Photoinduced inverse spin Hall effect in Pt/Ge(001) at room temperature

We performed photoinduced inverse spin Hall effect (ISHE) measurements on a Pt/Ge(001) junction at room temperature. The spin-oriented electrons, photogenerated at the direct gap of Ge using circularly polarized light, provide a net spin current which yields an electromotive field E_ISHE in the Pt layer. Such a signal is clearly detected at room temperature despite the strong {\Gamma} to L scattering which electrons undergo in the Ge conduction band. The ISHE signal dependence on the exciting photon energy is in good agreement with the electron spin polarization expected for optical orientation at the direct gap of Ge

Optical Anisotropy of Porphyrin Nanocrystals Modified by the Electrochemical Dissolution

Reflectance anisotropy spectroscopy (RAS) coupled to an electrochemical cell represents a powerful tool to correlate changes in the surface optical anisotropy to changes in the electrochemical currents related to electrochemical reactions. The high sensitivity of RAS in the range of the absorption bands of organic systems, such as porphyrins, allows us to directly correlate the variations of the optical anisotropy signal to modifications in the solid-state aggregation of the porphyrin molecules. By combining in situ RAS to electrochemical techniques, we studied the case of vacuum-deposited porphyrin nanocrystals, which have been recently observed dissolving through electrochemical oxidation in diluted sulfuric acid. Specifically, we could identify the first stages of the morphological modifications of the nanocrystals, which we could attribute to the single-electron transfers involved in the oxidation reaction; in this sense, the simultaneous variation of the optical anisotropy with the electron transfer acts as a precursor of the dissolution process of porphyrin nanocrystals

Ordered assembling of Co tetra phenyl porphyrin on oxygen-passivated Fe(001): from single to multilayer films

Tetra-phenyl prophyrins (TPP) are an interesting class of organic molecules characterized by a ring structure with a metal ion in their centre. An ordered growth of such molecules can be obtained even on metallic substrates by means of a proper modification of the reactive interface, as we demonstrated for ZnTPP molecules coupled to oxygen-passivated Fe(001) [G. Bussetti et al. Appl. Surf. Sci. 390, 856 (2016)]. More recently, we focused on CoTPP molecules, characterized by a not nil magnetic moment and therefore of potential interest for magnetic applications. As in the ZnTPP case, our results for one monolayer coverage report the formation of an ordered assembly of flat-lying molecules. However, some differences between the two molecular species are observed in the packing scheme and in the degree of electronic interaction with the substrate. With the aim of reaching, also for CoTPP, a comprehensive view of molecular organization on Fe, we complement here our previous investigations by following the growth of the CoTPP film for increasing coverage, showing that an ordered stacking of such molecules is indeed realized at least up to four molecular layers

Paramagnon-Enhanced Spin Currents in a Lattice near the Curie Point

Spin transport phenomena have been shown to be highly enhanced when the temperature approaches the Curie point of the material sustaining a spin flow. Here we propose a simple - yet unifying - explanation for such enhancements, based on a random-phase model accounting for the spin fluctuations within a ferromagnetic material in the paramagnetic phase. We show that pure spin currents carried by conduction electrons injected into a paramagnetic lattice of mutually interacting localized magnetic moments can be enhanced close to the Curie temperature by the exchange interaction between the lattice sites and the non vanishing spin density associated with the spin current. The latter partially aligns the magnetic moments of the lattice, generating a flow of paramagnons that contribute to the total spin current, resulting in an enhancement that can be as large as tenfold

Pure spin currents in Ge probed by inverse spin-Hall effect

We perform photoinduced inverse spin-Hall effect (ISHE) measurements on a Pt/Ge(001) junction at room temperature. The spin-oriented electrons are photogenerated at the Γ point of the Ge Brillouin zone using circularly-polarized light. After the ultrafast Γ−L scattering in the Ge conduction band, which partially preserves the spin polarization, electrons diffuse into the Pt layer where spin-dependent scattering with Pt nuclei yields a transverse electromotive field EISHE. The ISHE signal dependence as a function of the incident photon energy is investigated and interpreted in the frame of a one-dimensional spin drift-diffusion model. This allows estimating the electron spin lifetime at the L-valleys to be τs=1 ns

Optical generation of pure spin currents at the indirect gap of bulk Si

We report on the optical generation of a pure spin current at the indirect gap of bulk Si at room temperature in the photon energy range comprised between 1.2 and 1.8 eV. Spin-polarized electrons are promoted to the Δ-valleys of the Si Brillouin zone by circularly polarized light. The photo-generated spin current is then detected by exploiting a Schottky Pt/Si(001) junction: spin-polarized electrons diffuse toward the Pt/Si interface and enter the Pt layer where the spin current is converted into a transverse electromotive field through the inverse spin-Hall effect (ISHE). The photon energy dependence of the ISHE signal is interpreted in the frame of a one-dimensional spin drift-diffusion model, which allows estimating the electron spin lifetime to be τs=15±5 ns