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: Why Sn substitution should be preferred to Pb vacancy for optimum solar cell efficiency
摘要： Methylammonium lead halide (MAPbI3) perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-(cid:2)) are addressed in regulating stability and solar cell ef?ciency of MAPb1?X ?Y SnX (cid:2)Y I3 perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron’s self-interaction error are examined carefully. We ?nd to reduce the Pb content from pristine MAPbI3, Sn substitution has a more favorable thermodynamic stability than creating Pb-(cid:2). Moreover, on substituting Sn, due to strong s-p and p-p couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the band gap (direct). This further helps us to get a high optical absorption coef?cient (redshifted) and maximum solar cell ef?ciency in MAPb1?X SnX I3 for 0 < X (cid:2) 0.5.
关键词： spin-orbit coupling,MAPbI3,solar cell efficiency,Pb vacancy,thermodynamic stability,Sn substitution,Methylammonium lead halide,hybrid density functional theory,optical absorption coefficient
更新于2025-09-19 17:13:59
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Perdeuteration of poly[2-methoxy-5-(2a?2-ethylhexyloxy)-1,4-phenylenevinylene] (d-MEH-PPV): control of microscopic charge-carrier spina??spin coupling and of magnetic-field effects in optoelectronic devices
摘要： Control of the effective local hyperfine fields in a conjugated polymer, poly[2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), by isotopic engineering is reported. These fields, evident as a frequency-independent line broadening mechanism in electrically detected magnetic resonance (EDMR) spectroscopy, originate from the unresolved hyperfine coupling between the electronic spin of charge carrier pairs and the nuclear spins of surrounding hydrogen isotopes. The room temperature study of effects caused by complete deuteration of this polymer through magnetoresistance, magnetoelectroluminescence, coherent pulsed and multi-frequency EDMR, as well as inverse spin-Hall effect measurements, confirm the weak hyperfine broadening of charge-carrier magnetic resonance lines. As a consequence, we can resolve coherent charge-carrier spin-beating, allowing for direct measurements of the magnitude of electronic spin–spin interactions. In addition, the weak hyperfine coupling allows us to resolve substantial spin–orbit coupling effects in the EDMR spectra, even at low magnetic field strengths. These results illustrate the dramatic influence of hyperfine fields on the spin physics of organic light-emitting diode (OLED) materials at room temperature, and point to routes to reaching exotic ultra-strong resonant-drive regimes in the study of light-matter interactions.
关键词： spin–spin interactions,OLED materials,hyperfine fields,isotopic engineering,EDMR spectroscopy,spin–orbit coupling
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Direct Observation of Topological Edge States in Silicon Photonic Crystals
摘要： The concept of topology has proven immensely powerful in physics, describing new phases of matter with unique properties. There has been a recent surge in attempts to implement topological protection in the photonic domain, owing to the application potential of robust transport immune to scattering at disorder. A famous class of electronic topological insulators relies on the quantum spin-Hall effect (QSHE). Photonic analogues of QSHE were recently predicted to occur in photonic crystals with special symmetries [1, 2]. Interestingly, topological photonic crystals employing QSHE offer the possibility to access their properties via far-field radiation [3]. Here we directly observe topological photonic states at telecom wavelengths in photonic crystals in silicon-on-insulator (SOI) technology, and characterize their inherent spin, dispersion, and propagation. We reveal that the radiation of the topological states carries a signature of their origin in photonic spin-orbit coupling, linking unidirectional propagation to circular polarization (see Fig. 1a). The employed photonic crystals (inset of Fig. 1a) employ higher-order symmetry breaking to open bandgaps of different topological order at the Γ point [1, 2]. The edge between two domains supports topological states of differing pseudospin. We analyze these states by dispersing normal-incidence reflected intensity in both frequency and angle, mapping the edge state dispersion (in Fig. 1b). It displays the characteristic linear dispersion of edge states, with measured group velocity ～ c/6 and quality factor ～ 450. The positive and negative group velocity modes can be selectively excited with opposite circular polarization. Conversely, the states’ pseudospin can be probed directly in the far field through the S3 Stokes parameter obtained from polarimetry (Fig. 1c). Our Fourier spectroscopic measurements moreover reveal a small gap at the edge state crossing that is related to spin-spin scattering. This coupling is inherent to the symmetry breaking at the edge, and a defining difference between photonic and electronic topological insulators. Through the far-field spin-orbit link, we selectively excite edge states in opposite directions, and image their propagation in real-space microscopy. Figure 1d shows the routing of the edge state at a sharp waveguide junction. Interestingly, we observe an absence of backscattering or forward scattering, demonstrating the topological protection of unidirectional propagation. In fact, the states closely follow the photonic crystal edge — defined by the junction’s chiral structure of sub-unit cell size — even though their transverse extent is significantly larger. In conclusion, we observe the unique nature of topologically protected light transport in photonic crystals, through a technique that holds great promise for developing novel topological systems for various applications, including integrated photonic components, quantum optical interfaces, enantiomeric sensing, and nanoscale lasing.
关键词： photonic spin-orbit coupling,topological photonic states,unidirectional propagation,silicon-on-insulator,circular polarization
更新于2025-09-16 10:30:52
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Phase separation of vector solitons in spin-orbit-coupled spin-1 condensates
摘要： We study the phase separation in three-component bright vector solitons in a quasi-one-dimensional spin-orbit-coupled hyperfine spin F = 1 ferromagnetic Bose-Einstein condensate upon an increase of the strength of spin-orbit (SO) coupling px(cid:2)z above a critical value, where px is the linear momentum and (cid:2)z is the z component of the spin-1 matrix. The bright vector solitons are demonstrated to be mobile and dynamically stable. The collision between two such vector solitons is found to be elastic at all velocities with the conservation of density of each vector soliton. The two colliding vector solitons repel at small separation and at very small colliding velocity, they come close and bounce back with the same velocity without ever encountering each other. This repulsion produced by SO coupling is responsible for the phase separation in a vector soliton for large strengths of SO coupling. The collision dynamics is found to be completely insensitive to the relative phase of the colliding solitons. However, in the absence of SO coupling, at very small velocity, the two colliding vector solitons attract each other and form a vector soliton molecule and the collision dynamics is sensitive to the relative phase as in scalar solitons. The present investigation is carried out through a numerical solution and an analytic variational approximation of the underlying mean-field Gross-Pitaevskii equation.
关键词： Bose-Einstein condensate,spin-orbit coupling,collision dynamics,vector solitons,phase separation
更新于2025-09-16 10:30:52
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A Theoretical Study on Laser Cooling Feasibility of Group IVA Hydrides XH (X = Si, Ge, Sn, and Pb): The Role of Electronic State Crossing
摘要： The feasibility of direct laser cooling of SiH, GeH, SnH, and PbH is investigated and assessed based upon ?rst principles. The internally contracted multi-reference con?guration interaction method with the Davidson correction is applied. Very good agreement is obtained between our computed spectroscopic constants and the available experimental data. We ?nd that the locations of crossing point between the B26? and A21 states have the tendency of moving downwards from CH to SnH relative to the bottom of the corresponding A21 potential, which precludes the laser cooling of GeH, SnH, and PbH. By including the spin-orbit coupling effects and on the basis of the A215/2 →X253/2 transition, we propose a feasible laser cooling scheme for SiH using three lasers with wavelengths varying from 400 to 500 nm, which features a very large vibrational branching ratio (0.9954) and a very short radiative lifetime (575 ns). Moreover, similar studies are extended to carbon monosul?de (CS) with a feasible laser cooling scheme proposed. The importance of electronic state crossing in molecular laser cooling is underscored, and our work suggests useful caveats to the choice of promising candidates for producing ultracold molecules.
关键词： spin-orbit coupling,group IVA hydrides,electronic state crossing,ab initio,laser cooling
更新于2025-09-16 10:30:52
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The triplet mechanism of electron spin polarization in moderately coupled triplet-doublet rigid complexes as a source of the enhanced +1/2 ???1/2 transitions
摘要： The light-induced electron spin polarization generated in the excited quartet and doublet states of a system consisting of a chromophore with an attached radical is investigated theoretically. Excitation of the chromophore and subsequent relaxation leads to a coupled triplet-doublet spin system. In many such systems, the electronic coupling between the triplet and doublet spins is expected to be strong enough to split the spin system into so-called trip-doublet and trip-quartet states but sufficiently weak that it does not promote significant mixing between the sing-doublet and trip-doublet states. In such moderately coupled systems, the sing-doublet can relax to the trip-doublet and trip-quartet states by spin-orbit coupling mediated intersystem crossing within the chromophore. An analytical expression is derived for the intensity of the polarization generated by this mechanism for the ms = +1/2 ? ?1/2 electron paramagnetic resonance transitions of the trip-doublet and trip-quartet states. The expression shows that the intensity and sign of the polarization depend strongly on ratio jω = 3J/ω0 between the triplet-doublet exchange interaction J and the Zeeman energy ω0. The polarization becomes undefined when jω = 1 and when jω = 2 because level-anticrossings between the trip-doublet and trip-quartet sublevels occur. The sign of the polarization is also found to change above and below these values. Thus, for such moderately coupled systems, the sign of the polarization and its Zeeman energy dependence can be used to estimate the magnitude of the exchange coupling.
关键词： electron spin polarization,spin-orbit coupling,Zeeman energy,exchange interaction,triplet-doublet complexes
更新于2025-09-12 10:27:22
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Roles of spin-orbit coupling in tetragonal hybrid halide perovskite for photovoltaics light-absorber
摘要： Hybrid halide perovskite has been gain appropriate attraction because of their relatively high efficiency in most recently solid-state solar cell development. In this work, A first-principle calculation based on non-local van der Waals-corrected Density Functional Theory (vdW-DFT) is performed to investigate high accuracy atomic structures of a tetragonal structure methyl ammonium (CH3NH3) metal (Pb, Sn) halide (Br3, Cl3, I3). The calculated electronic structures were systematically studied using semi-local exchange-correlation functional (GGA-PBE), non-local functional (hybrid HSE06) and post-DFT approximation (GW). A relativistic effect in metal ion was taken into account by incorporating spin-orbit coupling (SOC) effect to obtain more accurate band gap properties of these materials. Our results shown that SOC corrected the electronic structures about 0.92 eV and 0.19 eV in case of lead ion and tin ion, respectively. The combination between GW approximation and spin-orbit coupling show a good agreement between DFT calculations and experimental studies. This computational scheme is necessary for high accuracy organic-inorganic solar cell design.
关键词： Spin-Orbit Coupling,Hybrid perovskite solar cell,Methyl ammonium metal halide,First-principle calculation
更新于2025-09-12 10:27:22
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Spin-orbit-coupled quantum memory of a double quantum dot
摘要： The concept of quantum memory plays an incisive role in the quantum information theory. As confirmed by the several recent rigorous mathematical studies, the quantum memory inmate in the bipartite system ρAB can reduce the uncertainty about part B, after measurements done on part A. In the present work, we extend this concept to systems with a spin-orbit coupling and introduce the notion of spin-orbit quantum memory. We self-consistently explore the Uhlmann fidelity, the pre- and the post-measurement entanglement entropy, and the post-measurement conditional quantum entropy of the system with spin-orbit coupling and show that measurement performed on the spin subsystem decreases the uncertainty of the orbital part. The uncovered effect enhances with the strength of the spin-orbit coupling. We study the concept of macroscopic realism introduced by Leggett and Garg [Phys. Rev. Lett. 54, 857 (1985)] and observe that POVM measurements done on the system under the particular protocol are noninvasive. For the extended system, we perform quantum Monte Carlo calculations and consider the reshuffling of the electron densities due to an external electric field.
关键词： quantum Monte Carlo,spin-orbit coupling,entanglement entropy,POVM measurements,conditional quantum entropy,quantum memory,Uhlmann fidelity
更新于2025-09-12 10:27:22
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Magnetic phase transitions of insulating spin-orbit coupled Bose atoms in one-dimensional optical lattices
摘要： We consider the insulating spin-orbit coupled Bose atoms con?ned within one-dimensional optical lattices and explore their ground-state magnetic phase transitions. Under strong interactions, the charge degrees of atoms are frozen and the system can be described by an anisotropic XXZ Heisenberg chain with Dzyaloshinskii-Moriya interaction and transverse ?eld. We apply the matrix product state method to obtain the ground states, and analyze spiral correlation functions, spin-spin correlation functions, and ?rst energy gap. Under weakly transverse ?elds, the ground state is a ferromagnetic phase if the interspin s-wave interaction strength is stronger than that of the intraspin ones, otherwise, it is a paramagnetic phase, an antiferromagnetic phase, or a gapless spiral phase with algebraic decaying spin correlations. When the transverse ?eld is strengthened, the gapless spiral phase is broken and a new spiral phase with long-range spin-spin correlations emerges.
关键词： optical lattices,XXZ Heisenberg chain,Bose atoms,magnetic phase transitions,Dzyaloshinskii-Moriya interaction,spin-orbit coupling,matrix product state method,transverse ?eld
更新于2025-09-12 10:27:22
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Vectorial nonlinear optics: Type-II second-harmonic generation driven by spin-orbit-coupled fields
摘要： Vectorial nonlinear optics refers to the investigation of optical processes whose nonlinear polarization (NP) undergoes spin-orbit-coupling (SOC) interactions where, in general, the driving light field or the new field generated by the interaction contains the SOC property. To contribute to fundamental knowledge in this domain, we examine the type-II second-harmonic generation (SHG) induced by vectorial laser modes. First, we provide a general theory to analyze the vectorial SHG process. Second, by using two typical vector modes as examples, we show how the SOC of the pump field dictates nonlinear interaction. Finally, we corroborate our theoretical predictions through experiments to confirm the crucial role of the SOC in nonlinear interactions. These results enhance our fundamental understanding of SOC-mediated nonlinear optics and lay the foundation for further fundamental studies as well as possible applications.
关键词： spin-orbit-coupling,Vectorial nonlinear optics,vector modes,type-II second-harmonic generation,nonlinear polarization
更新于2025-09-11 14:15:04