Search

This paper investigates spin-current transport in a GaMnAs/GaAs/GaMnAs magnetic semiconductor tunnel junctions under applied bias voltages. The 30-band k.p approach is used to describe the materials within the heterostructure, incorporating both spin-orbit and exchange interactions. We use the transfer-matrix formalism to derive numerical solutions for the wave functions. At specific bias values, we calculate the polarization of the spin-current component along the z direction of the structure. We show oscillations of the two spin-current components perpendicular to the magnetization with equal polarization amplitude and characteristic period. The polarization amplitude varies around 10%, reflecting the typical polarization in such type of material. The oscillation period - which relates to the Larmor frequency for spin precession - increases with the bias voltage values.

International audience; We report on carrier dynamics in a spin photodiode based on a ferromagnetic-metal–GaAs tunnel junction. We show that the helicity-dependent current is determined not only by the electron spin polarization and spin asymmetry of the tunneling but in great part by a dynamical factor resulting from the competition between tunneling and recombination in the semiconductor, as well as by a specific quantity: the charge polarization of the photocurrent. The two latter factors can be efficiently controlled through an electrical bias. Under longitudinal magnetic field, we observe a strong increase of the signal arising from inverted Hanle effect, which is a fingerprint of its spin origin. Our approach represents a radical shift in the physical description of this family of emerging spin devices.

We consider a transverse electrical and spin current response to a longitudinal electric field in a metallic or semiconductor system characterized by various types of chirality. Using the similar theoretical approach we study a skew scattering on magnetic skyrmions leading to topological Hall effect, tunneling anomalous Hall effect (TAHE) of electrons and holes across an interface between magnetic semiconductors and electron scattering on a magnetic center in a semiconductor. We demonstrate how the chiral symmetry of the system manifests itself in the Hall response and its dependence on the electron spin polarization.

International audience; Terahertz (THz) spin-to-charge conversion has become an increasingly important process for THz pulse generation and as a tool to probe ultrafast spin interactions at magnetic interfaces. However, its relation to traditional, steady state, ferromagnetic resonance techniques is poorly understood. Here we investigate nanometric trilayers of Co/X/Pt (X=Ti, Au or Au0:85W0:15) as a function of the 'X' layer thickness, where THz emission generated by the inverse spin Hall effect is compared to the Gilbert damping of the ferromagnetic resonance. Through the insertion of the 'X' layer we show that the ultrafast spin current injected in the non-magnetic layer defines a direct spin conductance, whereas the Gilbert damping leads to an effective spin mixing-conductance of the trilayer. Importantly, we show that these two parameters are connected to each other and that spinmemory losses can be modeled via an effective Hamiltonian with Rashba fields. This work highlights that magneto-circuits concepts can be successfully extended to ultrafast spintronic devices, as well as enhancing the understanding of spin-to-charge conversion processes through the complementarity between ultrafast THz spectroscopy and steady state techniques.

Non-coplanar spatial or momentum-space distribution of an effective magnetic field acting on a free electron due to exchange or spin-orbit interaction couples electron spin precession with its motion. This coupling gives rise to a skew scattering underlying anomalous and topological Hall effects. We show that in a non-adiabatic interaction regime the emergent skew scattering can be expressed in terms of chirality in real or momentum space. The approach appears to be rather universal for transport phenomena in systems with broken time reversal symmetry. We show that scattering on a chiral spin texture produces a transversal current proportional to the real space spin chirality. Using the similar approach combined with tunneling Hamiltonian formalism we explain the chirality-driven skew tunneling of electrons and holes at a semiconductor interface. The theory can be relevant for unidirectional magnetoresistance in dilute magnetic semiconductors and magnetic topological insulators.

In this talk, we will present our general multiband k. p approach to describe the properties of spin-polarized transport and spin-dependent tunneling within semiconductors interfaces and related heterostructures. Hereafter, we will apply our formalism and platform to describe the properties of spin-dependent tunneling along the particular [110]-direction. This represents a nontrivial case for the description of the spin-current because of the presence of order terms in the wave vector k higher than two in the effective Hamiltonian. We demonstrate here that the multiband techniques employed and developed here beyond the actual state of the art also appear to be a perfect numerical tool to check and validate some analytical developments e.g. based on perturbation technique approaches, also allowing to alleviate some fundamental analytical issues.

We extend our layer-by-layer model of photonic eigenmodes (resonance, polarization) of semiconductor laser and VCSELs (Fordos PRA 2017) by considering local optical properties in order to describe the above-threshold lasing even in the multimode regime. Such generalization, consistent with the semi-classical description based on the optical Bloch equations, allows to describe the optical gain and the wave propagation within the cavity in a more realistic way. The formalism is suitable to study the mode competition, since the important physical effects such as spatial-hole burning or cross-saturation mechanisms are included self-consistently. The only input parameters are those describing geometrical and local material properties of the cavity and the gain media, without using any mean-field approximations. We will present our generalized approach for modelling real devices and will show how it can serve in determining the main optical and physical properties of such devices.

Spinorbitronics in III-V semiconductors, e.g. involving the GaMnAs ferromagnetic semiconductors, uses the properties of spin-orbit coupling (SOC) to generate currents of angular momentum [1-2]. Thoses are now essential to control the magnetization state of a magnet [3], or moving a domain wall [4] via the generalized spin-Hall effect of III-V possibly involving Rashba and Dresselhaus terms [4]. The interplay between particle spin and orbital motion is also at the basis of new families of effects played e. g. by the Anomalous Tunnel Hall effect described by the appearance of a lateral charge current transverse to a tunneling spin-current [5–7] ; or the spin-galvanic effects [8]. The ensemble of those complex phenomena requires a clear description of the spin-currents anatomy with advance calculation tools. In this work, as an extension to previous contributions [5], we study unconventional quantum effects resulting in a giant transport asymmetry of carriers and spin-to-charge conversion in semiconductor interfaces, tunnel barriers or quantum wells. Those are composed of ferromagnets and strong spin-orbit materials, e. g. III-V compounds with magnetizations of opposite direction (AP) or in the geometry of spin-injection devices. The symmetry of the structure allows a difference of transmission upon respective positive or negative incidence vs. the reflection plane defined by the magnetization and the surface normal. We will restrict ourself to the effect of bulk Dresselhaus terms by using the simplest form of the quantum boundary conditions. We will first detail the robustness of our advanced 30-band and 40 band tunneling codes free of spurious states effects and involving the higher electronic bands involving the relevant spin-orbit contributions. We will demonstrate that refined boundary conditions involving surface potentials, like Rashba terms, arising from the symmetry breaking at interfaces may lead to equivalent effects by their own. In a second part, we emphasize on the perturbation calculation techniques needed to understand this phenomena and to the case of the core SOI in the valence band (VB). References: [1] Tomasz Dietl and Hideo Ohno, Rev. Mod. Phys. 86, 187 (2014). [2] T. Jungwirth et al., Rev. Mod. Phys. 86, 855 (2014). [3] M. Elsen et al., Phys. Rev. B 73, 035303 [4] L. Thevenard et al., Phys. Rev. B 95, 054422 (2017). [5] T. Huong Dang, H. Jaffres, T. L. Hoai Nguyen, and H.-J. Drouhin, Phys. Rev. B 92, 060403(R) (2015). [6] A. Matos-Abiague and J. Fabian, Phys. Rev. Lett. 115, 056602 (2015). [7] M. Jamet, A. Barski, T. Devillers, V. Poydenot et al., Nat. Mat. 5, 653-659 (2006). [10] S. D. Ganichev et al., Spinpolarization by current, ""Handbook of spin-transport & magnetism"", (Chapman and Hall), 2016.

Apart from classical and anomalous Hall effects, an appearance of transverse current in chiral systems has been recently discovered named as topological Hall effect (THE) as it was thought to be possible solely for topologically charged spin textures such as magnetic skyrmions. In this talk we focus on asymmetric electron scattering on chiral spin textures and tunnel transport across a semiconductor interface with account for exchange and spin-orbit interactions. We distinguish between chiral Hall effect (CHE) which requires local chirality of an effective magnetic field and the THE which requires also a non-zero topological charge. THE emerges in adiabatic regime of scattering, which can be described via geometrical Berry phase. With semi-classical approach we clarify why the spin Hall current in this case is proportional to the topological charge of a spin texture and does not depend on its size. For non-adiabatic regime we expand the scattering T-matrix in Born series and show that the scattering cross section acquires an asymmetric part, which depends on the local chirality of the spin texture leading to CHE independently of the topological charge. The analysis allowed us to clarify the reason for the spin Hall effect to vanish in this regime while preserving the charge Hall effect. We have also found theoretically the spin swapping effect for the exchange scattering on chiral spin textures. Further, with the T-matrix analysis we explain the asymmetry in the tunneling across a semiconductor interface emerging due to chiral configuration of exchange and spin-orbit fields leading to generation of transverse current.

Recent technological and scientific interest in spin-polarized vertical-cavity surface emitting lasers (spin-VCSELs) leads to development of advanced laser modeling tools [1]. The models describes arbitrary multilayer structure of spin-VCSELs including general anisotropy of optical properties of individual layers, and also anisotropy of gain. This important generalization allows not only for precise description of static properties of the resonant cavity, but can also be used to precisely calculate effective parameters used in dynamical models. [2] Applications of spin-lasers for high modulation and switching up to GHz/THz frequencies, advanced output beam shape manipulation, and use of active quantum dot structures leads to necessity to model spin-VCSELs with active and passive laterally periodic structures such as gratings, photonic crystals, and diffractive structures. In this paper, we will show the generalization of existing matrix-based models to describe spin-lasers with lateral periodicity. The generalized rigorous coupled-wave analysis (RCWA) will be discussed in details and it will be compared with grid-based techniques such as finite element methods (FEM) and finite-difference time-domain analysis (FDTD). We will also discuss effects of incoherent propagation and random phase during light propagation in the structure. The method will be applied to structures of practical interest consisting of anisotropic grating used for ultrafast laser modulation and photonic structure. [1] T. Fordos, et. al., J. Opt. 16 (2014) 065008, Phys. Rev. A 96, (2017) 043828. [2] M. Drong, et al. Proc. SPIE 10926, (2019) 1092614.

Spin-polarized lasers such as spin-polarized vertical-cavity surface-emitting laser (spin-VCSELs) are prospective devices in which the radiative recombination of spin-polarized carriers results in an emission of circularly-polarized photons. Nevertheless, additional linear in-plane anisotropies in the cavity generally lead in preferential linearlypolarized laser emission and to possible coupling between modes. Optimization of room-temperature spinVCSELs thus relies on a proper modeling method and on a good understanding of these anisotropies that may reveal (i) a local linear birefringence due to strain fields at the surface or (ii) a birefringence in quantum wells (QWs) due to phase-amplitude coupling originating from the reduction of the biaxial D2d to the C2v symmetry group at the III-V ternary semiconductor interfaces. We present a novel method for the modeling of steady-state and dynamical properties of generally anisotropic multilayer semiconductor lasers containing multiple QWs active region. In order to solve the dynamical properties of spin-VCSELs, we combine here optical Bloch equations for a 4-level system with the scattering-matrix formalism, which treats VCSELs as a multilayer structure containing classical active dipole layers [T. F¨ord¨os et al., Phys. Rev. A 96, 043828 (2017)]. The method is then demonstrated on real semiconductor laser structures with InGaAs/GaAsP quantum wells. It is used for calculation of the laser resonance condition, the polarization properties of eigenmodes, the electromagnetic-field distribution inside the laser cavity, and time-dependent properties of the emitted light.

We report on theoretical investigations of carrier scattering asymmetry at ferromagnet-semiconductor junctions. By an analytical $2\times 2$ spin model, we show that, when Dresselhaus interactions is included in the conduction band of III-V $T_d$ symmetry group semiconductors, the electrons may undergo a difference of transmission vs. the sign of their incident parallel wavevector normal to the in-plane magnetization. This asymmetry is universally scaled by a unique function independent of the spin-orbit strength. This particular feature is reproduced by a multiband $\mathbf{k}\cdot \mathbf{p}$ tunneling transport model. Astonishingly, the asymmetry of transmission persists in the valence band of semiconductors owing to the inner atomic spin-orbit strength and free of asymmetric potentials . We present multiband $14\times 14$ and $30\times 30$ $\mathbf{k}\cdot \mathbf{p}$ tunneling models together with tunneling transport perturbation calculations corroborating these results. Those demonstrate that a tunnel spin-current normal to the interface can generate a surface transverse charge current, the so-called Anomalous Tunnel Hall Effect., 6 pages, 3 figures, conference MIMS 2017 Moscow (submitted), Journal of Magnetism and Magnetic Materials (JMMM), 2017

Electrically and optically pumped spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) seem to attain improved performance compared to their conventional counterparts. Their dynamical properties are studied mostly in the framework of effective rate equations containing parameters that are difficult to directly relate with fundamental material properties. Consequently, such approaches are not suitable for the precise design and optimization of future spin-lasers with desirable dynamical properties. We propose a method for extraction of dynamics-related parameters for the spin-flip model, which is widely used for the description of spin-laser dynamics. This method is based on the correspondence between robust local computational tools and effective models. A general matrix formalism based on S-matrices and generalized Maxwell–Bloch equations is used to determine approximate values of parameters such as cavity decay rate or birefringence rate. This would allow us to tune laser properties by changing the optical properties of the laser cavities and active media according to our needs. The method is demonstrated on realistic anisotropic spin-VCSEL structures containing a 12-quantum-well InGaAs/GaAsP active region. The potential limitations of already existing effective models are discussed.

International audience; Spin-laser structures such as spin-polarized vertical-cavity surface-emitting lasers are semiconductor devices in which the radiative recombination processes involving spin-polarized carriers result in an emission of circularly polarized photons. Nevertheless, additional linear in-plane anisotropies in the cavity, e.g., interfacial and surface anisotropies, generally lead to preferential linearly polarized laser emission and to possible coupling between modes. We present Mueller matrix ellipsometric study of non-intentionally doped InGaAs/GaAsP laser structures devoted for optical pumping operations in the spectral range from 0.73 to 6.4 eV in order to disentangle surface and quantum wells contributions to the linear optical birefringence of the structures. The measurement of full 4 × 4 Mueller matrix for multiple angles of incidence and in-plane azimuthal angles in combination with proper parametrization of optical functions has been used for extraction of optical permittivity tensor components along [110] and [110] crystal axis of surface strained layers and quantum wells grown on [001]-substrate. Such spectral dependence of optical tensor elements is crucial for modeling of spin-laser eigenmodes, resonance conditions, and also for understanding of sources of structure anisotropies.

Magnonics aims to utilize magnons (quanta of spin-waves) to process and transfer digital and analog information, promising high throughput, low power computing for the post-CMOS era. Any such future magnonic circuits will require spin wave signal sources and amplifiers. We propose that acoustic pumping of spin waves provides a mechanism to implement these functions in efficient and highly localized devices. In support of this, we have developed a general theoretical model of linear and parametric magneto-acoustic interactions, covering all possible polarizations of acoustic waves and spin wave modes. The model combines the predictive power of analytical techniques with numerical micromagnetic simulations and is thus well-suited for the design of complex physical devices. Based on this, we determine the configurations most amenable to spin wave generation and amplification. As an experimental prototype we demonstrate an acoustically-pumped amplifier for spin-waves. Our device consists of an yttrium-iron-garnet (YIG) film grown on a gallium gadolinium garnet (GGG) substrate, with a bulk acoustic waves (BAW) transducer fabricated on the top of the GGG substrate. We show experimentally that the amplitude of the propagating spin-waves increases with the application of the BAW. Moreover, this scheme can be used as a signal correlator, where the modulated spin-waves and acoustic waves serve as signal inputs and the resulting modulation of the amplified spin wave serves as the output.

We have studied an infinite Hubbard chain with a spin-orbit coupling term, submitted to a uniform magnetic field as well as local phonons. By means of a Lang-Firsov transformation, we show that an effective interacting fermion model emerges. Moreover, a self-consistent mean-field theory of this model, formulated in terms of thermal Green's functions, shows that a BCS term emerges, thus leading to a superconducting phase transition at zero temperature. We find analytical expressions for the phase boundary, that agree well with exact numerical diagonalization of the Hamiltonian.

We present a general method for the modeling of semiconductor lasers such as a vertical-cavity surface-emitting laser and a vertical-external-cavity surface-emitting laser containing multiple quantum wells and involving anisotropies that may reveal (i) a local linear birefringence due to the strain field at the surface or (ii) a birefringence in quantum wells due to phase amplitude coupling originating from the reduction of the biaxial ${D}_{2d}$ symmetry group to the ${C}_{2v}$ symmetry group at the III-V ternary semiconductor interfaces. From a numerical point of view, a scattering S-matrix recursive method is implemented using a gain or amplification tensor derived analytically from the Maxwell-Bloch equations. It enables one to model the properties of the emission (threshold, polarization, and mode splitting) from the laser with multiple quantum well active zones by searching for the resonant eigenmodes of the cavity. The method is demonstrated on real laser structures and is presently used for the extraction of optical permittivity tensors of surface strain and quantum wells in agreement with experiments. The method can be generalized to find the laser eigenmodes in the most general case of circular polarized pumps (unbalance between the spin-up and spin-down channels) and/or dichroism allowing an elliptically polarized light emission as recently demonstrated experimentally when the linear birefringence is almost compensated [Joly et al., Opt. Lett. 42, 651 (2017)].

Spin torque magnetic memory (ST-MRAM) is currently under intense academic and industrial development, as it features non-volatility, high write and read speed and high endurance. However, one of its great challenge is the probabilistic nature of programming magnetic tunnel junctions, which imposes significant circuit or energy overhead for conventional ST-MRAM applications. In this work, we show that in unconventional computing applications, this drawback can actually be turned into an advantage. First, we show that conventional magnetic tunnel junctions can be reinterpreted as stochastic “synapses” that can be the basic element of low-energy learning systems. System-level simulations on a task of vehicle counting highlight the potential of the technology for learning systems. We investigate in detail the impact of magnetic tunnel junctions’ imperfections. Second, we introduce how intentionally superparamagnetic tunnel junctions can be the basis for low-energy fundamentally stochastic computing schemes, which harness part of their energy in thermal noise. We give two examples built around the concepts of synchronization and Bayesian inference. These results suggest that the stochastic effects of spintronic devices, traditionally interpreted by electrical engineers as a drawback, can be reinvented as an opportunity for low energy circuit design.

When electrons in a magnetic metal are driven far from equilibrium via ultrafast heating of the electrons, the magnetic order undergoes radical changes within tens of femtoseconds due to massive flows of energy and angular momentum between electrons, spins, and phonons. In ferrimagnetic metals such as GdFeCo, ultrafast optical heating can deterministically reverse the magnetization in less than a picosecond. In this talk, I describe our experimental work to gain a better understanding of how energy is exchanged between electrons, phonon, and spins in a magnetic metal following ultrafast heating. We use time-resolved measurements of the magneto-optic Kerr effect to record the response of ferro- and ferri-magnetic metals to heating via ultrafast optical or electrical pulses. Picosecond electrical pulses are generated with photoconductive Auston switches. By comparing the magnetic dynamics that result from electrical vs. optical heating, we identify differences in the rate of energy transfer to phonons from thermal vs. nonthermal electrons. We also find that both optical and electrical heating are effective for ultrafast switching of ferrimagnetic metals. We observe deterministic, repeatable ultrafast reversal of the magnetization of a GdFeCo thin film with a single sub-10 ps electrical pulse. The magnetization reverses in ~10 ps, which is more than one order of magnitude faster than other electrically controlled magnetic switching mechanisms.

The manipulation of magnetization by an electric current can be obtained thanks to the spin-transfer torque (STT) phenomenon. The two main mechanisms that give rise to this phenomenon are the spin filtering torque (SFT) and the spin-orbit torque (SOT). The former is obtained in multilayer systems by passing a spin-polarized current through the multilayers, whereas the latter is achieved through a direct transfer of angular momentum from the crystal lattice through the spin–orbit interaction. In this work, we study the influence of these two mechanisms on the magnetization dynamics of a three-terminal spin-torque oscillator. The device is composed of either a spin-valve (SV) or a magnetic tunnel junction (MTJ) on top of a Pt wire. The system can be excited either by SFT or by SOT depending on whether the current is applied through the magnetic structure (SV or MTJ) or through the Pt wire. Finally, each device is compared to a reference sample where the Pt wire is replaced by a Cu wire. Therefore, no SOT is expected in this second set of devices. In this presentation, we compare the different types of devices in order to understand the transport in the three terminal devices and study the role of the different mechanisms (SFT and STT) on the magnetization dynamics. Finally, we propose a method to compare the spin transfer efficiency of the two mechanisms on a single device.

Interfacial spin-orbit torques (SOTs) enable manipulation of the magnetization through an in-plane charge current, which has drawn increasing attention for spintronic applications. In the search for material systems that can provide efficient SOTs, much work has been focused on polycrystalline ferromagnetic metal/non-magnetic metal bilayers [1-3]. Here the current flows in the non-magnetic layers and induces a torque at the interfaces via the spin Hall effect of the non-magnetic layer [1], the Rashba effect at the interface [2] or spin-momentum locking when a topological insulator is involved [3]. In this presentation, we report the observation of robust SOT occuring in a well characterized single crystalline Fe/insulating GaAs (001) interface at room temperature where the SOT is caused by the lack of space inversion symmetry at the interface. We find that the magnitude of the interfacial SOT per unit charge current density is comparable in strength with that in ferromagnetic metal/non-magnetic metal systems. This large magnitude also allows for the observation of spin-to-charge current conversion at the interface, which is known as spin-galvanic effect [4]. The results suggest that single crystalline Fe/GaAs interfaces may enable efficient magnetization manipulation through purely electric means [5]. References [1] L. Liu, et al., Science 336, 555 (2012). [2] I. M. Miron, et al., Nature 476, 189 (2011). [3] A. R. Mellnik, et al., Nature 511, 449 (2014). [4] S. D. Ganichev, et al., Nature 417, 153 (2002). [5] L. Chen, et al., Nature Commun. 7, 13802 (2016).

In recent years, Spin Orbit interaction as a source of spin current has been widely used through the physics of Spin Hall Effect (SHE). The peculiar symmetry of SHE allows creating a spin accumulation at the interface between a spin-orbit metal and a magnetic insulator that could lead to a net pure spin current flowing from the metal into the insulator. This spin current will induce a torque on the magnetization and eventually could drive it into steady motion. As a ferromagnetic insulator with a very low Gilbert damping, Yttrium Iron Garnet (YIG) is a very promising candidate to investigate pure spin current phenomena. Only very recently, with the developments in preparation of high-quality nanometer-thick YIG films, the implementation of insulator-based spin-torque devices became practically feasible. Here, we report on the excitation of auto-oscillations in microstructures of YIG(20nm)\Pt(8nm) driven by Spin Orbit torque (SOT). By injection of a dc current in the adjacent Pt layer, we have been able to prove that the SOT due to SHE is sufficiently strong and efficient to drive the YIG magnetization dynamics at frequencies that closely follow the ferromagnetic resonance mode. These auto-oscillations have been detected either inductively using a spectrum analyzer or directly observed using micro-focus Brillouin Light Scattering. Furthermore, we achieved an efficient control of spin waves attenuation length in a YIG waveguide using the SHE in the sub-critical regime i.e. below the auto-oscillations threshold. We believe that our finding pave the path to active magnonics devices made out of YIG films.

In this presentation we will review the spintronic terahertz (THz) phenomena such as ultrafast transient demagnetization [1], generation of spin waves via THz Zeeman torque [2,3], Mott scattering [4], and ultrafast inverse spin-Hall effect [5]. [1] E. Beaurepaire, G. M. Turner, S. M. Harrel, M. C. Beard, J.-Y. Bigot, and C. A. Schmuttenmaer, "Coherent terahertz emission from ferromagnetic films excited by femtosecond laser pulses," Appl. Phys. Lett. 84, 3465 (2004) [2] T. Kampfrath, A. Sell, G. Klatt, A. Pashkin, S. Mahrlein, T. Dekorsy, M. Wolf, M. Fiebig, A. Leitenstorfer, and R. Huber, "Coherent terahertz control of antiferromagnetic spin waves," Nature Photonics 5, 31 (2011) [3] Z. Jin, Z. Mics, G. Ma, Z. Cheng, M. Bonn, and D. Turchinovich, "Single-pulse terahertz coherent control of spin resonance in the canted antiferromagnet YFeO3, mediated by dielectric anisotropy", Phys. Rev. B 87, 094422 (2013) [4] Z. Jin, A. Tkach, F. Casper, V. Spetter, H. Grimm, A. Thomas, T. Kampfrath, M. Bonn, M. Klaui, and D. Turchinovich, "Accessing the fundamentals of magnetotransport in metals with terahertz probes", Nature Physics 11, 761 (2015) [5] T. Seifert, S. Jaiswal, U. Martens, J. Hannegan, L. Braun, P. Maldonado, F. Freimuth, A. Kronenberg, J. Henrizi, I. Radu, F. Freimuth, E. Beaurepaire, Y. Mokrousov, P.M. Oppeneer, M. Jourdan, G. Jakob, D. Turchinovich, L. M. Hayden, M. Wolf, M. Munzenberg, M. Klaui, and T. Kampfrath, "Efficient metallic spintronic emitters of ultrabroadband terahertz radiation", Nature Photonics 10, 483 (2016)

In the last five years, Artificial Intelligence has made striking progress, and now defeating humans at subtle strategy games, such as Go, and even Poker. However, these algorithms are running on traditional processors which have a radically different architecture than the biological neural networks they are inspired from. This considerably slows them down and requires massive amounts of electrical power, more than ten thousand times what the brain typically need to function. This energy dissipation is not only becoming an environmental issue, but it also sets a limit to the size of neural networks that can be simulated. We are at a point where we need to rethink the way we compute, and build hardware chips directly inspired from the architecture of the brain. This is a challenge. Indeed, contrarily to current electronic systems, the brain is a huge parallel network closely entangling memory and processing. In this talk, I will show that, for building the neuromorphic chips of the future, we will need to emulate functionalities of synapses and neurons at the nanoscale. I will review the recent developments of memristive nano-synapses and oscillating nano-neurons, the physical mechanisms at stake, and the challenges in terms of materials. Finally, I will present the first achievements of neuromorphic computing with novel nanodevices and the fascinating perspectives of this emerging field.