arXiv subjects

F. M. Peeters

Publications and source records attributed to F. M. Peeters.

At least 19 recordsLinked to original sources

arXiv2026

Electrostatic control of Li+ density and transport rate in double-gated van der Waals devices

Ion transport in crystalline hosts is controlled by an applied potential that simultaneously sets ionic distribution and transport rate, restricting operation to a one-dimensional control space. Here we show that the transport rate of Li+ ions in double-gated van der Waals devices can be modulated while the system occupies fixed ionic-density states. We measure the ionic current along the van der Waals interfaces between hexagonal boron nitride and graphene or MoS2 while simultaneously monitoring the in-plane electronic response. The ionic current exhibits pronounced hysteresis, with plateaus marking discrete ionic-density states balanced by electronic charge, while an independently tuneable electrochemical-potential drop controls the ionic transport rate. The devices sustain over 1,000 switching cycles and function as hybrid ionic-electronic transistors capable of logic operations and memory retention, with ON/OFF ratios exceeding two orders of magnitude. This work demonstrates a two-dimensional control space for ions intercalated in layered materials.

cond-mat.mes-hall↗

arXiv2026

Layer-selective hydrogenation and proton transport in twisted bilayer graphene

Recent work investigated graphene's hydrogenation with independent control of the electric field, E, and charge density, n, in the crystal and showed that the process is controlled by n. Here, we demonstrate layer-selective conductor-insulator transitions in twisted bilayer graphene, driven by hydrogenation at fixed n under strong E. This process is accompanied by proton transport through the bilayer, enabling several parallel and configurable logic gates in the devices. Selectivity arises because the large twist angle decouples the two layers' electronic systems, enabling independent control of their charge densities. Polarisation by the field then induces a charge imbalance at fixed total n, triggering hydrogenation when one of the layers' charge densities reaches the threshold for monolayer hydrogenation. Our results introduce a new type of electrode-electrolyte interface in which electrochemical processes are controlled with two decoupled 2D electron gases, opening new design opportunities for energy and information processing devices.

cond-mat.mes-hall↗

arXiv2026

Chiral states induced by symmetry-breaking in $α-T_3$ lattices: Magnetic field effect

The sublattice-symmetry breaking in the $α-T_3$ lattice leads to a bandgap opening. A defect line in the substrate on which the $α-T_3$ lattice is deposited can be viewed as a topological change in the substrate that induces translational in-plane symmetry breaking, resulting in mid-gap states. These topologically protected states are confined along the defect line and exhibit preferential directional motion, with different signs for the different Dirac valleys. Within this context, we investigate how these unidirectional interface chiral states are affected in the presence of a perpendicular magnetic field and how they can be tuned by varying the controlling system parameter $α$. The latter tunes the $α-T_3$ structure from a honeycomb-like lattice ($α=0$) to a dice lattice ($α=1$). Our theoretical framework is based on the continuum approximation described by a $3\times 3$ matrix Hamiltonian with a sublattice symmetry-breaking term given by $Δ(x) diag(1,\quad -1,\quad 1)$, assuming $Δ(x)$ as a kink-like mass potential profile. Results for dispersion relations and wavefunction distributions for different $α$ parameters and magnetic field amplitudes are discussed. We demonstrate lifting of Landau levels degeneracy and of valley degeneracy. Our findings pave the way for proposing valley filter devices based on any evolutionary stage between the honeycomb-like and dice lattice structures of the $α-T_3$ phase, controlled by external fields.

cond-mat.mes-hall↗

arXiv2025

Tuning of exciton type by environmental screening

We theoretically investigate the binding energy and electron-hole (e-h) overlap of excitonic states confined at the interface between two-dimensional materials with type-II band alignment, i.e., with lowest conduction and highest valence band edges placed in different materials, arranged in a side-by-side planar heterostructure. We propose a variational procedure within the effective mass approximation to calculate the exciton ground state and apply our model to a monolayer MoS$_2$/WS$_2$ heterostructure. The role of nonabrupt interfaces between the materials is accounted for in our model by assuming a W$_x$Mo$_{1-x}$S$_2$ alloy around the interfacial region. Our results demonstrate that (i) interface-bound excitons are energetically favorable only for small interface thickness and/or for systems under high dielectric screening by the materials surrounding the monolayer, and that (ii) the interface exciton binding energy and its e-h overlap are controllable by the interface width and dielectric environment.

cond-mat.mes-hall↗

arXiv2025

Mechanism of the electrochemical hydrogenation of graphene

The electrochemical hydrogenation of graphene induces a robust and reversible conductor-insulator transition, of strong interest in logic-and-memory applications. However, its mechanism remains unknown. Here we show that it proceeds as a reduction reaction in which proton adsorption competes with the formation of H2 molecules via an Eley-Rideal process. Graphene's electrochemical hydrogenation is up to $10^6$ times faster than alternative hydrogenation methods and is fully reversible via the oxidative desorption of protons. We demonstrate that the proton reduction rate in defect-free graphene can be enhanced by an order of magnitude by the introduction of nanoscale corrugations in its lattice, and that the substitution of protons for deuterons results both in lower potentials for the hydrogenation process and in a more stable compound. Our results pave the way to investigating the chemisorption of ions in 2D materials at high electric fields, opening a new avenue to control these materials' electronic properties.

physics.chem-ph↗

arXiv2025

Plasmonic detection of Rashba spin-orbit coupling in monolayer transition-metal dichalcogenides

Rashba spin-orbit coupling (RSOC) induces strong momentum-dependent spin splitting and plays a crucial role in fields like spintronics and topological photonics. We here theoretically investigate the collective excitations in monolayer transition metal dichalcogenides (ML-TMDs) hosting RSOC, and conceive an approach to precisely quantify the strength of RSOC using plasmons. We determine the electron energy loss function (EELF) and plasmon dispersions for n-type ML-TMD from the dynamic dielectric function in the framework of the standard random phase approximation (RPA). In this system, both optical and acoustic plasmon modes are observed in the EELF and plasmon dispersions. Moreover, the plasmonic and spectral properties are tunable by electron density and dependent on RSOC. Crucially, we identify a minimum energy gap between the two plasmon modes to serve as a direct spectral signature of the RSOC strength. These results establish plasmons as a non-invasive, precise, and broadly tunable technique for determining RSOC in TMD van der Waals heterostructures and devices.

cond-mat.mes-hall↗

arXiv2025

Striped excitonic (super)solid in anisotropic semiconductors with screened exciton interactions

Within the Gross-Pitaevskii framework, we reveal the emergence of a crystallized phase of an exciton condensate in an atomically-thin anisotropic semiconductor, where screening of exciton-exciton interactions is introduced by a proximal doped graphene layer. While such screened interactions are expected to yield a hexagonal crystal lattice in the excitonic condensate in isotropic semiconductor quantum wells [see e.g. Phys. Rev. Lett. \textbf{108}, 060401 (2012)], here we show that for atomically thin semiconductors with strong electronic anisotropy, such as few-layer black phosphorus, the crystallized exciton phase acquires a parallel stripe structure - unanticipated to date. The optimal conditions for the emergence of this phase, as well as for its coexistence with excitonic superfluidity in a striped supersolid phase, are identified.

cond-mat.mes-hall↗

arXiv2024

Magneto-optical conductivity of monolayer transition metal dichalcogenides in the presence of proximity-induced exchange interaction and external electrical field

We theoretically investigate the magneto-optical (MO) properties of monolayer (ML) transition metal dichalcogenides (TMDs) in the presence of external electrical and quantizing magnetic fields and of the proximity-induced exchange interaction. The corresponding Landau Level (LL) structure is studied by solving the Schrödinger equation and the spin polarization in ML-TMDs under the action of the magnetic field is evaluated.The impact of trigonal warping on LLs and MO absorption is examined. Furthermore, the longitudinal MO conductivity is calculated through the dynamical dielectric function under the standard random-phase approximation (RPA) with the Kubo formula. We take ML-MoS$_2$ as an example to examine the effects of proximity-induced exchange interaction, external electrical and magnetic fields on the MO conductivity induced via intra- and interband electronic transitions among the LLs. For intraband electronic transitions within the conduction or valence bands, we can observe two absorption peaks in terahertz (THz) frequency range. While the interband electronic transitions between conduction and valence LLs show a series of absorption peaks in the visible range. We find that the proximity-induced exchange interaction, the carrier density, the strengths of the external electrical and magnetic fields can effectively modulate the positions of the absorption peaks and the shapes of the MO absorption spectra. The results obtained from this study can benefit to an in-depth understanding of the MO properties of ML-TMDs which can be potentially applied for magneto-optic, spintronic and valleytronic devices working in visible to THz frequency bandwidths.

cond-mat.mes-hall↗

arXiv2024

Longitudinal and transverse mobilities of $n$-type monolayer transition metal dichalcogenides in the presence of proximity-induced interactions at low temperature

We present a detailed theoretical investigation on the electronic transport properties of $n$-type monolayer (ML) transition metal dichalcogenides (TMDs) at low temperature in the presence of proximity-induced interactions such as Rashba spin-orbit coupling (RSOC) and the exchange interaction. The electronic band structure is calculated by solving the Schrödinger equation with a $\mathbf{k}\cdot\mathbf{p}$ Hamiltonian, and the electric screening induced by electron-electron interaction is evaluated under a standard random phase approximation approach. In particular, the longitudinal and transverse or Hall mobilities are calculated by using a momentum-balance equation derived from a semi-classical Boltzmann equation, where the electron-impurity interaction is considered as the principal scattering center at low temperature. The obtained results show that the RSOC can induce the in-plane spin components for spin-split subbands in different valleys, while the exchange interaction can lift the energy degeneracy for electrons in different valleys. The opposite signs of Berry curvatures in the two valleys would introduce opposite directions of Lorentz force on valley electrons. As a result, the transverse currents from nondegenerate valleys can no longer be canceled out so that the transverse current or Hall mobility can be observed. Interestingly, we find that at a fixed effective Zeeman field, the lowest spin-split conduction subband in ML-TMDs can be tuned from one in the $K'$-valley to one in the $K$-valley by varying the Rashba parameter. The occupation of electrons in different valleys also varies with changing carrier density. Therefore, we can change the magnitude and direction of the Hall current by varying the Rashba parameter, effective Zeeman field, and carrier density by, e.g., the presence of a ferromagnetic substrate and/or applying a gate voltage.

cond-mat.mes-hall↗

arXiv2024

Energy levels and Aharonov-Bohm oscillations in twisted bilayer graphene quantum dots and rings

We present a systematic study of the energy levels of twisted bilayer graphene (tBLG) quantum dots (QD) and rings (QR) under an external perpendicular magnetic field. The confinement structures are modeled by a circular dot-like- and ring-like-shaped site-dependent staggered potential, which prevents edge effects and leads to an energy gap between the electron and hole states. Results are obtained within the tight-binding model with interlayer hopping parameters defined by the Slater-Koster form for different interlayer twist angles $θ$. Our findings show that, for $θ$ around 0$^\circ$ or $60^\circ$, the energy spectra exhibit features resulting from the interplay between characteristics of the AA and AB/BA stacking orders that compose the moiré pattern of such tBLG, while the low-energy levels are shown to be nearly independent on the rotation angle for $10^\circ\lesssim θ\lesssim 50^\circ$. In the absence of a magnetic field, the energy levels of the QR scale with its width $W$ according to a power law $W^{-α}$, whose exponent $1 \lessapproxα\lessapprox 2$ depends on the twist angle. Most interestingly, the lowest energy states of tBLG QRs oscillate as a function of its average radius, with the oscillation period matching half of the moiré period. In the presence of an intense magnetic field, the lowest energy levels for the tBLG QDs and QRs match almost perfectly, regardless of whether the external radius of the quantum confinement structure is smaller or on the order of the moiré period, which is due to the interplay of the trigonal warping effect and the preferential localization of the eigenstates. Our results reveal relevant information about the moiré pattern in tBLG and its role in charge particle confinement.

cond-mat.mes-hall↗

arXiv2024

Electronic and magnetic properties of graphene-fluorographene nanoribbons: Controllable semiconductor-metal transition

We investigate the electronic and magnetic properties of graphene channels ($2$--$4$~nm wide) embedded within fluorographene, focusing on two distinct interfaces: the fully fluorinated $α$ interface and the half-fluorinated $β$ interface. Density functional theory (DFT) calculations reveal that $αα$ systems exhibit semiconducting behavior with antiferromagnetic ordering, closely resembling pristine zigzag graphene nanoribbons. In contrast, $αβ$ systems display ferromagnetism and a width-dependent semiconductor-to-metal transition. To enable the study of larger systems, we develop and validate effective Hubbard models for both $αα$ and $αβ$ channels. Building upon DFT results and a Wannier function analysis, these models accurately reproduce the electronic structure and magnetic ordering observed in DFT calculations. Crucially, our $αβ$ model successfully captures the semiconductor-to-metal transition. Application of this model to larger systems reveals the persistence of a ferromagnetic state with spin polarization localized at the $α$ edge. Our results demonstrate the potential of fluorination for targeted property engineering and provide a basis for exploring graphene-fluorographene systems in device applications ranging from microelectronics to spintronics.

cond-mat.mes-hall↗

arXiv2024

Ultrasensitive acoustic graphene plasmons in a graphene-transition metal dichalcogenide heterostructure: strong plasmon-phonon coupling and wavelength sensitivity enhanced by a metal screen

Acoustic plasmons in graphene exhibit strong confinement induced by a proximate metal surface and hybridize with phonons of transition metal dichalcogenides (TMDs) when these materials are combined in a van der Waals heterostructure, thus forming screened graphene plasmon-phonon polaritons (SGPPPs), a type of acoustic mode. While SGPPPs are shown to be very sensitive to the dielectric properties of the environment, enhancing the SGPPPs coupling strength in realistic heterostructures is still challenging. Here we employ the quantum electrostatic heterostructure model, which builds upon the density functional theory calculations for monolayers, to show that the use of a metal as a substrate for graphene-TMD heterostructures (i) vigorously enhances the coupling strength between acoustic plasmons and the TMD phonons, and (ii) markedly improves the sensitivity of the plasmon wavelength on the structural details of the host platform in real space, thus allowing one to use the effect of environmental screening on acoustic plasmons to probe the structure and composition of a van der Waals heterostructure down to the monolayer resolution.

cond-mat.mes-hall↗

arXiv2024

Control of proton transport and hydrogenation in double-gated graphene

The basal plane of graphene can function as a selective barrier that is permeable to protons but impermeable to all ions and gases, stimulating its use in applications such as membranes, catalysis and isotope separation. Protons can chemically adsorb on graphene and hydrogenate it, inducing a conductor-insulator transition that has been explored intensively in graphene electronic devices. However, both processes face energy barriers and various strategies have been proposed to accelerate proton transport, for example by introducing vacancies, incorporating catalytic metals or chemically functionalizing the lattice. However, these techniques can compromise other properties, such as ion selectivity or mechanical stability. Here we show that independent control of the electric field, E, at around 1 V nm-1, and charge-carrier density, n, at around 1 x 10^14 cm-2, in double-gated graphene allows the decoupling of proton transport from lattice hydrogenation and can thereby accelerate proton transport such that it approaches the limiting electrolyte current for our devices. Proton transport and hydrogenation can be driven selectively with precision and robustness, enabling proton-based logic and memory graphene devices that have on-off ratios spanning orders of magnitude. Our results show that field effects can accelerate and decouple electrochemical processes in double-gated 2D crystals and demonstrate the possibility of mapping such processes as a function of E and n, which is a new technique for the study of 2D electrode-electrolyte interfaces.

cond-mat.mes-hall↗

arXiv2024

Optical absorption window in Na$_3$Bi based three-dimensional Dirac electronic system

We present a detailed theoretical study of the optoelectronic properties of a Na$_3$Bi-based three-dimensional Dirac electronic system (3DDES). The optical conductivity is evaluated using the energy-balance equation derived from a Boltzmann equation, where the electron Hamiltonian is taken from a simplified $\mathbf{k}\cdotp \mathbf{p}$ approach. We find that for short-wavelength irradiation, the optical absorption in Na$_3$Bi is mainly due to inter-band electronic transitions. In contrast to the universal optical conductance observed for graphene, the optical conductivity for Na$_3$Bi based 3DDES depends on the radiation frequency but not on temperature, carrier density and electronic relaxation time. In the radiation wavelength regime of about 5 $μm<λ<$ 200 $μm$, an optical absorption window is found. This is similar to what is observed in graphene. The position and width of the absorption window depend on the direction of the light polarization and sensitively on temperature, carrier density, and electronic relaxation time. Particularly, we demonstrate that the inter-band optical absorption channel can be switched on and off by applying the gate voltage. This implies that similar to graphene, Na$_3$Bi based 3DDES can also be applied in infrared electro-optical modulators. Our theoretical findings are helpful in gaining an in-depth understanding of the basic optoelectronic properties of recently discovered 3DDESs.

cond-mat.mtrl-sci↗

arXiv2024

Valley-selective confinement of excitons in transition metal dichalcogenides with inhomogeneous magnetic fields

Magnetized ferromagnetic disks or wires support strong inhomogeneous fields in their borders. Such magnetic fields create an effective potential, due to Zeeman and diamagnetic contributions, that can localize charge carriers. For the case of two-dimensional transition metal dichalcogenides, this potential can valley-localize excitons due to the Zeeman term, which breaks the valley symmetry. We show that the diamagnetic term is negligible when compared to the Zeeman term for monolayers of transition metal dichalcogenides. The latter is responsible for trapping excitons near the magnetized structure border with valley-dependent characteristics, in which, for one of the valleys, the exciton is confined inside the disk, while for the other, it is outside. This spatial valley separation of exciton can be probed by circularly polarized light, and moreover, we show that the inhomogeneous magnetic field magnitude, the dielectric environment, and the magnetized structure parameters can tailor the spatial separation of the exciton wavefunctions.

cond-mat.mes-hall↗

arXiv2024

Two New Members of the Covalent Organic Frameworks Family: Crystalline 2D-Oxocarbon and 3D-Borocarbon Structures

While graphene oxide (GO) is representative of a disordered phase of oxocarbons with lackluster electronic properties, the coexistence of ordered, stoichiometric solid-state carbon oxides with graphene brings renewed momentum to the exploration of two-dimensional crystalline oxocarbons. This enduring subject, spanning decades, has recently witnessed significant advancements. In this context, our study delves into a novel material class, COF-66, notable for its meticulously ordered two-dimensional crystalline structure and intrinsic porosity. Employing a global optimization algorithm alongside density-functional calculations, our investigation highlights a standout member within the COF-66 family exceptional quasi-flat oxocarbon (C6O6)exhibiting an unconventional oxygen-decorated pore configuration. This pioneering study introduces C6O6 as an innovative entrant into the crystalline carbon oxide arena, augmenting the established understanding alongside the well-recognized graphene oxide and two graphene monoxide, i.e. α-GMO and \b{eta}-GMO. Expanding the exploration, the COF-66 series encompasses 2D-porous carbon nitride (C6N6) and the recently synthesized 2D-porous boroxine (B6O6), adhering to a generalized stoichiometry of X6Y6, where X = B, C, and Y = B, N, O, with X 6= Y. Remarkably, the entire COF-66 ensemble adopts a 2D-crystalline framework, with the exception of C6B6, which assumes a distinct 3D-crystalline arrangement. Employing the PBE (HSE06) level of theory, our electronic structure calculations yield band gap values of 0.01 (0.05) eV, 3.68 (5.29) eV, 0.00 (0.23) eV, and 1.53 (3.09) eV for B6N6, B6O6, C6B6, and C6N6, respectively, reinforcing and aligning with prior investigations.

cond-mat.mtrl-sci↗

arXiv2023

Optical spectrum of $n$-type and $p$-type monolayer MoS$_2$ in the presence of proximity-induced interactions

In this paper, we examined the effects of proximity-induced interactions such as Rashba spin-orbit coupling (SOC) and effective Zeeman fields (EZFs) on the optical spectrum of $n$-type and $p$-type monolayer (ML)-MoS$_2$. The optical conductivity is evaluated using the standard Kubo formula under Random phase approximation (RPA) with including the effective electron-electron interaction. It has been found that there exists two absorption peaks in $n$-type ML-MoS$_{2}$ and two knife shaped absorptions in $p$-type ML-MoS$_{2}$ which are contributed by the inter-subband spin flip electronic transitions within conduction and valence bands at valleys $K$ and $K'$ with a lifted valley degeneracy. The optical absorptions in $n$-type and $p$-type ML-MoS$_{2}$ occur in THz and infrared radiation regimes and the position, height, and shape of them can be effectively tuned by Rashba parameter, EZFs parameters, and carrier density. The interesting theoretical predictions in this study would be helpful for the experimental observation of the optical absorption in infrared to THz bandwidths contributed by inter-subband spin flip electronic transitions in a lifted valley degeneracy monolayer transition metal dichalcogenides (ML-TMDs) system. The obtained results indicate that ML-MoS$_{2}$ with the platform of proximity interactions make it a promising infrared and THz material for optics and optoelectronics.

cond-mat.mes-hall↗

arXiv2023

Gate-controlled suppression of light-driven proton transport through graphene electrodes

Recent experiments demonstrated that proton transport through graphene electrodes can be accelerated by over an order of magnitude with low intensity illumination. Here we show that this photo-effect can be suppressed for a tuneable fraction of the infrared spectrum by applying a voltage bias. Using photocurrent measurements and Raman spectroscopy, we show that such fraction can be selected by tuning the Fermi energy of electrons in graphene with a bias, a phenomenon controlled by Pauli blocking of photo-excited electrons. These findings demonstrate a dependence between graphene's electronic and proton transport properties and provide fundamental insights into molecularly thin electrode-electrolyte interfaces and their interaction with light.

cond-mat.mes-hall↗