy bands beyond the van Hove singularity due to the Moiré interference pattern. As the shape of the energy bands depends on the valley degree of freedom, the steered current is partially valley polarized. Our findings show how to control and manipulate the current flow in TBLG. Technologically, they are of relevance for applications in twistronics and valleytronics.

cond-mat.mes-hall↗

arXiv2020

Anomalous Floquet tunneling in uniaxially strained graphene

The interplay of strain engineering and photon-assisted tunneling of electrons in graphene is considered for giving rise to atypical transport phenomena. The combination of uniaxial strain and a time-periodic potential barrier helps to control the particle transmission for a wide range of tunable parameters. With the use of the tight-biding approach, the elasticity theory, and the Floquet scattering, we found an angular shift of the maximum transmission in the sidebands for uniaxial strains breaking the mirror symmetry with respect to the normal incidence, which is called anomalous Floquet tunneling. We show that electron tunneling depends strongly on the barrier width, incident angle, uniaxial strain, and the tuning of the time-periodic potential parameters. An adequate modulation of the barrier width and oscillation amplitude serves to select the transmission in the sidebands. These findings can be useful for controlling the electron current through the photon-assisted tunneling being used in multiple nanotechnological applications.

cond-mat.mes-hall↗

arXiv2020

Gradient-index electron optics in graphene pn junctions

We investigate the electron transport in smooth graphene pn junctions, generated by gradually varying electrostatic potentials. The numerically calculated coherent current flow patterns can be understood largely in terms of semi-classical trajectories, equivalent to the ones obtained for light beams in a medium with a gradually changing refractive index. In smooth junctions, energetically forbidden regions emerge, which increase reflections and can generate pronounced interference patterns, for example, whispering gallery modes. The investigated devices do not only demonstrate the feasibility of the gradient-index electron optics in graphene pn junctions, such as Luneburg and Maxwell lenses, but may have also technological applications, for example, as electron beam splitters, focusers and waveguides. The semi-classical trajectories offer an efficient tool to estimate the current flow paths in such nano-electronic devices.

cond-mat.mes-hall↗

arXiv2020

Phase-space representation of Landau and electron coherent states for uniaxially strained graphene

Recent experimental advances in the reconstruction of the Wigner function (WF) for electronic systems have led us to consider the possibility of employing this theoretical tool in the analysis of electron dynamics of uniaxially strained graphene. In this paper, we study the effect of strain on the WF of electrons in graphene under the interaction of a uniform magnetic field. This mechanical deformation modifies drastically the shape of the Wigner function of Landau and coherent states. The WF has a different behavior straining the material along the zigzag direction in comparison with the armchair one and favors the creation of electron coherent states. The time evolution of the WF for electron coherent states shows fluctuations between classical and quantum behavior around a closed path as time increases. The phase-space representation shows more clearly the effect of nonequidistant relative Landau levels in the time evolution of electron coherent states compared with other approaches. Our findings may be useful in establishing protocols for the realization of electron coherent states in graphene as well as a bridge between condensed matter and quantum optics.

quant-ph↗

arXiv2019

Electron optics in phosphorene pn junctions: Negative reflection and anti super-Klein tunneling

Ballistic electrons in phosphorene $pn$ junctions show optical-like phenomena. Phosphorene is modeled by a tight-binding Hamiltonian that describes its electronic structure at low energies, where the electrons behave in the zigzag direction as massive Dirac fermions and in the orthogonal armchair direction as Schrödinger electrons. Applying the continuum approximation, we derive the electron optics laws in phosphorene $pn$ junctions, which show very particular and unusual properties. Due to the anisotropy of the electronic structure, these laws depend strongly on the orientation of the junction with respect to the sublattice. Negative and anomalous reflection are observed for tilted junctions, while the typical specular reflection is found only, if the junction is parallel to the zigzag or armchair edges. Moreover, omni-directional total reflection, called anti-super Klein tunneling, is observed if the junction is parallel to the armchair edge. Applying the nonequilibrium Green's function method on the tight-binding model, we calculate numerically the current flow. The good agreement of both approaches confirms the atypical transport properties, which can be used in nano-devices to collimate and filter the electron flow, or to switch its direction.

cond-mat.mes-hall↗