Magnetotransport properties of an unconventional Rashba spin-orbit coupled two-dimensional electronic system

TL;DR

This work analyzes magnetotransport in a two-dimensional electron system with unconventional Rashba spin–orbit interaction, showing that each spin branch hosts two bands with opposite chirality between branches. Analytic Landau levels are derived, revealing intra-spin and inter-spin Landau level crossings, and the density of states exhibits Shubnikov–de Haas beating at low fields. Using Kubo formalism, the authors compute longitudinal and Hall conductivities, finding that beating patterns in σxx and a double-step quantization in σyx occur at LL crossing points, enabling potential spin-polarized transport by tuning the Fermi level. The results establish clear experimental signatures of URSOI in magnetotransport and highlight tunable spin-polarized responses in quantum Hall and SdH regimes.

Abstract

We study the magnetotransport properties of a two-dimensional electronic system with unconventional Rashba spin-orbit coupling in which the system is described by a pair of chiral spin texture in each spin branch, and the chirality is opposite in two spin branches. We obtain the Landau levels analytically and find that intra-spin and/or inter-spin Landau level crossing occurs. We compute the longitudinal conductivity and quantum Hall conductivity using the Kubo formalism based on linear response theory. We find that the usual Shubnikov-de Haas oscillation in longitudinal conductivity appears that can be made purely spin polarized by adjusting the Fermi level suitably. We observe a beating pattern in the Shubnikov-de Hass oscillation in the intra-spin branches, which arises due to the superposition of Shubnikov-de Hass oscillations corresponding to two bands in each spin branch. This is contrary to the conventional Rashba system, where such beating is due to the superposition of Shubnikov-de Hass oscillations corresponding to the two spin-branches. On the other hand, we note that quantum-Hall conductivity exhibits usual quantization in units of $e^2/h$ corresponding to each spin dependent Landau level. However, the Landau level crossing gives rise to the double jump in the Hall conductivity if the Fermi level is placed precisely at the crossing point.

Figures (10)

• Figure 1: Energy dispersion is plotted for the parameter ${\alpha}=0.1$ and ${\eta}=0.1$ that are normalized by a typical energy scale $\gamma_0=\hbar^2k_0^2/2m^*$ with $k_0$ being a wave vector corresponding to standard $2$D electron density . Blue and red lines denote two spin branches. Each spin branch again consists of two bands, denoted by dashed and solid lines. .
• Figure 2: Few Landau levels are plotted with the magnetic field in both spin branches. Landau level crossings between opposite spin branches are clearly visible here. We use parameter as: $\eta = 5$ meV and $\alpha = 2 \times 10^{-12}$eV m.
• Figure 3: Crossing of two Landau levels(intra-spin inter-band) is shown at high magnetic field for $\eta = 5$ meV and $\alpha = 5 \times 10^{-12}$eV m. The crossing point is shown by an arrow(red)
• Figure 4: We plot the density of states (DOS) as a function of the magnetic field. In Fig. \ref{['DOS_a']}, the DOS receives contributions solely from the lower energy branch, resulting in a beating pattern. In Fig. \ref{['DOS_b']}, where the DOS is shown at a relatively higher magnetic field, the beating pattern is suppressed and replaced by standard SdH oscillations. In Fig. \ref{['DOS_c']}, the Fermi energy is set to a higher value, allowing contributions from both branches and leading to the superposition of two distinct beating frequencies.
• Figure 5: Landau levels and Fermi level of the system at $T=5$mK as a function of magnetic field is shown for (a) $\alpha=7\times10^{-12}$eVm and (b) $\alpha=5\times10^{-12}$eVm. Electron concentration is taken to be $n_e = 2 \times 10^{16} \, m^{-2}$