Hyuk-Jae Jang

Geometric dephasing-limited Hanle effect in long-distance lateral silicon spin transport devices

Evidence of spin precession and dephasing (“Hanle effect”) induced by a magnetic field is the only unequivocal proof of spin-polarized conduction electron transport in semiconductor devices. However, when spin dephasing is very strong, Hanle effect in a uniaxial magnetic field can be impossible to measure. Using a silicon device with lateral injector-detector separation of over 2 mm and geometrically induced dephasing making spin transport completely incoherent, we show experimentally and theoretically that Hanle effect can still be measured using a two-axis magnetic field.

Spin polarized electron transport near the Si/SiO2 interface.

Using long-distance lateral devices, spin transport near the interface of Si and its native oxide (SiO(2)) is studied by spin-valve measurements in an in-plane magnetic field and spin precession measurements in a perpendicular magnetic field at 60 K. As electrons are attracted to the interface by an electrostatic gate, we observe shorter average spin transit times and an increase in spin coherence, despite a reduction in total spin polarization. This behavior, which is in contrast with the expected exponential depolarization seen in bulk transport devices, is explained using a transform method to recover the empirical spin current transit-time distribution and a simple two-stage drift-diffusion model. We identify strong interface-induced spin depolarization (reducing the spin lifetime by over 2 orders of magnitude from its bulk transport value) as the consistent cause of these phenomena.

Observation of spin-polarized electron transport in Alq3 by using a low work function metal

We present the observation of magnetoresistance in Co/Ca/Alq3/Ca/NiFe spin-valve devices. Thin Ca layers contacting 150 nm thick Alq3 enable the injection of spin-polarized electrons into Alq3 due to the engineering of the band alignment. The devices exhibit symmetric current-voltage (I–V) characteristics indicating identical metal contacts on Alq3, and up to 4% of positive magnetoresistance was observed at 4.5 K. In contrast, simultaneously fabricated Co/Alq3/NiFe devices displayed asymmetric I–V curves due to the different metal electrodes, and spin-valve effects were not observed.

Spin transport in memristive devices

We report on electron spin transport through electrochemically precipitated copper filaments formed in TaOx memristive devices consisting of Co/TaOx/Cu/Py with crossbar-type electrode geometry. The devices show memristive behavior having a typical OFF/ON resistance ratio of 105. Magnetoresistance measurements performed by sweeping an external magnetic field clearly indicate spin transport through an electrochemically formed copper nano-filament as long as 16 nm in the memristive ON-state at 77 K. Spin transport vanishes in the OFF-state. These data are strong evidence that the fundamental switching mechanism in these metal-oxide devices is the formation of continuous metallic conduction paths.

High performance Bi 2 Se 3 nanowire field-effect transistors

In this paper, we have fabricated Bi2Se3 nanowire FETs by using a self-alignment technique and observed excellent device characteristics. The FETs show unipolar, n-type behavior with a clear cutoff in the OFF-state with only thermally activated conduction at relatively high temperatures, and a well-saturated output current indicating surface metallic conduction. These data illustrate that charge transport in materials associated with topological insulator (TI) systems may be much more complicated than the conventional wisdom that has recently been developed for these novel systems.