Source: Nature Podcast for 30 November 2006.

    Chris Smith: Now to the world of metamaterials which are substances specifically designed to respond to certain frequencies of electromagnetic waves. At the moment computers work at giga hertz frequencies but wouldn¡¯t it be nice to make them work a thousand times faster - at the terahertz rate? Well the reason they currently don¡¯t is because materials capable of doing this don¡¯t crop up naturally which has made it difficult to exploit this part of the electromagnetic spectrum. But now Richard Averitt and his colleagues have developed a material that can work within the terahertz regime. Nature 444, 560¨C561 (30 November 2006) Nature 444, 597¨C600 (30 November 2006)

    Richard Averitt: There¡¯s this field of metamaterials where people really make artificial structures that have functionality that, maybe, doesn¡¯t occur naturally but those materials that they¡¯ve made, what we¡¯ve done is made them active, we¡¯ve made them be able to do something that you couldn¡¯t otherwise do and so a simple example of that is what¡¯s just like a solenoid. So you can imagine that if you have currents flowing through this solenoid then you get a magnetic field and so you get these interesting responses. What we¡¯ve been able to do is being able to just apply a simple voltage and shut off that solenoid, so that¡¯s just a very simple way to control the properties of this material. And then the question becomes at what frequencies are we doing this? And so the way to look at that is, while working in the so-called terahertz regime and to give you an idea of what a terahertz is, you know, most computers these days work at about a gigahertz and so the terahertz regime is three orders of magnitude faster than that, so we¡¯re working at about 1,000 gigahertz.

    Chris Smith: And why is that actually useful Richard?

    Richard Averitt: It¡¯s useful because in this part of the electromagnetic spectrum there¡¯s a dearth of devices to manipulate this radiation at these frequencies so this material that we¡¯ve developed, basically, allows us to switch the radiation on and off so we can change the transmission properties of a material just by applying a voltage at this frequency range and no-one has been able to do that before.

    Chris Smith: And turning now to Willie Padilla, who is one of the other researchers on the paper, Willie, what are the implications now that you¡¯ve arrived at this point? How can you see this being pushed into operation actually on the grand scale?

    Willie Padilla: This is already applicable to devices within the terahertz regime. The uniqueness of what we¡¯ve fabricated and demonstrated is that this metamaterial device or artificial device can be used right now within the terahertz regime. The reason being that the terahertz regime is the last undiscovered portion of the electromagnetic spectrum and so even though this is a first-generation device, it can be used already. And so one example of what it could be used for would be high bit rate communications at terahertz frequencies. What we¡¯ve demonstrated is a switching of terahertz radiation.

    Chris Smith: Why has it taken so long for us to be able to venture into this electromagnetic territory? Why couldn¡¯t we do this before?

    Willie Padilla: The terahertz regime of the electro magnetic spectrum is actually a universal gap in the electromagnetic spectrum. It happens to lie between two regimes in which there has been considerably more work such as the microwave, which is at lower frequencies, and the infrared regime, which is at higher frequencies, and it¡¯s really the region between a optical response, at higher frequencies and an electronic response at lower frequencies. So its so happens that the Universe is constructed such that materials naturally do not respond here. And so what metamaterials allow us to do it to, instead of being stuck with natural materials, as they occur and as we find them, we can construct an artificial material to have a designed response, so we can design a material to have an exact electromagnetic response at terahertz frequencies. And it¡¯s really a new design paradigm that permits the construction of devices to be operable within this range.

    Chris Smith: Introducing a new metamaterial, capable of supporting terahertz frequencies, that was Willie Padilla from Boston College and before him Richard Averitt from Los Alamos National Laboratory.