We report experimental investigation of the resistivity and Nernst effect in two-dimensional(2D)NbSe2 crystals.A strongly enhanced Nernst effect,100 times larger than that in bulk NbSe2,caused by moving vortices is ob...We report experimental investigation of the resistivity and Nernst effect in two-dimensional(2D)NbSe2 crystals.A strongly enhanced Nernst effect,100 times larger than that in bulk NbSe2,caused by moving vortices is observed in thin film.It is found that in the low temperature,high magnetic field regime,pinning effects show little dependence on the thickness and resistivity of the superconductor films.Strong Nernst signals persist above the superconducting transition,suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations.A magnetic field induced superconductor-insulator transition(SIT)is evident,which is surprising in that such a SIT usually takes place in disordered dirty superconductors,while our samples are highly crystalline and close to the clean limit.Hence,our results expand the scope of SIT into 2D crystal clean superconductors.展开更多
Based on the empirical electron surface model （EESM）,the covalent electron density of dangling bonds （CEDDB） was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculat...Based on the empirical electron surface model （EESM）,the covalent electron density of dangling bonds （CEDDB） was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface.The calculated surface energy is in agreement with experimental and other theoretical values.The calculated surface energy of the close-packed （111） surface has the lowest surface energy,which agrees with the theoretical prediction.Also,it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces.Therefore,CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.展开更多
In this work, we propose an efficient numerical method for computing the electrostatic interaction between two like-charged spherical particles which is governed by the nonlinear Poisson-Boltzmann equation. The nonlin...In this work, we propose an efficient numerical method for computing the electrostatic interaction between two like-charged spherical particles which is governed by the nonlinear Poisson-Boltzmann equation. The nonlinear problem is solved by a monotone iterative method which leads to a sequence of linearized equations. A modified central finite difference scheme is developed to solve the linearized equations on an exterior irregular domain using a uniform Cartesian grid. With uniform grids, the method is simple, and as a consequence, multigrid solvers can be employed to speed up the convergence. Numerical experiments on cases with two isolated spheres and two spheres confined in a charged cylindrical pore are carried out using the proposed method. Our numerical schemes are found efficient and the numerical results are found in good agreement with the previous published results.展开更多
We propose a variant modified skew-normal splitting iterative method to solve a class of large sparse non-Hermitian positive definite linear systems.Applying the preconditioning technique we also construct the precond...We propose a variant modified skew-normal splitting iterative method to solve a class of large sparse non-Hermitian positive definite linear systems.Applying the preconditioning technique we also construct the preconditioned version of the proposed method.Theoretical analysis shows that the proposed method is unconditionally convergent even when the real part and the imaginary part of the coefficient matrix are non-symmetric.Meanwhile,when the real part and the imaginary part of the coefficient matrix are symmetric positive definite,we prove that the preconditioned variant modified skew-normal splitting iterative method will also unconditionally converge.Numerical experiments are presented to illustrate the efficiency of the proposed method and show better performance of it when compared with some other methods.展开更多
基金the National Key Basic Research Program of China(Grant No.2016YFA0300600)the National Natural Science Foundation of China(Grant Nos.11574005 and 11774009).
文摘We report experimental investigation of the resistivity and Nernst effect in two-dimensional(2D)NbSe2 crystals.A strongly enhanced Nernst effect,100 times larger than that in bulk NbSe2,caused by moving vortices is observed in thin film.It is found that in the low temperature,high magnetic field regime,pinning effects show little dependence on the thickness and resistivity of the superconductor films.Strong Nernst signals persist above the superconducting transition,suggesting that the Nernst effect is a sensitive probe to superconducting fluctuations.A magnetic field induced superconductor-insulator transition(SIT)is evident,which is surprising in that such a SIT usually takes place in disordered dirty superconductors,while our samples are highly crystalline and close to the clean limit.Hence,our results expand the scope of SIT into 2D crystal clean superconductors.
基金supported by the Beijing Natural Science Foundation,China (No.2072014)the Ph.D. Program Foundation of the Ministry of Education of China (No.200800100006)
文摘Based on the empirical electron surface model （EESM）,the covalent electron density of dangling bonds （CEDDB） was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface.The calculated surface energy is in agreement with experimental and other theoretical values.The calculated surface energy of the close-packed （111） surface has the lowest surface energy,which agrees with the theoretical prediction.Also,it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces.Therefore,CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.
基金The research of the first author is supported by the Hong Kong Baptist University. The research of the second author is partially supported by a USA-AR0 grant 43751-MA and USA- NFS grants DMS0201094 and DMS-0412654. The third author is partially supported by CERG Grants of Hong Kong Research Grant Council, FRG grants of Hong Kong Baptist University, and an NSAF Grant （#10476032） of National Science Foundation of Chian.
文摘In this work, we propose an efficient numerical method for computing the electrostatic interaction between two like-charged spherical particles which is governed by the nonlinear Poisson-Boltzmann equation. The nonlinear problem is solved by a monotone iterative method which leads to a sequence of linearized equations. A modified central finite difference scheme is developed to solve the linearized equations on an exterior irregular domain using a uniform Cartesian grid. With uniform grids, the method is simple, and as a consequence, multigrid solvers can be employed to speed up the convergence. Numerical experiments on cases with two isolated spheres and two spheres confined in a charged cylindrical pore are carried out using the proposed method. Our numerical schemes are found efficient and the numerical results are found in good agreement with the previous published results.
基金R.Li is funded by the China Scholarship Council(File No.201808330668)the National Natural Science Foundation of China(Grant No.11701221)+1 种基金J.-F.Yin is funded by the National Natural Science Foundation of China(Grant No.11971354)Z.Li is partially supported by a Simon’s grant 63372.
文摘We propose a variant modified skew-normal splitting iterative method to solve a class of large sparse non-Hermitian positive definite linear systems.Applying the preconditioning technique we also construct the preconditioned version of the proposed method.Theoretical analysis shows that the proposed method is unconditionally convergent even when the real part and the imaginary part of the coefficient matrix are non-symmetric.Meanwhile,when the real part and the imaginary part of the coefficient matrix are symmetric positive definite,we prove that the preconditioned variant modified skew-normal splitting iterative method will also unconditionally converge.Numerical experiments are presented to illustrate the efficiency of the proposed method and show better performance of it when compared with some other methods.
