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Register a new userDisentangling spin-orbit coupling and local magnetism in a quasi-two-dimensional electron system
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Quantum interference between time-reversed electron paths in two dimensions leads to the well-known weak localization correction to resistance. If spin-orbit coupling is present, the resistance correction is negative, termed weak anti-localization (WAL). Here we report the observation of WAL coexisting with exchange coupling between itinerant electrons and localized magnetic moments. We use low-temperature magneto-transport measurements to investigate the quasi-two-dimensional, high-electron-density interface formed between SrTiO$_3$ (STO) and the anti-ferromagnetic Mott insulator NdTiO$_3$ (NTO). As the magnetic field angle is gradually tilted away from the sample normal, the data reveals the interplay between strong $k$-cubic Rashba-type spin-orbit coupling and a substantial magnetic exchange interaction from local magnetic regions. The resulting quantum corrections to the conduction are in excellent agreement with existing models and allow sensitive determination of the small magnetic moments (22 $mu_B$ on average), their magnetic anisotropy and mutual coupling strength. This effect is expected to arise in other 2D magnetic materials systems.
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We study theoretically the spin and orbital angular momentum (OAM) Hall effect in a high mobility two-dimensional electron system with Rashba and Dresselhuas spin-orbit coupling by introducing both the spin and OAM torque corrections, respectively, to the spin and OAM currents. We find that when both bands are occupied, the spin Hall conductivity is still a constant (i.e., independent of the carrier density) which, however, has an opposite sign to the previous value. The spin Hall conductivity in general would not be cancelled by the OAM Hall conductivity. The OAM Hall conductivity is also independent of the carrier density but depends on the strength ratio of the Rashba to Dresselhaus spin-orbit coupling, suggesting that one can manipulate the total Hall current through tuning the Rashba coupling by a gate voltage. We note that in a pure Rashba system, though the spin Hall conductivity is exactly cancelled by the OAM Hall conductivity due to the angular momentum conservation, the spin Hall effect could still manifest itself as nonzero magnetization Hall current and finite magnetization at the sample edges because the magnetic dipole moment associated with the spin of an electron is twice as large as that of the OAM. We also evaluate the electric field-induced OAM and discuss the origin of the OAM Hall current. Finally, we find that the spin and OAM Hall conductivities are closely related to the Berry vector (or gauge) potential.
We study the effect of Rashba spin-orbit coupling (SOC) on the charge and spin degrees of freedom of a quasi-one-dimensional (quasi-1D) Wigner crystal. As electrons in a quasi-1D Wigner crystal can move in the transverse direction, SOC cannot be gauged away in contrast to the pure 1D case. We show that for weak SOC, a partial gap in the spectrum opens at certain ratios between density of electrons and the inverse Rashba length. We present how the low-energy branch of charge degrees of freedom deviates due to SOC from its usual linear dependence at small wave vectors. In the case of strong SOC, we show that spin sector of a Wigner crystal cannot be described by an isotropic antiferromagnetic Heisenberg Hamiltonian any more, and that instead the ground state of neighboring electrons is mostly a triplet state. We present a new spin sector Hamiltonian and discuss the spectrum of Wigner crystal in this limit.
We demonstrate that spin-orbit coupling (SOC) strength for electrons near the conduction band edge in few-layer $gamma$-InSe films can be tuned over a wide range. This tunability is the result of a competition between film-thickness-dependent intrinsic and electric-field-induced SOC, potentially, allowing for electrically switchable spintronic devices. Using a hybrid $mathbf{kcdot p}$ tight-binding model, fully parameterized with the help of density functional theory computations, we quantify SOC strength for various geometries of InSe-based field-effect transistors. The theoretically computed SOC strengths are compared with the results of weak antilocalization measurements on dual-gated multilayer InSe films, interpreted in terms of Dyakonov-Perel spin relaxation due to SOC, showing a good agreement between theory and experiment.
Using time-resolved Faraday rotation, the drift-induced spin-orbit Field of a two-dimensional electron gas in an InGaAs quantum well is measured. Including measurements of the electron mobility, the Dresselhaus and Rashba coefficients are determined as a function of temperature between 10 and 80 K. By comparing the relative size of these terms with a measured in-plane anisotropy of the spin dephasing rate, the Dyakonv-Perel contribution to spin dephasing is estimated. The measured dephasing rate is significantly larger than this, which can only partially be explained by an inhomogeneous g-factor.
Effects of the spin-orbit interactions on the energy spectrum, Fermi surface and spin dynamics are studied in structural- and bulk-inversion asymmetric quasi-two-dimensional structures with a finite thickness in the presence of a parabolic transverse confining potential. One-particle quantum mechanical problem in the presence of an in-plane magnetic field is solved numerically exact. Interplay of the spin-orbit interactions, orbital- and Zeeman-effects of the in-plane magnetic field yields a multi-valley subband structure, typical for realization of the Gunn effect. A possible Gunn-effect-mediated spin accumulation is discussed.
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