Gems¹ are known for the beauty of the light that passes through them. But it is the fixed² atomic arrangements of these crystals that determine the light frequencies permitted passage. Now a Sandia-led team has created a plasmonic, or plasma³-containing, crystal that is tunable⁴. The effect is achieved by adjusting a voltage applied⁵ to the plasma. Because the crystal then is agile⁶（敏捷的） in transmitting terahertz light at varying frequencies, it could increase the bandwidth of high-speed communication networks and generally enhance high-speed electronics.

 

"Our experiment is more than a curiosity precisely⁷ because our plasma resonances⁸（等离子体共振） are widely tunable," says Sandia researcher Greg Dyer, co-primary investigator⁹ of a recently published online paper in Nature Photonics, expected in print in November. "Usually, electromagnetically induced transparencies in more widely known systems like atomic gases, photonic（光激性的） crystals and metamaterials require tuning¹⁰ a laser's frequencies to match a physical system. Here, we tune¹¹ our system to match the radiation source. It's inverting¹² the problem, in a sense."

 

Photonic crystals are artificially built to allow transmission of specific wavelengths¹³. Metamaterials require micron- or nano-sized bumps to tailor interactions between humanmade structures and light. The plasmonic crystal, with its ability to direct light like a photonic crystal, along with its sub-wavelength, metamaterial-like size, in effect hybridizes the two concepts. Its methods could be used to shrink the size of photonic crystals and to develop tunable metamaterials.

 

The crystal's electron plasma forms naturally at the interface¹⁴ of semiconductors¹⁵ with different band gaps. It sloshes between their atomically smooth boundaries that, properly aligned¹⁶, form a crystal. Patterned metal electrodes allow its properties to be reconfigured, altering its light transmission range. In addition, defects intentionally¹⁷ mixed into the electron fluid allow light to be transmitted where the crystal is normally opaque¹⁸（不透明的）.

 

However, this crystal won't be coveted¹⁹（梦寐以求的） for the beauty of its light. First, the crystal transmits in the terahertz spectrum²⁰, a frequency range invisible to the human eye. And scientists must tweak the crystal's two-dimensional electron gas to electronically vary its output frequencies, something casual crystal buyers probably won't be able to do.

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