Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 18: Focus Session: Nanoscale Light-matter Interaction I

HL 18.3: Invited Talk

Tuesday, March 18, 2025, 10:30–11:00, H17

Real space mapping of electrically tunable anisotropic THz plasmon polaritons in hBN encapsulated black phosphorus — •Eva Pogna — Institute of Photonics and Nanotechnology, CNR-IFN, Milan, Italy

Polaritons in two-dimensional layered crystals offer effective means to confine and manipulate terahertz (THz) electromagnetic waves at the nanoscale, a crucial step in advancing photonic technologies.

In this study, we investigate anisotropic plasmon polaritons in black phosphorus nanoflakes at THz frequencies, utilizing near-field photocurrent nanoscopy combined with THz hyperspectral near-field scattering techniques.

Encapsulation with hexagonal boron nitride protects black phosphorus from air-induced degradation, while field-effect transistor (FET) devices enable photo-thermoelectric detection of plasmon polaritons.

Our findings reveal highly confined, gate-tunable plasmon polaritons with subwavelength dispersion (∼λ/76 at 2.01 THz).

The dielectric anisotropy of black phosphorus leads to polaritons with elliptic wavefronts at THz frequencies, enabling enhanced confinement and control over THz field propagation. Moreover, electrostatic control of carrier density allows precise tuning of polariton wavelength, highlighting the versatility of this platform for nanoscale THz light manipulation and reconfigurable infrared nanophotonics.

Notably, the four-gate FET architecture introduced here to examine in-plane propagation anisotropy can be readily adapted for the study of other anisotropic conductive materials.

Keywords: THz polaritons; black-phosphorus; photocurrent nanoscopy; plasmon polaritons; anisotropy