arXiv subjects

Jorge Pedrós

Publications and source records attributed to Jorge Pedrós.

9 recordsLinked to original sources

arXiv2026

Hyperbolic exciton-plasmon polaritons in MoS$_2$/MoOCl$_2$ van der Waals heterostructures

Polaritons formed by strong coupling between excitons and confined electromagnetic modes underpin emerging nanophotonic technologies, yet platforms based on isotropic metals or optical microcavities provide limited control over propagation direction. Here we predict that monolayer MoS$_2$ on the in-plane hyperbolic conductor MoOCl$_2$ supports hyperbolic exciton-plasmon polaritons governed by crystallographic direction, slab thickness, and hyperbolic mode order. Using an anisotropic transfer-matrix model coupled to a dissipative three-level Hamiltonian, we obtain wavevector-dependent anticrossings between the MoOCl$_2$ plasmons and the spin-orbit-split A and B excitons of MoS$_2$, yielding lower, middle, and upper polariton branches with coupling energies $g_A$ = 64.7 meV and $g_B$ = 61.2 meV. Rotating the in-plane wavevector tunes the plasmon-exciton detuning, while increasing the MoOCl$_2$ thickness activates higher-order hyperbolic Fabry-Pérot modes. Their coupling follows an approximate effective-mode-volume scaling. Strong coupling persists for excitonic linewidths up to 50 meV, with the normalised spectral-resolution ratio remaining above unity. These results establish MoS$_2$/MoOCl$_2$ as a lithography-free platform for directional and multimode exciton-plasmon polariton engineering in the visible spectral range.

cond-mat.mes-hall↗

arXiv2026

Drift-Induced Nonreciprocal Hyperbolic Polaritons in Graphene/$α$-MoO$_3$ Heterostructures

Achieving optical isolation requires breaking symmetry between forward- and backward-propagating light, a long-standing challenge at the nanoscale in the absence of magnetic fields. Here we theoretically demonstrate electrically tunable nonreciprocal phonon-plasmon polaritons in a graphene/$α$-MoO$_3$/SiC heterostructure operating in the mid-infrared. A dc current in graphene induces a wavevector-dependent Doppler shift that breaks reciprocity and generates strong directional asymmetry in hybrid plasmon-phonon propagation. In the reciprocal regime, hybridization between graphene plasmons and hyperbolic phonon polaritons in $α$-MoO$_3$, further shaped by the SiC substrate, enables gate-controlled transitions of isofrequency contours, including canalization along orthogonal crystal axes. At drift velocities of 5% of the Fermi velocity, the system exhibits pronounced momentum-dependent nonreciprocity with contrast reaching $\sim$ 0.3, while directions orthogonal to the drift remain unaffected due to symmetry imposed constraints. Real-space calculations confirm that this momentum-space asymmetry translates into directional near-field intensity modulation. These results establish current-biased van der Waals heterostructures as a platform for electrically tunable, magnet-free nonreciprocal nanophotonics in the mid-infrared.

cond-mat.mes-hall↗

arXiv2025

Moving magnetic domain walls with sound alone

Surface Acoustic Waves (SAW) have been used in spintronic applications to decrease the magnetic field or the electric current required to act on the magnetization. A common belief is that a SAW alone cannot achieve a directed magnetic switching in a device without an assisting magnetic field or electric current. In this work, we demonstrate magnetic domain wall motion driven solely by an acoustic wave. Using XMCD-PEEM, we show extensive evidence of SAW-induced and field-free magnetic domain wall motion (DW) in the direction of the wave propagation. Our micromagnetic simulations reveal a mechanism that allows the SAW to transfer linear momentum to the DW. Experimentally, the largest DW average velocity measured was ~12 m/s, although our simulations predict that velocities in the range of 100 m/s could be attained. This new mechanism opens the door to designing innovative spintronic devices where the magnetization can be controlled exclusively by an acoustic wave.

cond-mat.mes-hall↗

arXiv2020

Exciton-Plasmon Coupling in 2D Semiconductors by Surface Acoustic Waves

We theoretically demonstrate the coupling between excitons in 2D semiconductors and surface plasmons in a thin metal film by means of a surface acoustic wave (SAW), proving that the generated exciton-plasmon polaritons (or plexcitons) are in the strong coupling regime. The strain field of the SAW creates a dynamic diffraction grating providing the momentum match for the surface plasmons, whereas the piezoelectric field, that could dissociate the excitons, is cancelled out by the metal. This is exemplified for monolayer MoS$\mathrm{_{2}}$ and mono- and few-layer black phosphorus on top of a thin silver layer on a LiNbO$\mathrm{_{3}}$ piezoelectric substrate, providing Rabi splittings of 100-150 meV. Thus, we demonstrate that SAWs are powerful tools to modulate the optical properties of supported 2D semiconductors by means of the high-frequency localized deformations tailored by the acoustic transducers, that can serve as electrically switchable launchers of propagating plexcitons suitable for active high-speed nanophotonic applications.

cond-mat.mes-hall↗

arXiv2019

Dynamic local strain in graphene generated by surface acoustic waves

We experimentally demonstrate that the Raman active optical phonon modes of single layer graphene can be modulated by the dynamic local strain created by surface acoustic waves (SAWs). In particular, the dynamic strain field of the SAW is shown to induce a Raman scattering intensity variation as large as 15% and a phonon frequency shift of up to 10 cm$^{-1}$ for the G band, for instance, for an effective hydrostatic strain of 0.24% generated in a single layer graphene atop a LiNbO$_{3}$ piezoelectric substrate with a SAW resonator operating at a frequency of $ \sim $ 400 MHz. Thus, we demonstrate that SAWs are powerful tools to modulate the optical and vibrational properties of supported graphene by means of the high-frequency localized deformations tailored by the acoustic transducers, which can also be extended to other 2D systems.

cond-mat.mes-hall↗

arXiv2019

Reducing sheet resistance of self-assembled transparent graphene films by defect patching and doping with UV/ozone treatment

Liquid phase exfoliation followed by Langmuir-Blodgett self-assembly (LBSA) is a promising method for scalable production of thin graphene films for transparent conductor applications. However, monolayer assembly into thin films often induces a high density of defects, resulting in a large sheet resistance that hinders practical use. We introduce UV/ozone as a novel photochemical treatment that reduces sheet resistance of LBSA graphene threefold, while preserving the high optical transparency. The effect of such treatment on our films is opposite to the effect it has on mechanically exfoliated or CVD films, where UV/ozone creates additional defects in the graphene plane, increasing sheet resistance. Raman scattering shows that exposure to UV/ozone reduces the defect density in LBSA graphene, where edges are the dominant defect type. FTIR spectroscopy indicates binding of oxygen to the graphene lattice during exposure to ozone. In addition, work function measurements reveal that the treatment dopes the LBSA film, making it more conductive. Such defect patching paired with doping leads to an accessible way of improving the transparent conductor performance of LBSA graphene, making solution-processed thin films a candidate for industrial use.

cond-mat.mtrl-sci↗

arXiv2019

Single-photon Emission from an Acoustically-driven Lateral Light-emitting Diode

Single-photon sources are essential building blocks in quantum photonic networks, where quantum-mechanical properties of photons are utilised to achieve quantum technologies such as quantum cryptography and quantum computing. Most conventional solid-state single-photon sources are based on single emitters such as self-assembled quantum dots, which are created at random locations and require spectral filtering. These issues hinder the integration of a single-photon source into a scaleable photonic quantum network for applications such as on-chip photonic quantum processors. In this work, using only regular lithography techniques on a conventional GaAs quantum well, we realise an electrically triggered single-photon source with a GHz repetition rate and without the need for spectral filtering. In this device, a single electron is carried in the potential minimum of a surface acoustic wave (SAW) and is transported to a region of holes to form an exciton. The exciton then decays and creates a single photon in a lifetime of ~ 100ps. This SAW-driven electroluminescence (EL) yields photon antibunching with $g^{(2)}(0) = 0.39 \pm 0.05$, which satisfies the common criterion for a single-photon source $g^{(2)}(0) < 0.5$. Furthermore, we estimate that if a photon detector receives a SAW-driven EL signal within one SAW period, this signal has a 79%-90% chance of being a single photon. This work shows that a single-photon source can be made by combining single-electron transport and a lateral n-i-p junction. This approach makes it possible to create multiple synchronised single-photon sources at chosen positions with photon energy determined by quantum-well thickness. Compared with conventional quantum-dot-based single-photon sources, this device may be more suitable for an on-chip integrated photonic quantum network.

cond-mat.mes-hall↗

arXiv2018

Impact of 2D-Graphene on SiN Passivated AlGaN/GaN MIS-HEMTs under Mist Exposure

The effect of a two dimensional (2D) graphene layer (GL) on top of the silicon nitride (SiN) passivation layer of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) has been systematically analyzed. Results showed that in the devices without the GL, the maximum drain current density (I_D,max) and the maximum transconductance (g_m,max) decreased gradually as the mist exposure time increased, up to 23% and 10%, respectively. Moreover, the gate lag ratio (GLR) increased around 10% during mist exposure. In contrast, devices with a GL showed a robust behavior and not significant changes in the electrical characteristics in both DC and pulsed conditions. The origin of these behaviors has been discussed and the results pointed to the GL as the key factor for improving the moisture resistance of the SiN passivation layer.

physics.app-ph↗

arXiv2013

Coupling light into graphene plasmons through surface acoustic waves

We propose a scheme for coupling laser light into graphene plasmons with the help of electrically generated surface acoustic waves. The surface acoustic wave forms a diffraction grating which allows to excite the long lived phonon-like branch of the hybridized graphene plasmon-phonon dispersion with infrared laser light. Our approach avoids patterning the graphene sheet, does not rely on complicated optical near-field techniques, and allows to electrically switch the coupling between far field radiation and propagating graphene plasmons.

cond-mat.mes-hall↗