快猫短视频

TO REVOLUTIONISE electronics, researchers may have to keep their faces
straight鈥攖he faces of their semiconductors, that is. Rough spots on
surfaces of semiconductors topple spinning electrons, says a team of physicists,
so avoiding them could be key to developing 鈥渟pintronics,鈥� which uses electrons
all spinning in the same direction.

Conventional electronics simply exploits electrons鈥� charge, but a flow of
electrons spinning in the same direction also carries a 鈥渟pin current鈥�. This
gives circuit designers another property to play with, and researchers hope to
use spin currents to create everything from optical sensors to 鈥渜ubits鈥�, the
ephemeral bits of information manipulated by quantum computers.

But while spin currents travel easily through semiconductors, the challenge
is in getting them to flow into the materials in the first place. 鈥淭here鈥檚 a lot
of scattering at the interface that degrades the transport of spin,鈥� says
Vincent LaBella of the University of Arkansas in Fayetteville.

Now LaBella and his colleagues have shown that much of that scattering is
caused by atomic-scale imperfections on the surface. They used a scanning
tunnelling microscope to pass a tiny current through a nickel tip less than a
nanometre wide, across a gap and into a crystal of gallium arsenide. Because the
nickel tip also consisted of a single crystal, it produced a completely
polarised flow of electrons.

When the tip hovered above the smooth face of the crystal, the current
remained more than 90 per cent polarised. But when the tip hovered near a step
in the surface just 5 nanometres high, the polarisation plummeted to a sixth of
the original value.

鈥淭he data is absolutely beautiful,鈥� says David Awschalom of the University of
California, Santa Barbara. Awschalom says the makers of spintronic devices may
try to avoid surface defects by making metal contacts small enough to fit
between such imperfections.