Spin filter and a memory using such a spin filter

A spin filtering device comprising:

• a spin filter having an input region for carrying a current, an output region for carrying a current, and a three-dimensionally quantum confined region arranged to operate in the Coulomb blockade regime and separating the input and output regions whereby charge carriers can only pass from the input region to the output region by tunneling through the quantum region;
• Zeeman splitting means for causing Zeeman splitting in the spin filter such that the Zeeman splitting in the input and output regions is less than the Fermi energy such that, in operation, the spin filter outputs a tunneling current predominantly of one spin polarity;
• and
• control means for controlling the predominant spin polarity of the tunneling current, wherein the quantum region has a gate and the control means comprises means for controlling at least one of a gate voltage and a voltage between the input and output regions to control whether the quantum region contains an odd or even number of electrons.

A photo emissive device, comprising:

• a spin filter having an input region for carrying a current, an output region for carrying a current, and a three-dimensionally quantum confined region arranged to operate in the Coulomb blockade regime and separating the input and output regions whereby charge carriers can only pass from the input region to the output region by tunneling through the quantum region;
• Zeeman splitting means for causing Zeeman splitting in the spin filter such that the Zeeman splitting in the input and output regions is less than the Fermi energy such that, in operation, the spin filter outputs a tunneling current predominantly of one spin polarity;
• and
• a photo emitter coupled to receive a spin polarized current from the spin filtering device and to emit photons having a polarization dependent on the spin polarization of the current supplied by the spin filtering device.

A memory comprising:

• a two-dimensional array of spin filters each having an input region for carrying an electron current, an output region for carrying an electron current, and a three-dimensionally quantum confined region arranged to operate in the Coulomb blockade regime and separating the input and output regions whereby electrons can only pass from the input region to the output region by tunneling through the quantum region;
• Zeeman splitting means for causing Zeeman splitting in the spin filters, the quantum region and input and output regions being formed such that the Zeeman splitting in the input and output regions is less than the Fermi energy such that the tunnelling current supplied, in operation, by the spin filter is predominantly of one spin polarity;
• control means for controlling the Zeeman splitting within an individual spin filter to control the predominant spin polarization of the tunneling current through that filter;
• addressing means for individually addressing each spin filter;
• and
• read-out means for detecting the predominant spin polarization of the current supplied by an addressed spin filter.