Contact resistance has been a bottleneck in estimating the performance limits of 2-D-field effect transistor (FET) performance; most reports still parameterize contact performance into a single value, i.e., contact resistance (R-C) , which is inadequate to understand the physics of contact transport. Here, we deconvolute that value into two parts: the transport at the interface, characterized by the interface resistance (R-INT) , or the specific contact resistivity (rho(C)) ; and the undercontact transport by the charge-transfer-dependent sheet resistivity (R-SK) . Using structures like cross-bridge kelvin resistor (CBKR), contact end (CE) along with transmission line model (TLM) method on monolayer MoS2, clear, bias dependence estimates of both resistance components could be determined. CBKR approach yields a reliable benchmark for rho C and CE approach provides a cross-check of rho(C) and L-T. This deconvolution turns contact resistance (R-C) from a single figure of merit into a design map, indicating when very short contacts are viable and which interface steps matter most.

Two-dimensional semiconductors are promising channel materials for continuing transistor scaling and extending Moore's law. However, as transistor density increases, the area available for contacts shrinks, making low-resistance contacts a critical challenge. Here, we theoretically investigate the performance and scalability of edge, top, and hybrid contacts to MoS2 monolayers. Using a quantum transport model that includes key mechanisms such as image-force barrier lowering as well as open vertical metal leads, we compare the contact resistance of these geometries while analyzing the impact of parameters such as doping concentration, surrounding dielectrics, metal work functions, van der Waals gap thickness, and contact length. We find that hybrid contacts generally yield the best performance, especially when scaled to contact lengths below 10 nm, achieving a contact resistance close to the quantum limit at doping concentrations above 1013 cm-2. The edge contact exhibits the poorest performance under most circumstances, as it suffers from higher Schottky barriers and lacks mechanisms to reduce them. While the top contact performs well, the hybrid contact shows significantly lower resistances at extreme scaling because it is less sensitive to long transfer lengths.

In this work, we investigate the differential voltage generation arising from the direct magnetoelectric (ME) effect in nanoscale composite devices upon magnetization rotation from the magnetic ground state to an out-of-plane (OOP) configuration. These composite devices comprise a magnetostrictive ferromagnetic layer and a piezoelectric layer, mechanically coupled through strain. Using a finite element method (FEM) model, developed in COMSOL Multiphysics, we provide a comprehensive analysis of strain transfer mechanisms and resulting voltage generations. Here, the influence of dimensional and material parameters on the device performance is systematically examined. Our results indicate the presence of two distinct strain transfer mechanisms at scaled dimensions, where the device aspect ratio and the magnetic state both determine the dominant mechanism influencing the strain transfer to the piezoelectric layer. Moreover, we observed that the influence of surface clamping diminished as the pillar area was reduced. We also saw that the strain transfer to the piezoelectric layer can be enhanced by using stiffer electrodes or clamping layers. Lastly, we concluded that magnetostrictive materials with large magnetoelastic coupling constants or large Poisson ratios may strongly increase the output voltage at small dimensions. This study provides insight in the dimension and material selection when designing scaled ME pillars, with the aim of generating large output voltages. We showed that output voltages exceeding 200 mV can be achieved in scaled devices, underscoring the potential of these structures for integration into microelectronic applications.

We present a flexible modeling framework for flopping-mode spin qubits that captures the spatial structure of the double-well confinement and magnetic-field-gradient profile going beyond conventional low-energy descriptions. By using this approach, we simulate electric dipole spin resonance-based single-qubit control and evaluate the frequency and spectral purity of the Rabi oscillations across different parameter regimes. Our analysis reveals a fundamental tradeoff between fast electrical driving and clean single-mode Rabi oscillations, and demonstrates that the standard two-site low-energy approximation can overestimate the Rabi frequency by up to ∼ 20% in certain parameter regimes. We also investigate two-qubit control by considering two capacitively coupled flopping-mode qubits and derive the corresponding exchange interaction with an appropriately restricted configuration interaction treatment. Our approach reveals the interplay between the spatial profile of the double-well confinement, magnetic field gradient, and Coulomb interaction, which together govern the effective exchange coupling strength. Our spatially resolved modelling framework enables efficient exploration of double-well confinement parameters and magnetic field gradient profiles, enabling a transparent mapping from spatial device properties to flopping-mode qubit parameters and quality metrics.

Donor spin systems host a native Hilbert space whose dimension exceeds that of a qubit, meaning they can be used as qudits. Here we study a Si:P donor spin system through leakage-aware randomized benchmarking (RB) of native ququart 𝒞_4 and encoded two-qubit 𝒞_2^⊗ 2 Clifford groups. We implement adiabatic ramps to operate electron dipole spin resonance (EDSR) pulses at the ionization point, where the electron is shared halfway between the donor and the interface, and to operate electron spin resonance (ESR) pulses near the interface, motivated by the sensitivity of the effective magnetic field to charge noise at the ionization point. By placing the electron near the ionization point only during EDSR control and using sufficiently long displacement ramp durations, leakage outside the computational basis is strongly suppressed, which is crucial for optimized qudit control. We find in our analysis based on leakage RB that 𝒞_4 consistently achieves ∼ 40–50% lower (lower-bound) error rates ε^LB_PT with respect to 𝒞_2^⊗ 2, due to its reduced circuit complexity. These results indicate that donor spin qudits benefit from genuine qudit operation as opposed to imposed encoded qubit operation.

ABSTRACT Chirally coupled magnetic tunnel junctions (MTJs) have been proposed as a route toward compact spin logic architectures. Micromagnetic simulations indeed show that chiral coupling between adjacent MTJs with perpendicular magnetic anisotropy (PMA) can be achieved through an in‐plane (IP) interconnection mediated by the Dzyaloshinskii–Moriya interaction, eliminating the need for current‐driven domain‐wall motion. Nevertheless, experimental implementation of this concept requires precise manipulation of PMA to define IP interconnections between MTJs, as well as independent control of DMI to ensure reliable coupling. Here, we introduce a hybrid free layer (HFL) stack comprising an Ir/Co bottom layer and a CoFeB/MgO top layer providing PMA. We show that ultrathin Pt insertion layers at the Ir/Co interface provide an effective means to tune the DMI without affecting PMA, enabling independent control of both properties. Finally, we develop an ion beam etching (IBE) process on a 300‐mm platform that selectively suppresses the CoFeB/MgO contribution to PMA, thereby converting the stack to IP magnetization. This approach enables the manipulation of the PMA of the interconnecting free layer during MTJ patterning, providing a scalable pathway for the fabrication of chirally coupled MTJs.

Protecting superconducting qubits from low-frequency noise by operating them on dynamical sweet-spot manifolds has proven to be a promising setup, theoretically as well as experimentally. These dynamical sweet spots are induced by an externally applied Floquet drive, and various drive forms have been studied in different types of qubits. In this work we study the effects of using two-tone drives on the applied magnetic flux of the form phi(ac)(t) = phi(m)cos(mw(d)t) + phi(n) cos(nw(d)t + phi), where m, n is an element of N->0, on the coherence times of fluxonium qubits. Through analysis using perturbation theory in the strong-drive limit, we show which sets of drive parameters increase the dephasing times, based upon first-order coupling between Floquet modes. These are further analyzed using numerical calculations. We further show that this type of drive allows for more tunability of the quasienergy spectrum, creating higher and wider peaks of the dephasing time without affecting the relaxation times too strongly. Lastly, we show that temporarily modulating the drive form using a second commensurable tone can be used to implement an improved phase gate compared to implementations with a single tone, supported by Monte Carlo simulations.

We present an analytical model for power transfer in a magnetoelectric-film bulk-acoustic resonator (FBAR) comprising a piezoelectric-magnetostrictive bilayer. The model describes the power flow between the elastic and magnetic systems, quantifying the transduction efficiency when the FBAR operates as a magnetic transducer. By applying the model to example systems using piezoelectric ScAlN and magnetostrictive CoFeB, Ni, or Terfenol-D layers, we demonstrate the potential for achieving high efficiencies in magnetoelectric transducers, rendering them ideal for efficient ferromagnetic resonance excitation. The validity of the model's assumptions is confirmed through comparison with a numerical finite-element resonator model in COMSOL. The finite-element model further enables a comprehensive study of the resonator's dynamic behavior, including transient and steady-state regimes, and the identification of resonant frequencies within the system.

We present micromagnetic simulations and experiments on voltage-assisted field switching in perpendicular magnetic tunnel junctions (MTJs) with a synthetic antiferromagnetic (SAF) free layer, where the magnetic state of one sublayer is detected via tunneling magnetoresistance (TMR). Simulations reveal that local modulation of perpendicular magnetic anisotropy in one SAF sublayer leads to distinct switching characteristics. The switching field varies linearly with the anisotropy field, indicating voltage-controlled magnetic anisotropy (VCMA)-dominated dynamics similar to single free-layer devices. We then experimentally study the magnetic switching field of MTJ devices with SAF free layers under applied gate voltage. By varying the MgO tunnel barrier thickness to systematically modulate the resistance-area (RA) product, we enable quantitative separation of spin-transfer torque (STT), VCMA, and Joule heating contributions. Our findings indicate that VCMA dominates in devices with a high-RA product, while low-RA devices exhibit nonlinear switching behavior due to enhanced contributions from STT and Joule heating. Furthermore, the effective fields derived from STT, VCMA, and Joule heating contributions under various gate voltages show minimal dependence on device critical dimensions, indicating favorable scaling behavior. This work presents a unified framework analyzing the roles of STT, VCMA, and Joule heating in SAF-based voltage-gated spin-orbit torque (SOT) magnetic random-access memory (MRAM), offering key insights for the optimization of performance, energy efficiency, and scalability in SOT-MRAM technologies.

This work investigates the direct magnetoelectric effect in thin-film lab scale composite heterostructures comprising a 100 nm thick piezoelectric Sc0.4Al0.6N (ScAlN) and a magnetostrictive Ni with 100-200 nm thickness, fabricated on Si/SiO2 substrates. The films are patterned into square pillar arrays with lateral dimensions down to 500 nm x 500 nm. Vibrating sample magnetometry (VSM) measurements reveal in-plane magnetic anisotropy in the Ni films, attributed to strain induced by the underlying ScAlN layer. Nitrogen-vacancy (NV) magnetometry imaging confirms the formation of magnetic domains at remanence in polycrystalline Ni when patterned in sub-microscale structures. Capacitance measurements reveal a ScAlN dielectric constant at the device level consistent with unpatterned thin films, confirming the preservation of electrical integrity at the sub-microscale. The direct magnetoelectric effect is demonstrated through quasi-static charge measurements under applied out-of-plane DC magnetic fields, yielding equivalent open-circuit voltages up to 1.17 mV.

This study investigates the direct magnetoelectric effect in thin film composites comprising a 550 nm thick poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) layer spin-coated onto a 500 mu m thick Ni foil substrate. Direct measurements of charge accumulation on dot capacitors with Au top electrodes, induced by the rotation of Ni magnetization from in-plane to out-of-plane orientation by an applied magnetic field, reveal pronounced magnetoelectric coupling. Polarization differences between in-plane and out-of-plane magnetization states of up to (13.8 +/- 0.8) x 10-4 mu C cm-2 are derived from charge measurements. This corresponds to a maximum open circuit voltage difference of up to 75 +/- 6 mV and a magnetoelectric coupling coefficient with respect to magnetization changes of 310 +/- 27 mVA-1. Finite element simulations using COMSOL Multiphysics corroborate experimental findings, indicating near-independence of generated polarizations and open circuit voltages when lateral capacitor dimensions are reduced into the nanometer range. Simulations of nanoscale pillar devices on rigid substrates, employing materials with optimized piezoelectric and magnetostrictive parameters, predict the potential for generating large open circuit voltage differences exceeding 2 V, highlighting the prospects of such devices for spintronic applications.

Conventional treatments of Josephson junctions (JJs) are typically not current-conserving. In the mean-field BCS theory, current conservation is only guaranteed if the superconducting order parameter is treated self-consistently. We show that this requirement has significant consequences for the current-phase relation (CPR) in certain regimes, where the current density in the superconducting leads is non-negligible. To this end, we introduce a numerical method for the self-consistent treatment of the BdG equations with current conservation for quasi-1D superconductor-normal (metal)-superconductor (SNS) JJs. Our model incorporates a phase gradient of the order parameter in the leads, which is set to match the Josephson current through the weak link. We compare our method to standard, non-current-conserving approaches by calculating the CPR for SNS JJs while varying lengths and gate voltages controlling the normal metal. We show that current conservation has significant implications for the Josephson harmonics and can weaken or even reverse forward skewness of the CPR.

As device dimensions approach the nanoscale, contact resistance increasingly limits performance, particularly in low-dimensional systems where quantum mechanical effects dominate. In this work, we systematically investigate the quantum limit (QL) of contact resistance in 1D, 2D, and 3D semiconductors. Using general analytical expressions derived from ballistic transport theory and Fermi-Dirac statistics, we evaluate the QL across both the non-degenerate (Maxwell-Boltzmann) and degenerate (low-temperature) regimes. These expressions are validated against numerical simulations that incorporate electrostatic effects via the Poisson equation, allowing us to assess both fundamental and practical limits of contact resistance. Our results show that in the non-degenerate limit, all dimensionalities exhibit similar behavior, whereas in the degenerate limit, resistance increases exponentially as dimensionality decreases. When realistic contact electrostatics are included, the intrinsically weaker screening in lower-dimensional systems leads to more extended depletion regions, which influence resistance scaling in the non-degenerate regime. In contrast, in the degenerate limit, contact resistance is primarily governed by the quantum limit.

Conventional treatments of Josephson junctions (JJs) are typically not current conserving. In the mean-field Bardeen-Cooper-Schrieffer theory, current conservation is only guaranteed if the superconducting order parameter is treated self-consistently. We show that this requirement has significant consequences for the current-phase relation (CPR) in certain regimes, where the current density in the superconducting leads is non-negligible. To this end, we introduce a numerical method for the self-consistent treatment of the Bogoliubov-de Gennes equations with current conservation for quasi-one-dimensional superconductor-normal (metal)-superconductor (SNS) JJs. Our model incorporates a phase gradient of the order parameter in the leads, which is set to match the Josephson current through the weak link. We compare our method to standard, noncurrent conserving approaches by calculating the CPR for SNS JJs while varying lengths and gate voltages controlling the normal metal. We show that current conservation has significant implications for the Josephson harmonics and can weaken or even reverse forward skewness of the CPR.

We investigate the impacts of layer number and heterostructure stacking on the transport of 2D cold-metal-source FETs within the DFT-NEGF framework using our NEGF solver, ATOMOS, which enables electron-phonon coupling analysis. Our simulations demonstrate that optimized $\text{NbS}_{2} / \text{WS}_{2}$ stacking reduces the van der Waals gap, enhancing on-current, while additional cold-metal layers introduce density of states near the Fermi level, further improving the on-current. This study presents an effective design strategy for cold-source materials and contacts to achieve steep-slope transport.

Theoretical efforts to study transport properties in 2D are either limited to a simplified analytical description with limited applicability beyond the low-field regime or a numerically intensive full-band approach that is prone to discretization errors. In this paper, we describe a first-principles full-band Monte-Carlo method that utilizes full scattering matrix-elements while retaining the benefits of the analytical approach. We apply this method to the study of field-dependent electron transport in monolayer $\text{WS}_{2}$. To show the limits of applicability, we compare our approach to a simplified effective mass method. For the effective mass method, we extract inter- and intra-valley deformation potentials to match closely the scattering rates of the full-band approach.

Using Hubbard-U-corrected density functional theory calculations, lattice Monte Carlo simulations, and spin Monte Carlo simulations, we investigate the impact of dopant clustering on the magnetic properties of WSe2 doped with period four transition metals. We use manganese (Mn) and iron (Fe) as candidate n-type dopants and vanadium (V) as the candidate p-type dopant, substituting the tungsten (W) atom in WSe2. Specifically, we determine the strength of the exchange interaction in Fe-, Mn-, and V-doped WSe2 in the presence of clustering. We show that the clusters of dopants are energetically more stable than discretely doped systems. Further, we show that in the presence of dopant clustering, the magnetic exchange interaction significantly reduces because the magnetic order in clustered WSe2 becomes more itinerant. Finally, we show that the clustering of the dopant atoms has a detrimental effect on the magnetic interaction, and to obtain an optimal Curie temperature, it is important to control the distribution of the dopant atoms.