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Within the framework of the self-consistent effective field approximation of the time-dependent perturbation theory, an influence of the electron tunneling on the spontaneously induced order parameters in a normal metal–superconductor hybrid structure is considered. For a normal-metal model, which does not take into account electron-electron scattering, as well as electron-phonon coupling, a critical barrier transparency, corresponding to the disappearance of superconductivity in the ground state, was obtained. The presence of incoherent excitations leads to a complex relationship between the effects of ordering, thermal fluctuations, and tunneling. Near the critical barrier transparency, this can stabilize a superconducting state in the certain temperature intervals. As a result, a reentrant superconductivity phenomenon was observed. The studied spectral properties of the hybrid structure reflect the existence of both coherent and incoherent elementary excitations. [ABSTRACT FROM AUTHOR]

We report herein existence of a critical tunnelling width beyond which graphitic tunnelling nanostructures exhibit asymmetric spin polarized negative differential resistance feature. Our theoretical foray quite clearly establishes that even with a simple two‐dimensional tunnelling nanostructure created by an assembly of ferromagnetic graphitic carbon nitride (g‐C4N3) electrodes separated by insulating graphene sheet of variable lengths, there exists a critical tunnelling width at which the system switches from symmetric to asymmetric negative differential resistance feature. Presence of robust spin filer efficiency (100 %) over a wide range of bias variation (−1.0 to +1.0 V) added with negative differential resistance action makes the device with shorter tunnelling width of 22.36 Å and 31. 96 Å potentially useful as multifunctional spintronic device. However, at the critical tunnelling width of 36.69 Å and beyond the forward bias negative differential resistance features completely switches off and same is observed only in reverse bias. This switching action certainly opens up the prospect of logic gates operation in quantum circuits. Results obtained has been explained through transmission spectra, transmission pathways and molecular projected self‐consistent Hamiltonian states analysis. Emergence of asymmetric I−V curve beyond critical tunnelling width has been explained by examining differences in spin injection coefficients. [ABSTRACT FROM AUTHOR]

We report herein existence of a critical tunnelling width beyond which graphitic tunnelling nanostructures exhibit asymmetric spin polarized negative differential resistance feature. Our theoretical foray quite clearly establishes that even with a simple two‐dimensional tunnelling nanostructure created by an assembly of ferromagnetic graphitic carbon nitride (g‐C4N3) electrodes separated by insulating graphene sheet of variable lengths, there exists a critical tunnelling width at which the system switches from symmetric to asymmetric negative differential resistance feature. Presence of robust spin filer efficiency (100 %) over a wide range of bias variation (−1.0 to +1.0 V) added with negative differential resistance action makes the device with shorter tunnelling width of 22.36 Å and 31. 96 Å potentially useful as multifunctional spintronic device. However, at the critical tunnelling width of 36.69 Å and beyond the forward bias negative differential resistance features completely switches off and same is observed only in reverse bias. This switching action certainly opens up the prospect of logic gates operation in quantum circuits. Results obtained has been explained through transmission spectra, transmission pathways and molecular projected self‐consistent Hamiltonian states analysis. Emergence of asymmetric I−V curve beyond critical tunnelling width has been explained by examining differences in spin injection coefficients. [ABSTRACT FROM AUTHOR]

The injection of spin-polarized electrons from a magnetic material into semiconductor is currently one of the foremost challenges in semiconductor spin electronics. Here, we have studied the efficient electrical spin injection and detection from nickel doped Fe3O4 (NFO) into the p-Si having (100) crystal orientation via MgO thin insulating tunnel barrier with the help of three-terminal Hanle measurement. The NFO/MgO/p-Si heterojunction has been prepared using pulsed laser deposition (PLD) technique. Clear Hanle and Inverted Hanle signals have been noticed in spin injection and detection condition of the heterojunction. A large value of Hanle signal (ΔV = 2.4 mV) has been detected at room temperature (300 K). Pure spin accumulation in p-Si resulted from spin injection from strong ferromagnetic NFO via MgO tunnel barrier has been corroborated by a meticulous experiment incorporating a non-magnetic Ag/MgO/p-Si heterostructure. The bias dependent ΔV and spin lifetime (τ) suggest that the transport of the heterojunction is governed by the spin tunnelling via pin-hole free MgO tunnel barrier. Hence the oxide magnetic materials establish a decent platform in spin injection and detection for the development and improvement of room temperature spin-based electronic devices. [ABSTRACT FROM AUTHOR]

Single-electron tunneling transistors (SETs) and boxes (SEBs) exploit the phenomenon of Coulomb blockade to achieve unprecedented charge sensitivities. Single-electron boxes, however, despite their simplicity compared to SETs, have rarely been used for practical applications. The main reason for that is that unlike a SET where the gate voltage controls conductance between the source and the drain, an SEB is a two terminal device that requires either an integrated SET amplifier or high-frequency probing of its complex admittance by means of radio frequency reflectometry (RFR). The signal to noise ratio (SNR) for a SEB is small, due to its much lower admittance compared to a SET and thus matching networks are required for efficient coupling ofSEBs to an RFR setup. To boost the signal strength by a factor of N (due to a random offset charge) SEBs can be connected in parallel to form arrays sharing common gates and sources. The smaller the size of the SEB, the larger the charging energy of a SEB enabling higher operation temperature, and using devices with a small footprint (<0.01 µm2), a large number of devices (>1000) can be assembled into an array occupying just a few square microns. We show that it is possible to design SEB arrays that may compete with an SET in terms of sensitivity. In this, we tested SETs using RF reflectometry in a configuration with no DC through path ("DC-decoupled SET" or DCD SET) along with SEBs connected to the same matching network. The experiment shows that the lack of a path for a DC current makes SEBs and DCD SETs highly electrostatic discharge (ESD) tolerant, a very desirable feature for applications. We perform a detailed analysis of experimental data on SEB arrays of various sizes and compare it with simulations to devise several ways for practical applications of SEB arrays and DCD SETs. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose the use of electrostatic doping for n+ drain region formation in Junctionless accumulation mode field effect transistors (JAMFET). This electrostatically doped drain (EDD) JAMFET employs an additional unbiased electrode (auxiliary electrode) of low workfunction on the intrinsic drain region. This technique effectively suppresses the tunneling leakage, thereby reducing IOFF by 6 orders. The tunneling of electrons from valence band of channel to conduction band of drain happens due to enhanced band bending in OFF‐state (VGS = 0 V, VDS = 1 V). The presence of additional electrode in EDD‐JAMFET increases the width of tunnel barrier formed at channel–drain junction in OFF‐state improving the ION/IOFF ratio by 6 orders. The gate length scaling demonstrates that leakage suppression of EDD‐JAMFET is more effective with approximately 3 orders smaller IOFF even at gate length of 5 nm. The performance of graded channel device (GC‐EDD‐JAMFET) by electrostatic doping is also explored. Significant improvements are observed in terms of ION/IOFF, subthreshold slope SS, DIBL and fT. Finally, the analogue parameters such as Transconductance generation factor Gm/ID, Intrinsic gain AV, output conductance GD, and 'Gm/ID × fT' performance metrics are investigated which show significant improvement at small bias current, making it suitable for ultra‐low power applications. [ABSTRACT FROM AUTHOR]

High switching speed, endurance, and low-current-based perpendicular magnetic tunnel junction (p-MTJ) memory is attracting wide interest as a key promising candidate for next-generation spintronic memory technology. p-MTJ-based spin-transfer torque RAM (STT-RAM) has been extensively investigated, and despite the promise, there is concern about the high switching current density and low stability with regard to scaling. In this work, the current controllability of p-MTJ in iron (Fe)-enriched Co20Fe60B20 with a newly designed MgOxN1–x tunnel layer is systematically investigated, with the expectation that the introduction of N minimizes the oxidation of Fe to improve the performance of the device. A facile, plasma-based oxynitridation (MgOx = 0.57N1–x=0.43) of MgO through RF-sputter deposition serves as a reliable procedure to establish a tunnel barrier for an MTJ structure fabricated with ~300-nm diameter and pinned with synthetic antiferromagnetic (SAF) [Co/Pt]n multilayer stack. Current-controlled tunneling magnetoresistance (TMR) up to ~65% was observed at room temperature (RT) with ultralow switching current density (Jc) of 136 ± 17 kA/cm2. TMR along with tunnel conductance (g(V)) was measured to be highly stable in the read-bias regime (−200 to +200 mV) for MgOxN1–x as compared to the reported MgO barrier. The analogous MgOxN1–x-based MTJ structures were modeled using the nonequilibrium Green’s function (NEGF) with appropriate tunnel barrier parameters and incorporating modulated barrier height as compared with the MgO barrier. The current–voltage characteristics of the modeled device showed close agreement with experimental data indicating high spin current. Based on the field-induced magnetization analysis, the macro-magnetic reversal analysis suggests the free-layer switching duration of ~3 ns. These observations show the strong candidature of MgOxN1–x (x = 0.57) MTJs for STT-RAM device application. [ABSTRACT FROM AUTHOR]

Single-electron tunneling transistors (SETs) and boxes (SEBs) exploit the phenomenon of Coulomb blockade to achieve unprecedented charge sensitivities. Single-electron boxes, however, despite their simplicity compared to SETs, have rarely been used for practical applications. The main reason for that is that unlike a SET where the gate voltage controls conductance between the source and the drain, an SEB is a two terminal device that requires either an integrated SET amplifier or high-frequency probing of its complex admittance by means of radio frequency reflectometry (RFR). The signal to noise ratio (SNR) for a SEB is small, due to its much lower admittance compared to a SET and thus matching networks are required for efficient coupling ofSEBs to an RFR setup. To boost the signal strength by a factor of N (due to a random offset charge) SEBs can be connected in parallel to form arrays sharing common gates and sources. The smaller the size of the SEB, the larger the charging energy of a SEB enabling higher operation temperature, and using devices with a small footprint (2), a large number of devices (>1000) can be assembled into an array occupying just a few square microns. We show that it is possible to design SEB arrays that may compete with an SET in terms of sensitivity. In this, we tested SETs using RF reflectometry in a configuration with no DC through path (“DC-decoupled SET” or DCD SET) along with SEBs connected to the same matching network. The experiment shows that the lack of a path for a DC current makes SEBs and DCD SETs highly electrostatic discharge (ESD) tolerant, a very desirable feature for applications. We perform a detailed analysis of experimental data on SEB arrays of various sizes and compare it with simulations to devise several ways for practical applications of SEB arrays and DCD SETs.

Within the framework of the scattering matrix formalism, the nonlinear Kubo theory for electron transport in the metal with a tunnel barrier has been considered. A general expression for the mean electrical current was obtained. It significantly simplifies the calculation of nonlinear contributions to the conductivity of various hybrid structures. In the model of the tunnel Hamiltonian, all linear and nonlinear contributions to a mean electrical current are evaluated. The linear approximation agrees with results of other theories. For effective barrier transmission, the ballistic transport is realised with a value of the Landauer conductivity equal to. [ABSTRACT FROM PUBLISHER]

The quality of the tunnel barrier at the ferromagnet/graphene interface plays a pivotal role in graphene spin valves by circumventing the impedance mismatch problem, decreasing interfacial spin dephasing mechanisms and decreasing spin absorption back into the ferromagnet. It is thus crucial to integrate superior tunnel barriers to enhance spin transport and spin accumulation in graphene. Here, we employ a novel tunnel barrier, strontium oxide (SrO), onto graphene to realize high quality spin transport as evidenced by room-temperature spin relaxation times exceeding a nanosecond in graphene on silicon dioxide substrates. Furthermore, the smooth and pinhole-free SrO tunnel barrier grown by molecular beam epitaxy (MBE), which can withstand large charge injection current densities, allows us to experimentally realize large spin accumulation in graphene at room temperature. This work puts graphene on the path to achieve efficient manipulation of nanomagnet magnetization using spin currents in graphene for logic and memory applications. [ABSTRACT FROM AUTHOR]