Fig. 1
From: Gate-tunable large magnetoresistance in an all-semiconductor spin valve device
Devices and measurement configurations. a Colored SEM image of one of the gated devices. Two narrow contacts in the middle, 500 and 700 nm wide, separated by 3.6 µm, are the ferromagnetic source (S) and drain (D) leads. Two electrostatic gates are used to confine the spins between S and D for V G < 0. Additionally, the electric circuit for 2T measurements is sketched. The scale bar length is 2 µm. b Nonlocal configuration, with S being an injector and D a detector. The majority spins are injected into the channel from the negatively biased S and diffuse along the channel. The solid line indicates the spin accumulation profile \(\mu ^{\mathrm{s}}(x) = \frac{1}{2}\left( {\mu _ \uparrow (x) - \mu _ \downarrow (x)} \right)\), where \(\mu _{ \uparrow ( \downarrow )}\) is the quasichemical potential for the corresponding spin direction. The dashed line shows \(\mu ^{\mathrm{s}}(x)\) when either the polarity of the injection current j or the magnetization direction of the source has been reversed. \(\mu ^{\mathrm{s}}\) underneath the drain induces the spin-dependent voltage \({\mathrm{\delta }}V\), measured nonlocally as \(V^{{\mathrm{nl}}}\), which changes by \({\mathrm{\Delta }}V^{{\mathrm{nl}}} = 2{\mathrm{\delta }}V\) each time the magnetization of either of the contacts is reversed. c, d 2T configuration with a positively biased source and a negatively biased drain for antiparallel and parallel orientation of the magnetization of the contacts, respectively. Solid lines indicate the total spin accumulation \(\mu ^{\mathrm{s}}(x) = \mu _{\mathrm{S}}^{\mathrm{s}}(x) + \mu _{\mathrm{D}}^{\mathrm{s}}(x)\), where \(\mu _{{\mathrm{S}}\left( {\mathrm{D}} \right)}^{\mathrm{s}}\)(dashed line) is the spin accumulation generated at the source (drain). In AP (P) configuration, both components have the same (opposite) sign. As a result, \(\mu ^{\mathrm{s}}\) is larger (smaller) in the AP (P) configuration. The 2T voltage difference between both configurations is given by \({\mathrm{\Delta }}V = 2{\mathrm{\delta }}V_{{\mathrm{S}},{\mathrm{D}}} + 2{\mathrm{\delta }}V_{{\mathrm{D}},{\mathrm{S}}}\), where \({\mathrm{\delta }}V_{i,j}\) is the voltage drop at contact i due to \(\mu _j^{\mathrm{s}}\)
