Recent experimental work on Au thin films demonstrated signs of charge current-induced spin polarization through open circuit voltage measurements. In this study, we are investigating the underlying mechanism(s) that induces this measured signal in the Au devices. We determine the theoretically expected spin polarization from both Rashba-Edelstein effect and bulk spin Hall effect. The discrepancy in the scaling of the measured signal as a function of the thickness of the Au thin film in the two cases is our key to differentiate between the two effects when compared to experimental data. Experiments show reversal of spin polarization at a critical thickness which reveals the presence of multiple spin polarization mechanisms. Characteristics of both RashbaEdelstein and spin Hall effects are observed in different thickness regimes. In addition, we study the magnetoresistance of the same Au samples, which reveal the presence of weak anti-localization (WAL) at low temperatures for the low-thickness samples. More interestingly, it is revealed that the open circuit voltage difference and magnetoresistance due to WAL have very similar scaling with film thickness and temperature, suggesting the crucial importance of spin-orbit interaction in understanding the phenomenon.
We consider a single molecule circuit embedded into solvent. The Born dielectric solvation model is combined with Keldysh nonequilibrium Green's functions to describe the electron transport properties of the system. Depending on the dielectric constant, the solvent induces multiple nonequilibrium steady states with corresponding hysteresis in molecular current-voltage characteristics as well as negative differential resistance. We identify the physical range of solvent and molecular parameters where the effects are present. The position of the negative differential resistance peak can be contr…
Understanding the origin of hysteresis in the channel resistance from top gated graphene transistors is important for transistor applications. Capacitance - voltage measurements across the gate oxide on top gated bilayer graphene show hysteresis with a charging and discharging time constant of ~100 μs. However, the measured capacitance across the graphene channel does not show any hysteresis, but shows an abrupt jump at a high channel voltage due to the emergence of an order, indicating that the origin of hysteresis between gate and source is due to charge traps present in the gate oxide and g…
A spin-dependent quantum transport is investigated in a paramagnetic resonant tunneling diode (RTD) based on a Zn$_{1-x}$Mn$_x$Se/ZnBeSe heterostructure. Using the Wigner-Poisson method and assuming the two-current model we have calculated the current-voltage characteristics, potential energy profiles and electron density distributions for spin-up and spin-down electron current in an external magnetic field. We have found that -- for both the spin-polarized currents -- two types of the current hysteresis appear on the current-voltage characteristics. The current hysteresis of the first type oc…
Graphene field effect transistors commonly comprise graphene flakes lying on SiO2 surfaces. The gate-voltage dependent conductance shows hysteresis depending on the gate sweeping rate/range. It is shown here that the transistors exhibit two different kinds of hysteresis in their electrical characteristics. Charge transfer causes a positive shift in the gate voltage of the minimum conductance, while capacitive gating can cause the negative shift of conductance with respect to gate voltage. The positive hysteretic phenomena decay with an increase of the number of layers in graphene flakes. Self-…
We investigate theoretically the V-I characteristics and voltage noise of superconducting tunnel junctions with small critical current via the matrix-continued-fraction method. Special attention is paid to the large hysteresis in the V-I characteristics and to the voltage-noise anomaly observed in preliminary experiments. The current dependence of the voltage noise shows a strong asymmetry between the forward and backward current ramping and a discontinuous change of the noise close to its measured maximum occurring at the switching current. We show that both the large hysteresis and the volta…
A reversible handle on graphene carrier density, other than the gate electric field, is desirable for memory applications of graphene. Our experiments show that the commonly observed carrier density hysteresis in graphene on SiO$_2$ due to interface water/oxygen vanishes at temperatures below 250 K. The state of these species, which affects the graphene carrier density, at low temperatures can be reversibly controlled by thermal cycling to room temperature at different gate voltages. Further, devices prepared with relatively dry interface, and thus showing negligible hysteresis at room tempera…
In this work we present and discuss theoretical models of redox molecular junctions that account for recent observations of nonlinear charge transport phenomena, such as hysteresis and hysteretic negative differential resistance (NDR). A defining feature in such models is the involvement of at least two conduction channels - a slow channel that determines transitions between charge states of the bridge and a fast channel that dominates its conduction. Using Marcus theory of heterogeneous electron transfer (ET) at metal-molecule interfaces we identify and describe different regimes of nonlinear…
Hysteresis exhibited by current-voltage characteristics during field-emission experiments is often considered undesirable in terms of practical applications. However, this is an appealing effect for the purposes of memristive devices. We developed a two-stage model to describe hysteretic characteristics, with a particular focus on the system which includes a cathode made of a single-layered graphene sheet on a substrate. In addition to hysteresis, the current-voltage curves display also an unusual self-crossing behavior. The presented memristive model can be used for quantitative descriptions …
We performed self-consistent modelling of electrotransport and electromechanical response of solid electrolyte thin films allowing for steric effects of mobile charged defects (ions, protons or vacancies), electron degeneration and Vegard stresses. We establish correlations between the features of the space-charge dynamics, current-voltage and bending-voltage curves in the wide frequency range of applied electric voltage. The pronounced ferroelectric-like hysteresis of bending-voltage loops and current maxima on double hysteresis current-voltage loops appear for the electron-open electrodes. T…
A ferromagnet can resonantly absorbs rf radiation to sustain a steady precession of the magnetization around an internal or applied magnetic field. We show that under these ferromagnetic resonance (FMR) conditions, a dc voltage is generated at a normal-metal electric contact to a ferromagnet with spin-flip scattering. This mechanism allows an easy electric detection of magnetization dyamics.
Mechanisms of the recently demonstrated ex-situ thermal control of the indirect exchange coupling in magnetic multilayer are discussed for different designs of the spacer layer. Temperature-induced changes in the hysteresis of magnetization are shown to be associated with different types of competing interlayer exchange interactions. Theoretical analysis indicates that the measured step-like shape and hysteresis of the magnetization loops is due to local in-plane magnetic anisotropy of nano-crystallites within the strongly ferromagnetic films. Comparison of the experiment and theory is used to…
We describe electrical detection of spin pumping in metallic nanostructures. In the spin pumping effect, a precessing ferromagnet attached to a normal-metal acts as a pump of spin-polarized current, giving rise to a spin accumulation. The resulting spin accumulation induces a backflow of spin current into the ferromagnet and generates a dc voltage due to the spin dependent conductivities of the ferromagnet. The magnitude of such voltage is proportional to the spin-relaxation properties of the normal-metal. By using platinum as a contact material we observe, in agreement with theory, that the v…
We investigate the electronic transport properties of a ferromagnet/normal/ferromagnet junction on the surface of a topological insulator with a gate voltage exerted on the normal segment. It is found that the conductance oscillates with the width of normal segment and gate voltage, and the maximum of conductance gradually decreases while the minimum of conductance approaches zero as the width increases. The conductance can be controlled by tuning the gate voltage like a spin field-effect transistor. It is found that the magnetoresistance ratio can be very large, and can also be negative owing…
It was recently predicted [Phys. Rev. B 75, 193301 (2007)] that spin blockade may develop at nonmagnetic semiconductor/perfect ferromagnet junctions when the electron flow is directed from the semiconductor into the ferromagnet. Here we consider current-voltage characteristics of such junctions. By taking into account the contact resistance, we demonstrate a current stabilization effect: by increasing the applied voltage the current density through the junction saturates at a specific value. The transient behavior of the current density is also investigated.
A silicon micromechanical torsional oscillator is used to measure the hysteresis loops of two manganite La_0.67Ca_0.33MnO_3 nanotubes at different temperatures, applying an external field along its main axes. These structures are composed of nanograins with a ferromagnetic core surrounded by a dead layer. Micromagnetic calculations based on the stochastic Landau-Lifshitz-Gilbert equation, are performed to validate a simple model that allows for quantitatively describing the ferromagnetic behavior of the system. Further simulations are used to analyze the experimental data more in depth and to …
Heterostructures of 2D van der Waals semiconductor materials offer a diverse playground for exploring fundamental physics and potential device applications. In InSe/GaSe heterostructures formed by sequential mechanical exfoliation and stacking of 2D monochalcogenides InSe and GaSe, we observe charge transfer between InSe and GaSe due to the 2D van der Waals interface formation and a strong hysteresis effect in the electron transport through the InSe layer when a gate voltage is applied through the GaSe layer. A gate voltage dependant conductance decay rate is also observed. We relate these obs…
We investigate the Fourier transform of the current through a memristor when the applied-voltage frequency is smaller than the characteristic memristor frequency, and the memristor shows hysteresis in the current-voltage plane. We find that when the hysteresis curve is "smooth", the current Fourier transform has weights at odd and even harmonics that decay rapidly and monotonically with the order of the harmonic; when the hysteresis curve is "sharp", the Fourier transform of the current is significantly broader, with non-monotonic weights at high harmonics. We present a simple model which show…
As a non-magnetic heavy metal is attached to a ferromagnet, a vertically flowing heat-driven spin current is converted to a transverse electric voltage, which is known as the longitudinal spin Seebeck effect (SSE). If the ferromagnet is a metal, this voltage is also accompanied by voltages from two other sources, i.e. the anomalous Nernst effect in both the ferromagnet and the proximity-induced ferromagnetic boundary layer. By properly identifying and carefully separating those different effects, we find that in this pure spin current circuit the additional spin current drawn by the heavy meta…
We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs. As an example, we show that VCMA can increase the sensitivity of an MTJ-based microwave signal detector to the sensitivity level of semiconductor Schottk…
Current-voltage characteristics of H2-Au molecular junctions exhibit intriguing steps around a characteristic voltage of 40 mV. Surprisingly, we find that a hysteresis is connected to these steps with a typical time scale > 10 ms. This time constant scales linearly with the power dissipated in the junction beyond an ofset power P_s = IV_s. We propose that the hysteresis is related to vibrational heating of both the molecule in the junction and a set of surrounding hydrogen molecules. Remarkably, we can engineer our junctions such that the hysteresis' characteristic time becomes >days. We demon…
We experimentally investigate second-harmonic transverse voltage response to ac electrical current for a magnetic nodal-line semimetal Fe$_3$GeTe$_2$. For zero magnetic field, the observed response depends as a square of the longitudinal current, as it should be expected for non-linear Hall effect. The magnetic field behavior is found to be sophisticated: while the first-harmonic response shows the known anomalous Hall hysteresis in FGT, the second-harmonic Hall voltage is characterized by the pronounced high-field hysteresis and flat ($B$-independent) region with curves touching at low fields…
We investigate the origin of the hysteresis observed in the transfer characteristics of back-gated field-effect transistors with an exfoliated MoS2 channel. We find that the hysteresis is strongly enhanced by increasing either gate voltage, pressure, temperature or light intensity. Our measurements reveal a step-like behavior of the hysteresis around room temperature, which we explain as water-facilitated charge trapping at the MoS2/SiO2 interface. We conclude that intrinsic defects in MoS2, such as S vacancies, which result in effective positive charge trapping, play an important role, beside…
We present a novel memory device that consists of a thin ferromagnetic layer of Fe deposited on topological insulator thin film, Bi2Se3. The ferromagnetic layer has perpendicular anisotropy, due to MgO deposited on the top surface of Fe. When current is passed on the surface of Bi2Se3, the surface of the Bi2Se3 becomes spin polarized and strong exchange interaction occurs between the d electrons in the ferromagnet and the electrons conducting the current on the surface of the Bi2Se3. Part of the current is shunted through the ferromagnet which generates spin transfer torque in the ferromagnet.…
We present a theoretical analysis of current driven ferromagnetic resonance in a ferromagnet/normal-metal/ferromagnet tri-layer. This method of driving ferromagnetic resonance was recently realized experimentally by Tulapurkar et al. [Nature 438, 339 (2005)] and Sankey et al. [Phys. Rev. Lett. 96, 227601 (2006)]. The precessing magnetization rectifies the alternating current applied to drive the ferromagnetic resonance and leads to the generation of a dc voltage. Our analysis shows that a second mechanism to generate a dc voltage, rectification of spin currents emitted by the precessing magnet…
We analyse a model describing hysteretic behaviour of the reflectivity R for the system 'graphene-Pb(ZrxTi1-x)O3 (PZT) ferroelectric substrate-gate' with a gate voltage variation, which takes into account trapping of electrons into the graphene-PZT interface states. We demonstrate that the hysteresis in the R parameter can be observed experimentally for the telecommunication-range radiation (the wavelength λ = 1.55 μm) at low gate voltages and, moreover, the phenomenon can be used while creating fast bistable systems for the novel nonvolatile memory devices with on-chip optical interconnection…
Formation of a magnetic hysteresis loop with respect to a bias voltage is investigated theoretically in a spin-valve device based on a single magnetic molecule. We consider a device consisting of two ferromagnetic electrodes bridged by a carbon nanotube, acting as a quantum dot, to which a spin-anisotropic molecule is exchange coupled. Such a coupling allows for transfer of angular momentum between the molecule and a spin current flowing through the dot, and thus, for switching orientation of the molecular spin. We demonstrate that this current-induced switching process exhibits a hysteretic b…
In many transition metal oxides the electrical resistance is observed to undergo dramatic changes induced by large biases. In magnetite, Fe$_3$O$_4$, below the Verwey temperature, an electric field driven transition to a state of lower resistance was recently found, with hysteretic current-voltage response. We report the results of pulsed electrical conduction measurements in epitaxial magnetite thin films. We show that while the high- to low-resistance transition is driven by electric field, the hysteresis observed in $I-V$ curves results from Joule heating in the low resistance state. The sh…
We report very low temperature magnetoconductance DeltaG measurements on graphene devices with the magnetic field H applied parallel to the carbon sheet. The DeltaG(H) signal depends on the gate voltage Vg and its sign is related with the universal conductance fluctuations. When the magnetic field is swept at fast rates, DeltaG displays hysteresis loops evident for different sizes and at different transport regimes of the devices. We attribute this to the magnetization reversal of paramagnetic centres in graphene layer, which might originate from defects in our devices.
We observe sharp peaks and strong hysteresis in the electronic transport of a two-dimensional electron gas (2DEG) in the region of the integral quantum Hall effect. The peaks decay on time scales ranging from several minutes to more than an hour. Momentary grounding of some of the contacts can vastly modify the strength of the peaks. All these features disappear under application of a negative bias voltage to the backside of the specimen. We conclude, that a conduction channel parallel to the high mobility 2DEG is the origin for the peaks and their hysteretic behavior.
Theory of current hysteresis for tunneling through a molecular quantum dot (MQD) with strong electron-vibron interactions and attractive electron-electron correlations is developed. The dot is modeled as a d-fold degenerate energy level weakly coupled to the leads. The effective attractive interaction between polarons in the dot results in a "switching" phenomenon in the current-voltage characteristics when d>2, in agreement with the results for the phenomenological negative-U model. The degenerate MQD with strong electron-vibron coupling has two stable current states in certain interval of th…
We present in this paper experimental results on the transport hysteresis in electron double quantum well structures. Exploring the measurement technique of fixing the magnetic field and sweeping a front gate voltage (Vg), we are able to study the hysteresis by varying the top layer Landau level fillings while maintaining a relatively constant filling factor in the bottom layer, allowing us to tackle the question of the sign of Rxx(up)-Rxx(down), where Rxx(up) is the magnetoresistance when Vg is swept up and Rxx(down) when Vg swept down. Furthermore, we observe that hysteresis is generally str…
Silicon nanowires (Si NW) are ideal candidates for solution processable field effect transistors (FETs). The interface between the nanowire channel and the gate dielectric plays a crucial role in the FET performance, and it can be responsible for unwanted effects such as hysteresis of the I-V characteristics due to threshold voltage shift when the gate voltage is applied. Using gate-voltage bias stress measurements we show that a large hysteresis of up to 40V in Si NW FETs with SiO2 dielectric is mainly due to the holes traps at the nanowire/SiO2 interface. An approach for reducing this hyster…
We have fabricated n-layer graphene field effect transistors on epitaxial ferroelectric Pb(Zr_0.2Ti_0.8)O_3 (PZT) thin films. At low gate voltages, PZT behaves as a high-k dielectric with k up to 100. An unusual resistance hysteresis occurs in gate sweeps at high voltages, with its direction opposite to that expected from the polarization switching of PZT. The relaxation of the metastable state is thermally activated, with an activation barrier of 50-110 meV and a time constant of 6 hours at 300 K. We attribute its origin to the slow dissociation/recombination dynamics of water molecules adsor…
We consider a non-local spin valve in a Van der Pauw cross geometry with four ferromagnetic electrodes. Two antiparallel ferromagnets are used as (charge) source and drain while the detector circuit involves measuring the voltage between two collinear ferromagnets with parallel or antiparallel magnetizations. We find a potentially large increase of the non-local spin voltage. The setup displays several additional interesting properties: (i) infinite GMR for the non-local resistance (if a symmetry requirement for the device is met); (ii) ON-OFF switch effect, when the injector electrodes are pa…
The steady current-voltage characteristics of ferromagnet-silicon-ferromagnet channels with tunable emitter and collector polarizations are investigated in the presence of spin blockade generalizing the model developed by Pershin Yu V and Di Ventra M (2008 {\it Phys. Rev.} B {\bf 77} 073301). The dependence of the critical current on both collector and emitter polarizations is obtained analytically. It is found that the current amplitude in the channel can be effectively tuned by varying the difference between the collector and emitter ferromagnet polarizations which allows to perform the magn…
We report the rectifying effect of a constant-wave radio frequency (RF) current by a magnetic domain wall (DW) on a single-layered ferromagnetic wire. A direct-current (DC) voltage is generated by the spin torque diode effect, which is a consequence of magnetoresistance oscillation due to the resonant spin wave excitation induced by the spin-polarized RF current. The DC voltage spectrum strongly depends on the internal spin structure in the DW, which corresponds to the magnetic fingerprint of the spin structure in the ferromagnetic wire.
Experiments on a nearly spin degenerate two-dimensional electron system reveals unusual hysteretic and relaxational transport in the fractional quantum Hall effect regime. The transition between the spin-polarized (with fill fraction $ν= 1/3$) and spin-unpolarized ($ν= 2/5$) states is accompanied by a complicated series of hysteresis loops reminiscent of a classical ferromagnet. In correlation with the hysteresis, magnetoresistance can either grow or decay logarithmically in time with remarkable persistence and does not saturate. In contrast to the established models of relaxation, the relaxat…
We study the subgap spin and charge transport in normal metal-ferromagnet-superconductor trilayers induced by bias voltage and/or magnetization precession. Transport properties are discussed in terms of time-dependent scattering theory. We assume the superconducting gap is small on the energy scales set by the Fermi energy and the ferromagnetic exchange splitting, and compute the non-equilibrium charge and spin current response to first order in precession frequency, in the presence of a finite applied voltage. We find that the voltage-induced instantaneous charge current and longitudinal spin…
We predict that the Curie temperature of a ferromagnetic resonant tunneling diode will decrease abruptly, by approximately a factor of two, when the downstream chemical potential falls below the quantum well resonance energy. This property follows from elementary quantum transport theory notions combined with a mean field description of diluted magnetic semiconductor ferromagnetism. We illustrate this effect by solving coupled non-equilibrium Green's function, magnetic mean-field, and electrostatic Poisson equations self-consistently to predict the bias voltage and temperature dependence of th…
We employ optical pump-probe spectroscopy to investigate the voltage dependence of spontaneous electron and nuclear spin polarizations in hybrid MnAs/n-GaAs and Fe/n-GaAs Schottky diodes. Through the hyperfine interaction, nuclear spin polarization that is imprinted by the ferromagnet acts on conduction electron spins as an effective magnetic field. We demonstrate tuning of this nuclear field from <0.05 to 2.4 kG by varying a small bias voltage across the MnAs device. In addition, a connection is observed between the diode turn-on and the onset of imprinted nuclear polarization, while traditio…
The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT) /ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90 in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demon…
This work reports a novel time-domain expression for the current-response kernels of a Josephson tunnel junction between BCS superconductors with in general different energy gaps, and its use to simulate the classical dynamics of such junctions. The simulations show a dynamic regime characterized by the resonance between the Josephson oscillations and the gap oscillations in the asymptotics of the current kernels that has not been studied previously. The resonance manifests itself as a hysteresis in the dc current-voltage characteristics of the current-biased junctions in the voltage range abo…
Experimental results of rectification of a constant wave radio frequency (RF) current flowing in a single-layered ferromagnetic wire are presented. We show that a detailed external magnetic field dependence of the RF current induced a direct-current voltage spectrum. The mechanism of the rectification is discussed in a term of the spin transfer torque, and the rectification is closely related to resonant spin wave excitation with the assistant of the spin-polarized RF current. The micromagnetic simulation taking into account the spin transfer torque provides strong evidence which supports the …
Hysteresis curves for finite arrays of $N\times N$ ferromagnetic nano dots subject to the dipole-dipole interaction are investigated for $N=2... 13$. Spin arrangements up to N=6 are presented, which indicate the onset of bulk-like behavior associated with odd (N=5) and even (N=6) systems. The effect of field misalignment on the hysteresis loops is also studied for $N=3... 6$. The area $A_N$ of the hysteresis loop is studied as a function of $N$. We find that $A_N-A_\infty$ approximately scales as $N^{-{3/2}}$ for $N$ odd and as $N^{-2}$ for $N$ even.
The electromotive forces induced by surface acoustic waves (SAWs) are investigated in ferromagnetic thin films. CoFeB thin films deposited on LiNbO$_3$ substrates are patterned into Hall-bars to study the acoustoelectric transport properties of the device. The longitudinal and transverse dc voltages that develop in the Hall bars, which are parallel and orthogonal to the flow of the SAW, respectively, are measured under application of an in-plane magnetic field. The longitudinal voltage scales linearly with the SAW power and reverses its polarity upon changing the direction to which the SAW pro…
We theoretically investigate an opportunity to implement a source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor (SFS) voltage-biased junction in the regime of essential proximity effect and calculate the current flowing through the probe electrode tunnel coupled to the ferromagnetic interlayer region. It is shown that while the polarization of the dc current component is generally small in case of weak exchange field of the ferromagnet, there is an ac component of the current in the system. This ac current is highly spin-polarized and entire…
We present a quantitative study of the current-voltage characteristics (CVC) of SFIFS Josephson junctions (S denotes bulk superconductor, F - metallic ferromagnet, I - insulating barrier) with weak ferromagnetic interlayers in the diffusive limit. The problem is solved in the framework of the nonlinear Usadel equations. We consider the case of a strong tunnel barrier such that the left SF and the right FS bilayers are decoupled. We calculate the density of states (DOS) in SF bilayers using a self-consistent numerical method. Then we obtain the CVC of corresponding SFIFS junctions, and discuss …
The Andreev reflection of narrow ferromagnet/superconductor point contacts is theoretically studied. We show that the conductance quantization depends on whether the contact region is superconducting or ferromagnetic as well as on the strength of the exchange field in the ferromagnet. The Andreev reflection of the ferromagnetic contact is more suppressed than that of the superconducting contact. We also show that the conductance-voltage curve has a bump at zero bias-voltage if there is no interfacial-scattering. On the contrary, the conductance-voltage curve shows a dip if the system has an in…
Spin pumping by a moving magnetization gives rise to an electric voltage over a spin valve. Thermal fluctuations of the magnetization manifest themselves as increased thermal voltage noise with absorption lines at the ferromagnetic resonance frequency and/or zero frequency. The effect depends on the magnetization configuration and can be of the same order of magnitude as the Johnson-Nyquist thermal noise. Measuring colored voltage noise is an alternative to ferromagnetic resonance experiments for nano-scale ferromagnetic circuits.
Spin accumulation in a paramagnetic semiconductor due to voltage-biased current tunneling from a polarized ferromagnet is experimentally manifest as a small additional spin-dependent resistance. We describe a rigorous model incorporating the necessary self-consistency between electrochemical potential splitting, spin-dependent injection current, and applied voltage that can be used to simulate this so-called "3T" signal as a function of temperature, doping, ferromagnet bulk spin polarization, tunnel barrier features and conduction nonlinearity, and junction voltage bias.
We measure top-gated graphene field effect transistors (GFETs) with nanosecond-range pulsed gate and drain voltages. Due to high-k dielectric or graphene imperfections, the drain current decreases ~10% over time scales of ~10 us, consistent with charge trapping mechanisms. Pulsed operation leads to hysteresis-free I-V characteristics, which are studied with pulses as short as 75 ns and 150 ns at the drain and gate, respectively. The pulsed operation enables reliable extraction of GFET intrinsic transconductance and mobility values independent of sweep direction, which are up to a factor of two…
We propose a two terminal nanomagnetic memory element based on magnetization reversal of a perpendicularly magnetized nanomagnet employing a unipolar voltage pulse that modifies the perpendicular anisotropy of the system. Our work demonstrates that the presence of Dzyaloshinskii-Moriya Interaction (DMI) can create alternative route for magnetization reversal that obviates the need for utilizing precessional magnetization dynamics as well as a bias magnetic field that are employed in traditional voltage control of magnetic anisotropy (VCMA) based switching of perpendicular magnetization. We sho…
We consider bilayer quantum Hall systems at total filling factor $ν=1$ in presence of a bias voltage $Δ_v$ which leads to different filling factors in each layer. We use auxiliary field functional integral approach to study mean-field solutions and collective excitations around them. We find that at large layer separation, the collective excitations soften at a finite wave vector leading to the collapse of quasiparticle gap. Our calculations predict that as the bias voltage is increased, bilayer systems undergo a phase transition from a compressible state to a $ν=1$ phase-coherent state {\it w…
We theoretically study the recently observed tunnel-barrier-enhanced dc voltage signals generated by magnetization precession in magnetic tunnel junctions. While the spin pumping is suppressed by the high tunneling impedance, two complimentary processes are predicted to result in a sizable voltage generation in ferromagnet (F)|insulator (I)|normal-metal (N) and F|I|F junctions, with one ferromagnet being resonantly excited. Magnetic dynamics in F|I|F systems induces a robust charge pumping, translating into voltage in open circuits. In addition, dynamics in a single ferromagnetic layer develop…
Steep-slope $β$-Ga$_2$O$_3$ nano-membrane negative capacitance field-effect transistors (NC-FETs) are demonstrated with ferroelectric hafnium zirconium oxide in gate dielectric stack. Subthreshold slope less than 60 mV/dec at room temperature is obtained for both forward and reverse gate voltage sweeps with a minimum value of 34.3 mV/dec at reverse gate voltage sweep and 53.1 mV/dec at forward gate voltage sweep at $V_{DS}$=0.5 V. Enhancement-mode operation with threshold voltage ~0.4 V is achieved by tuning the thickness of $β$-Ga$_2$O$_3$ membrane. Low hysteresis of less than 0.1 V is obtain…
Magnetic skyrmions have potential applications in next-generation spintronics devices with ultralow energy consumption. In this work, the current-driven skyrmion motion in a narrow ferromagnetic nanotrack with voltage-controlled magnetic anisotropy (VCMA) is studied numerically. By utilizing the VCMA effect, the transport of skyrmion can be unidirectional in the nanotrack, leading to a one-way information channel. The trajectory of the skyrmion can also be modulated by periodically located VCMA gates, which protects the skyrmion from destruction by touching the track edge. In addition, the loc…
