The conduction band degeneracy in Si is detrimental to quantum computing based on spin qubits, for which a nondegenerate ground orbital state is desirable. This degeneracy is lifted at an interface with an insulator as the spatially abrupt change in the conduction band minimum leads to intervalley scattering. We present a theoretical study of the interface-induced valley splitting in Si that provides simple criteria for optimal fabrication parameters to maximize this splitting. Our work emphasizes the relevance of different interface-related properties to the valley splitting.
Orbital degeneracy of the electronic conduction band edge in silicon is a potential roadblock to the storage and manipulation of quantum information involving the electronic spin degree of freedom in this host material. This difficulty may be mitigated near an interface between Si and a barrier material, where intervalley scattering may couple states in the conduction ground state, leading to nondegenerate orbital ground and first excited states. The level splitting is experimentally found to have a strong sample dependence, varying by orders of magnitude for different interfaces and samples. …
Coherent optical dressing of quantum materials offers technological advantages to control their electronic properties, such as the electronic valley degree of freedom in monolayer transition metal dichalcogenides (TMDs). Here, we observe a new type of optical Stark effect in monolayer WS2, one that is mediated by intervalley biexcitons under the blue-detuned driving with circularly polarized light. We found that such helical optical driving not only induces an exciton energy downshift at the excitation valley, but also causes an anomalous energy upshift at the opposite valley, which is normall…
The variety of excitonic states in tungsten-based dichalcogenide monolayers stems from unique interplay between the spin and valley degrees of freedom. One of the exciton species is the indirect exciton (momentum or valley dark), which is responsible to a series of resonances when the monolayer is charge neutral. We investigate the short-range electron-hole exchange interaction of the indirect exciton, as well as its recombination mechanism mediated by impurities. The analysis provides thorough understanding of the energy and polarization of the zero-phonon indirect exciton resonance in the em…
Through the theoretical study of electron spin lifetime in the 2DEG of doped Si, we highlight a dominant spin relaxation mechanism induced by the impurity central-cell potential near an interface via intervalley electron scattering. At low temperatures and with modest doping, this Yafet spin flip mechanism can become much more important than the Dyakonov-Perel spin relaxation indcued by the structural Rashba spin-orbit coupling field. As the leading-order impurity-induced spin flip happens only between two non-opposite valleys in Si, two-dimensional electron gas (2DEG) systems in Si MOSFETs or…
Vortex is a universal and significant phenomenon that has been known for centuries. However, creating vortices to the atomic limit has remained elusive because that the characteristic length to support a vortex is usually much larger than the atomic scale. Very recently, it was demonstrated that intervalley scattering induced by the single carbon defect of graphene leads to phase winding over a closed path surrounding the defect. Motivated by this, we demonstrate, in this Letter, that the single carbon defects at A and B sublattices of graphene can be regarded as pseudospin-mediated atomic-sca…
Interfacial spin to charge conversion arises due to an electric potential perpendicular to the interface. The electric potential can be artificially induced, for example, using ferroelectric and piezoelectric thin films at the interface. An alternate way to induce the electric potential could be flexoelectric field. The flexoelectricity can be observed in all the material that either have or lack inversion symmetry, additionally no large gate bias is needed. In this experimental study, we report large spin to charge conversion (spin-Hall angle- 0.578) at Ni80Fe20/amorphous-Si interfaces attrib…
We present a phenomenological scheme to study the size-dependent electric voltage-controlled magnetic anisotropy in ferromagnetic (FM)/ferroelectric (FE) heterostructures. The FM layers are either metallic Fe(001), Ni(001), Co(0001), or half-metallic (La, Sr)MnO3 films. Two magnetoelectric mechanisms, i.e., interface-charge and strain-mediated couplings, are considered. We show that the interface-charge mediated coupling is the main mechanism for the magnetoelectic coupling when the FM film thickness is below a certain transition thickness dtr while the strain-mediated coupling dominates above…
The motion of interfaces is an essential feature of microstructure evolution in crystalline materials. While atomic-scale descriptions provide mechanistic clarity, continuum descriptions are important for understanding microstructural evolution and upon which microscopic features it depends. We develop a microstructure evolution simulation approach that is linked to the underlying microscopic mechanisms of interface migration. We extend the continuum approach describing the disconnection-mediated motion of interfaces introduced in Part I [Han, Srolovitz and Salvalaglio, 2021] to a diffuse inte…
A long-standing goal of materials science is to understand, predict and control the evolution of microstructures in crystalline materials. Most microstructure evolution is controlled by interface motion; hence, the establishment of rigorous interface equations of motion is a universal goal of materials science. We present a new model for the motion of arbitrarily curved interfaces that respects the underlying crystallography of the two phases/domains meeting at the interface and is consistent with microscopic mechanisms of interface motion; i.e., disconnection migration (line defects in the in…
Local electronic structures of nanometer-sized patches of epitaxial graphene and its interface layer with SiC(0001) have been studied by atomically resolved scanning tunneling microscopy and spectroscopy. Localized states belonging to the interface layer of a graphene/SiC system show to have an essential influence on the electronic structure of graphene. Giant enhancement of inelastic tunneling, reaching 50% of the total tunneling current, has been observed at the localized states on a nanometer-sized graphene monolayer surrounded by defects.
Through the combination of transmission electron microscopy analysis of the deformed microstructure and molecular dynamics computer simulations of the deformation processes, the mechanisms of plastic strain recovery in bulk AgCu eutectic with either incoherent twin or cube-on-cube interfaces between the Ag and Cu layers and a bilayer thickness of 500 nm have been revealed. The character of the incoherent twin interfaces changed uniquely after dynamic compressive loading for samples that exhibited plastic strain recovery and was found to drive the recovery, which is due to dislocation retractio…
While tremendous success has been achieved to date in creating both single phase and composite magnetoelectric materials, the quintessential electric-field control of magnetism remains elusive. In this work, we demonstrate a linear magnetoelectric effect which arises from a novel carrier-mediated mechanism, and is a universal feature of the interface between a dielectric and a spin-polarized metal. Using first-principles density functional calculations, we illustrate this effect at the SrRuO$_3$/SrTiO$_3$ interface and describe its origin. To formally quantify the magnetic response of such an …
A Mesoscale Model for Interface-Mediated Plasticity: Investigation of Ductile and Brittle Fracture
City University of Hong Kong（香港城市大学）；University of California, Los Angeles（加州大学洛杉矶分校）；The University of Hong Kong（香港大学）；University of Birmingham（伯明翰大学）
In thin magnetic layers with structural inversion asymmetry and spin-orbit coupling, a Dzyaloshinskii-Moriya interaction arises at the interface. When a spin wave current ${\bf j}_m$ flows in a system with a homogeneous magnetization {\bf m}, this interaction produces an effective field-like torque on the form ${\bf T}_{\rm FL}\propto{\bf m}\times({\bf z}\times{\bf j}_m)$ as well as a damping-like torque, ${\bf T}_{\rm DL}\propto{\bf m}\times[({\bf z}\times{\bf j}_m)\times{\bf m}]$ in the presence of spin-wave relaxation (${\bf z}$ is normal to the interface). These torques mediated by the mag…
The surfactant mediated growth of Ti/Ni multilayers is studied. They were prepared using ion beam sputtering at different adatom energies. It was found that the interface roughness decreased significantly when the multilayers were sputtered with Ag as surfactant at an ion energy of 0.75 keV. On the other hand, when the ion energy was increased to 1 keV, it resulted in enhanced intermixing at the interfaces and no appreciable effect of Ag surfactant could be observed. On the basis of the obtained results, the influence of adatom energy on the surfactant mediated growth mechanism is discussed.
Hybrid nanocrystals (HNCs), based on ZnO nanorods (NRs) decorated with magnetic Fe-based domains, were synthesized via a colloidal seeded-growth method. The approach involved heterogeneous nucleation of Fe nanocrystals on size-tailored ZnO nanorod seeds in a noncoordinating solvent, followed by partial surface oxidation of the former to the corresponding Fe@FexOy core@shell domains. HNCs with variable population and size of the Fe-based nanodomains could be synthesized depending on the surface reactivity of the ZnO seeds. The structure-property relationships in these HNCs were carefully studie…
SrTiO$_3$ is a superconducting semiconductor with a pairing mechanism that is not well understood. SrTiO$_3$ undergoes a ferroelastic transition at $T=$ 105 K, leading to the formation of domains with boundaries that can couple to electronic properties. At two-dimensional SrTiO$_3$ interfaces, the orientation of these ferroelastic domains is known to couple to the electron density, leading to electron-rich regions that favor out-of-plane distortions and electron-poor regions that favor in-plane distortion. Here we show that ferroelastic domain walls support low energy excitations that are anal…
Using ab initio methods, we examine the the charge distribution at the interface of alpha-alumina-supported Pt films, and we consider the influence of this interface on CO adsorption. We demonstrate that a combination of electrostatic charge transfer and covalent bonding governs the interfacial interactions, and that these interactions play an important role in the metal reactivity. By modifying the interface and varying the Pt film thickness over a nanoscale range, CO adsorption can be significantly enhanced or diminished. These observations could be used to tune the reactivity of Pt particle…
High velocity impact between crystalline surfaces is important for a range of material phenomena, yet a fundamental understanding of the effect of surface structure, energetics and kinetics on the underlying thermo-mechanical response remains elusive. Here, we employ non-equilibrium molecular dynamics (NEMD) simulations to describe the nanoscale dynamics of the high velocity impact between commensurate and incommensurate monocrystalline (001) copper surfaces. For impact velocities in the range 100-1200 m/s, the kinetic energy dissipation involves nucleation and emission of dislocation loops fr…
We investigated the mechanism for photoconduction in multi-walled carbon nanotube (MWNT) film of various electrode separations upon near infrared illumination. In addition to observing strong dependence of photocurrent on the position of the laser spot, we found that the time constant of the dynamic photoresponse is slow and increases with increasing electrode separations. The photoconduction mechanism can be explained by the Schottky barrier modulation at the metal-nanotube film interface and charge carrier diffusion through percolating MWNT networks.
We investigate theoretically the magnetic dynamics in a ferroelectric/ferromagnetic heterostructure coupled via strain-mediated magnetoelectric interaction. We predict an electric field-induced magnetic switching in the plane perpendicular to the magneto-crystalline easy axis, and trace this effect back to the piezoelectric control of the magnetoelastic coupling. We also investigate the magnetic remanence and the electric coercivity.
Magnetoelectric (ME) effect has been studied in a structure of a magnetostrictive TbFe2 alloy, two piezoelectric Pb(Zr,Ti)O3 (PZT) ceramics, and two nonmagnetic flakes. The ME coupling originates from the magnetic-mechanical-electric transform of the magnetostrictive effect in TbFe2 and the piezoelectric effect in PZT by end bonding, instead of interface bonding. Large ME coefficients of 10.5 and 9.9 Vcm-1Oe-1 were obtained at the first planar acoustic and third bending resonance frequencies, which are larger than that of conventional layered TbFe2/PZT composites. The results show that the lar…
Interfacial polar molecules feature a strongly anisotropic response to applied electric field, favoring dipole orientations parallel to the interface. In water, in particular, this effect combines with generic orientational preferences induced by spatial asymmetry of water hydrogen bonding under confined geometry, which may give rise to a Janus interface. The two effects manifest themselves in considerable dependence of water polarization on both the field direction relative to the interface, and the polarity (sign) of the field. Using molecular simulations, we demonstrate strong field-induced…
Strain-Mediated Lattice Reconstruction Enhances Ferromagnetism in Cr2Ge2Te6/WTe2 van der Waals Heterobilayers
Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and the Barcelona Institute of Science and Technology (BIST)（加泰罗尼亚纳米科学和纳米技术研究所（ICN2），西班牙高等科学研究委员会（CSIC）和巴塞罗那科学与技术研究所（BIST））；Universitat Autònoma de Barcelona（巴塞罗那自治大学）；Institut de Ciència de Materials de Barcelona, ICMAB-CSIC（巴塞罗那材料科学研究所，西班牙高等科学研究委员会（ICMAB-CSIC））；Research Center for Electronic and Optical Materials, National Institute for Materials Science（电子与光学材料研究中心，日本物质材料研究机构）；Research Center for Materials Nanoarchitectonics, National Institute for Materials Science（材料纳米结构研究中心，日本物质材料研究机构）；Institute of Optical Materials and Technologies, Bulgarian Academy of Science（保加利亚科学院光学材料与技术研究所）；Institute of Solid State Physics, Bulgarian Academy of Sciences（保加利亚科学院固体物理研究所）；Quantum Innovation Centre (Q. InC), Agency for Science Technology and Research (A*STAR)（量子创新中心（Q. InC），新加坡科技研究局（A*STAR））
We investigate theoretically magnon-mediated superconductivity in a heterostructure consisting of a normal metal and a two-sublattice antiferromagnetic insulator. The attractive electron-electron pairing interaction is caused by an interfacial exchange coupling with magnons residing in the antiferromagnet, resulting in p-wave, spin-triplet superconductivity in the normal metal. Our main finding is that one may significantly enhance the superconducting critical temperature by coupling the normal metal to only one of the two antiferromagnetic sublattices employing, for example, an uncompensated …
Defect-Mediated Phase Engineering of 2D Ag at the Graphene/SiC Interface
The Pennsylvania State University（宾夕法尼亚州立大学）；Max-Planck-Institut für Festkörperforschung（马克斯·普朗克固体研究所）；National University of Singapore（新加坡国立大学）；University of Münster（明斯特大学）；Paul-Drude-Institut für Festkörperelektronik（保罗·德鲁德固体电子学研究所）；University of Pittsburgh（匹兹堡大学）；Juniata College（朱尼阿塔学院）
Two-dimensional (2D) crystals have emerged as a class of materials with tuneable carrier density. Carrier doping to 2D semiconductors can be used to modulate manybody interactions and to explore novel composite particles. Holstein polaron is a small composite particle of an electron carrying a cloud of self-induced lattice deformation (or phonons), which has been proposed to play a key role in high-temperature superconductivity and carrier mobility in devices. Here, we report the discovery of Holstein polarons in a surface-doped layered semiconductor, MoS2, where a puzzling 2D superconducting …
Omni-directional light coupling to surface plasmon polariton (SPP) modes to make use of plasmon mediated near-field enhancement is challenging. We report possibility of near dispersion-less modes in structures with unpatterned metal-dielectric interfaces having 2-D dielectric patterns on top. We show that the position and dispersion of the excited modes can be controlled by the excitation geometry and the 2-D pattern. The anti-crossings resulting from the in-plane coupling of different SPP modes are also shown.
