Generation and Detection of Spin Currents in Semiconductor Nanostructures with Strong Spin-Orbit Interaction

Abstract

Storing, transmitting, and manipulating information using the electron spin resides at the heart of spintronics. Fundamental for future spintronics applications is the ability to control spin currents in solid state systems. Among the different platforms proposed so far, semiconductors with strong spin-orbit interaction are especially attractive as they promise fast and scalable spin control with all-electrical protocols. Here we demonstrate both the generation and measurement of pure spin currents in semiconductor nanostructures. Generation is purely electrical and mediated by the spin dynamics in materials with a strong spin-orbit field. Measurement is accomplished using a spin-to-charge conversion technique, based on the magnetic field symmetry of easily measurable electrical quantities. Calibrating the spin-to-charge conversion via the conductance of a quantum point contact, we quantitatively measure the mesoscopic spin Hall effect in a multiterminal GaAs dot. We report spin currents of 174 pA, corresponding to a spin Hall angle of 34%.The generation and detection of spin currents in nanostructures is the central challenge of semiconductor spintronics. On the one hand, spin injection cannot be easily achieved by coupling semiconductors to ferromagnets [1] because of the lack of control over material interfaces [2]. On the other hand, magnetoelectric alternatives exploiting the celebrated spin Hall effect (SHE) [3,4], have delivered only qualitative measurement protocols in transport experiments [5]. Alternatively to all-electrical setups, spin polarizing the current through a quantum point contact (QPC) with a magnetic field allows a quantitative control over spin current generation and detection at the nanoscale [6][7][8]. The latter approach typically requires such high magnetic fields (6 − 8 Tesla) that, as a drawback, the desired magnetoelectric effects are either suppressed or totally altered. This Letter reports two major advances of nanoscale semiconductor spintronics. Namely, we develop novel experimental methods to electrically generate and quantitatively measure spin currents in a two-dimensional semiconductor nanostructure.It is predicted that charge currents flowing through spin-orbit interaction (SOI)-coupled nanostructures are generically accompanied by spin currents, if the spinorbit time is shorter than the electron dwell time [9][10][11][12]. This spin current generation mechanism is purely electrical and based on the mesoscopic SHE (MSHE) [9,10], where the electronic orbital dynamics in chaotic nanostructures cooperates with the SOI to make transport spin dependent. We will consider an open three-terminal quantum dot as represented in Fig. 1(a), where each lead i is a QPC carrying N i spin degenerate modes. Running a charge current I between terminals 1 and 2, a spin current in all terminals, including 3, is expected due to the MSHE.For a weak SOI, the spin currents' amplitude fluctuates from sample to sample with zero average. For cavities with a strong SOI, geometric correlations between ...

Magneto-transport Spectroscopy of the First and Second Two-dimensional Subbands in Al0.25Ga0.75N/GaN Quantum Point Contacts

“…Quantum point contact (QPC) is a typical type of 1D system that can be realized based on two-dimensional electron gas (2DEG) in semiconductor heterostructures. Recent experiments proved an exciting possibility of using QPCs for spin injection and detection for spin field effect transistors 9 10 , yet little has been studied about the transport properties in GaN based QPCs. In this letter, the magneto-transport spectroscopy of the energy levels in the QPCs based on Al 0.25 Ga 0.75 N/GaN heterostructures was studied in magnetic fields up to 14 T. In a QPC with two two-dimensional (2D) subbands in the 2DEG occupied, the perpendicular field is found to depopulate the energy levels in the first 2D subband faster than those in the second one.…”

Full counting statistics of spin-flip and spin-conserving charge transitions in Pauli-spin blockade

“…Since the late 2000s, the development of spintronics in mesoscopic devices is remarkable. For example, generation of spin current due to spin-orbit interaction has been detected in semiconductor devices [22,23]. Studies on the charge and spin statistics of such phenomena will reveal the microscopic dynamics of the charge-spin conversion and improve the conversion rate.…”

All-electric spin pumping in quantum channels with a single finger-gate capacitor

“…At the heart of spintronics, however, is all-electric spin current generation in all-semiconductor devices [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], where no ferromagnetic materials and magnetic fields are involved. Configurations with two spatially separated time-modulated regions for spin pumping were proposed.…”

“…Aside from pumping, spin-polarized current schemes for QC of high intrinsic SOI had been studied. It is by imposing a highly asymmetric lateral QC confinement [25], a potential barrier located at and along the QC central line [30], or a transverse lead, as in a mesoscopic spin Hall effect configuration, for spin current extraction when a charge current passes through the source and drain leads [31]. These spin-polarized current schemes, however, operate with a finite source-drain bias.…”