US scientists have succeeded in maintaining electronic spin coherence across an interface between two different semiconducting materials, a move that could lead to faster electronic circuits than those based on charge carriers.
Reported in Nature, the work was led by David Awschalom, director of the Center for Spintronics and Quantum Computation at the University of California, and Nitin Samarth, a materials physicist at Penn State University.
"We have managed to maintain the spin across an interface, in particular a heterojunction with n-n and p-n junctions," said Awschalom. "Using this, we could develop spin diodes."
The interface which Awschalom and Samarth used is a GaAs/ZnSe interface. They used optical excitation to produce a non-equilibrium burst of spin coherent electrons across the junction. The scientists say that, compared with previous work, coherence across the boundary has been improved by 4000%.
"Spin appears to be remarkably robust and moves relatively easily between semiconductors," said Awschalom. "Previously, theories of electron transport from one material to another suggested that the spin would lose its orientation or scatter from impurities or structural effects. These experiments point out that this is not the case."
The movement across the material boundary consisted of a cloud of electrons with a density of 1016/cm3.
"This is quite a low density," said Awschalom. "In the future, it will be individual electrons. Because spin is a quantum mechanical variable, the intention is to develop low-power, high-speed electronics and ultimately quantum computing with many states."
Having established a spin transmission across a material boundary, the next step is to achieve the same with the three-way interface needed for a transistor.