Layered Metals as Polarized Transparent Conductors

TL;DR

This paper introduces layered anisotropic metals as a new class of polarized transparent conductors, leveraging their electronic structure to achieve high in-plane conductivity and optical transparency at visible wavelengths.

Contribution

It demonstrates that layered oxides like Sr₂RuO₄ and Tl₂Ba₂CuO₆+δ can serve as polarized transparent conductors, overcoming traditional trade-offs through anisotropic electronic properties.

Findings

Layered oxides are transparent at >2μm thickness for c-axis polarized light.

Out-of-plane slabs were fabricated using focused ion beam milling.

These materials exhibit high in-plane conductivity with optical transparency in the visible range.

Abstract

The quest to improve transparent conductors balances two key goals: increasing electrical conductivity and increasing optical transparency. To improve both simultaneously is hindered by the physical limitation that good metals with high electrical conductivity have large carrier densities that push the plasma edge into the ultra-violet range. Transparent conductors are compromises between electrical conductivity, requiring mobile electrons, and optical transparency based on immobile charges to avoid screening of visible light. Technological solutions reflect this trade-off, achieving the desired transparencies by reducing the conductor thickness or carrier density at the expense of a lower conductance. Here we demonstrate that highly anisotropic crystalline conductors offer an alternative solution, avoiding this compromise by separating the directions of conduction and transmission. Materials with a quasi-two-dimensional electronic structure have a plasma edge well below the range of visible light while maintaining excellent in-plane conductivity. We demonstrate that slabs of the layered oxides Sr$_2$RuO$_4$ and Tl$_2$Ba$_2$CuO$_{6+\delta}$ are optically transparent even at macroscopic thicknesses >2$\mu$m for c-axis polarized light. Underlying this observation is the fabrication of out-of-plane slabs by focused ion beam milling. This work provides a glimpse into future technologies, such as highly polarized and addressable optical screens, that advancements in a-axis thin film growth will enable.