Origin of inverse Rashba-Edelstein effect detected at the Cu/Bi interface using lateral spin valves

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Origin of inverse Rashba-Edelstein effect detected at the Cu/Bi interface using lateral spin valves

Miren Isasa, M. Carmen Martínez-Velarte, Estitxu Villamor, César Magén, Luis Morellón, José M. De Teresa, M. Ricardo Ibarra, Giovanni Vignale, Evgueni V. Chulkov, Eugene E. Krasovskii, Luis E. Hueso, and Fèlix Casanova

Phys. Rev. B 93, 014420 – Published 13 January 2016

Abstract

The spin transport and spin-to-charge current conversion properties of bismuth are investigated using permalloy/copper/bismuth (Py/Cu/Bi) lateral spin valve structures. The spin current is strongly absorbed at the surface of Bi, leading to ultrashort spin-diffusion lengths. A spin-to-charge current conversion is measured, which is attributed to the inverse Rashba-Edelstein effect at the Cu/Bi interface. The spin-current-induced charge current is found to change direction with increasing temperature. A theoretical analysis relates this behavior to the complex spin structure and dispersion of the surface states at the Fermi energy. The understanding of this phenomenon opens novel possibilities to exploit spin-orbit coupling to create, manipulate, and detect spin currents in two-dimensional systems.

Received 7 September 2015
Revised 19 November 2015

DOI:https://doi.org/10.1103/PhysRevB.93.014420

Physics Subject Headings (PhySH)

Spin current Spin-orbit coupling Spintronics

Multilayer thin films Spin valves Two-dimensional electron gas

First-principles calculations Transport techniques

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Miren Isasa¹, M. Carmen Martínez-Velarte^2,3, Estitxu Villamor¹, César Magén^2,3,4, Luis Morellón^2,3, José M. De Teresa^2,3,5, M. Ricardo Ibarra^2,3, Giovanni Vignale^6,7, Evgueni V. Chulkov^8,9,10, Eugene E. Krasovskii^8,9,11, Luis E. Hueso^1,11, and Fèlix Casanova^1,11,*

¹CIC nanoGUNE, 20018 Donostia-San Sebastian, Basque Country, Spain
²Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, Edificio I+D, 50018 Zaragoza, Spain
³Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain
⁴Fundación ARAID, 50004 Zaragoza, Spain
⁵Instituto de Ciencia de Materiales de Aragón (ICMA), Facultad de Ciencias, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
⁶Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
⁷Dipartimento di Fisica, Italian Institute of Technology at Sapienza, Università La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy
⁸Departamento de Física de Materiales, Facultad de Ciencias Químicas, Universidad del País Vasco/Euskal Herriko Unibertsitatea, 20080 Donostia-San Sebastian, Basque Country, Spain
⁹Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastian, Basque Country, Spain
¹⁰Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, 20018 Donostia-San Sebastian, Basque Country, Spain
¹¹IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Basque Country, Spain

^*Email address: f.casanova@nanogune.eu

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Vol. 93, Iss. 1 — 1 January 2016

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Images

Figure 1
(a) Rashba energy dispersion for a 2DEG. (b) Schematic of the detection of the inverse Rashba-Edelstein effect using the spin absorption (SA) method where Cu acts as a pure spin-current channel. The red (blue) arrows represent the current for spin-up (spin-down) electrons, the green arrow represents the 3D spin current (Is) through Cu, and the black arrows represent the 2D charge current (Ic) through the Bi metallic surface.
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Figure 2
(a) Colored scanning electron microscope (SEM) image of two Py/Cu LSVs, the left one with a Bi wire in between the Py electrodes and the right one without a Bi wire in between the Py electrodes. The measurement configuration, the direction of the applied magnetic field (H), and the materials are shown. (b) Red (blue) curve represents the nonlocal resistance $R_{N L}$ as a function of H at 10 K in a Py/Cu LSV without (with) a Bi wire in between the electrodes. A current of $I_{c} = 0.1 mA$ is injected. The corresponding spin signals are tagged as $Δ R_{N L}^{r e f}$ and $Δ R_{N L}^{a b s}$ , respectively. The solid (dashed) line represents the increasing (decreasing) sweep of H. (c) Colored SEM image of a typical device to measure the spin-to-charge conversion. The materials (Py, Cu, and Bi), the direction of the magnetic field (H), and the measurement configuration are shown. (d) Nonlocal resistance $R_{SCC}$ for Bi detected when measuring in the spin-to-charge conversion configuration as a function of H at 10 K (blue curve). The spin-to-charge conversion signal is tagged as $2 Δ R_{SCC}$ . A current of $I_{c} = 1 mA$ is injected. The inset: $R_{SCC}$ as a function of H at 300 K (red curve). The black solid lines are the sine of the magnetization rotation angle (ψ), which serves as a guide for the expected shape of the spin-to-charge conversion curve [32].
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Figure 3
(a) Temperature evolution of the IREE length of Bi as obtained from four different samples. (b) Energy dependence of the spectral current density $j_{E}^{'} (E)$ calculated by using $s_{λ} (k_{| |})$ for $n_{λ} (k_{| |})$ .
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Figure 4
(a) $k_{| |}$ -projected spin spectral density for $k_{| |}$ along $\bar{Γ M}$ . The calculation is performed for a slab of 16 Bi bilayers with the full-potential linear augmented plane-wave method [41]. Surface states are shown by distinct thick lines, and the bulk states are presented by smearing the slab levels with a Gaussian of 0.15 eV FWHM. (b) Constant energy contours in the 30° sector of the 2D Brillouin zone for $E = 0.02 eV$ (green lines) and $E = - 0.04 eV$ (black lines) relative to the Fermi energy. The sign of the spin projection $s_{λ} (k_{| |})$ of the contour is indicated by ↑ or ↓, and the line thickness is proportional to the absolute value of the spin projection. The value at the ↑ or ↓ symbol (in arbitrary units) indicates the contribution of that branch of the contour to $j_{E}^{'}$ .
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