arXiv subjects

O. Popova

Publications and source records attributed to O. Popova.

4 recordsLinked to original sources

arXiv2026

Room-temperature graphene sub-terahertz detector integrated on a silicon dielectric waveguide

Terahertz (THz) photonics offers a promising platform for next-generation 6G wireless communications, on-chip spectrometers, and non-invasive biomedical sensors. In the near- and mid-infrared, monolithically integrated photodetectors are a cornerstone of photonic integrated circuits (PICs). In the THz range, however, such integration on low-loss dielectric waveguides remains an open challenge: to date, room-temperature on-waveguide detection has been realized only through hybrid flip-chip assembly of discrete elements, which leads to poor mode coupling, larger footprint, and reduced mechanical stability. Here we address this gap by demonstrating a room-temperature graphene sub-THz detector monolithically integrated on a high-resistivity silicon dielectric waveguide for D-band (110-170 GHz) operation. We couple an hBN-encapsulated graphene channel to the guided mode using a tapered slot-line antenna patterned directly onto the silicon surface. The detector achieves a voltage responsivity of 11.5 V/W and a 3 dB bandwidth of 1.94 GHz, with the latter currently limited by parasitic inductance of the readout interconnects rather than by the intrinsic graphene response. This platform provides a practical pathway to fully integrated room-temperature THz photonic circuits, where electrostatic gating and impedance matching can improve both responsivity and bandwidth by roughly an order of magnitude.

physics.optics↗

arXiv2026

Gate-Tunable Photoresponse of Graphene Josephson Junctions at Terahertz Frequencies

Graphene Josephson junctions (JJ) provide a promising platform for ultra-broadband quantum sensing of light owing to graphene's frequency-independent absorption, vanishing electronic heat capacity, and weak electron-phonon coupling, which enable rapid suppression of the critical current through radiation-induced electron heating. Existing investigations have been confined to the microwave and infrared regimes, where competing detector technologies are already established; by contrast, the terahertz (THz) band - where sensitivity is most urgently lacking and no mature quantum sensor exists - has remained largerly unexplored. Here we demonstrate a strong photoresponse of graphene JJs at THz frequencies, establishing a first experimental step towards graphene-based THz quantum sensors. Under low-intensity illumination, we observe a pronounced suppression of the critical current that generates a strong photovoltage (Vph) under current bias. By tracking this Vph and independently measuring the electron temperature as a function of absorbed power, we extract a responsivity of 88 kV W^-1 and a noise-equivalent power of 45 aW Hz^-1/2 at 1.7 K. Furthermore, gate tunability of our JJ enables access to a regime where hysteretic current-voltage characteristics persist up to 0.9 K, offering a potential route toward single-photon THz detection beyond millikelvin (mK) temperatures. These findings establish graphene JJ as a versatile platform for broadband cryogenic radiation sensing and point towards their use as quantum sensors at THz frequencies.

cond-mat.mes-hall↗

arXiv2025

Interaction-limited conductivity of twisted bilayer graphene revealed by giant terahertz photoresistance

Identifying the microscopic processes that limit conductivity is essential for understanding correlated and quantum-critical states in quantum materials. In twisted bilayer graphene (TBG) and other twist-controlled materials, the temperature dependence of metallic resistivity follows power-law scaling, with the exponent spanning a broad range, rendering standard transport measurements insufficient to unambiguously identify the dominant scattering processes and giving rise to competing interpretations ranging from phonon-limited transport and umklapp scattering to strange metallicity and heavy fermion renormalization. Here, we use terahertz (THz) excitation to selectively raise the electron temperature in TBG while keeping the lattice cold, enabling a direct separation of electron-electron and electron-phonon contributions to resistivity. We observe a giant THz photoresistance, reaching up to 70% in magic-angle devices, demonstrating that electronic interactions dominate transport even in regimes previously attributed to phonons, including the linear-in-temperature resistivity near the magic angle. Away from the magic angle, we observe coexisting photoresistance and robust quadratic-in-temperature resistivity at extremely low carrier densities where standard electron-electron scattering mechanisms (umklapp and Baber inter-band scattering) are kinematically forbidden. Our analysis identifies the breakdown of Galilean invariance in the Dirac-type dispersion as a possible origin of the interaction-limited conductivity, arising from inter-valley electron-electron collisions. Beyond twisted bilayer graphene, our approach establishes THz-driven hot-electron transport as a general framework for disentangling scattering mechanisms in low-density quantum materials.

cond-mat.mes-hall↗

arXiv2024

Anomalous terahertz photoconductivity caused by the superballistic flow of hydrodynamic electrons in graphene

Light incident upon materials can induce changes in their electrical conductivity, a phenomenon referred to as photoresistance. In semiconductors, the photoresistance is negative, as light-induced promotion of electrons across the band gap enhances the number of charge carriers participating in transport. In superconductors, the photoresistance is positive because of the destruction of the superconducting state, whereas in normal metals it is vanishing. Here we report a qualitative deviation from the standard behavior in metallic graphene. We show that Dirac electrons exposed to continuous wave (CW) terahertz (THz) radiation can be thermally decoupled from the lattice by 50~K which activates hydrodynamic electron transport. In this regime, the resistance of graphene constrictions experiences a decrease caused by the THz-driven superballistic flow of correlated electrons. We analyze the dependencies of the negative photoresistance on the carrier density, and the radiation power and show that our superballistic devices operate as sensitive phonon-cooled bolometers and can thus offer a picosecond-scale response time. Beyond their fundamental implications, our findings underscore the practicality of electron hydrodynamics in designing ultra-fast THz sensors and electron thermometers.

cond-mat.mes-hall↗