Materials Today � Volume 00, Number 00 �May 2014 NEWS

NewsLet’s get meta physicalAn extremely thin, periodic meta material

that incorporates quantum cascade struc-

tures has been devised by researchers at

Vienna University of Technology.

Karl Unterrainer and colleagues were fully

aware that the subtle interplay between elec-

trons and photons is key to electrical illumi-

nation, solar energy conversion and light

detection alike. Unfortunately, until now it

has been difficult to couple light into thin

layered semiconductor systems. The rules of

quantum mechanics prohibit photons of

specific polarization from interacting with

the electrons of the semiconductor system.

Light which hits the layered surface head-on,

cannot influence the electron in the semi-

conductor. The team, however, has now

demonstrated that a meta material with a

microscopic structure can manipulate elec-

tromagnetic radiation at terahertz frequen-

cies and rotate the plane of polarization of

incident light.

‘‘Ultra-thin layered semiconductor sys-

tems have the great advantage, that their

electronic properties can be very precisely

tuned’’, explains Unterrainer. They could

have a geometry devised to allow the con-

struction of a quantum cascade laser in

which excited electrons leap from layer to

layer and emit a photon with each jump.

Conversely, a light detector of selective

sensitivity for one particular frequency

might be developed.

The team worked with radiation of much

shorter frequency, longer wavelength, than

visible light, terahertz is in an overlapping

middle ground between the infrared and the

microwave region of the spectrum with a

wavelength of about a tenth of a millimeter

(1–0.1 mm by definition, 300 GHz to 3 THz).

Radiation of this frequency could have many

novel technological applications and so

despite the inherent difficulties of working

with it, it is an important focus of research

with a view to creating the next generation

of computer technology for instance

This latest discovery by the team in

Vienna [A. Benz, et al. Sci. Rep. 4 (2014)

4269] opens up the possibility of integrat-

ing a light detector for terahertz radiation

into a chip and thus opening up the so-

called technological ‘‘terahertz gap’’. This

gap in technology exists because the fre-

quencies involved are at the limits of elec-

tronic counters, which simply cannot keep

up with the cycle rate and conversely the

generators do not exist in conventional

electronics circuitry as they do for radio

wave and microwave generation, for

instance.

Unterrainer and colleagues suggest the

meta material approach might overcome

many of the terahertz problems. ‘‘With

conventional fabrication methods, large

arrays of such detectors can be built,’’ he

explains. They are compact with layers

just a few nanometers thick being able

to detect radiation as the detector is more

than a thousand times thinner than the

wavelength of the radiation it seeks to

detect.

David Bradley

Please cite this article in press as: D. Bradley, Mater. Today (2014), http://dx.doi.org/10.1016/j.mattod.2014.04.032

1369-7021/ http://dx.doi.org/10.1016/j.mattod.2014.04.032

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