Meir Yigal: Solving the "0.7 Anomaly"
simplest nanoelectronics device, and the basic building block for more
complicated devices, is a "quantum point contact," a constriction
connecting large electron reservoirs (see picture on the right). According to quantum
mechanics the conductance through such a device should increase
as the gap grew bigger by integer steps of universal value.
Surprisingly, an additional first step approximately 0.7 times the
expected universal value had also been observed, which became known as
"the 0.7 anomaly" (see
picture on the left). Previously we demonstrated that the phenomenology
of this anomaly can be explained by the existence of a magnetic impurity, a localized
electron in the quantum-point contact [PRL
89, 196802 (2002)] . Using
extensive density-functional calculations we demonstrated
the emergence of
a magnetic impurity at the quantum point contact (see picture on the
a lower density of the electrons near the quantum point attracts the
other electrons towards it. The wavy nature of such electrons
then causes ripples, trapping an electron and
causing the 0.7 anomaly.