Interlayer interaction could substantially affect the electrical transport in transition metal dichalcogenides, serving as an effective way to control the device performance. However, it is still challenging to utilize interlayer interaction in weakly interlayer-coupled materials such as pristine MoS2 to realize layer-dependent tunable transport behavior. Here, we demonstrate that, by substitutional doping of vanadium atoms in the Mo sites of the MoS2 lattice, the vanadium-doped monolayer MoS2 device exhibits an ambipolar field effect characteristic, while its bilayer device demonstrates a heavy p-type field effect feature, in sharp contrast to the pristine monolayer and bilayer MoS2 devices, both of which show similar n-type electrical transport behaviors. Moreover, the electrical conductance of the doped bilayer MoS2 device is drastically enhanced with respect to that of the doped monolayer MoS2 device. Employing first-principle calculations, we reveal that such striking behaviors arise from the presence of electrical transport networks associated with the enhanced interlayer hybridization of S-3p z orbitals between adjacent layers activated by vanadium dopants in the bilayer MoS2, which is nevertheless absent in its monolayer counterpart. Our work highlights that the effect of dopant not only is confined in the in-plane electrical transport behavior but also could be used to activate out-of-plane interaction between adjacent layers in tailoring the electrical transport of the bilayer transitional metal dichalcogenides, which may bring different applications in electronic and optoelectronic devices.
Berry phase effects have significant influences on the electronic properties of condensed matter. In particular, the anomalous Hall conductivity has been recognized as an intrinsic property of the systems with non-zero Berry curvature. Here, we present the anomalous Hall effect observed in the non-magnetic material ZrTe5, which hosts a large Zeeman splitting with Landé g-factor of 26.49. The quantum oscillation analysis reveals non-linear band dispersion near the top of valence band in bulk band structure, and no Weyl node forms with applied magnetic field. The anomalous Hall conductivity reaches 129 Ω−1 cm−1 at 2 K, and shows weak temperature dependence. All these combined with theoretical analysis suggest that the anomalous Hall effect observed in ZrTe5 originates from the non-vanishing Berry curvature induced by combining large Zeeman splitting and strong spin–orbit coupling. Remarkably, the anomalous Hall resistivity reverses its sign from negative to positive at a hydrostatic pressure P = 1.3 GPa, which confirms that the anomalous Hall effect in ZrTe5 is highly related to the band structure-dependent Berry curvature. Our results have verified the anomalous Hall mechanism in ZrTe5 and offer a new platform to study the anomalous Hall effect.
The energy gap of graphene nanoflakes is important for their potential application in nano-devices; however, it is still a challenge to perform a systemic search of systems with large gaps due to the presence of numerous candidates. Herein, we showed an ideal feasible approach that involved structural recognition, simplified effective evaluation, and successive optimization strategy. Considering the local bonding environment of carbon atoms, we first proposed a tight-binding model with the parameters fitted from the first-principles calculations of possible GNFs; this model provided an ideal avenue to screen the candidates with high accuracy and efficiency. Via combining the Monte Carlo tree search method and the congruence check, we determined the correlation between structures and the gap distributions according to the carbon numbers, and the results were confirmed via the first-principles calculations. The structural stabilities of the candidates with different numbers of hydrogen atoms might be modulated by the chemical potential of hydrogen, whereas the candidates with larger gaps might be more stable for the isomers with the same number of C and H atoms. Note that the gap variation is dominated by the structural features despite the quantum confinement effect since the gap maximum fluctuates rather than gradually decreasing with the increase in size. Our finding shows the gap variety of GNFs due to the configuration diversity, which may help explore the potential application of GNFs in nano-devices and fluorescence labeling in biomedicine.
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