Many-body theory of spin-orbit coupled materials and novel spin drag effects

该奖项支持具有强自旋轨道相互作用的材料的理论研究和教育。这些材料在基于电子自旋的新一代电子设备中具有潜在的重要意义。自旋轨道相互作用传统上是在单电子的背景下研究的，但也有电子-电子相互作用与自旋轨道相互作用相结合以产生有趣的集体效应的例子。这方面的例子是自旋霍尔阻力和自旋波的非均匀吉尔伯特阻尼。PI的目标是：(i)识别和研究自旋轨道耦合系统中的新型多体效应，以及（ii）研究新条件下的库仑阻力效应，例如在接近磁有序跃迁的稀磁性半导体中，在接近电子-空穴配对跃迁的半导体双层中，以及在具有强自旋轨道相互作用的半导体中。(i)自旋轨道耦合系统中的多体效应——固体系统中的自旋轨道耦合改变了电子-电子相互作用，产生了类似于量子电动力学中的Breit相互作用的有效相互作用，但强度要大得多。PI将研究这种相互作用在库仑耦合双层系统和单层二维电子液体中的影响。PI将进一步发展耦合电流-自旋激励的多体理论和单层系统在正常和超导状态下以及在磁场存在下的光学导电性。特别是，他将在Bychkov-Rashba和Dresselhaus自旋轨道耦合的系统中研究这些效应，在“中性点”附近，两种相互作用相互平衡。（ii）库仑-阻力效应——PI将把他对自旋库仑阻力的研究扩展到处于相变边缘的电子系统，如稀磁半导体中的磁有序和半导体双层中的电子-空穴配对。在这两种情况下，由于自旋涨落或配对涨落对有效电子-电子或电子-空穴相互作用的贡献，预计阻力效应会有很强的增强。在这种情况下，PI将研究在磁有序跃迁附近的Dyakonov-Perel自旋弛豫时间的行为。在与实验学家的合作下，PI将计算在铁磁跃迁附近的空穴掺杂磁性半导体中光激发电子的自旋库仑阻力参数。PI还计划在中性点附近的Bychkov-Rashba和Dresselhaus自旋轨道耦合下研究量子阱中光诱导自旋光栅的输运和自旋弛豫动力学。最近引入的自旋-密度动力学映射将用于将存在自旋-轨道耦合的自旋弛豫时间与不存在自旋-轨道耦合的自旋库仑阻力时间联系起来。相互作用自旋轨道耦合系统的研究将对自旋电子学领域产生重大影响，并为可能的新电子器件技术奠定理论基础。该奖项和支持的研究有助于研究生和博士后研究人员的教育。该奖项支持理论研究和教育，以研究电子经历强自旋轨道相互作用的材料。电子有一种叫做自旋的固有特性，它看起来就像一个小陀螺。电子的自旋也与其固有的磁性有关；它的行为就像一个小条形磁铁。当一个电子在固体中移动时，相对论认为它会经历晶格中原子核心的磁场。电子与磁场的相互作用产生自旋轨道相互作用。自旋轨道相互作用特别强的材料最近作为可能的新一代电子设备的关键角色而受到关注，自旋电子设备就像普通电子设备一样使用电子电荷。这种兴趣在很大程度上是由实现与晶体管类似的自旋电子的希望所推动的，即“自旋晶体管”，其中通过控制电子的自旋来实现开/关状态，这种控制方式不使用磁场，而是利用我们控制电子运动和自旋轨道相互作用的能力。基本上，自旋轨道相互作用允许我们用电场来操纵电子自旋。传统的自旋轨道相互作用研究忽略了电子之间的相互作用。但是，在某些情况下，电子之间的相互作用会与自旋轨道相互作用相结合，从而产生有趣的效果。例如，在两个相距很近但明显分开的电子层的系统中，流过其中一层的电流会引起另一层的自旋积累。这种效应被称为自旋霍尔阻力，是由不同层中电子之间的库仑相互作用以及每层中电子的自旋轨道相互作用引起的。这种效应是更广泛的“库仑拖拽效应”的一个例子，在这种效应中，一组电子的运动被用来拖拽另一组电子，这样做会产生期望的性质。该奖项支持旨在发现具有强自旋轨道相互作用的材料的新效应的研究，重点是库仑阻力效应。PI还将研究新条件下的库仑阻力效应，例如在接近磁性的新材料中。相互作用自旋轨道耦合系统的研究将对自旋电子学领域产生重大影响，并为可能的新电子器件技术奠定理论基础。该奖项和支持的研究有助于研究生和博士后研究人员的教育。

Technical SummaryThis award supports theoretical research and education on materials with strong spin-orbit interaction. These materials are potentially important in a new generation of electronic devices, based on the electron spin. Spin-orbit interactions are traditionally studied within a one-electron context, but there are instances in which electron-electron interactions latch-on to spin-orbit interactions to produce intriguing collective effects. Examples of this are the spin Hall drag and the inhomogeneous Gilbert damping of spin waves. The PI aims: (i) to identify and study novel many-body effects in spin-orbit coupled systems, and (ii) to study Coulomb drag effects under novel conditions, e.g. in dilute magnetic semiconductors close to the magnetic ordering transition, in semiconductor bi-layers close to an electron-hole pairing transition, and in semiconductors with strong spin-orbit interactions.(i) Many-body effects in spin-orbit-coupled systems - Spin-orbit coupling in solid-state systems modifies the electron-electron interaction, producing an effective interaction similar to the Breit interaction of quantum electrodynamics, but considerably stronger. The PI will investigate the effects of this interaction in Coulomb-coupled bilayer systems and in single-layer two-dimensional electron liquids. The PI will further develop the many-body theory of coupled current-spin excitations and the optical conductivity in the single-layer systems, both in the normal and in the superconducting state and in the presence of a magnetic field. In particular, he will study these effects in systems with Bychkov-Rashba and Dresselhaus spin-orbit coupling, in the vicinity of the 'neutrality point' where the two interactions balance each other. (ii) Coulomb-drag effects - The PI will extend his investigations of spin Coulomb drag to electronic systems on the verge of phase transitions, such as magnetic ordering in dilute magnetic semiconductors and electron-hole pairing in semiconductor bilayers. In both cases, a strong enhancement of the drag effect is expected due to the contribution of spin fluctuations or pairing fluctuations to the effective electron-electron or electron-hole interaction. In this context the PI will study the behavior of the Dyakonov-Perel spin relaxation time near the magnetic ordering transition. In collaboration with experimentalists, the PI will calculate spin Coulomb drag parameters of optically excited electrons in hole-doped magnetic semiconductors near the ferromagnetic transition. The PI also plans to investigate the transport and spin relaxation dynamics of optically induced spin gratings in quantum wells with Bychkov-Rashba and Dresselhaus spin-orbit coupling, near the neutrality point. A recently introduced spin-to-density dynamics mapping will be used to connect the spin relaxation time in the presence of spin-orbit coupling to the spin Coulomb drag time without spin-orbit coupling.Research on interacting spin-orbit coupled systems can have a large impact on the field of spintronics and contributes to the intellectual foundations upon which possible new electronic device technologies rest. This award and the supported research contribute to the education of graduate students and postdoctoral researchers.Non-Technical SummaryThis award supports theoretical research and education to study materials in which electrons experience strong spin-orbit interactions. Electrons have an intrinsic property called spin where it appears as if the electron spins like a tiny top. The spin of the electron is also connected to its intrinsic magnetic properties; it behaves as though it was a tiny bar magnet. As an electron moves through a solid the theory of relativity says that it will experience a magnetic field from the atomic cores in the lattice. The interaction of the electron with this magnetic field gives rise to the spin-orbit interaction. Materials where spin-orbit interactions are particularly strong have recently gained the spotlight as key actors in a possible new generation of electronic devices, spintronic devices, which use the electron spin just as ordinary electronic devices use the electron charge. This interest has largely been fueled by the hope to realize the spintronic analog to a transistor, the 'spin transistor,' in which the on/off state would be achieved through control of the electron's spin in a way that does not use a magnetic field but exploits our ability to control the electron's motion and the spin-orbit interaction. Basically, the spin-orbit interaction allows us to manipulate the electron spin using an electric field.Spin-orbit interactions are traditionally studied ignoring the interaction of electrons with each other. But, there are instances in which interactions between electrons latch-on to spin-orbit interactions to produce interesting effects. For example, in a system of two closely spaced but clearly separated electron layers, a current flowing in one of the two layers can induce a spin accumulation in the other layer. This effect, known as spin Hall drag, is caused by the Coulomb interaction between electrons in different layers, coupled with spin-orbit interaction of electrons in each layer. This effect is one instance of a broader class of 'Coulomb drag effects' in which the motion of one group of electrons is used to drag along a second group of electrons and, in so doing, induces a desired property. This award supports research with the aim to discover new effects in materials with strong spin-orbit interactions, with an emphasis on Coulomb drag effects. The PI will also study Coulomb drag effects under novel conditions, for example in novel materials close that are close to becoming magnetic.Research on interacting spin-orbit coupled systems can have a large impact on the field of spintronics and contributes to the intellectual foundations upon which possible new electronic device technologies rest. This award and the supported research contribute to the education of graduate students and postdoctoral researchers.