Intrinsic Coupling Research Articles

Ising superconductivity induced from spin-selective valley symmetry breaking in twisted trilayer graphene

We show that the e-e interaction induces a strong breakdown of valley symmetry for each spin channel in twisted trilayer graphene, leading to a ground state where the two spin projections have opposite sign of the valley symmetry breaking order parameter. This leads to a spin-valley locking in which the electrons of a Cooper pair are forced to live on different Fermi lines attached to opposite valleys. Furthermore, we find an effective intrinsic spin-orbit coupling explaining the protection of the superconductivity against in-plane magnetic fields. The effect of spin-selective valley symmetry breaking is validated as it reproduces the experimental observation of the reset of the Hall density at 2-hole doping. It also implies a breakdown of the symmetry of the bands from C6 to C3, with an enhancement of the anisotropy of the Fermi lines which is at the origin of a Kohn-Luttinger (pairing) instability. The isotropy of the bands is gradually recovered, however, when the Fermi level approaches the bottom of the second valence band, explaining why the superconductivity fades away in the doping range beyond 3 holes per moiré unit cell in twisted trilayer graphene.

Optical manipulation and conversion in whispering gallery mode resonators with pump depletion

In this work, we study optical manipulation and conversion in the high-power regime, and thus the unavoidable intrinsic coupling between the pump light and the signal light, i.e. pump depletion, needs to be included. Compared with the transmission properties that are insensitive to the power of the signal light in the low-power regime with pump non-depletion, our results in the high-power regime with pump depletion show that the resonant transmission coefficients of the nonlinearity can be manipulated from 0 to non-zero by adjusting the intensities of the signal light, and thus it behaves as an intensity-dependent all-optical switch. Although the resonant conversion efficiencies from four-wave mixing of the nonlinearity are generally suppressed by power-dependent frequency shifts as a result of self-phase modulation (SPM) and cross-phase modulation (XPM) in the high-pump regime, the conversion efficiencies can be amplified by tuning the frequency detuning of the signal and pump lights. The optical transmission coefficients and conversion efficiencies can also be enhanced by utilizing the interplay between and nonlinearities in the high-pump regime. The mechanism of enhancing the conversion efficiencies to overcome the suppression from SPM and XPM provides a new way to convert frequency with high efficiencies.

Antenna-coupled infrared nanospectroscopy of intramolecular vibrational interaction

Many photonic and electronic molecular properties, as well as chemical and biochemical reactivities are controlled by fast intramolecular vibrational energy redistribution (IVR). This fundamental ultrafast process limits coherence time in applications from photochemistry to single quantum level control. While time-resolved multidimensional IR-spectroscopy can resolve the underlying vibrational interaction dynamics, as a nonlinear optical technique it has been challenging to extend its sensitivity to probe small molecular ensembles, achieve nanoscale spatial resolution, and control intramolecular dynamics. Here, we demonstrate a concept how mode-selective coupling of vibrational resonances to IR nanoantennas can reveal intramolecular vibrational energy transfer. In time-resolved infrared vibrational nanospectroscopy, we measure the Purcell-enhanced decrease of vibrational lifetimes of molecular vibrations while tuning the IR nanoantenna across coupled vibrations. At the example of a Re-carbonyl complex monolayer, we derive an IVR rate of (25±8) cm-1 corresponding to (450±150) fs, as is typical for the fast initial equilibration between symmetric and antisymmetric carbonyl vibrations. We model the enhancement of the cross-vibrational relaxation based on intrinsic intramolecular coupling and extrinsic antenna-enhanced vibrational energy relaxation. The model further suggests an anti-Purcell effect based on antenna and laser-field-driven vibrational mode interference which can counteract IVR-induced relaxation. Nanooptical spectroscopy of antenna-coupled vibrational dynamics thus provides for an approach to probe intramolecular vibrational dynamics with a perspective for vibrational coherent control of small molecular ensembles.

Bloch theorem dictated wave chaos in microcavity crystals

Universality class of wave chaos emerges in many areas of science, such as molecular dynamics, optics, and network theory. In this work, we generalize the wave chaos theory to cavity lattice systems by discovering the intrinsic coupling of the crystal momentum to the internal cavity dynamics. The cavity-momentum locking substitutes the role of the deformed boundary shape in the ordinary single microcavity problem, providing a new platform for the in situ study of microcavity light dynamics. The transmutation of wave chaos in periodic lattices leads to a phase space reconfiguration that induces a dynamical localization transition. The degenerate scar-mode spinors hybridize and non-trivially localize around regular islands in phase space. In addition, we find that the momentum coupling becomes maximal at the Brillouin zone boundary, so the intercavity chaotic modes coupling and wave confinement are significantly altered. Our work pioneers the study of intertwining wave chaos in periodic systems and provide useful applications in light dynamics control.

Single Photon Emitters with Polarization and Orbital Angular Momentum Locking in Monolayer Semiconductors.

Excitons in monolayer transition metal dichalcogenide are endowed with intrinsic valley-orbit coupling between their center-of-mass motion and valley pseudospin. When trapped in a confinement potential, e.g., generated by strain field, we find that intralayer excitons are valley and orbital angular momentum (OAM) entangled. By tuning the trap profile and external magnetic field, one can engineer the exciton states at the ground state and realize a series of valley-OAM entangled states. We further show that the OAM of excitons can be transferred to emitted photons, and these novel exciton states can naturally serve as polarization-OAM locked single photon emitters, which under certain circumstance become polarization-OAM entangled, highly tunable by strain trap and magnetic field. Our proposal demonstrates a novel scheme to generate polarization-OAM locked/entangled photons at the nanoscale with a high degree of integrability and tunability, pointing to exciting opportunities for quantum information applications.

Ferromagnetism by p−d exchange spin-orbit coupling in n -type ferromagnetic semiconductors

The exchange interaction between carrier and localized spin in magnets generates intrinsic spin-orbit coupling induced by the magnetism. Recent studies for the exchange spin-orbit coupling (ESOC) in ferromagnets and antiferromagnets suggest the ESOC and the transport phenomena for spintronics. However, the study on the effects of ESOC on the magnetic phase transition has been still lacking especially for ferromagnets even though the ESOC should be one of the fundamental interactions to stabilize the magnetic phase. In this paper, we study the role of the ferromagnetic properties of the ESOC induced by the $p\text{\ensuremath{-}}d$ exchange interaction of the valence band in $n$-type ferromagnetic semiconductors. Based on the mean-field and $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ methods, our theory explains the spin polarization of localized and carrier spin, and the Curie temperature ${T}_{c}$ for the iron concentration, electron density, and host semiconductor dependence. The theoretical ${T}_{c}$ fits experimental values well in low iron concentration and intermediate electron density regions, and the $p\text{\ensuremath{-}}d$ exchange interaction is essential for ${T}_{c}$. Furthermore, the ${T}_{c}$ is higher for narrower gap host semiconductors to provide insights into higher ${T}_{c}$. The theoretical framework of this paper is not limited to the specific materials and will find potential materials for spintronics and the fundamental aspects.

Topological superconductivity driven by correlations and linear defects in multiband superconductors

There have been several proposals for platforms sustaining topological superconductivity in high temperature superconductors, in order to make use of the larger superconducting gap and the expected robustness of Majorana zero modes towards perturbations. In particular, the iron-based materials offer relatively large $T_c$ and nodeless energy gaps. In addition, atomically flat surfaces enable the engineering of defect structures and the subsequent measurement of spectroscopic properties to reveal topological aspects. From a theory perspective, a materials-specific description is challenging due to the correlated nature of the materials and complications arising from the multiband nature of the electronic structure. Here we include both aspects in realistic interacting models, and find that the correlations themselves can lead to local magnetic order close to linear potential scattering defects at the surface of the superconductor. Using a self-consistent Bogoliubov-de Gennes framework in a real-space setup using a prototype electronic structure, we allow for arbitrary magnetic orders and show how a topological superconducting state emerges. The calculation of the topological invariant and the topological gap allows us to map out the phase diagram for the case of a linear chain of potential scatterers. While intrinsic spin-orbit coupling is not needed to enter the topological state in presence of spin-spiral states, it enlarges the topological phase. We discuss the interplay of a triplet component of the superconducting order parameter and the spin spiral leading effectively to extended spin orbit coupling terms, and connect our results to experimental efforts on the Fe(Se,Te) system.

Hybrid magnonics in hybrid perovskite antiferromagnets

Hybrid magnonic systems are a newcomer for pursuing coherent information processing owing to their rich quantum engineering functionalities. One prototypical example is hybrid magnonics in antiferromagnets with an easy-plane anisotropy that resembles a quantum-mechanically mixed two-level spin system through the coupling of acoustic and optical magnons. Generally, the coupling between these orthogonal modes is forbidden due to their opposite parity. Here we show that the Dzyaloshinskii–Moriya-Interaction (DMI), a chiral antisymmetric interaction that occurs in magnetic systems with low symmetry, can lift this restriction. We report that layered hybrid perovskite antiferromagnets with an interlayer DMI can lead to a strong intrinsic magnon-magnon coupling strength up to 0.24 GHz, which is four times greater than the dissipation rates of the acoustic/optical modes. Our work shows that the DMI in these hybrid antiferromagnets holds promise for leveraging magnon-magnon coupling by harnessing symmetry breaking in a highly tunable, solution-processable layered magnetic platform.

Current-induced spin polarization in Janus WSSe monolayer

Janus engineering of transition metal dichalcogenide monolayers breaks the vertical mirror symmetry and induces huge built-in polarization and large Rashba spin-orbit coupling. By performing first-principles calculations, we find that the Rashba spin-orbit coupling induces sizable current-induced spin polarization in both the conduction and valence bands in the Janus WSSe monolayer, which is comparable to that in perovskite oxide interfaces. By constructing the low-energy $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ Hamiltonian from the invariant theory, we find a sign change of the current-spin conductivity at chemical potential $\ensuremath{\mu}\ensuremath{\approx}\ensuremath{-}0.73$ eV, which indicates the flip of spin polarization and is attributed to the competition between the intrinsic Rashba spin-orbit coupling and the hexagonal warping of the valence bands. Our numerical and analytic results suggest that the current-induced spin polarization in the Janus WSSe monolayer is insensitive to temperature and impurity concentration but can be effectively tuned by external biaxial or uniaxial strain. The Janus WSSe monolayer could be a promising candidate to realize flexible two-dimensional spintronics devices.

Symmetry-engineered nodal lines and hourglass fermions in patterned two-dimensional electron gas

In most cases, the formation of topological quantum states requires intrinsic crystalline symmetry to protect either discrete or continuous degeneracies in real materials, which greatly hinders their realization in practice. Patterned two-dimensional electron gas (2DEG), on the other hand, has become a very effective external means to manipulate the symmetry to whatever we want. Here, taking nonsymmorphic symmetries as the focus of attention, based on patterned 2DEG decoration, we reveal rich band-crossing features in two-dimensional systems. It is demonstrated that in the presence of intrinsic spin-orbital coupling (SOC), wallpaper groups $p2mg,p2gg$, and $p4mg$ possess fourfold-degenerate Dirac nodal lines, and if Rashba SOC is further considered, the fourfold-degenerate nodal lines disappear and hourglass Weyl fermions then emerge. Our results not only afford an attractive route for designing robust nodal-line and hourglass Weyl semimetals in reality, but also pave the way for designing ideal macroscale materials through rational extrinsic symmetry engineering.

Observation of Perfectly-Chiral Exceptional Point via Bound State in the Continuum.

Chirality is one of the fundamentals of nature with strong ties to asymmetry. In wave physics, it is conventionally characterized by asymmetric scattering of circularly polarized waves but suffers from two-state polarization. To overcome the limitation, here we demonstrate the concept of extreme chirality regarding orbital angular momentum (OAM) helicity, originating from a chiral quasibound state in the continuum held by a mirror-symmetry-broken metasurface. Empowered by the intrinsic OAM-selective coupling nature of the metasurface, the system arrives at a peculiar state where the left-handed incident vortex is completely absorbed while the right-handed counterpart is totally reflected, namely, a perfectly-chiral exceptional point. The realization of asymmetric OAM modulation creates the possibility to explore chirality with unlimited states. Our work raises a new paradigm for the study of extreme OAM chirality and enriches the physics of chiral wave-matter interaction.

Muscarinic cholinergic modulation of cardiovascular variables in spinal cord injured rats

Spinal cord injury (SCI) leads not only to major impairments in sensorimotor control but also to dramatic dysregulation of autonomic functions including major cardiovascular disturbances. Consequently, individuals with SCI endure daily episodic hypo/hypertension and are at increased risk for cardiovascular disease. Several studies have suggested that an intrinsic spinal coupling mechanism between motor and sympathetic neuronal networks exist and that propriospinal cholinergic neurons may be responsible for a synchronized activation of both somatic and sympathetic outputs. We therefore investigated in the present study, the effect of cholinergic muscarinic agonists on cardiovascular parameters in freely moving adult rats after SCI. Female Sprague-Dawley rats were implanted with radiotelemetry sensors for long-term in vivo monitoring of blood pressure (BP). From BP signal, we calculated heart rate (HR) and respiratory frequency. We first characterized the physiological changes occurring after a SCI performed at the T3-T4 level in our experimental model system. We then investigated the effects on BP, HR and respiration, of the muscarinic agonist oxotremorine using one variant that crossed the blood brain barrier (Oxo-S) and one that does not (Oxo-M) in both Pre- and Post-SCI animals. After SCI, both HR and respiratory frequency increased. BP values exhibited an immediate profound drop before progressively increasing over the three-week post-lesion period but remained below control values. A spectral analysis of BP signal revealed the disappearance of the low frequency component of BP (0.3-0.6Hz) referred to as Mayer waves after SCI. In Post-SCI animals, central effects mediated by Oxo-S led to an increase in HR and MAP, a slowdown in respiratory frequency and to an increased power in the 0.3-0.6Hz frequency band. This study unravels some of the mechanisms by which muscarinic activation of spinal neurons could contribute to partial restoration of BP after SCI.

Port-Hamiltonian Formulations of Some Elastodynamics Theories of Isotropic and Linearly Elastic Shells: Naghdi–Reissner’s Moderately Thick Shells

The port-Hamiltonian system approach is intended to be an innovative and unifying way of modeling multiphysics systems, by expressing all of them as systems of conservation laws. Indeed, the increasing developments in recent years allow finding better control and coupling strategies. This work aimed to apply such an approach to Naghdi–Reissner’s five-kinematic-field shell model in linear elasticity, while including often-neglected higher-order intrinsic geometric coupling effects, therefore preparing the theoretical background required for the coupling (or interconnection) with an acoustic fluid model and the different types of interactions that can arise among them. The model derived thusly can be used for controller design in a wide variety of applications such as inflatable space structures, launcher tank vibration damping, payload vibration protection using smart materials, and many other related applications.

Universal intrinsic higher-rank spin tensor Hall effect

The spin Hall effect with nonzero transverse spin current but vanishing charge current has important applications in spintronics. Owing to the half-spin nature of electrons, the spin transport has hitherto been restricted to the rank-1 spin vector, whereas higher-rank spin tensors exist and play important roles in larger-spin ($\ensuremath{\ge}1$) systems. For instance, there are five linearly independent rank-2 spin quadrupole tensors, characterizing the spin nematics, in a spin-1 system. While these internal spin-tensor degrees of freedom substantially enrich the quantum phases and dynamics of large-spin ultracold gases, the quantum transport of spin tensors remains largely unexplored yet. Here we investigate the higher-rank spin tensor current and introduce the concept of the spin tensor Hall effect (STHE) in a large-spin system. We find that a net transverse spin tensor current can be driven by an external field in the longitudinal direction, while no lower-rank spin or charge current exists. Significantly, we identify a universal rank-2 spin tensor Hall conductivity $q/8\ensuremath{\pi}$ (with the carrier charge $q$) in a spin-1 model with intrinsic spin-orbit coupling, which is independent of the detailed model parameters. The STHE requires the violation of time-reversal symmetry (TRS) but can be protected by a unique pseudo-TRS associated with the rank-2 spin tensor. An experimental scheme is proposed to realize and detect the STHE with pseudospin-1 ultracold fermionic atoms and through the spin tensor accumulation. A general route towards the generalization of the STHE for larger spins is provided, using the SU(2) subalgebra and generalized Gell-Mann matrix representation of the $\mathrm{SU}(N$) group. Our work reveals an intrinsic spin tensor transport phenomenon and introduce a new member to the Hall effect families, which may pave the way to spin-tensor-tronics.

Spin-orbit enhancement in Si/SiGe heterostructures with oscillating Ge concentration

Electrons in Si/SiGe quantum dots are a promising platform for quantum computation. Many leading designs, however, rely on synthetic spin-orbit coupling arising from micromagnets, leading to challenges in scaling. Here, it is shown that the intrinsic spin-orbit coupling of the conduction-band valleys can be enhanced by over an order of magnitude by including Ge concentration oscillations of an appropriate wavelength within the quantum-well region. This enables fast spin manipulation using electric dipole spin resonance in the absence of micromagnets.

Magnetoelastic primary resonance of an axially moving ferromagnetic plate in an air gap field

The air gap field widely exists in mechatronic systems to realize energy transfer, but the components in such systems are often regarded as rigid bodies. In this paper, elastomers in an air gap field are discussed for the first time. The magnetoelastic primary resonance of an axially moving ferromagnetic plate in an air gap field is investigated. With the magnetic wall armature as the electromagnetic source, the ferromagnetic thin plate moves axially parallel to the armature. An air gap field excited by the armature is distributed in thin air gap space between them. In addition to eddy current effects, the ferromagnetic thin plate in the air gap field will be magnetized to generate a harmonic magnetic force to excite the plate vibration, which results in the system existing nonlinear coupling characteristics between armature, plate deformation and air gap field. Considering the dynamic feedback of thin plate vibration on the air gap field by changing the air gap thickness, the magnetoelastic vibration equation of the plate is derived by the Hamilton's principle. The vibration differential equation for the simply supported plate is obtained via Galerkin method, and the static deflection of the plate under static magnetic load is solved. The multi-scale and Lyapunov methods are utilized to analyze the primary resonance under harmonic magnetic force, thus obtaining the steady-state resonance equation and the stability discriminants of stationary solutions. Through numerical simulations, the curves and three-dimensional surfaces of amplitude varying with different parameters are plotted. The variation of magnetic field strength, magnetic force, and electromagnetic torques under steady-state response is obtained. The results show that amplitude decreases with the increase of initial air gap thickness but increases with the increase of magnetic potential amplitude on the armature. Velocity has a suppression effect on system resonance, and there is an intrinsic coupling mechanism of action and reaction between the thin plate and air gap field.

Magnetic order and magnetic anisotropy in two-dimensional ilmenenes.

Iron ilmenene is a new two-dimensional material that has recently been exfoliated from the naturally occurring iron titanate found in ilmenite ore, a material that is abundant on the earth's surface. In this work, we theoretically investigate the structural, electronic and magnetic properties of 2D transition-metal-based ilmenene-like titanates. The study of magnetic order reveals that these ilmenenes usually present intrinsic antiferromagnetic coupling between the 3d magnetic metals decorating both sides of the Ti-O layer. Furthermore, the ilmenenes based on late 3d brass metals, such as CuTiO3 and ZnTiO3, become ferromagnetic and spin compensated, respectively. Our calculations which include spin-orbit coupling reveal that the magnetic ilmenenes have large magnetocrystalline anisotropy energies when the 3d shell departs from being either filled or half-filled, with their spin orientation being out-of-plane for elements below half-filling of 3d states and in-plane above. These interesting magnetic properties of ilmenenes make them useful for future spintronic applications because they could be synthesized as already realized in the iron case.

Research on the Construction of New Rural Credit Evaluation Ind ex System under the Background of Rural Governance Modernization

Based on sorting out the high intrinsic value coupling between the modernization of rural governance and the development of rural credit system in China, following the development requirements of rural revitalization and the principles of credit evaluation index system construction. This paper develops a new type of rural credit evaluation evaluation system by Delphi method and Analytic hierarchy process, which contains 6 first-level indicators of economic dimension, political dimension, cultural dimension, social dimension, ecological dimension and incentive dimension, and 23 second-level indicators. The results were also analyzed.

Dynamic Reconfiguration of Dominant Intrinsic Coupling Modes in Elderly at Prodromal Alzheimer's Disease Risk.

Large-scale human brain networks interact across both spatial and temporal scales. Especially for electro- and magnetoencephalography (EEG/MEG), there are many evidences that there is a synergy of different subnetworks that oscillate on a dominant frequency within a quasi-stable brain temporal frame. Intrinsic cortical-level integration reflects the reorganization of functional brain networks that support a compensation mechanism for cognitive decline. Here, a computerized intervention integrating different functions of the medial temporal lobes, namely, object-level and scene-level representations, was conducted. One hundred fifty-eight patients with mild cognitive impairment underwent 90min of training per day over 10weeks. An active control (AC) group of 50 subjects was exposed to documentaries, and a passive control group of 55 subjects did not engage in any activity. Following a dynamic functional source connectivity analysis, the dynamic reconfiguration of intra- and cross-frequency coupling mechanisms before and after the intervention was revealed. After the neuropsychological and resting state electroencephalography evaluation, the ratio of inter versus intra-frequency coupling modes and also the contribution of β1 frequency was higher for the target group compared to its pre-intervention period. These frequency-dependent contributions were linked to neuropsychological estimates that were improved due to intervention. Additionally, the time-delays of the cortical interactions were improved in {δ, θ, α2, β1} compared to the pre-intervention period. Finally, dynamic networks of the target group further improved their efficiency over the total cost of the network. This is the first study that revealed a dynamic reconfiguration of intrinsic coupling modes and an improvement of time-delays due to a target intervention protocol.

Temperature-dependent zero-field splittings in graphene

The topological bandgap of graphene induced by intrinsic spin-orbit coupling is so narrow that it was experimentally identified for the first time only in 2019. In this work, the authors use a specific electron spin resonance technique, based on photoconductivity measurements using graphene-based terahertz detectors, to probe zero-field splittings of graphene as a function of temperature. They demonstrate experimentally that the intrinsic spin-orbit coupling and the staggered sublattice potential, which reduces the topological gap, are both temperature dependent.