Prof. Felix Baumberger, Department of Quantum Matter Physics, University of Geneva & Swiss Light Source, Paul Scherrer Institute

The electronic structure of few-layer black phosphorus

Black phosphorus stands out among two-dimensional (2D) semiconductors because of its high mobility and direct band gap. These key-properties have already enabled prototype sensors and optoelectronic devices at technologically relevant wavelengths and with promising performance. In this talk I will present direct electronic structure measurements of exfoliated few-layer black phosphorus using a home built micro-ARPES instrument. Our measurements unveil ladders of quantized subbands with characteristics not normally found in conventional semiconductor quantum wells. Specifically, we find anisotropic effective masses with a strong thickness dependence and subband energies that deviate from the scaling with the square of the subband index. An analysis of the spectral function further provides direct evidence for surprisingly strong coupling to bosonic modes. We interpret the latter as electron-phonon coupling and show that this interpretation is fully consistent with the temperature dependence of the mobility.