Ultrafast switching of surface plasmonic conditions in nonplasmonic metals

Emile Bévillon (1) , Jean-Philippe Colombier (1) , Vanina Recoules (2) , Hao Zhang (1) , Chen Li (1, 3) , Razvan Stoian (1)

1 LHC - Laboratoire Hubert Curien
2 DAM/DIF - DAM Île-de-France
3 EAST CHINA UNIVERSITY

We demonstrate that ultrafast carrier excitation can drastically affect electronic structures in nonplasmonic metals and determine a transient, brief surface plasmonic state, potentially creating the conditions for a plasmonic switch. The initial state can be related to d-band partial filling and splitting, with a pseudo-band-gap accommodating the chemical potential. This determines a quasi-resonant-like spectral behavior of the optical constants for pumping carriers across the d-band pseudogap, i.e., visible frequencies. The relation between real and imaginary parts of the refractive index does not fulfill surface plasmonic conditions in the visible photon range. Using first-principles molecular dynamics and Kubo-Greenwood formalism for laser-excited tungsten we show that carrier heating mobilizes d electrons into collective inter-and intraband transitions leading to a sign flip in the imaginary optical conductivity, activating plasmonic properties for the initial nonplasmonic phase. The drive for the laser-induced optical evolution in this case does not rely on a variation of the free electron number but can be visualized as an increasingly damped character of the quasiresonance at visible frequencies. Here laser heating determines an energy-dependent degree of occupation with broadening profiles. The subsequent evolution of optical indices for the excited material is confirmed by time-resolved ultrafast ellipsometry. The large optical tunability extends the existence spectral domain of surface plasmons in ranges typically claimed in laser self-organized nanostructuring. Nonequilibrium heating is thus a strong factor for engineering optical control of evanescent excitation waves, particularly important in laser nanostructuring strategies.

Domains: Condensed Matter [cond-mat]

Emile Bévillon, Jean-Philippe Colombier, Vanina Recoules, Hao Zhang, Chen Li, et al.. Ultrafast switching of surface plasmonic conditions in nonplasmonic metals. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2016, 93, pp.165416. ⟨10.1103/PhysRevB.93.165416⟩. ⟨ujm-01340983⟩