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Register a new userGate-controlled Persistent Spin Helix State in Materials with Strong Spin-Orbit Interaction
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In layered semiconductors with spin-orbit interaction (SOI) a persistent spin helix (PSH) state with suppressed spin relaxation is expected if the strengths of the Rashba and Dresselhaus SOI terms, alpha and beta, are equal. Here we demonstrate gate control and detection of the PSH in two-dimensional electron systems with strong SOI including terms cubic in momentum. We consider strain-free InGaAs/InAlAs quantum wells and first determine alpha/beta ~ 1 for non-gated structures by measuring the spin-galvanic and circular photogalvanic effects. Upon gate tuning the Rashba SOI strength in a complementary magneto-transport experiment, we then monitor the complete crossover from weak antilocalization via weak localization to weak antilocalization, where the emergence of weak localization reflects a PSH type state. A corresponding numerical analysis reveals that such a PSH type state indeed prevails even in presence of strong cubic SOI, however no longer at alpha = beta.
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The spin orbit interaction plays a crucial role in diverse fields of condensed matter, including the investigation of Majorana fermions, topological insulators, quantum information and spintronics. In III V zinc blende semiconductor heterostructures, two types of spin orbit interaction, Rashba and Dresselhaus act on the electron spin as effective magnetic fields with different directions. They are characterized by coefficients alpha and beta, respectively. When alpha is equal to beta, the so called persistent spin helix symmetry is realized. In this condition, invariance with respect to spin rotations is achieved even in the presence of the spin orbit interaction, implying strongly enhanced spin lifetimes for spatially periodic spin modes. Existing methods to evaluate alpha/beta require fitting analyses that often include ambiguity in the parameters used. Here, we experimentally demonstrate a simple and fitting parameter free technique to determine alpha/beta and to deduce the absolute values of alpha and beta. The method is based on the detection of the effective magnetic field direction and the strength induced by the two spin orbit interactions. Moreover, we observe the persistent spin helix symmetry by gate tuning.
We show that the spin-orbit interaction (SOI) produced by the Coulomb fields of charged impurities provides an efficient mechanism for the bound states formation. The mechanism can be realized in 2D materials with sufficiently strong Rashba SOI provided that the impurity locally breaks the structure inversion symmetry in the direction normal to the layer.
We study the tunability of the spin-orbit interaction in a two-dimensional electron gas with a front and a back gate electrode by monitoring the spin precession frequency of drifting electrons using time-resolved Kerr rotation. The Rashba spin splitting can be tuned by the gate biases, while we find a small Dresselhaus splitting that depends only weakly on the gating. We determine the absolute values and signs of the two components and show that for zero Rashba spin splitting the anisotropy of the spin-dephasing rate vanishes.
We study the phase diagram of the interacting two-dimensional electron gas (2DEG) with equal Rashba and Dresselhaus spin-orbit coupling, which for weak coupling gives rise to the well-known persistent spin-helix phase. We construct the full Hartree-Fock phase diagram using a classical Monte-Carlo method analogous to that used in Phys.Rev.B 96, 235425 (2017). For the 2DEG with only Rashba spin-orbit coupling, it was found that at intermediate values of the Wigner-Seitz radius rs the system is characterized by a single Fermi surface with an out-of-plane spin polarization, while at slightly larger values of rs it undergoes a transition to a state with a shifted Fermi surface and an in-plane spin polarization. The various phase transitions are first-order, and this shows up in discontinuities in the conductivity and the appearance of anisotropic resistance in the in-plane polarized phase. In this work, we show that the out-of-plane spin-polarized region shrinks as the strength of the Dresselhaus spin-orbit interaction increases, and entirely vanishes when the Rashba and Dresselhaus spin-orbit coupling strengths are equal. At this point, the system can be mapped onto a 2DEG without spin-orbit coupling, and this transformation reveals the existence of an in-plane spin-polarized phase with a single, displaced Fermi surface beyond rs > 2.01. This is confirmed by classical Monte-Carlo simulations. We discuss experimental observation and useful applications of the novel phase, as well as caveats of using the classical Monte-Carlo method.
We theoretically study the profile of a supercurrent in two-dimensional Josephson junctions with Rashba-Dresselhaus spin-orbit interaction (RDSOI) in the presence of a Zeeman field. Through investigating self-biased supercurrent (so called $varphi_0$-Josephson state), we obtain explicit expressions for the functionality of the $varphi_0$ state with respect to RDSOI parameters ($alpha,beta$) and in-plane Zeeman field components ($h_x,h_y$). Our findings reveal that, when the chemical potential ($mu$) is high enough compared to the energy gap ($Delta$) in superconducting electrodes, i.e., $mu gg Delta$, RSOI and DSOI with equal strengths ($|alpha|=|beta|$) cause vanishing $varphi_0$ state independent of magnetization and the type of RDSOI. A Zeeman field with unequal components, i.e., $|h_x| eq |h_y|$, however, can counteract and nullify the destructive impact of equal-strength RDSOIs (for one type only), where $musimDelta$, although $|h_x|= |h_y|$ can still eliminate the $varphi_0$ state. Remarkably, in the $musimDelta$ limit, the $varphi_0$ state is proportional to the multiplication of both components of an in-plane Zeeman field, i.e., $h_xh_y$, which is absent in the $mu gg Delta$ limit. Furthermore, our results of critical supercurrents demonstrate that the persistent spin helices can be revealed in a high enough chemical potential regime $mugg Delta$, while an opposite regime, i.e., $musimDelta$, introduces an adverse effect. In the ballistic regime, the maximum of the critical supercurrent occurs at $|alpha|=|beta|$ and the Zeeman field can boost this feature. The presence of disorder and nonmagnetic impurities change this picture drastically so the minimum of the critical supercurrent occurs at and around the symmetry lines $|alpha|=|beta|$.
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