Spin current can be controlled in same way as electrical current

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An international research team, formed of physicists from the Hitachi Cambridge Laboratory, the University of Cambridge, the Institute of Physics of the Academy of Sciences, Charles University and Texas A&M University, has developed technology which is said to enable spin current to be controlled and measured in the same way as electrical current.

The technology developed is a new concept, based on the second basic attribute of an electron – its elementary magnetic moment, or 'spin'. While the theory of controlling and measuring the spin of an electron electrically was proposed 20 years ago, many fundamental and critical issues in spintronics needed to be understood. Until now, there have been no experiments to manipulate or measure spin current in the same way as electrical current. In 2005, the international research team and Hitachi measured separately an up and down spin in a GaAs semiconductor at -269°C. Then, in 2009, the team measured the flow of spin polarised current over a few microns in the same GaAs semiconductor at a temperature of -53°C. In the latest development, the up or down spin was controlled by a gate voltage and the on/off operation as a transistor verified. The device consists of a planar photodiode with a pn-junction diode and a n-type channel which forms the hole bar. By shining light on the diode, photoexcited electrons generated by the photovoltaic effect are injected into the device. The degree of circular polarisation of the incident light is used to generate the spin polarised electrons. The injected spin precede as a spin-current. At this point, if a p-type electrode is formed above the n-type channel and a voltage is applied, according to quantum relativistic effects, the precession of the spins are controlled by the input gate-electrode voltages. These effects are also responsible for the onset of transverse electrical voltages in the device, which represent the output signal, dependent on the local orientation of precessing electron spins. A solid state device which can control and detect the polarisation of the light is believed to open the way for even larger capacity information transmission systems, or in new analytical systems to which use the polarisation of light to study the characteristics of biological or molecular material.