We have studied the circular photogalvanic effect (CPGE) in Cu/Bi bilayers. When a circularly polarized light in the visible range is irradiated to the bilayer from an oblique incidence, we find a photocurrent that depends on the helicity of light. Such photocurrent appears in a direction perpendicular to the light plane of incidence but is absent in the parallel configuration. The helicity dependent photocurrent is significantly reduced for a Bi single layer film and the effect is nearly absent for a Cu single layer film. Conventional interpretation of the CPGE suggests the existence of spin-momentum locked band(s) of a Rashba type in the Cu/Bi bilayer. In contrast to previous reports on the CPGE studied in other systems, however, the light energy used here to excite the carriers is much larger than the band gap of Bi. Moreover, the CPGE of the Cu/Bi bilayer is larger when the energy of the light is larger: the helicity dependent photocurrent excited with a blue light is nearly two times larger than that of a red light. We therefore consider the CPGE of the Cu/Bi bilayer may have a different origin compared to conventional systems.Spin-momentum locked bands are one of the key signatures of the emergence of topologically protected states in topological insulators and Weyl semimetals [1]. Such bands also appear in heterostructures with broken structure inversion symmetry and/or large spin orbit coupling (SOC) [2][3][4]. The spin texture of the spin-momentum locked bands in the reciprocal space depends on the symmetry of the system. For example, the electron's spin and momentum directions are orthogonal to each other for systems that can be described by a Rashba Hamiltonian [5,6].The presence of spin-momentum locked bands within the bulk or at surfaces/interfaces allows generation of non-equilibrium spin accumulation when current is passed to the system [7,8]. Significant effort has been placed to generate spin accumulation in semiconductor heterostructures [9,10]. Recent studies have extended such effort into metallic heterostructures [2,6,11,12], where the SOC can be larger than that of typical semiconductor heterostructure constituents. Current-induced spin accumulation at interfaces has been reported in metallic heterostructures which manifests itself in magnetization switching and domain wall motion [13,14]. It is thus of high importance to identify the presence of spinmomentum locked bands in thin film heterostructures.Angle resolved photoemission spectroscopy (ARPES) is a powerful tool to study band structures and has been used to reveal the surface electronic states of, for example, topological insulators and Weyl semimetals[1]. However, its use is typically limited to clean surfaces and involves difficulty in studying interface states of films which are not particularly clean (e.g. films deposited by sputtering). To study spin-momentum locking of such interface states, it has been shown recently that combination of spin pumping and the inverse Rashba-Edelstein effect (IREE) allows its direct probing [2][3]...

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We report on a spin-charge fluctuation in the all-in/all-out pyrochlore magnet Cd 2 Os 2 O 7 , where the spin fluctuation is driven by the conduction of thermally excited electrons/holes and associated fluctuation of Os valence. The fluctuation exhibits an activation energy significantly greater than the spin-charge excitation gap and a peculiar frequency range of 10 6-10 10 s −1. These features are attributed to the hopping motion of carriers as small polarons in the insulating phase, where the polaron state is presumably induced by the magnetoelastic coupling via the strong spin-orbit interaction. Such a coupled spin-charge-phonon fluctuation manifests as a part of the metal-insulator transition that is extended over a wide temperature range due to the modest electron correlation comparable with other interactions characteristic for 5d-subshell systems.

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We demonstrated that thin films of bismuth emit helicity-dependent terahertz-waves when illuminated with circularly polarized near-infrared femtosecond laser pulses from an oblique incidence. The helicity-dependent terahertz-wave appears only in the polarization perpendicular to the incident plane and is the most dominant contribution to terahertz emission in this polarization. By increasing the thickness of the film, the helicity-dependent terahertz-wave emission enhances significantly, taking a maximum at around 70-nm-thickness, which is well beyond the penetration depth of the near-infrared laser. From this thickness dependence, we identify the photoinduced inverse spin Hall effect as the most plausible mechanism behind the helicity-dependent terahertz emission. By lowering the temperature, we find a significant enhancement of the high-frequency component of the helicity-dependent terahertz-waves for the 30-nm-thick sample. The current dynamics are extracted from the terahertz-waves, and we find that the enhancement comes from the increasing photocurrent’s relaxation rate when the temperature is lowered. By considering two different spin relaxation mechanisms, namely the Elliott-Yafet mechanism and the D’yakonov-Perel’ mechanism, we attribute the sharp increase of the relaxation rate seen for the 30-nm-thick film to the D’yakonov-Perel’ mechanism. Our findings highlight the unique characteristics of bismuth as a beneficial platform for terahertz spintronics, and the potential of terahertz emission spectroscopy as a useful probe for ultrafast spin/charge dynamics.