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Different from conventional ferromagnetic methods, producing a spin-polarized current through electrical ways in spintronic devices can greatly increase operating speed, reduce power consumption, and improve device integration. Inspired by recent experimental progress on the synthesis of a heptauthrene molecule, we investigate its spin-dependent transport contacted with Au electrodes through first-principles calculations. By applying a gate voltage, the transmission can be switched between completely spin-up and spin-down polarized states, achieving an electrically controlled dual-spin filter. Furthermore, a fine tuning on the spin polarization, between 100% and − 100%, can also be realized, where the transport with any ratio of spin-up to spin-down electron quantities can be realized beyond the traditional devices. The peculiar transmission spectra and their shift are found to play crucial roles, where transmission peaks distribute on both sides of the Fermi level with opposite spin components. Such a spin-polarization modulating effect is found to be robust to the molecule-electrode contacting site, indicating it is an intrinsic feature of such systems. Moreover, the dimension of the device is at the single-molecule level, suggesting great application potential. [ABSTRACT FROM AUTHOR]

The unique edge states of the zigzag β-SiC7 nanoribbons aroused our attention, and therefore, based on first-principles calculations, we investigated their spin-dependent electronic transport properties by constructing controllable defects to modulate these special edge states. Interestingly, by introducing rectangular edge defects in the SiSi and SiC edge-terminated systems, not only the spin-unpolarized is successfully converted to completely spin-polarized, but also the direction of polarization can be switched, thus enabling a dual spin filter. The analyses further reveal that the two transmission channels with opposite spins are spatially separated and that the transmission eigenstates are highly concentrated at the relative edges. The specific edge defect introduced only suppresses the transmission channel at the same edge but reserves the transmission channel at the other edge. In addition, for the CSi and CC edge-terminated systems, an additional spin-down band exists due to spin splitting in the spin-up band at EF, so that besides the original spatially separated two spin-opposite channels, an extra spin channel is distributed at the upper edge, resulting in unidirectional fully spin-polarized transport. The peculiar spatially separated edge states and excellent spin filtering properties could open up further possibilities for β-SiC7-based electronic devices in spintronics applications. [ABSTRACT FROM AUTHOR]

Ferroelectricity in two-dimensional (2D) systems generally arises from phonons and has been widely investigated. On the contrary, electronic ferroelectricity in 2D systems has been rarely studied. Using first-principles calculations, the ferroelectric behavior of the buckled blue SiSe monolayer under strain are explored. It is found that the direction of the out-of-plane ferroelectric polarization can be reversed by applying an in-plane strain. And such polarization switching is realized without undergoing geometric inversion. Besides, the strain-triggered polarization reversal emerges in both biaxial and uniaxial strain cases, indicating it is an intrinsic feature of such a system. Further analysis shows that the polarization switching is the result of the reversal of the magnitudes of the positive and negative charge center vectors. And the variation of buckling is found to play an important role, which results in the switch. Moreover, a non-monotonic variation of band gap with strain is revealed. Our findings throws light on the investigation of novel electronic ferroelectric systems. [ABSTRACT FROM AUTHOR]

Different from the honeycomb monolayer (like graphene), the single-layer boron chalcogenide B2X3 (X = S, Se, Te) exhibits a kagome lattice. Using the first-principles calculations, the existence of sliding ferroelectricity in van der Waals kagome-B2X3 bilayers is demonstrated. The sliding ferroelectricity results from the breaking of the inversion symmetry by interlayer sliding. In addition, there are multiple stable states in a unit cell for kagome-lattice bilayers. The bandgap is found to vary with sliding distance. By choosing specific pathways, not only the out-of-plane polarization but also the in-plane polarization can be reversed by interlayer sliding. Such a simultaneous reversal for both in-plane and out-of-plane polarizations by sliding would be useful for applications in various devices. These behaviors are found in all the three configurations (X = S, Se, Te), suggesting they are the intrinsic features of such systems and may throw light on the development of future devices. [ABSTRACT FROM AUTHOR]

Inspired by the recent experimental progress on the synthesization of a new type of molecule, a polyyne wire doped with the organometallic Ru (dppe) 2 fragment, which exhibits superior electronic properties to similar organic molecules reported before, we studied the electronic transport of it contacted with Au electrodes through first-principles calculations. Multiple striking negative differential resistance (NDR) behavior is observed, where the current could decrease to nearly zero. Moreover, such a phenomenon is found to be robust to the conformational change of the molecule, indicating it is the intrinsic feature of it. Further analysis shows that it is the suppression of the transmission peaks at the border of the bias window that results in the NDR. And, the suppression is resulted from the decay of the local density of states in the two-probe system, especially in the central axis of the molecule, where the states are found to originate from the p orbital of C atoms and the d orbital of Ru atoms. The multiple striking NDR behavior is achieved at the single-molecule level under low bias, showing great application potentials. These findings may throw light on the development of molecular devices. [ABSTRACT FROM AUTHOR]

Compared with conventional magnetic ways, modulating a spin-polarized current through electrical means could greatly reduce nano-devices' energy consumption and dimensions, which emerges as a new research area in spintronics. Inspired by the experimental progress on the synthesis of helically twisted graphene, we study the electronic transport of kekulene-like helical graphene nanoribbons through first-principles calculations. By applying a gate voltage, the system can be switched between spin-unpolarized and completely spin-polarized states, realizing an electrically controlled spin filter. Moreover, a fine modulation of the spin polarization can also be achieved, where transmission with any ratio of spin-up to spin-down electrons can be obtained, beyond the traditional spin filter. The analysis shows that it is the particular transmission spectra that play a key role, where two wide peaks with opposite spins reside partially overlapped around the Fermi level. They originate from the p orbitals of the zigzag edge part in the helical structure. Since the configuration only consists of carbon atoms, the electrical control of spin polarization is realized in a pure-carbon nano-system, showing great application potentials. [ABSTRACT FROM AUTHOR]

Inspired by recent progress of experimental fabrication of partial structure of the helical graphenes, we construct helical graphene nanoribbons and study the electronic structure and transport properties of them, through first-principles calculations. It is found that a metal-semiconductor transition occurs when the pitch of the configuration changes, and the whole transition process can be divided into three regimes, i.e., metallic, fast changing bandgap, and slowly changing bandgap ones. Further analysis shows that, interlayer transmission, interlayer interaction (bilayer graphenelike state) and intralayer interaction are the mechanisms behind, respectively. Moreover, such a transition and corresponding mechanisms show good robustness to the size of the helical graphene nanoribbons, suggesting great application potential. As the systems are pure-carbon and graphene-based ones, as well as an adjustable and reversible bandgap, such configurations might be quite useful in future nanodevices. [ABSTRACT FROM AUTHOR]

Among many modulation methods, strain engineering is often chosen for nanomaterials to produce tunable band gaps continuously. Inspired by the recently reported two-dimensional material PC3, we explore the tuning of strain on the spin-dependent transport properties of PC3 nanoribbons using the first-principle approach. Surprisingly, strain regulation achieves uninterrupted completely dual-spin polarization over a wide energy range near EF. Analysis reveals that the peculiar transmission spectra arise from the interesting evolution of the band structure, in which strain induces bands to shift and broaden/flatten. This results in triggering the transition of PC3NRs from bandgap-tunable bipolar magnetic semiconductors to spin-gapless semiconductors to ferromagnetic metals or half-metal magnets. Their unique performance demonstrates great potential in spintronics, and our study is expected to provide ideas and theoretical support for the design and application of novel PC3-based spintronic devices in the future. [ABSTRACT FROM AUTHOR]

Compared with traditional magnetic approaches, electrical modulation of spin-polarized current can greatly reduce the energy consumption and scale of nanodevices and improve their operating speed, which has become a promising research field in spintronics. Motivated by the latest reported novel two-dimensional material β-SiC7, we employ first-principles calculations to investigate its spin-dependent electron transport with diverse edge configurations. By introducing a gate voltage, the three-terminal device can not only switch between spin-unpolarized and fully spin-polarized states, but also easily change the polarization direction, behaving as an excellent electrically modulated reversible dual-spin filter. Surprisingly, an arbitrary proportion of spin-up and spin-down electron numbers is achieved, enabling precise control of spin polarization. Analysis reveals that it is attributed to the peculiar transmission spectrum, where two broad peaks with opposite spins are located around the Fermi level and respond differently to gate voltage. They belong to the spatially separated edge states originating from the p orbitals of the edge atoms. This feature is robust to different edge configurations of β-SiC7 nanoribbons, indicating that this may be an intrinsic property of such systems, showing great potential for applications. [ABSTRACT FROM AUTHOR]

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Different from conventional materials, structures with a negative Poisson's ratio (NPR) contract/expand laterally under a longitudinal compressive/tensile strain, usually exhibiting peculiar features. Through first-principles calculations, we investigate the electronic and transport properties of Pd9B16 molecules. Its Poisson's ratio is found to be negative under uniaxial strain along a specific direction. By contacting with Au nanowires, atomic Au chains and atomic C chain electrodes, two kinds of transitions for transmission states could be realized by the modulation of the strain and the contacting site, i.e., metallic–semiconducting transition and spin polarized–unpolarized transition. Further analysis shows that it is the suppression and shifting of density of states, caused by the strain or contacting electrodes, that trigger the transitions. Those findings combine NPR and spintronics at the single-molecule level, which may throw light on the development of nanoelectronic devices. [ABSTRACT FROM AUTHOR]