Department of Physics

Research

Electron transport in ultra-narrow nanowires

With the natural tendency of modern nanoelectronics for higher integration and miniaturization it is believed that basic property of a metallic wire to conduct electric current is preserved with reduction of its cross section. However, there are certain fundamental limitations which might ruin these naive expectations. In case of normal metal wires electric conductivity is blocked at diameters below the de Broglie wave length of the electron. For sufficiently narrow 1D superconductors quantum fluctuations of the order parameter suppress the supercurrent even at temperatures close to absolute zero.
Evolution of the sample shape while sputtering measured by SPM. Bright colour above the grey plane corresponds to Al, blue one below the plane is Si. The effective diameter of the narrowest wire is about 18 nm.


Non-equilibrium superconductivity

When an electron is injected into a superconductor (e.g. through a tunnel barrier) it takes some time (quasiparticle relaxation time) before it finds a matching ‘partner’ to form a Cooper pair. Though the effect is known for decades, very few is known about the processes at temperatures much below the critical temperature of the superconductor: both experimental and theoretical. If non-paired (=non-equilibrium) electrons are additionally spin-polarized, then the necessity to equalize number of spin-up and spin-down particles should inevitably increase the corresponding relaxation time.
SEM image of a typical NIS structure.


Non-equilibrium superconductivity

When an electron is injected into a superconductor (e.g. through a tunnel barrier) it takes some time (quasiparticle relaxation time) before it finds a matching ‘partner’ to form a Cooper pair. Though the effect is known for decades, very few is known about the processes at temperatures much below the critical temperature of the superconductor: both experimental and theoretical. If non-paired (=non-equilibrium) electrons are additionally spin-polarized, then the necessity to equalize number of spin-up and spin-down particles should inevitably increase the corresponding relaxation time.
SEM image of a typical NIS structure.