Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

We propose a new idea to generate pure spin current with photogalvanic effect (PGE) by designing devices with spatial inversion symmetry based on two-dimensional spin semiconducting materials Due to the preservation of spatial inversion symmetry, the electric current generated by the PGE must be zero However, finite spin-dependent current ${I}_{\ensuremath{\uparrow}/\ensuremath{\downarrow}}$ may still be produced Once an amount of spin-up electrons flow into the device region from lead $\ensuremath{\alpha}$ and flow out from lead $\ensuremath{\beta}$ under light irradiation, the same amount of spin-down electrons will flow into the device region from lead $\ensuremath{\beta}$ and flow out from lead $\ensuremath{\alpha}$, which results in ${I}_{c}^{\ensuremath{\alpha}/\ensuremath{\beta}}={I}_{\ensuremath{\uparrow}}^{\ensuremath{\alpha}/\ensuremath{\beta}}+{I}_{\ensuremath{\downarrow}}^{\ensuremath{\alpha}/\ensuremath{\beta}}=0$ and ${I}_{s}^{\ensuremath{\alpha}/\ensuremath{\beta}}={I}_{\ensuremath{\uparrow}}^{\ensuremath{\alpha}/\ensuremath{\beta}}\ensuremath{-}{I}_{\ensuremath{\downarrow}}^{\ensuremath{\alpha}/\ensuremath{\beta}}\ensuremath{\ne}0$ simultaneously for each lead and thus finite pure spin current arises As a concrete example, this idea is demonstrated by calculating the PGE in a photoelectric device constructed with an armchair-edged graphene nanoribbon which is divided into two semi-infinite ribbons The two semi-infinite ribbons are then periodically and symmetrically patterned with ferromagnetic triangle antidots in the form of ``$▹◃$'' to achieve spatial inversion symmetry of the device We find that the pure spin current can be robustly generated, neither dependent on the photon energy and polarization/helicity angle, nor dependent on whether it is linearly, circularly, or elliptically polarized

Pure spin current generation via photogalvanic effect with spatial inversion symmetry

In the multiferroic tunnel junction (MFTJ) composed of ferromagnetic and ferroelectric materials, the tunneling electroresistance (TER) coexists with the tunneling magnetoresistance (TMR), making it an ideal platform for designing multifunctional electronic devices. Recently, the rapid development of van der Waals (vdW) materials opened up a new avenue of MFTJ due to their atomic thickness and signiﬁcance in miniaturizing device sizes. Here by employing the nonequilibrium Green’s function combined with density-functional theory, we systemically study the spin-dependent electronic transport properties of Fe 3 GeTe 2 (FGT)/bilayer α -In 2 Se 3 (BIS)/FGT vdW MFTJs. We ﬁnd that the MFTJ can form multiple nonvolatile resistance states by altering the polarization orientation of the ferroelectric barrier BIS and the magnetization alignment of the two ferromagnetic FGT electrodes, with a maximum TMR (TER) ratio up to 1 . 1 × 10 7 % (744%). The TER ratio can be further increased to 1868% by using left and right symmetrical copper electrodes. More interestingly, the perfect spin ﬁltering effect can be realized in our MFTJs and the spin current can be controlled by the sign of bias voltages, suggesting a promising route for spin valves that can ﬂexibly manipulate spin currents. Our results demonstrate that giant TMR, large TER, as well as a tunable spin ﬁlter can coexist in one system, and that the feasible tunability of such kind of vdW MFTJs is beneﬁcial in designing next-generation logic and memory devices.

Giant tunneling magnetoresistance and electroresistance in 
α−In2Se3
-based van der Waals multiferroic tunnel junctions

Gate controllable optical spin current generation in zigzag graphene nanoribbon

A promising polarization-sensitive ultraviolet photodetector based on the two-dimensional ZrNBr-ZrNCl lateral heterojunction with enhanced photoresponse: A theoretical prediction

Using nonequilibrium Green's function combined with density functional theory, we investigate the spin-related current generated by the photogalvanic effect (PGE) in monolayer zigzag SiC nanoribbons (ZSiCNRs) by first-principles calculations. Due to its unique atomic structure and band structure properties, we find that 100% spin polarized photocurrent can be easily obtained in a wide range of photon energies by shining linearly/circularly polarized light when ZSiCNRs are in the anti-ferromagnetic (AFM) state. In comparison, when the ZSiCNRs are in the ferromagnetic (FM) state, the spin polarization of photocurrent can vary from 0% to 100% by changing the photon energy or polarization angle. More interestingly, pure spin current can also be generated by changing the circular polarization angle in the FM state. Thus, by properly tuning the photon energy, one can obtain 100% spin polarized current regardless of its magnetic configuration and pure spin current in its FM state. Our numerical findings pave a feasible way for ZSiCNRs’ novel applications in spintronics.

Photogalvanic effect induced fully spin polarized current and pure spin current in zigzag SiC nanoribbons

We report a first principles study of the gate tunable spin transport properties in trilayer black phosphorus (BP) placed on a Ni(100) electrode. In the proposed spintronic device, the spin-dependent conductance and the corresponding spin polarization can be largely modulated by the gate voltage. Instead of resorting to the gate tunable spin orbital interaction (SOI) mechanism in the traditional spintronic devices, the control scheme here is achieved by the giant Stark effect induced semiconducting-metallic phase transition of the few-layer BP. It is found that the quantum tunneling effect is gradually reduced as the gate voltage increases. During this process, the conductances of spin up and spin down components increase differently and hence the spin polarization is largely varied from 7% to 77% in parallel configuration (PC) and from 1% to 54% in anti-parallel configuration (APC). More importantly, the maximum magnetoresistance (MR) value can reach as large as 80%. Finally, we find that the non-equilibrium spin-polarized current can also be controlled by the external bias voltage. For instance, a large turn on/off ratio can be realized by the gate voltage (4239 for spin down current and 1809 for spin up current) when the bias voltage is fixed at 0.01 V. Our theoretical findings pave a feasible way for the novel application of few-layer BP in spintronic nanodevices.

Gate-tunable large spin polarization in a few-layer black phosphorus-based spintronic device

Based on non-equilibrium Green's function combined with density functional theory (NEGF-DFT), we investigate the spin dependent transport in the ferromagnetic 6,6,12/γ-graphyne zigzag nanoribbon (GYZNR) heterojunction under different magnetic configurations. It is found that, at low bias ([−0.05, 0.1] V), the junction presents metallic transport with negligible spin polarization in parallel configuration (PC) while it behaves as an insulator in anti-parallel configuration (APC), which results in giant magnetoresistance. Interestingly, when we increase the bias voltage beyond [−0.05, 0.1] V, dual spin filtering characterized by electron transport of different spin channels under different polarity of bias is observed in APC but not in PC. All these findings are understood from the symmetry matching of wave functions in two nanoribbons at equilibrium or finite bias. Furthermore, dual spin filtering can also be achieved in PC by applying a gate voltage on the central interface region, which arises from the shift of different single spin channel of the central gate region into the bias window at a different polarity of the gate voltage. Thus, our work demonstrates the great potential of the 6,6,12/γ-GYZNR heterojunction as a multi-functional device and its great perspectives in carbon-based nanoelectronics and spintronics.

Giant magnetoresistance and dual spin filtering effect in ferromagnetic 6,6,12/γ-graphyne zigzag nanoribbon lateral heterojunction

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Photogalvanic effect induced fully spin polarized current and pure spin current in zigzag SiC nanoribbons

Gate-tunable large spin polarization in a few-layer black phosphorus-based spintronic device

Giant magnetoresistance and dual spin filtering effect in ferromagnetic 6,6,12/γ-graphyne zigzag nanoribbon lateral heterojunction