This paper analyzes theoretically the signal propagation in spin transport by modulating the current passing through magnetic multilayers. Using a macroscopic description of spin transport based on the dynamical Boltzmann equation, we show that time-dependent spin transport possesses a wave-like character that leads to modifications of pure spin-diffusion dynamics. In particular, the wave-like characteristics allow one to extract a finite spin signal-propagation velocity.Comment: 10 pages, 10 figures, corrected typos (including numerical values

Optimizing active layer morphology and broadening spectrum utilization range are important methods to improve the performance of organic solar cells (OSCs). In this study, PM6/Y6:PC71BM pseudo-bilayer ternary organic solar cells...

Spin and charge-current dynamics after ultrafast spin-polarized excitation in a normal metal are studied theoretically using macroscopic wave-diffusion equations for spin resolved carrier and current densities. It is shown analytically how this set of equations yields a unified description of ballistic and diffusive properties of spin and charge transport, including the intermediate regime between these two limits. In the framework of the wave-diffusion approach, ultrafast excitation of spin polarized carriers in thin gold films is modeled assuming slightly spin-dependent momentum relaxation times along with standard parameters (Fermi velocity, spin and momentum relaxationtimes). The unified treatment of diffusive and ballistic transport yields robust signatures in the spin and charge dynamics that are in qualitative agreement with recent experimental results [Phys. Rev. Lett. 107, 076601 (2011)]. The influence of boundary effects on the temporal signatures of spin transport is also studied.

Considering the effects of the built-in electric field (BEF) induced by the spontaneous and piezoelectric polarizations of wurtzite GaN/AlN quantum wells (QW's), the polaron energy shift and the effective mass due to the electron interactions with the interface optical-phonons are investigated theoretically by means of Lee-Low-Pines variational approach. We find that the BEF has a remarkable influence on the polaron effects especially for a QW with well width d > 6 nm. The polaron energy shift increases slowly and its effective mass approaches to a constant if d is further increased. On the contrary, both the polaron energy shift and the effective mass decrease slowly with the increasing of d if the BEF is ignored.

Searching for energetic photovoltaic absorbers is a favorable solution to the current energy crisis. As a star material for solar cells, MAPbI3 (MA = CH3NH3) has a suitable band gap, strong optical absorption, great defect tolerance, and high certified power conversion efficiency (PCE) up to 25.2%. However, the lead toxicity and poor long-term stability limit its application in photovoltaic devices. To break through these bottlenecks, we design two-dimensional (2D) Dion–Jacobson (DJ)-type (n = 3) chalcogenide perovskites A′La2B3S10 (A′ = Ba, Sr, Ca; B = Hf, Zr), with optimal band gap, strong optical absorption, high carrier mobility, and excellent optoelectronic properties, based on the powerful first-principles and advanced HSE06 calculations. Especially, we find that, superior to MAPbI3, 2D A′La2B3S10 perovskites have the following several outstanding properties. (1) They are Pb-free and environmentally friendly. (2) The structural stability is better than that of MAPbI3. (3) The direct band gap (∼1.33 eV of BaLa2Hf3S10), i.e., the optimal value of the SQ limit, is more suitable than that of MAPbI3 (∼1.55 eV) with a 0.22 eV energy-loss spectrum. (4) The carrier mobility (1.8–2.6 × 103 cm2 V–1 s–1) is larger than that of MAPbI3 (∼37 cm2 V–1 s–1). (5) The optical absorption (∼6 × 105 cm–1) in the visible range is three times stronger than that of MAPbI3 (∼2 × 105 cm–1). (6) The estimated PCE (∼30.9% in BaLa2Hf3S10) is higher than that of MAPbI3 (∼30%). These amazing characteristics indicate that 2D A′La2B3S10 perovskites are promising absorbers for photovoltaics.