NbIr2B2 and TaIr2B2 – New Low Symmetry Noncentrosymmetric Superconductors with Strong Spin–Orbit Coupling

Superconductivity was first observed more than a century ago, but the search for new superconducting materials remains a challenge. The Cooper pairs in superconductors are ideal embodiments of quantum entanglement. Thus, novel superconductors can be critical for both learning about electronic systems in condensed matter and for possible application in future quantum technologies. Here two previously unreported materials, NbIr₂B₂ and TaIr₂B₂, are presented with superconducting transitions at 7.2 and 5.2 K, respectively. They display a unique noncentrosymmetric crystal structure, and for both compounds the magnetic field that destroys the superconductivity at 0 K exceeds one of the fundamental characteristics of conventional superconductors (the “Pauli limit”), suggesting that the superconductivity may be unconventional. Supporting this experimentally based deduction, first-principle calculations show a spin-split Fermi surface due to the presence of strong spin–orbit coupling. These materials may thus provide an excellent platform for the study of unconventional superconductivity in intermetallic compounds.     

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

Unexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures, J_eff = 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities.     

GeTe中铁电极化对自旋霍尔电导的调控研究

利用电场控制电荷的自旋流与电流相互转换是自旋电子器件的关键所在,而这种控制机制在铁电半导体GeTe中可以得到实现,因为其铁电极化可以改变自身的自旋织构.基于密度泛函理论计算,我们发现可以通过铁电极化可以进一步调节自旋霍尔电导(spin Hall conductivity,简记为SHC),通过计算得到自旋霍尔电导的一个分...     

稀磁半导体ZnX∶Co2+光磁性质的双共价因子和双ξ模型

考虑到d电子t2g轨道与eg轨道局域性的差异,用双共价因子研究了掺Co2+的共价晶体ZnX(X=S,Se)的光学吸收谱.在研究顺磁g因子时,除考虑中心离子的旋-轨耦合贡献外,还计及配体的旋-轨耦合贡献(双ξ模型).研究表明,计算结果与实验值吻合得很好,对于一些共价性较强的化合物晶体,该方法更加有效.     

Enhancement of Spin–Orbit Torque by Strain Engineering in SrRuO3 Films

Complex oxides with 4d/5d transition metal ions, e.g., SrRuO₃, usually possess strong spin–orbit coupling, which potentially leads to efficient charge-spin interconversion. As the electrical transport property of SrRuO₃ can be readily tuned via structure control, it serves as a platform for studying the manipulation of charge-spin interconversion. Here, a factor of twenty enhancement of spin–orbit torque (SOT) efficiency via strain engineering in a SrRuO₃/Ni₈₁Fe₁₉ bilayer is reported. The results show that an orthorhombic SrRuO₃ leads to a higher SOT efficiency than the tetragonal one. By changing the strain from compressive to tensile in the orthorhombic SrRuO₃, the SOT efficiency can be increased from an average value of 0.04 to 0.89, corresponding to a change of spin Hall conductivity from 27 to 441 × ħ/e (S cm⁻¹). The first-principles calculations show that the intrinsic Berry curvature can give rise to a large spin Hall conductivity (SHC) via the strain control, which is consistent with the experimental observations. The results provide a route to further enhance the SOT efficiency in complex oxide-based heterostructures, which will potentially promote the application of complex oxides in energy-efficient spintronic devices.     

Anisotropic Interlayer Dzyaloshinskii–Moriya Interaction in Synthetic Ferromagnetic/Antiferromagnetic Sandwiches

The interfacial Dzyaloshinskii–Moriya interaction (DMI) in ferromagnetic/non-magnetic-metal bilayers is essential to stabilize chiral spin textures for potential applications. Recent works reveal that the interlayer DMI is beneficial to designing 3D chiral spin textures that possess fundamental importance and the associated technological promises. Here, the interlayer DM constants are determined quantitatively in synthetic ferromagnetic/antiferromagnetic Pt/Co/Pt/Ru/Pt/Co/Ta structures. The results demonstrate that the interlayer DMI shows uniaxial anisotropic characteristics. The first-principles calculations elucidate that the anisotropic interlayer DMI is induced by the in-plane symmetry breaking along two high symmetric directions, which favors the magnetization of adjacent ferromagnetic layers canting in different directions. The anisotropic interlayer DMI is also confirmed by spin-orbit torque driven asymmetric magnetization switching. Moreover, the interlayer DMI can be tuned by the Ru-layer-thickness and beneficial to designing 3D spin textures for future spintronic devices.     

Spontaneous spin polarization in organic thiophene oligomers

We studied the spin polarization phenomenon of injected charges in organic thiophene oligomer by using extended Su–Schrieffer–Heeger (SSH) model including electron–electron interaction, spin–orbit coupling as well as spin-flip effect. Our simulation shows that a charged carrier is spontaneously spin polarized, which has a lower energy than the non-polarized one. This polarization is related with the amount of injected charges and the polymerization of the molecule.     

Simulations of polaron spin inversion in an organic semiconductor: Comparison of two mechanisms

We present a model study of the effects of two mechanisms, the Rashba spin–orbit coupling and the spin-flip term, on the polaron spin inversion in an organic semiconductor. We find that, while both mechanisms can impact the polaron spin by changing the polaron level from a spin eigenstate to a spin superposition state, substantial difference can be observed in the static and dynamical properties of the polaron. Given the values of model parameters relevant to conjugated polymers, the magnitude of the polaron spin inversion caused by the spin–orbit coupling is much smaller than that by the spin-flip term. When the dynamical properties of the polaron are considered, spin oscillations induced by both mechanisms are observed when the polaron moves along the polymer chain driven by external electric field. Interestingly, the length of the polaron motion during one spin oscillation period remains constant in the case of spin–orbit coupling, while it is enhanced with increasing the driven electric field in the case of spin-flip term, in which larger spin diffusion length and longer spin relaxation time can be expected.