Physicists at The University of Texas at Austin, in collaboration with colleagues in Taiwan and China, have developed the world's smallest semiconductor laser, a breakthrough for emerging photonic technology with applications from computing to medicine.

Miniaturization of semiconductor lasers is key for the development of faster, smaller and lower energy photon-based technologies, such as ultrafast computer chips; highly sensitive biosensors for detecting, treating and studying disease; and next-generation communication technologies.

Such photonic devices could use nanolasers to generate optical signals and transmit information, and have the potential to replace electronic circuits. But the size and performance of photonic devices have been restricted by what's known as the three-dimensional optical diffraction limit.

"We have developed a nanolaser device that operates well below the 3-D diffraction limit," said Chih-Kang "Ken" Shih, professor of physics at The University of Texas at Austin. "We believe our research could have a large impact on nanoscale technologies."

In the current paper, Shih and his colleagues report the first operation of a continuous-wave, low-threshold laser below the 3-D diffraction limit. When fired, the nanolaser emits a green light. The laser is too small to be visible to the naked eye.

The device is constructed of a gallium nitride nanorod that is partially filled with indium gallium nitride. Both alloys are semiconductors used commonly in LEDs. The nanorod is placed on top of a thin insulating layer of silicon that in turn covers a layer of silver film that is smooth at the atomic level.

It's a material that the Shih lab has been perfecting for more than 15 years. That "atomic smoothness" is key to building photonic devices that don't scatter and lose plasmons, which are waves of electrons that can be used to move large amounts of data.

"Atomically smooth plasmonic structures are highly desirable building blocks for applications with low loss of data," said Shih.

Nanolasers such as this could provide for the development of chips where all processes are contained on the chip, so-called "on-chip" communication systems. This would prevent heat gains and information loss typically associated with electronic devices that pass data between multiple chips.

"Size mismatches between electronics and photonics have been a huge barrier to realize on-chip optical communications and computing systems," said Shangjr Gwo, professor at National Tsing Hua University in Taiwain and a former doctoral student of Shih's.

Physicists Explore Properties of Electrons in Revolutionary Material

Scientists from Georgia State University and the Georgia Institute of Technology have found a new way to examine certain properties of electrons in graphene -- a very thin material that may hold the key to new technologies in computing and other fields.

Ramesh Mani, associate professor of physics at GSU, working in collaboration with Walter de Heer, Regents' Professor of physics at Georgia Tech, measured the spin properties of the electrons in graphene, a material made of carbon atoms that is only one atom thick.

The research was published this week in the online-only journal Nature Communications.

Electrons, which follow orbits around the nucleus in atoms, have two important characteristics -- charge and spin.

The electric charge is the basis of most electronic devices, but spin -- which Mani and co-workers examined using a new technique -- forms the basis of new "spintronic" devices, and can serve as a building block for new computers in a field called quantum computing, as well as other technologies.

Graphene is thought to be a key material for spintronic devices, but it is so new that scientists must perform a lot of research on it to understand its capability. The GSU and Georgia Tech study propels this research forward.

"We tried to use the electrical resistance to detect spin resonance. When you shine microwaves on the device, and the microwave energy equals the spin-splitting energy," Mani explained.

"The device absorbs the microwave energy, and that changes the resistance of the device. But this is usually such a small effect that one hardly expects to see it. Fortunately, this material allowed us to see the effect. Measuring spin resonance electrically is especially useful for nanoscale devices."

"By doing such a measurement, we can measure properties like the spin splitting energy, and the spin relaxation time directly," he continued. "There have been other measurements, but those have been a little more indirect."

With the advance in measuring the properties of an electron's spin in graphene, it will allow scientists to carry out further studies of this novel material -- giving researchers ways to optimize graphene for spintronic applications.

Mani noted that that the experiments which were conducted at GSU, were very labor intensive. Simply creating graphene -- which de Heer's laboratory accomplished -- is very time consuming and requires enormous experience.

Measurements use very sophisticated equipment, requiring the researchers to immerse samples in liquid Helium at temperatures close to absolute zero -- about 460 degrees Fahrenheit below zero.

Atlanta has become a center for graphene research, Mani said.

"The confluence of available experimental capability in Atlanta, a hotbed for graphene science and technology, made possible this important advance in the world of spintronics physics," he explained.

The team included Mani of GSU, de Heer, John Hankinson and Claire Berger of Georgia Tech.

Source:- http://www.sciencedaily.com

Original Journal:-Ramesh G Mani, John Hankinson, Claire Berger, Walter A de Heer. Observation of resistively detected hole spin resonance and zero-field pseudo-spin splitting in epitaxial graphene. Nature Communications, 2012; 3: 996 DOI: