Solid-State Synapse Based on Magnetoelectrically Coupled Memristor

Brain-inspired computing architectures attempt to emulate the computations performed in the neurons and the synapses in the human brain. Memristors with continuously tunable resistances are ideal building blocks for artificial synapses. Through investigating the memristor behaviors in a La_0.7Sr_0.3MnO₃/BaTiO₃/La_0.7Sr_0.3MnO₃ multiferroic tunnel junction, it was found that the ferroelectric domain dynamics characteristics are influenced by the relative magnetization alignment of the electrodes, and the interfacial spin polarization is manipulated continuously by ferroelectric domain reversal, enriching our understanding of the magnetoelectric coupling fundamentally. This creates a functionality that not only the resistance of the memristor but also the synaptic plasticity form can be further manipulated, as demonstrated by the spike-timing-dependent plasticity investigations. Density functional theory calculations are carried out to describe the obtained magnetoelectric coupling, which is probably related to the Mn–Ti intermixing at the interfaces. The multiple and controllable plasticity characteristic in a single artificial synapse, to resemble the synaptic morphological alteration property in a biological synapse, will be conducive to the development of artificial intelligence

Asymmetric Modulation on Exchange Field in a Graphene/BiFeO₃ Heterostructure by External Magnetic Field

Graphene, having all atoms on its surface, is favorable to extend the functions by introducing the spin–orbit coupling and magnetism through proximity effect. Here, we report the tunable interfacial exchange field produced by proximity coupling in graphene/BiFeO₃ heterostructures. The exchange field has a notable dependence with external magnetic field, and it is much larger under negative magnetic field than that under positive magnetic field. For negative external magnetic field, interfacial exchange coupling gives rise to evident spin splitting for <i>N</i> ≠ 0 Landau levels and a quantum Hall metal state for <i>N</i> = 0 Landau level. Our findings suggest graphene/BiFeO₃ heterostructures are promising for spintronics

Hierarchically Structured Thermoelectric Materials in Quaternary System Cu–Zn–Sn–S Featuring a Mosaic-type Nanostructure

Multinary chalcogenide semiconductors in the Cu–Zn–Sn–S system have numerous potential applications in the fields of energy production, photocatalysis and nonlinear optics, but characterization and control of their microstructures remains a challenge because of the complexity resulting from the many mutually soluble metallic elements. Here, using state-of-the-art scanning transmission electron microscopy, energy dispersive spectroscopy, first-principles calculations and classical molecular dynamics simulations, we characterize the structures of promising thermoelectric materials Cu₂(Zn,Sn)­S₃ at different length scales to gain a better understanding of how the various components influence the thermoelectric behavior. We report the discovery of a mosaic-type domain nanostructure in the matrix grains comprising well-defined cation-disordered domains (the “tesserae”) coherently bonded to a surrounding network phase with semiordered cations. The network phase is found to have composition Cu_4+<i>x</i>Zn_<i>x</i>Sn₂S₇, a previously unknown phase in the Cu–Zn–Sn–S system, while the tesserae have compositions closer to that of the nominal composition. This nanostructure represents a new kind of phonon-glass electron-crystal, the cation-disordered tesserae and the abrupt domain walls damping the thermal conductivity while the cation-(semi)­ordered network phase supports a high electronic conductivity. Optimization of the hierarchical architecture of these materials represents a new strategy for designing environmentally benign, low-cost thermoelectrics with high figures of merit

Giant Photoresponse in Quantized SrRuO₃ Monolayer at Oxide Interfaces

The photoelectric effect in semiconductors is the main mechanism for most modern optoelectronic devices, in which the adequate bandgap plays the key role for acquiring high photoresponse. Among numerous material categories applied in this field, the complex oxides exhibit great possibilities because they present a wide distribution of band gaps for absorbing light with any wavelength. Their physical properties and lattice structures are always strongly coupled and sensitive to light illumination. Moreover, the confinement of dimensionality of the complex oxides in the heterostructures can provide more diversities in designing and modulating the band structures. On the basis of this perspective, we have chosen itinerary ferromagnetic SrRuO₃ as the model material, and fabricated it in one-unit-cell thickness in order to open a small band gap for effective utilization of visible light. By inserting this SrRuO₃ monolayer at the interface of the well-developed two-dimensional electron gas system (LaAlO₃/SrTiO₃), the resistance of the monolayer can be further revealed. In addition, a giant enhancement (>300%) of photoresponse under illumination of visible light with power density of 500 mW/cm² is also observed. Such can be ascribed to the further modulation of band structure of the SrRuO₃ monolayer under the illumination, confirmed by cross-section scanning tunneling microscopy (XSTM). Therefore, this study demonstrates a simple route to design and explore the potential low dimensional oxide materials for future optoelectronic devices