Hyperbolic Metamaterial with Field-Effect Induced Transitions of the Dispersion Surface

Georgia Papadakis Applied Physics, CALTECH, Pasadena, California, USA Krishnan Thyagarajan Applied Physics, CALTECH, Pasadena, California, USA Ho Wai Lee Applied Physics, CALTECH, Pasadena, California, USA Harry A. Atwater Applied Physics, CALTECH, Pasadena, California, USA

The realization of metamaterials that support different dispersion types within the visible regime and the potential of tuning their effective response provides the means for designing novel optical components like smart switches and tunable polarizers. Active control over the amplitude and phase of the scattered fields is also important for holographic display applications.

We present a planar metamaterial with integrated transparent conductive oxides. It consists of two 20 nm layers of Ag, separated by a 10 nm active layer of ITO with carrier concentration 5⋅1020/cm3. The two materials are isolated from each other by 10nm Al2O3 layers. Under applied bias between the Ag and the ITO, an accumulation layer is formed at the Al2O3-ITO interface[1]. We use the field effect to electrically modulate the permittivity of ITO via changes in carrier density, yielding active tuning of the effective response of the metamaterial.

Upon application of the transfer matrix method and retrieval of the effective electric permittivity and magnetic permeability along different coordinate directions[2], we find that the effective permittivity along the optical axis exhibits a resonance at 445nm. Upon application of voltage, we observe a blue-shifting of the effective epsilon-near-zero wavelength by up to 60nm. New resonances for longer wavelengths are also observed. Additionally, we find that this metamaterial is strongly diamagnetic with tunable magnetic permeability.

Next, by examining the band structure and isofrequency contours and taking losses into account, we show that this multilayer design supports optical band gaps bounded between hyperbolic regions within the visible spectrum. This yields drastic changes in the density of optical states.

We are currently fabricating tunable metamaterials and ellipsometric measurements for demonstrating the active tuning of the effective parameters will be discussed, as well as photoluminescence measurements to map the extrema in the density of optical states within the visible-near IR regime.

  1. Feigenbaum et al., Nano Lett. 10, 2111-2116 (2010)
  2. Papadakis et. al, submitted arXiv:1411.6312

gpapadak@caltech.edu









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