Duke University researchers have studied the individual phase slips in aluminum nanowires and have demonstrated the characteristics and temperature, at which they take place.
According to Albert Chang, a physicist at Duke University and the leader of the study, this finding could assist researchers to eliminate phase slips from nano-scale devices, which in turn results in more dependable nanowires and highly efficient nano-electronics.
Macroscopic quantum tunneling effect was first noticed in a device known as a Josephson junction, which features a thin insulating layer linking two superconductors that have a three-dimensional form and a width of several nanometers.
Physicists observed millions of electrons tunneling together through an energy barrier
To analyze phase slips and macroscopic quantum tunneling effect in a simple system, Chang and his team utilized individual, one-dimensional aluminum nanowires with widths in the range of 5-10 nm and length in the range of 1.5-10 µm. These nanowires were then cooled to a temperature near absolute zero, approximately 1° K or −458° F.
At this temperature, the crystal lattice of a metal vibrates in a manner that enables electrons to surmount their negative repulsion between them, resulting in the pairing of electrons and flowing of electric current without any resistance, eventually forming a superconductor. On their movement in a quantum-mechanical space, electrons have to scale a wall or a barrier, resulting in the consumption of energy and release of heat. The building of heat due to consecutive scaling attempts causes a phase slip to a non-superconducting state from the superconducting state in a portion of the naonwire.
Chang and his team altered the amount of current and temperatures via the aluminum nanowires to accurately demonstrate the occurrence of phase slips. The findings showed that at higher temperatures in the range of 1.5° K and near the critical temperature, at which the wires are naturally in a non-superconducting state, electrons have sufficient energy to shift over the barrier that maintains the stability of the superconducting current and the pairing of electrons.
When the nanowires were cooled below 1° K, electrons did not have the energy to scale the barrier and they tunnel or pass through the barrier together simultaneously, stated Gleb Finkelstein, a physicist at Duke University and a partner of Chang. The study also demonstrated that at the moderately higher temperatures, single jumps over the barrier did not produce sufficient heat to cause the phase slip but occurs due to multiple jumps.
Investigating the behavior of electrons at particular temperatures offers researchers with the information to develop ultrathin superconducting wires without phase slips. These enhanced wires could be utilized in ultra-compact electrical components for ultra-compact electronics like the quantum bit in a quantum computer, Chang added.
Source: http://www.duke.edu