Influence of Device Geometry and Imperfections on the Interpretation of Transverse Magnetic Focusing Experiments

Abstract

Spatially separating electrons of different spins and efficiently generating spin currents are crucial steps towards building practical spintronics devices. Transverse magnetic focusing is a potential technique to accomplish both those tasks. In a material where there is significant Rashba spin–orbit interaction, electrons of different spins will traverse different paths in the presence of an external magnetic field. Experiments have demonstrated the viability of this technique by measuring conductance spectra that indicate the separation of spin-up and spin-down electrons. However the effect that the geometry of the leads has on these measurements is not well understood. By simulating an InGaAs-based transverse magnetic focusing device, we show that the resolution of features in the conductance spectra is affected by the shape, separation and width of the leads. Furthermore, the number of subbands occupied by the electrons in the leads affects the ratio between the amplitudes of the spin-split peaks in the spectra. We simulated devices with random onsite potentials and observed that transverse magnetic focusing devices are sensitive to disorder. Ultimately we show that careful choice and characterisation of device geometry are crucial for correctly interpreting the results of transverse magnetic focusing experiments.

Spin polarization and spin-dependent scattering of holes observed in transverse magnetic focusing

“…The HH-spin peak displays structure similar to a spin split focussing peak, however this splitting is too small to be caused by spin. The structure on the HH-peak is most likely due to an interference effect, as similar (but smaller amplitude) oscillations are visible on the low B side of the peak, a characteristic signature of interference due to diffraction in focussing [12,34]. Finally, as the focussing diameter is increased to 3100nm (Fig 5c) the amplitude of the HH+ and HH-peaks is further reduced, with the HH+ peak barely resolved due to scattering.…”

“…perimposed interference structure [12,20,33,34]. The HH-spin peak displays structure similar to a spin split focussing peak, however this splitting is too small to be caused by spin.…”

“…Starting with the QW sample (Fig 3a), we observe a clear spin split focussing peak in positive B, with higher order peaks also observed. No splitting of higher order peaks is observed due to spin-flip reflections from the boundary [12,32]. Vertical dashed lines indicate the position of the spinsplit first focussing peaks.…”

“…In systems with a spin-orbit interaction (SOI), the magnetic focussing trajectories become spin dependent as the spin states are now coupled to momentum. If the SOI is sufficiently large, magnetic focussing can spatially separate the spin states and create a spin-dependent mass spectrometer [5][6][7][8][9][10][11][12]. The high mobility and large SOI of 2D hole systems in GaAs has made them an ideal candidate for spin-dependent magnetic focussing experiments.…”

Probing the Anisotropic Fermi Surface in Tetralayer Graphene via Transverse Magnetic Focusing

“…Prior methods, including ballistic transport in bilayer graphene with superimposed antidot arrays and quantum point contacts, have been employed. However, these approaches could introduce inhomogeneity that can mask the intrinsic transport characteristics of bilayer graphene . In our study, we leverage transverse magnetic focusing (TMF) on 4LG to investigate the low-energy anisotropic band structure associated with TW.…”