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Register a new userTwo-dimensional electron gas in a modulation-doped SrTiO3/Sr(Ti,Zr)O3 heterostructure
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A two-dimensional electron gas (2DEG) in SrTiO3 is created via modulation doping by interfacing undoped SrTiO3 with a wider-band-gap material, SrTi1-xZrxO3, that is doped n-type with La. All layers are grown using hybrid molecular beam epitaxy. Using magnetoresistance measurements, we show that electrons are transferred into the SrTiO3, and a 2DEG is formed. In particular, Shubnikov-de Haas oscillations are shown to depend only on the perpendicular magnetic field. Experimental Shubnikov-de Haas oscillations are compared with calculations that assume multiple occupied subbands.
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We explore the second order bilinear magnetoelectric resistance (BMER) effect in the d-electron-based two-dimensional electron gas (2DEG) at the SrTiO3 (111) surface. We find an evidence of a spin-split band structure with the archetypal spin-momentum locking of the Rashba effect for the in-plane component. Under an out-of-plane magnetic field, we find a BMER signal that breaks the six-fold symmetry of the electronic dispersion, which is a fingerprint for the presence of a momentum dependent out-of-plane spin component. Relativistic electronic structure calculations reproduce this spin-texture and indicate that the out-of-plane component is a ubiquitous property of oxide 2DEGs arising from strong crystal field effects. We further show that the BMER response of the SrTiO3 (111) 2DEG is tunable and unexpectedly large.
Understanding, creating, and manipulating spin polarization of two-dimensional electron gases at complex oxide interfaces presents an experimental challenge. For example, despite almost a decade long research effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3 heterojunction is still an open question. Here, by using a prototypical two-dimensional electron gas (2DEG) which emerges at the interface between band insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3 , the experiment reveals the evidence for magnetic phase separation in hole-doped Ti d1 t2g system resulting in spin-polarized 2DEG. The details of electronic and magnetic properties of the 2DEG were investigated by temperature-dependent d.c. transport, angle-dependent X-ray photoemission spectroscopy, and temperature-dependent magnetoresistance. The observation of clear hysteresis in magnetotransport at low magnetic fields implies spin-polarization from magnetic islands in the hole rich LaTiO3 near the interface. These findings emphasize the role of magnetic instabilities in doped Mott insulators thus providing another path for designing all-oxide structures relevant to spintronics applications.
We report on a systematic investigation of the dominant scattering mechanism in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped GaAs/Al_{x}Ga_{1-x}As heterostructures. The power-law exponent of the electron mobility versus density, mu propto n^{alpha}, is extracted as a function of the 2DEGs depth. When shallower than 130 nm from the surface, the power-law exponent of the 2DEG, as well as the mobility, drops from alpha simeq 1.65 (130 nm deep) to alpha simeq 1.3 (60 nm deep). Our results for shallow 2DEGs are consistent with theoretical expectations for scattering by remote dopants, in contrast to the mobility-limiting background charged impurities of deeper heterostructures.
We report on the realization and top-gating of a two-dimensional electron system in a nuclear spin free environment using 28Si and 70Ge source material in molecular beam epitaxy. Electron spin decoherence is expected to be minimized in nuclear spin-free materials, making them promising hosts for solid-state based quantum information processing devices. The two-dimensional electron system exhibits a mobility of 18000 cm2/Vs at a sheet carrier density of 4.6E11 cm-2 at low temperatures. Feasibility of reliable gating is demonstrated by transport through split-gate structures realized with palladium Schottky top-gates which effectively control the two-dimensional electron system underneath. Our work forms the basis for the realization of an electrostatically defined quantum dot in a nuclear spin free environment.
We designed and performed low temperature DC transport characterization studies on two-dimensional electron gases confined in lattice-matched In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As quantum wells grown by molecular beam epitaxy on InP substrates. The nearly constant mobility for samples with the setback distance larger than 50nm and the similarity between the quantum and transport life-time suggest that the main scattering mechanism is due to short range scattering, such as alloy scattering, with a scattering rate of 2.2 ps$^{-1}$. We also obtain the Fermi level at the In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As surface to be 0.36eV above the conduction band, when fitting our experimental densities with a Poisson-Schrodinger model.
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