Juan Antonio Delgado Notario

Graphene plasmons confine incident terahertz fields far below the diffraction limit and, when hosted by a gate‐defined Fabry–Perot cavity, they enable electrically tunable, frequency‐selective photodetectors. In a magnetic field, these plasmons hybridize with the cyclotron motion to form magnetoplasmons, offering a platform for fundamental studies and for nonreciprocal, spectrally selective, and ultrasensitive terahertz photonics. However, implementing magnetoplasmon‐assisted resonant transistors at terahertz frequencies has remained challenging so far. Here, we extend the resonant Dyakonov–Shur graphene TeraFET framework into the magnetoplasmonic regime and use gate‐dependent, on‐chip terahertz photocurrent spectroscopy combined with a perpendicular magnetic field to resolve and probe the evolution of resonant magnetoplasmons in antenna‐coupled monolayer and bilayer graphene TeraFETs. In monolayer graphene, the dispersion reflects the Dirac nature of the carriers, exhibiting a nonmonotonic density dependence due to the interplay of plasma resonance and cyclotron motion, with an inflection point at maximal plasmon–cyclotron coupling. In contrast, in bilayer graphene, we recover and map a magnetoplasmon dispersion consistent with the conventional Schrödinger‐type picture. These results establish graphene TeraFET devices as a robust on‐chip platform for resonant magnetoplasmonics at terahertz frequencies, opening avenues toward magnetically programmable, frequency‐selective terahertz photodetectors.

Highly sensitive photovoltage detection in gigahertz/terahertz (THz) graphene sensors enables direct probing of electron spin resonances (ESRs) and provides access to the intrinsic spin–orbit coupling (SOC) and sublattice-potential gaps in graphene-based systems. In this work, we employ a sub-THz photoconductivity-based technique to investigate spin-flip transitions in bilayer graphene and graphene/MoS ₂ heterostructures at low temperatures. In both systems, three spin resonances are observed corresponding to Zeeman, intrinsic SOC, and sublattice-potential splittings. The resonance frequencies and extracted [ ]-factors and spin relaxation times are nearly identical in the two structures, indicating that the proximity of MoS ₂ does not significantly enhance graphene’s SOC under the present conditions. The energy gaps show a pronounced temperature dependence, increasing steadily as the temperature decreases and suggesting a contribution from thermally induced strain or electron–phonon coupling. Notably, all resonances are accompanied by a characteristic drop in photovoltage, consistent with spin-dependent recombination of photoexcited carriers. These findings establish THz photovoltage spectroscopy as a powerful, contact-free, and on-chip method for probing spin-dependent electronic structure and relaxation phenomena in the material forming the detector.

Graphene plasmons confine incident terahertz fields far below the diffraction limit and, when hosted by a gate-defined Fabry-Perot cavity, enable electrically tunable, frequency-selective photodetectors. In a magnetic field, these plasmons hybridize with the cyclotron motion to form magnetoplasmons, offering a platform for fundamental studies and for nonreciprocal, spectrally selective, ultrasensitive terahertz photonics. However, implementing magnetoplasmon-assisted resonant transistors at terahertz frequencies has remained challenging so far. Here we use gate-dependent, on-chip terahertz photocurrent spectroscopy combined with a perpendicular magnetic field to resolve and probe the evolution of resonant magnetoplasmons in antenna-coupled monolayer and bilayer graphene TeraFETs. In monolayer graphene the dispersion reflects the Dirac nature of the carriers, exhibiting a non-monotonic density dependence due to the interplay of plasma resonance and cyclotron motion, with an inflection point at maximal plasmon-cyclotron coupling. In contrast, in bilayer graphene we recover and map a magnetoplasmon dispersion consistent with the conventional Schrödinger-type picture. These results establish graphene TeraFET devices as a robust on-chip platform for resonant magnetoplasmonics at terahertz frequencies, enabling magnetically programmable, frequency-selective photonics and opening avenues toward photodetectors with enhanced sensitivity.

Moiré superlattices formed at the interface between stacked two-dimensional atomic crystals offer limitless opportunities to design materials with widely tunable properties and engineer intriguing quantum phases of matter. However, despite progress, precise probing of the electronic states and tantalizingly complex band textures of these systems remain challenging. Here, we present gate-dependent terahertz photocurrent spectroscopy as a robust technique to detect, explore and quantify intricate electronic properties in graphene moiré superlattices. Specifically, using terahertz light at different frequencies, we demonstrate distinct photocurrent regimes evidencing the presence of avoided band crossings and tiny (~1-20 meV) inversion-breaking global and local energy gaps in the miniband structure of minimally twisted graphene and hexagonal boron nitride heterostructures, key information that is inaccessible by conventional electrical or optical techniques. In the off-resonance regime, when the radiation energy is smaller than the gap values, enhanced zero-bias responsivities arise in the system due to the lower Fermi velocities and specific valley degeneracies of the charge carriers subjected to moiré superlattice potentials. In stark contrast, above-gap excitations give rise to bulk photocurrents -- intriguing optoelectronic responses related to the geometric Berry phase of the constituting electronic minibands. Besides their fundamental importance, these results place moiré superlattices as promising material platforms for advanced, sensitive and low-noise terahertz detection applications.

Moiré superlattices formed at the interface between stacked 2D atomic crystals offer limitless opportunities to design materials with widely tunable properties and engineer intriguing quantum phases of matter. However, despite progress, precise probing of the electronic states and tantalizingly complex band textures of these systems remain challenging. Here, we present gate-dependent terahertz photocurrent spectroscopy as a robust technique to detect, explore, and quantify intricate electronic properties in graphene moiré superlattices. Specifically, using terahertz light at different frequencies, we demonstrate distinct photocurrent regimes, evidencing the presence of avoided band crossings and tiny (∼1 to 20 meV) inversion-breaking global and local energy gaps in the miniband structure of minimally twisted graphene and hexagonal boron nitride heterostructures, key information that is inaccessible by conventional electrical or optical techniques. In the off-resonance regime, when the radiation energy is smaller than the gap values, enhanced zero-bias responsivities arise in the system due to the lower Fermi velocities and specific valley degeneracies of the charge carriers subjected to moiré superlattice potentials. In stark contrast, the above-gap excitations give rise to bulk photocurrents─intriguing optoelectronic responses related to the geometric Berry phase of the constituting electronic minibands. Besides their fundamental importance, these results place moiré superlattices as promising material platforms for advanced, sensitive, and low-noise terahertz detection applications.

In recent years, graphene Field-Effect-Transistors (GFETs) have demonstrated an outstanding potential for Terahertz (THz) photodetection due to their fast response and high-sensitivity. Such features are essential to enable emerging THz applications, including 6G wireless communications, quantum information, bioimaging and security. However, the overall performance of these photodetectors may be utterly compromised by the impact of internal resistances presented in the device, so-called access or parasitic resistances. In this work, we provide a detailed study of the influence of internal device resistances in the photoresponse of high-mobility dual-gate GFET detectors. Such dual-gate architectures allow us to fine tune (decrease) the internal resistance of the device by an order of magnitude and consequently demonstrate an improved responsivity and noise-equivalent-power values of the photodetector, respectively. Our results can be well understood by a series resistance model, as shown by the excellent agreement found between the experimental data and theoretical calculations. These findings are therefore relevant to understand and improve the overall performance of existing high-mobility graphene photodetectors.

In recent years, graphene field-effect-transistors (GFETs) have demonstrated an outstanding potential for terahertz (THz) photodetection due to their fast response and high-sensitivity. Such features are essential to enable emerging THz applications, including 6G wireless communications, quantum information, bioimaging and security. However, the overall performance of these photodetectors may be utterly compromised by the impact of internal resistances presented in the device, so-called access or parasitic resistances. In this work, we provide a detailed study of the influence of internal device resistances in the photoresponse of high-mobility dual-gate GFET detectors. Such dual-gate architectures allow us to fine tune (decrease) the internal resistance of the device by an order of magnitude and consequently demonstrate an improved responsivity and noise-equivalent-power values of the photodetector, respectively. Our results can be well understood by a series resistance model, as shown by the excellent agreement found between the experimental data and theoretical calculations. These findings are therefore relevant to understand and improve the overall performance of existing high-mobility graphene photodetectors. Graphical Abstract

Graphene-based superlattices offer a unique materials playground to exploit and control a higher number of electronic degrees of freedom, such as charge, spin, or valley for disruptive technologies. Recently, orbital effects, emerging in multivalley band structures lacking inversion symmetry, have been discussed as possible mechanisms for developing orbitronics. Here, we report nonlocal transport measurements in small gap hBN/graphene/hBN moiré superlattices which reveal very strong magnetic field-induced chiral response which is stable up to sizable temperatures. The measured sign dependence of the nonlocal signal with respect to the magnetic field orientation clearly indicates the manifestation of emerging orbital magnetic moments. The interpretation of experimental data is well supported by numerical simulations, and the reported phenomenon stands as a formidable way of in situ manipulation of the transverse flow of orbital information that could enable the design of orbitronic devices.

The photothermal conversion in plasmonic nanohelices is studied, unveiling how helical nanostructures made from metals with a notable interband activity ‐such as cobalt (Co) and nickel (Ni)‐ exhibit a remarkable temperature rise ΔT up to ≈1000 K under illumination. Such outstanding ΔT values exclusively occur at wavelengths close to their localized plasmon resonances (ΔT is significantly lower off resonance), and therefore the photothermal conversion of these nanoparticles is spectrally selective. The exceptional and spectrally selective temperature rise is demonstrated at near infrared (NIR) wavelengths, which prompts the use of Co and Ni helical nanoparticles in a wide range of photothermal applications including solar energy conversion, seawater desalination, catalysis, or nanomedicine.