Tomoyasu Kakegawa

Spin‐orbit Interactions in High In‐content InGaAs/InAlAs Inverted Heterojunctions for Rashba spintronics Devices

We studied novel InxGa1−xAs/InxAl1−xAs (x=0.5 and 0.75) inverted modulation‐doped heterojunctions (HJs) as a candidate material for realistic Rashba spintronics devices. Large Spin‐orbit coupling constants, α > ∼10×10−12 eVm, have been estimated in these HJs with both the In contents. Also the larger α s were found in the HJs with thinner InGaAs channels due to the increase of the hetero‐interface electric field. Moreover, higher In‐content HJs seem to give larger α s, since they have a narrower bandgap as well as a smaller electron effective mass.

Spin‐splitting characterization of an InGaSb 2DEG by using magnetoresistance measurements with tilted magnetic fields

We investigated spin‐splitting properties in a metamorphic In0.89Ga0.11Sb/In0.88Al0.12Sb two‐dimensional electron gas (2DEG) by means of magnetoresistance measurements with tilted magnetic fields. In magnetoresistance curves with perpendicular magnetic field, we observed clear Shubnikov‐de Haas oscillations with the Zeeman‐type spin‐splitting over 1 T, and spin‐splitting vanishing around 1 T. By tilting the 2DEG, we also observed the equidistant separation between the spin‐split Landau levels and the coincidence of the spin‐up and spin‐down levels from the neighboring Landau levels. From these results, we concluded that the dominant zero‐field spin‐splitting is the Dresselhaus‐type but with some contribution of the Rashba term. Additionally, we obtained a 2DEG g‐factor |g| ≈ 31 from the coincidence method.

Side‐Gate Control of Rashba Spin Splitting in a In0.75Ga0.25As/In0.75Al0.25As Heterojunction Narrow Channel: Toward Spin‐Transistor Based Qubits

Side‐gate (SG) control of Rashba spin‐orbit interaction (SOI) in a diffusive wire made at InGaAs/InAlAs narrow‐gap heterojunction has been studied. The wires have four‐terminal structure and side‐gates are prepared between the voltage probes on both side of the wire via small air‐gap. By applying negative voltages in single (one gate biased and another grounded) and dual (two gates equally or unequally biased) bias conditions, spin‐orbit coupling constant, α, estimated from low‐field Schubnikov de‐Haas oscillation was found to show drastic increase followed by saturation or reduction. This behavior could be attributed to the asymmetric lateral electric field, Easym, created also by SG bias, since it can additionally contribute to the total SOI via the new effective magnetic field, Beff ∝ v (electron velocity) × Easym.