Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate ...Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate moiré pattern,and uncommon electronic behaviors may appear due to the absence of phase coherence. Such a system is extremely sensitive to further twist and many intriguing phenomena will occur. Based on first-principles calculations we show that, for further twist near 30°, there could induce dramatically different dielectric behaviors of electron between left and right-twisted cases. Specifically, it is found that the left and right twists show suppressed and amplified dielectric response under vertical electric field, respectively. Further analysis demonstrate that such an exotic dielectric property can be attributed to the stacking dependent charge redistribution due to twist,which forms twist-dependent pseudospin textures. We will show that such pseudospin textures are robust under small electric field. As a result, for the right-twisted case, there is almost no electric dipole formation exceeding the monolayer thickness when the electric field is applied. Whereas for the left case, the system could even demonstrate negative susceptibility, i.e., the induced polarization is opposite to the applied field, which is very rare in the nature. Such findings not only enrich our understanding on moiré systems but also open an appealing route toward functional 2D materials design for electronic, optical and even energy storage devices.展开更多
The persistent spin helix(PSH)system is considered to have promising applications in energy-conservation spintronics because it supports an extraordinarily long spin lifetime of carriers.Here,we predict that the exist...The persistent spin helix(PSH)system is considered to have promising applications in energy-conservation spintronics because it supports an extraordinarily long spin lifetime of carriers.Here,we predict that the existence of PSH state in two-dimensional(2 D)ferroelectric NbOI_(2)monolayers.Our first-principles calculation results show that there exists Dresselhaus-type spin-orbit coupling(SOC)band splitting near the conduction-band minimum(CBM)of the NbOI_(2)monolayer.It is revealed that the spin splitting near CBM merely refers to out-of-plane spin configuration in the wave vector space,which gives rise to a long-lived PSH state that can be controlled by reversible ferroelectric polarization.We believe that the coupling characteristics of ferroelectric polarization and spin texture in NbOI_(2)provide a platform for the realization of fully electric controlled spintronic devices.展开更多
基金Supported by the National Key Research and Development Program of China(Grant No.2017YFA0303403)the Shanghai Science and Technology Innovation Action Plan(Grant No.19JC1416700)+1 种基金the National Natural Science Foundation of China(Grant No.11774092)the ECNU Multifunctional Platform for Innovation。
文摘Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate moiré pattern,and uncommon electronic behaviors may appear due to the absence of phase coherence. Such a system is extremely sensitive to further twist and many intriguing phenomena will occur. Based on first-principles calculations we show that, for further twist near 30°, there could induce dramatically different dielectric behaviors of electron between left and right-twisted cases. Specifically, it is found that the left and right twists show suppressed and amplified dielectric response under vertical electric field, respectively. Further analysis demonstrate that such an exotic dielectric property can be attributed to the stacking dependent charge redistribution due to twist,which forms twist-dependent pseudospin textures. We will show that such pseudospin textures are robust under small electric field. As a result, for the right-twisted case, there is almost no electric dipole formation exceeding the monolayer thickness when the electric field is applied. Whereas for the left case, the system could even demonstrate negative susceptibility, i.e., the induced polarization is opposite to the applied field, which is very rare in the nature. Such findings not only enrich our understanding on moiré systems but also open an appealing route toward functional 2D materials design for electronic, optical and even energy storage devices.
基金the National Key Research and Development Program of China(Grant No.2017YFA0303403)the Shanghai Science and Technology Innovation Action Plan(Grant No.19JC1416700)+1 种基金the National Natural Science Foundation of China(Grant No.11774092)the ECNU Multifunctional Platform for Innovation。
文摘The persistent spin helix(PSH)system is considered to have promising applications in energy-conservation spintronics because it supports an extraordinarily long spin lifetime of carriers.Here,we predict that the existence of PSH state in two-dimensional(2 D)ferroelectric NbOI_(2)monolayers.Our first-principles calculation results show that there exists Dresselhaus-type spin-orbit coupling(SOC)band splitting near the conduction-band minimum(CBM)of the NbOI_(2)monolayer.It is revealed that the spin splitting near CBM merely refers to out-of-plane spin configuration in the wave vector space,which gives rise to a long-lived PSH state that can be controlled by reversible ferroelectric polarization.We believe that the coupling characteristics of ferroelectric polarization and spin texture in NbOI_(2)provide a platform for the realization of fully electric controlled spintronic devices.
