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Percorrer por autor "Ribeiro, Sofia"

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  • Casimir-mediated amplification of flexural modes in suspended graphene
    Publication . Ribeiro, Sofia; Terças, Hugo
    We develop a minimal theoretical framework to describe near-field Casimir-mediated coupling between two suspended nanomembranes: a graphene sheet and a gold-coated GaAs membrane separated by a micrometer-scale vacuum gap. Coherent excitation of flexural (out-of-plane) modes in the gold membrane, provided by an external piezoelectric drive, enables efficient energy transfer to graphene through static vacuum electromagnetic coupling. Using a coupled-mode description equivalent to the classical equations of motion, we identify hybridized flexural modes exhibiting avoided crossings, tunable spectral response, and drive-dependent energy exchange. Under experimentally accessible conditions, Casimir-mediated mode hybridisation transfers energy from the driven gold membrane to graphene at rates comparable to or exceeding the intrinsic mechanical losses of graphene, resulting in a strong enhancement of its flexural response and linewidth narrowing. The Casimir interaction acts here solely as a static, non-contact coupling mechanism, while all energy is supplied externally through coherent mechanical driving, yielding drive-induced amplification without intrinsic negative damping. Our results establish Casimir coupling as a practical resource for controlling flexural dynamics in graphene nanomembranes and provide a platform for non-contact energy transfer and mode-selective amplification in two-dimensional mechanical systems.
    2026-09-15Artigo de investigação Acesso aberto Ver mais
  • Quantum theory of plasmon-phonon scattering in multisubband systems
    Publication . Ribeiro, Sofia; Terças, Hugo
    We present a first-principles quantum theory of a critical yet unexplored energy-loss pathway in low-dimensional semiconductors: resonant second-order scattering between multisubband (MSB) plasmons mediated by longitudinal optical phonons. Specifically, we demonstrate how a high-energy MSB plasmon decays into a lower-energy plasmon state via phonon emission-a fundamental process governing energy relaxation and decoherence in quantum wells. Through exact diagonalization of the coupled plasmon-phonon system and derivation of an effective Hamiltonian, we identify density-tunable resonance conditions that maximize scattering efficiency. Our numerical simulations for GaInAs quantum wells reveal scattering rates ( similar to 10ns-1) competitive with radiative losses, with carrier density acting as a control knob. These results resolve the interplay of collective electronic and vibrational modes in confined systems, providing design principles to mitigate losses in infrared photodetectors, quantum cascade lasers, and plasmon-based quantum devices.
    2026-01-09Artigo de investigação Acesso aberto Ver mais