Detection of inverse Rashba-Edelstein effect at Cu/Bi interface using lateral spin valves Miren Isasa 1 , M. Carmen Martínez-Velarte 2,3 , Estitxu Villamor 1 , Luis Morellón 2,3 , José M. De Teresa 2,3,4 , Manuel R. Ibarra 2,3 , Luis E. Hueso 1,5 , Fèlix Casanova 1,5,* 1 CIC nanoGUNE, 20018 Donostia-San Sebastian, Basque Country, Spain. 2 Laboratorio de Microscopía Avanzada (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, Edificio I+D, 50018 Zaragoza, Spain. 3 Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza, Spain. 4 Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de Zaragoza-CSIC, Facultad de Ciencias, 50009 Zaragoza, Spain. 5 IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Basque Country, Spain. *E-mail: f.casanova@nanogune.eu The spin transport properties of bismuth (Bi) have been investigated using permalloy/bismuth/copper (Py/Bi/Cu) lateral spin valve structures. From spin absorption experiments, we show that the metallic surface of Bi acts as a strong spin sink. Moreover, we have measured a spin-to- charge current conversion that is attributed to the inverse Rashba- Edelstein effect (IREE) occurring at the Bi/Cu interface. By analyzing this spin-to-charge conversion as a function of temperature, the measurements exhibit a clear sign change at ∼125 K, corresponding to a change on the type of carriers dominating the electronic transport. These results evidence that the IREE arises from the spin splitting of the bulk states due to the Rashba effect at the metallic-Bi interface. Spin-orbit interaction is an essential ingredient in materials and interfaces that has been gaining interest in the last years due to the advantages it offers to exploit the coupling between spin and orbital momentum of electrons in spintronic devices [1], leading to the emerging field of spin-orbitronics. For instance, magnetization switching of ferromagnetic elements has been recently achieved with torques arising from mechanisms such as spin Hall, Rashba or Dresselhaus effects [2,3]. Of particular interest is the spin Hall effect (SHE), which can be used to create and detect a pure spin current without the use of ferromagnets or magnetic fields. This is a phenomenon appearing in materials with strong spin-orbit coupling (SOC) in which a charge current flowing through a non-magnetic material creates a spin current in the transverse direction to the charge current [4,5]. Reciprocally, a spin current through a non- magnetic material creates a transverse charge current, i.e., the inverse SHE (ISHE) [6,7]. Very recently, a new way of converting spin into charge current has been experimentally reported: the Inverse Rashba-Edelstein effect (IREE) [8]. This phenomenon arises from the SOC in a two-dimensional electron gas (2DEG), i.e. Rashba coupling, that appears at interfaces or surface states (SSs), leading to the conversion of a 3D spin current into a 2D charge current [9]. An interesting system to study the SOC is thus the SS of a semimetal. Bismuth (Bi) in particular is a group V semimetal with an anisotropic Fermi surface, where small electron and hole pockets give rise to a low carrier density, n~p~3·10 17 cm −3 , high resistivity (~100 µΩ·cm) and relatively large Fermi wavelength (~30 nm) [10]. For thin films, the energy band structure changes. When film dimensions are