▎ 摘　　要

Friedel oscillations (FO) of electron density caused by a deltalike neutral impurity in two-dimensional (2D) systems in a magnetic field are calculated. Three 2D cases are considered: free electron gas, monolayer graphene, and group-VI dichalcogenides. An exact form of the renormalized Green's function is used in the calculations, as obtained by a summation of the infinite Dyson series and regularization procedure. Final results are valid for large ranges of potential strengths V-0, electron densities ne, magnetic fields B, and distances from the impurity r. Realistic models for the impurities are used. The first FO of induced density in WS2 are described by the relation Delta n(r) alpha sin(2 pi r/T-FO)/r(2), where T-FO alpha 1/root E-F. For weak impurity potentials, the amplitudes of FO are proportional to V-0. For attractive potentials and high fields, the total electron density remains positive for all r. On the other hand, for low fields, repulsive potentials and small r, the total electron density may become negative, so that many-body effects should be taken into account.