Resistive switching in HfO2-x/La0.67Sr0.33MnO3 heterostructure: An intriguing case of low H-field susceptibility of an E-field controlled active interface
High-performance non-volatile resistive random access memories (ReRAM) and their small stimuli control are of immense interest for high-speed computation and big-data processing in the emergent Internet of Things (IOT) arena. Here, we examine the resistive switching (RS) behavior in growth controlled HfO2/La0.67Sr0.33MnO3 heterostructures and their tunability under low magnetic field. It is demonstrated that oxygen-deficient HfO2 films show bipolar switching with high on/off ratio, stable retention, as well as good endurance owing to the orthorhombic-rich phase constitution and charge (de)-trapping-enabled Schottky-type conduction. Most importantly, we have demonstrated that, the RS can be tuned by a very low externally applied magnetic field (0-30 mT). Remarkably, application of a magnetic field of 30 mT causes the RS to be fully quenched and frozen in the high resistance state (HRS) even after the removal of magnetic field. However, the quenched state could be resurrected by applying higher bias voltage than the one for initial switching. This is argued to be a consequence of the electronically and ionically active nature of the HfO2-x/LSMO interface on both sides, and its susceptibility to the electric and low magnetic field effects. This result could pave the way for new designs of interface engineered high-performance oxitronic ReRAM devices.
We demonstrate the feasibility of multilevel recording in Pt/Bi(1-d)FeO3/SrRuO3 capacitors using the ferroelectric resistive switching phenomenon exhibited by the Pt/Bi(1-d)FeO3 interface. A tunable population of up and down ferroelectric domains able to modulate the Schottky barrier height at the Pt/Bi(1-d)FeO3 interface can be achieved by means of either a collection of SET/RESET voltages or current compliances. This programming scheme gives rise to well defined resistance states, which form the basis for a multilevel storage nonvolatile memory.
We report on the growth and characterization of Ti/$La_{1/3}$$Ca_{2/3}$Mn$O_3$/Si$O_x$/n-Si memristive devices. We demonstrate that using current as electrical stimulus unveils an intermediate resistance state, in addition to the usual high and low resistance states that are observed in standard voltage controlled experiments. Based on thorough electrical characterization (impedance spectroscopy, current-voltage curves analysis), we disclose the contribution of three different microscopic regions of the device to the transport properties: an ohmic incomplete metallic filament, a thin manganite…
We propose a tunneling heterostructure by replacing one of the metal electrodes in a metal/ferroelectric/metal ferroelectric tunnel junction with a heavily doped semiconductor. In this metal/ferroelectric/semiconductor tunnel diode, both the height and the width of the tunneling barrier can be electrically modulated due to the ferroelectric field effect, leading to a colossal tunneling electroresistance. This idea is implemented in Pt/BaTiO3/Nb:SrTiO3 heterostructures, in which an ON/OFF conductance ratio above 10$^4$ can be readily achieved at room temperature. The colossal tunneling electror…
The electric conductivity behavior in the single and double tunnel-coupled quantum wells (QW) with different doping profile caused by impact of short pulses of the strong longitudinal (in the quantum wells plane) electric field has been investigated. It is established that at low temperatures (4 K) after such impact the long-term metastable state with increased electric conductance may be observed in the case of the asymmetric QW couple with the impurity delta shaped layer in the narrower QW. It is not observed in the structures with other configurations. The observed effect is explained by th…
The electric-field-modulated resistance switching in VO2 thin films grown on piezoelectric (111)-0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) substrates has been investigated. Large relative change in resistance (10.7%) was observed in VO2/PMN-PT(111) hererostructures at room temperature. For a substrate with a given polarization direction, stable resistive states of VO2 films can be realized even when the applied electric fields are removed from the heterostructures. By sweeping electric fields across the heterostructure appropriately, multiple resistive states can be achieved. These stable resis…
It has been shown that W in its resistive form possesses the largest spin-Hall ratio among all heavy transition metals, which makes it a good candidate for generating efficient dampinglike spin-orbit torque (DL-SOT) acting upon adjacent ferromagnetic or ferrimagnetic (FM) layer. Here we provide a systematic study on the spin transport properties of W/FM magnetic heterostructures with the FM layer being ferromagnetic Co$_{20}$Fe$_{60}$B$_{20}$ or ferrimagnetic Co$_{63}$Tb$_{37}$ with perpendicular magnetic anisotropy. The DL-SOT efficiency $|ξ_{DL}|$, which is characterized by a current-induced…
Functional oxides based resistive memories are recognized as potential candidate for the next-generation high density data storage and neuromorphic applications. Fundamental understanding of the compositional changes in the functional oxides is required to tune the resistive switching characteristics for enhanced memory performance. Herein, we present the micro/nano-structural and compositional changes induced in a resistive oxide memory during resistive switching. Oxygen deficient amorphous chromium doped strontium titanate (Cr:$a$-SrTiO$_{3-x}$) based resistance change memories are fabricate…
Reversible resistive switching between high-resistance and low-resistance states in metal-oxide-metal heterostructures makes them very interesting for applications in random access memories. While recent experimental work has shown that inserting a metallic "oxygen scavenger layer" between the positive electrode and oxide improves device performance, the fundamental understanding of how the scavenger layer modifies heterostructure properties is lacking. We use density functional theory to calculate thermodynamic properties and conductance of TiN/HfO$_2$/TiN heterostructures with and without Ta…
Two-dimensional (2D) magnets have broad application prospects in the spintronics, but how to effectively control them with a small electric field is still an issue. Here we propose that 2D magnets can be efficiently controlled in a multiferroic heterostructure composed of 2D magnetic material and perovskite oxide ferroelectric (POF) whose dielectric polarization is easily flipped under a small electric field. We illustrate the feasibility of such strategy in the bilayer CrI3/BiFeO3(001) heterostructure by using the first-principles calculations. Different from the traditional POF multiferroic …
The observation of low energy edge photoluminescence and its beneficial effect on the solar cell efficiency of Ruddlesden-Popper perovskites has unleashed an intensive research effort to reveal its origin. This effort, however, has been met with more challenges as the underlying material structure has still not been identified; new modellings and observations also do not seem to converge. Using 2D (BA)2(MA)2Pb3Br10 as an example, we show that 3D MAPbBr3 is formed due to the loss of BA on the edge. This self-formed MAPbBr3 can explain the reported edge emission under various conditions, while t…
Reverse and stable bipolar resistive switching effect was observed in planar NdCeCuO - NdCeO - Ag heterostructures. It was shown that the current voltage charactereriscs of the BRSE observed has a diode character. Simulations were used to consider the influence of the nonuniform distribution of an electric field at the interface of a heterojunction on the effect of bipolar resistive switching in investigated structures. The inhomogeneous distribution of the electric field near the contact edge creates regions of higher electric field strength which, in turn, stimulates motion and redistributio…
The photovoltaic effect in the BiFeO3/TiO2 heterostructures can be tuned by epitaxial strain and an electric field in the visible-light region which is manifested by the enhancement of absorption activity in the heterojunction under tensile strain and an electric field based on the first-principles calculations. It is suggested that there are coupling between photon, spin carrier, charge, orbital, and lattice in the interface of the bilayer film which makes the heterojunction an intriguing candidate towards fabricating the multifunctional photoelectric devices based on spintronics. The microsc…
The spin Hall effect (SHE) is found to be strong in heavy transition metals (HM), such as Ta and W, in their amorphous and/or high resistivity form. In this work, we show that by employing a Cu-Ta binary alloy as buffer layer in an amorphous Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructure with perpendicular magnetic anisotropy (PMA), the SHE-induced damping-like spin-orbit torque (DL-SOT) efficiency $|ξ_{DL}|$ can be linearly tuned by adjusting the buffer layer resistivity. Current-induced SOT switching can also be achieved in these Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructures, and…
We report a THz emitter with excellent performances based on nonmagnetic (NM) and ferromagnetic (FM) heterostructures. The spin currents are first excited by the femtosecond laser beam in the NM/FM bilayer, and then transient charge currents are generated by inverse spin Hall effect, leading to THz emission out of the structure. The broadband THz waves emitted from our film stacks have a peak intensity exceeding 500 um thick ZnTe crystals (standard THz emitters). Our device is insensitive to the polarization of an incident laser beam which indicates the noise resistive feature. In contrast, th…
We report on the electric-field-induced reversible metal-insulator transition (MIT) of the insulating LaAlO3 thin films observed in metal/LaAlO3/Nb-SrTiO3 heterostructures. The switching voltage depends strongly on the thickness of the LaAlO3 thin film which indicates that a minimum thickness is required for the MIT. A constant opposing voltage is required to deplete the charges from the defect states. Our experimental results exclude the possibility of diffusion of the metal electrodes or oxygen vacancies into the LaAlO3 layer. Instead, the phenomenon is attributed to the formation of a quasi…
A new multisensor (i.e. resistive and magnetic) $CrI_{3}$-$WTe_{2}$ heterostructure (HS) to detect the toxic gases $BrF_3$ and $COCl_2$ (Phosgene) has been theoretically studied in our present investigation. The HS has demonstrated sensitivity towards both the gases by varying its electronic and magnetic properties when gas molecule interacts with the HS. Fast recovery time ($< 0.14 fs$) under UV radiation has been observed. We have considered two configurations of $BrF_3$ adsorbed HS; 1) when F ion interacts with HS (C1) and 2) when Br ion interacts with HS (C2). In C1 case the adsorption ene…
By performing density functional theory (DFT) and Green's functions calculations, complemented by X-ray Photoemission Spectroscopy, we investigate the electronic structure of Fe/GeTe(111), a prototypical ferromagnetic/Rashba-ferroelectric interface. We reveal that such system exhibits several intriguing properties resulting from the complex interplay of exchange interaction, electric polarization and spin-orbit coupling. Despite a rather strong interfacial hybridization between Fe and GeTe bands, resulting in a complete suppression of the surface states of the latter, the bulk Rashba bands are…
The interlayer coupling in van der Waals heterostructures governs a variety of optical and electronic properties. The intrinsic dipole moment of Janus transition metal dichalcogenides (TMDs) offers a simple and versatile approach to tune the interlayer interactions. In this work, we demonstrate how the van der Waals interlayer coupling and charge transfer of Janus MoSSe/MoS2 heterobilayers can be tuned by the twist angle and interface composition. Specifically, the Janus heterostructures with a sulfur/sulfur (S/S) interface display stronger interlayer coupling than the heterostructures with a …
Interfacial perpendicular magnetic anisotropy, which is characterized by the first-order (K1) and second-order (K2) anisotropies, is the core phenomenon for nonvolatile magnetic devices. A sizable K2 satisfying a specific condition stabilizes the easy-cone state, where equilibrium magnetization forms at an angle from the film normal. The easy-cone state offers intriguing possibilities for advanced spintronic devices and unique spin textures, such as spin superfluids and easy-cone domain walls. Experimental realization of the easy-cone state requires understanding the origin of K2, thereby enha…
Topological magnetism in low-dimensional systems is of fundamental and practical importance in condensed-matter physics and material science. Here, using first-principles and Monte-Carlo simulations, we present that multiple topological magnetism (i.e., skyrmion and bimeron) can survive in van der Waals Heterostructure of MnTe2ZrS2. Arising from interlayer coupling, MnTe2ZrS2 can harbor a large Dzyaloshinskii-Moriya interaction. This, combined with ferromagnetic exchange interaction, yields an intriguing skyrmion phase consisting of sub-10 nm magnetic skyrmions under a tiny magnetic field of 7…
A microscopic model Hamiltonian for the ferroelectric field effect is introduced for the study of oxide heterostructures with ferroelectric components. The long-range Coulomb interaction is incorporated as an electrostatic potential, solved self-consistently together with the charge distribution. A generic double-exchange system is used as the conducting channel, epitaxially attached to the ferroelectric gate. The observed ferroelectric screening effect, namely the charge accumulation/depletion near the interface, is shown to drive interfacial phase transitions that give rise to robust magneto…
Electrical manipulation of skyrmions attracts considerable attention for its rich physics and promising applications. To date, such a manipulation is realized mainly via spin-polarized current based on spin-transfer torque or spin-orbital torque effect. However, this scheme is energy-consuming and may produce massive Joule heating. To reduce energy dissipation and risk of heightened temperatures of skyrmion-based devices, an effective solution is to use electric field instead of current as stimulus. Here, we realize an electric-field manipulation of skyrmions in a nanostructured ferromagnetic/…
Novel phenomena appear when two different oxide materials are combined together to form an interface. For example, at the interface of LaAlO3/SrTiO3, two dimensional conductive states form to avoid the polar discontinuity and magnetic properties are found at such interface. In this work, we propose a new type of interface between two nonmagnetic and nonpolar oxides that could host a conductive state with magnetic properties, where it is the ferroelectric polarization discontinuity instead of the polar discontinuity that leads to the charge transfer, forming the interfacial conductive or magnet…
Three-dimensional topological insulator films in contact with magnetic layers exhibit intriguing magneto-optical and magnetoelectric phenomena, but little is known beyond the linear response regime. We demonstrate that the presence of two electric fields parallel to the surface of the film induces a perpendicular AC polarization, whereas a static polarization can be induced by applying a single circularly polarized electromagnetic wave. These phenomena are determined by the second-order susceptibility, which also controls the manner in which the anomalous Hall current is modulated by a perpend…
We present a model artificial multiferroic system consisting of a (011)-oriented ferroelectric Pb(Mg,Nb,Ti)O$_3$ substrate intimately coupled to a ferromagnetic (La,Sr)MnO$_3$ film through epitaxial strain and converse piezoelectric effects. Electric field pulse sequences of less than 6 kV/cm were shown to induce large reversible and bistable remanent strains in the manganite film. Magnetic hysteresis loops demonstrate that the changes in strain states result in significant changes in magnetic anisotropy from a highly anisotropic two-fold magnetic symmetry to a more isotropic one. Such changes…
Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) for technological applications. While most studies have focused on doping magnetic impurities to open a gap at the surface-state Dirac point, many undesirable effects have been reported to appear in some cases that makes it difficult to determine whether the gap opening is due to the time-reversal symmetry breaking or not. Furthermore, the realization of the QAHE has been limited to low temperatures. Here we have succeeded in generating a massive Dirac co…
The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. Here we create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of the spin and valley pseudospin in WSe2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting and polarization via flipping of the CrI3 magnetization. The WSe2 phot…
The intrinsic magnetism observed in two-dimensional (2D) van der Waals (vdW) materials provides a unique opportunity for exploring the 2D topological magnetic textures, in particular skyrmionic magnetic textures (SMTs) including skyrmion and its topological equivalents. Since the experimental discovery of skyrmions in the 2D vdW materials and their heterostructures, a critical challenge lies in the control of these SMTs to translate their intriguing features into spintronic applications. Here, we review the recent experimental and theoretical progresses on the modulations of SMTs in 2D vdW mon…
Topological insulators (TIs) are bulk insulators that possess robust helical conducting states along their interfaces with conventional insulators. A tremendous research effort has recently been devoted to TI-based heterostructures, in which conventional proximity effects give rise to a series of exotic physical phenomena. This paper reviews our recent works on the potential existence of topological proximity effects at the interface between a topological insulator and a normal insulator or other topologically trivial systems. Using first-principles approaches, we have established the tunabili…
Spintronics-based nonvolatile components in neuromorphic circuits offer the possibility of realizing novel functionalities at low power. Current-controlled electrical switching of magnetization is actively researched in this context. Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA), consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material contenders. Utilizing the crystal orientation, magnetic anisotropy in such simple heterostructures can be tuned to either exhibit a perfect or slightly tilted PMA. Here, we investigate current-induced magnetization…
The shortcomings of mono-component systems, e.g., the gapless nature of graphene, the lack of air-stability in phosphorene, etc. have drawn great attention toward stacked materials expected to show interesting electronic and optical properties. Using the tight-binding approach and the Green's function method, we investigate the electronic properties of armchair-edged lateral phosphorene/graphene heterostructures, which are either semiconductor/semiconductor or semiconductor/metal heterostructures, depending on the width of graphene ribbon. It is found that the system is narrow-gapped, and the …
Topological insulators are characterized by a nontrivial band topology driven by the spin-orbit coupling. To fully explore the fundamental science and application of topological insulators, material realization is indispensable. Here we predict, based on tight-binding modeling and first-principles calculations, that bilayers of perovskite-type transition-metal oxides grown along the [111] crystallographic axis are potential candidates for two-dimensional topological insulators. The topological band structure of these materials can be fine-tuned by changing dopant ions, substrates, and external…
The exchange bias (EB) effect is known as a fundamentally and technologically important magnetic property of a magnetic bilayer film. It is manifested as a horizontal shift in a magnetic hysteresis loop of a film subject to cooling in the presence of a magnetic field. The EB effect in van der Waals (vdW) heterostructures offers a novel approach for tuning the magnetic properties of the newly discovered single-layer magnets, as well as adds a new impetus to magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been reported in a variety of low-dimensional vdW magnetic syste…
Oxide heterostructures exhibit a rich variety of magnetic and transport properties which arise due to contact at an interface. This can lead to surprising effects that are very different from the bulk properties of the materials involved. We report the magnetic properties of bilayers of SrRuO3, a well known ferromagnet, and CaRuO3, which is nominally a paramagnet. We find intriguing features that are consistent with CaRuO3 developing dual magnetic character, with both a net moment as well as antiferromagnetic order. We argue the ordered SrRuO3 layer induces an undulating polarization profile i…
Mixed-dimensional magnetic heterostructures are intriguing, newly available platforms to explore quantum physics and its applications. Using state-of-the-art many-body perturbation theory, we predict the energy level alignment for a self-assembled monolayer of cobalt phthalocyanine (CoPc) molecules on magnetic VSe 2 monolayers. The predicted projected density of states on CoPc agrees with experimental scanning tunneling spectra. Consistent with experiment, we predict a shoulder in the unoccupied region of the spectra that is absent from mean-field calculations. Unlike the nearly spin-degenerat…
In past few decades, Rashba spin-orbit coupling (SOC) has been successfully employed for the emergence of exotic phenomena at the quantum oxide interfaces. In these systems, the combined effect of charge transfer, broken symmetries and SOC yields intriguing interfacial magnetism and transport properties. Here, we provide an insight to control and tune interfacial phenomena in CaMnO3/CaIrO3 based 3d-5d oxide heterostructures by the charge transfer driven Rashba SOC. Anomalous Hall effect in these canted antiferromagnetic heterostructures originates from the intrinsic contribution associated wit…
Proximity-induced spin-orbit coupling in graphene has led to the observation of intriguing phenomena like time-reversal invariant $\mathbb{Z}_2$ topological phase and spin-orbital filtering effects. An understanding of the effect of spin-orbit coupling on the band structure of graphene is essential if these exciting observations are to be transformed into real-world applications. In this research article, we report the experimental determination of the band structure of single-layer graphene (SLG) in the presence of strong proximity-induced spin-orbit coupling. We achieve this in high-mobility…
The emerging Ni-based superconducting oxide thin films are rather intriguing to the entire condensed matter physics. Here we report some brief experimental results on transport measurements for a 14-nm-thick superconducting Nd0.8Sr0.2NiO2/SrTiO3 thin-film heterostructure with an onset transition temperature of ~9.5 K. Photoluminescence measurements reveal that there is negligible oxygen vacancy creation in the SrTiO3 substrate during thin-film deposition and post chemical reduction for the Nd0.8Sr0.2NiO2/SrTiO3 heterostructure. It was found that the critical current density of the Nd0.8Sr0.2Ni…
Multiple magnetic skyrmion phases add an additional degree of freedom for skyrmion based ultrahigh-density spin memory devices. Extending the field to two-dimensional van der Waals magnets is a rewarding challenge, where the realizable degree of freedoms (e.g. thickness, twisting angle and electrical gating) and high skyrmion density result in intriguing new properties and enhanced functionality. We report a van der Waals interface, formed by two 2D ferromagnets Cr2Ge2Te6 and Fe3GeTe2 with a Curie temperature of ~65 K and ~205 K, respectively, hosting two groups of magnetic skyrmions. Two sets…
Obtaining an accurate theoretical description of the emergent phenomena in oxide heterostructures is a major challenge. Recently, intriguing paramagnetic spin and pinned orbital moments have been discovered by x-ray magnetic circular dichroïsm measurements at the Cu $L_{2,3}$-edge of a tetragonal CuO/SrTiO$_3$ heterostructure. Using first principles calculations, we propose a scenario that explains both types of moments, based on the formation of oxygen vacancies in the TiO$_2$ interface layer. We show the emergence of a paramagnetic 2D electron gas hosted in the interface CuO layer. It is inv…
The spin Hall effect originating from 5d heavy transition metal thin films such as Pt, Ta, and W is able to generate efficient spin-orbit torques that can switch adjacent magnetic layers. This mechanism can serve as an alternative to conventional spin-transfer torque for controlling next-generation magnetic memories. Among all 5d transition metals, W in its resistive amorphous phase typically shows the largest spin-orbit torque efficiency ~ 0.20-0.50. In contrast, its conductive and crystalline $α$ phase possesses a significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has…
The evidence for proximity-induced superconductivity in heterostructures of topological insulators and high-Tc cuprates has been intensely debated. We use molecular beam epitaxy to grow thin films of topological insulator Bi2Te3 on a cuprate Bi2Sr2CaCu2O8+x, and study the surface of Bi2Te3 using low-temperature scanning tunneling microscopy and spectroscopy. In few unit-cell thick Bi2Te3 films, we find a V-shaped gap-like feature at the Fermi energy in dI/dV spectra. By reducing the coverage of Bi2Te3 films to create nanoscale islands, we discover that this spectral feature dramatically evolve…
Advances in synthesis techniques and materials understanding have given rise to oxide heterostructures with intriguing physical phenomena that cannot be found in their constituents. In these structures, precise control of interface quality, including oxygen stoichiometry, is critical for unambiguous tailoring of the interfacial properties, with deposition of the first monolayer being the most important step in shaping a well-defined functional interface. Here, we studied interface formation and strain evolution during the initial growth of LaAlO3 on SrTiO3 by pulsed laser deposition, in search…
Infinite-layer nickelate thin films materialize an intriguing new platform for high-temperature unconventional superconductivity, with LaNiO$_2$/SrTiO$_3$ as reference setup. We discuss the relative stability of the elementary interfaces of this system and determine the corresponding electronic band structure. We find substantial changes compared to the bulk, in particular in relation to the 5$d$ orbital contributions to the low-energy physics which can be totally replaced by purely Ni-3$d$ flat bands. The $d^9$ configuration characteristic of cuprates can thus be supplemented by an extra inte…
