Electrical tuning of a quantum plasmonic resonance

Abstract

Surface plasmon (SP) excitations in metals facilitate confinement of light into deep-subwavelength volumes and can induce strong light-matter interaction. Generally, the SP resonances supported by noble metal nanostructures are explained well by classical models, at least until the nanostructure size is decreased to a few nanometres, approaching the Fermi wavelength λ of the electrons. Although there is a long history of reports on quantum size effects in the plasmonic response of nanometre-sized metal particles, systematic experimental studies have been hindered by inhomogeneous broadening in ensemble measurements, as well as imperfect control over size, shape, faceting, surface reconstructions, contamination, charging effects and surface roughness in single-particle measurements. In particular, observation of the quantum size effect in metallic films and its tuning with thickness has been challenging as they only confine carriers in one direction. Here, we show active tuning of quantum size effects in SP resonances supported by a 20-nm-thick metallic film of indium tin oxide (ITO), a plasmonic material serving as a low-carrier-density Drude metal. An ionic liquid (IL) is used to electrically gate and partially deplete the ITO layer. The experiment shows a controllable and reversible blue-shift in the SP resonance above a critical voltage. A quantum-mechanical model including the quantum size effect reproduces the experimental results, whereas a classical model only predicts a red shift.

Two-fluid hydrodynamic model for semiconductors

“…(29). The coefficients a r l are related to oscillations of the magnetic type, and the expression is identical to the one found in the classical local derivation [59].…”

“…Furthermore, intrinsic semiconductors may contain plasmas created either thermally or by external excitations (e.g., from a laser), and here the electron density can be controlled dynamically with the temperature or the excitation energy, respectively. Plasmonics has already been shown in several papers for doped semiconductors [16][17][18][19][20][21][22][23][24][25][26][27][28], biased semiconductors [29][30][31][32], laser excited semiconductors [33], and thermally excited intrinsic semiconductors [34][35][36][37].…”

“…[24][25][26][27][28][29][30] investigated plasmons in nanostructures of semiconductors, but except for Refs. [27,29] they all used the Drude model to describe their results. And just as for metals one would expect that the Drude model only is accurate for semiconductor structures down to a certain size.…”

Tunable Metasurfaces Based on Active Materials

“…For example, in InGaAs/InAlAs quantum wells, the energy and strength of their intersubband transitions can be modulated through a bias voltage, resulting in a refractive index modulation orders of of magnitude greater than that of the free carrier effect . Interesting tuning mechanisms may also emerge when the thickness of TCOs is reduced to a few nanometers, where quantum effect becomes relevant . In terms of 2D materials, despite graphene, there exist a large body of monolayer transition metal dichacoginides, which also manifest fascinating tunable optical properties.…”

Active control of plasmonic colors: emerging display technologies

“…This includes gate-tunable conductive oxides that can change permittivity and induce phase changes for light waves in thin films, but remain limited to the infrared. 42,43,44 To maintain focus of the review, devices where the colors are not based on metallic structures will not be covered, although it should be noted that other interesting electrochromic devices exist, such as amorphous/crystalline phase change materials. 45 There are also other emerging plasmonic technologies which cannot exactly be classified as dynamic color displays, but certainly closely related, like the plasmonic "liquid mirror".…”