arXiv subjects

V. M. Fomin

Publications and source records attributed to V. M. Fomin.

40 records · Page 3Linked to original sources

arXiv2000

Bipolaron Binding in Quantum Wires

A theory of bipolaron states in quantum wires with a parabolic potential well is developed applying the Feynman variational principle. The basic parameters of the bipolaron ground state (the binding energy, the number of phonons in the bipolaron cloud, the effective mass, and the bipolaron radius) are studied as a function of sizes of the potential well. Two cases are considered in detail: a cylindrical quantum wire and a planar quantum wire. Analytical expressions for the bipolaron parameters are obtained at large and small sizes of the quantum well. It is shown that at $R\gg 1$ [where $R$ means the radius (halfwidth) of a cylindrical (planar) quantum wire, expressed in Feynman units], the influence of confinement on the bipolaron binding energy is described by the function $\sim 1/R^{2}$ for both cases, while at small sizes this influence is different in each case. In quantum wires, the bipolaron binding energy $W(R) $ increases logarithmically with decreasing radius. The shapes and the sizes of a nanostructure, which are favorable for observation of stable bipolaron states, are determined.

cond-mat.str-el↗

arXiv2000

Quantum transport in the cylindrical nanosize silicon-based MOSFET

A model is developed for a detailed investigation of the current flowing through a cylindrical nanosize MOSFET with a close gate electrode. The quantum mechanical features of the lateral charge transport are described by Wigner distribution function which is explicitly dealing with electron scattering due to acoustic phonons and acceptor impurities. A numerical simulation is carried out to obtain a set of I-V characteristics for various channel lengths. It is demonstrated that inclusion of the collision term in the numerical simulation is important for low values of the source-drain voltage. The calculations have further shown that the scattering leads to an increase of the electron density in the channel thereby smoothing out the threshold kink in I-V characteristics. An analysis of the electron phase-space distribution shows that scattering does not prevent electrons from flowing through the channel as a narrow stream, and that features of both ballistic and diffusive transport may be observed simultaneously.

cond-mat.mes-hall↗

arXiv2000

Impurity spin magnetization of thin Fe doped Au films

In order to probe the influence of the surface-induced anisotropy on the impurity spin magnetization, we measure the anomalous Hall effect in thin AuFe films at magnetic fields up to 15 T. The observed suppression of the anomalous Hall resistivity at low fields as well as the appearance of a minimum in the differential Hall resistivity at higher fields can be explained by our theoretical model which takes into account the influence of a polycrystalline film structure on the surface-induced anisotropy. Our results imply that the apparent discrepancy between different experimental results for the size effects in dilute magnetic alloys can be linked to a different microstructure of the samples.

cond-mat.mes-hall↗

arXiv2000

Superconductivity in a Mesoscopic Double Square Loop: Effect of Imperfections

We have generalized the network approach to include the effects of short-range imperfections in order to analyze recent experiments on mesoscopic superconducting double loops. The presence of weakly scattering imperfections causes gaps in the phase boundary $B(T)$ or $Φ(T)$ for certain intervals of $T$, which depend on the magnetic flux penetrating each loop. This is accompanied by a critical temperature $T_c(Φ)$, showing a smooth transition between symmetric and antisymmetric states. When the scattering strength of imperfections increases beyond a certain limit, gaps in the phase boundary $T_c(B)$ or $T_c(Φ)$ appear for values of magnetic flux lying in intervals around half-integer $Φ_0=hc/2e$. The critical temperature corresponding to these values of magnetic flux is determined mainly by imperfections in the central branch. The calculated phase boundary is in good agreement with experiment.

cond-mat.supr-con↗