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The demonstration of quantized spin splitting by Stern and Gerlach is one of the most important experiments in modern physics. Their discovery was the precursor of recent developments in spin-based technologies. Although electrical spin separation of charged particles is fundamental in spintronics, in non-uniform magnetic fields it has been difficult to separate the spin states of charged particles due to the Lorentz force, as well as to the insufficient and uncontrollable field gradients. Here we demonstrate electronic spin separation in a semiconductor nanostructure. To avoid the Lorentz force, which is inevitably induced when an external magnetic field is applied, we utilized the effective non-uniform magnetic field which originates from the Rashba spin–orbit interaction in an InGaAs-based heterostructure. Using a Stern–Gerlach-inspired mechanism, together with a quantum point contact, we obtained field gradients of 108 T m−1 resulting in a highly polarized spin current.

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We measured the shot noise in the CoFeB/MgO/CoFeB-based magnetic tunneling junctions with a high tunneling magnetoresistance ratio (over 200 % at 3 K). Although the Fano factor in the anti-parallel configuration is close to unity, it is observed to be typically 0.91±0.01 in the parallel configuration. It indicates the sub-Poissonian process of the electron tunneling in the parallel configuration due to the relevance of the spin-dependent coherent transport in the low bias regime.

The low-frequency and shot noises in spin-valve CoFeB/MgO/CoFeB magnetic tunneling junctions were studied at low temperature. The measured 1/f noise around the magnetic hysteresis loops of the free layer indicates that the main origin of the 1/f noise is the magnetic fluctuation, which is discussed in terms of a fluctuation-dissipation relation. Random telegraph noise (RTN) is observed to be symmetrically enhanced in the hysteresis loop with regard to the two magnetic configurations. We found that this enhancement is caused by the fluctuation between two magnetic states in the free layer. Although the 1/f noise is almost independent of the magnetic configuration, the RTN is enhanced in the antiparallel configuration. These findings indicate the presence of spin-dependent activation of RTN. Shot noise reveals the spin-dependent coherent tunneling process via a crystalline MgO barrier.

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We developed a shot noise measurement system for mesoscopic conductors (typical resistance h/2e2 = 12.9 kΩ) at very low temperature (∼20 mK). To realize required high-resolution measurement, we made a high-electron-mobility-transistor (HEMT)-based cryogenic amplifier working at a target frequency range (∼2.5 MHz), whose gain flatness and input voltage noise were carefully tuned. We can suppress the 1/f noise of the amplifier by using two HEMTs in parallel. The performance of the noise measurement system at 20 mK was demonstrated for a quantum point contact with high experimental accuracy below 10−29 A2/Hz.