Power-law dependence of the angular momentum transition fields in few-electron quantum dots

We show that the critical magnetic fields at which a few-electron quantum dot undergoes transitions between successive values of its angular momentum (M), for large M values follow a very simple power-law dependence on the effective inter-electron interaction strength. We obtain this power law analytically from a quasi-classical treatment and demonstrate its nearly-universal validity by comparison with the results of exact diagonalization.Comment: Uses RevTeX4, 6 figures included in the tex

Generic ordering of structural transitions in quasi-one-dimensional Wigner crystals

We investigate the dependence of the structural phase transitions in an infinite quasi-one-dimensional system of repulsively interacting particles on the profile of the confining channel. Three different functional expressions for the confinement potential related to real experimental systems are used that can be tuned continuously from a parabolic to a hard-wall potential in order to find a thorough understanding of the ordering of the chain-like structure transitions. We resolve the longstanding issue why the most theories predicted a 1-2-4-3-4 sequence of chain configurations with increasing density, while some experiments found the 1-2-3-4 sequence.Comment: 7 pages, 5 figure

From vortex molecules to the Abrikosov lattice in thin mesoscopic superconducting disks

Stable vortex states are studied in large superconducting thin disks (for numerical purposes we considered with radius R = 50 \xi). Configurations containing more than 700 vortices were obtained using two different approaches: the nonlinear Ginzburg-Landau (GL) theory and the London approximation. To obtain better agreement with results from the GL theory we generalized the London theory by including the spatial variation of the order parameter following Clem's ansatz. We find that configurations calculated in the London limit are also stable within the Ginzburg-Landau theory for up to ~ 230 vortices. For large values of the vorticity (typically, L > 100), the vortices are arranged in an Abrikosov lattice in the center of the disk, which is surrounded by at least two circular shells of vortices. A Voronoi construction is used to identify the defects present in the ground state vortex configurations. Such defects cluster near the edge of the disk, but for large L also grain boundaries are found which extend up to the center of the disk.Comment: 15 pages, 10 figures, RevTex4, submitted to Phys. Rev.

Resistance effects due to magnetic guiding orbits

The Hall and magnetoresistance of a two dimensional electron gas subjected to a magnetic field barrier parallel to the current direction is studied as function of the applied perpendicular magnetic field. The recent experimental results of Nogaret {\em et al.} [Phys. Rev. Lett. {\bf 84}, 2231 (2000)] for the magneto- and Hall resistance are explained using a semi-classical theory based on the Landauer-B\"{u}ttiker formula. The observed positive magnetoresistance peak is explained as due to a competition between a decrease of the number of conducting channels as a result of the growing magnetic field, from the fringe field of the ferromagnetic stripe as it becomes magnetized, and the disappearance of snake orbits and the subsequent appearance of cycloidlike orbits.Comment: 7 pages, 7 figure

Strain-induced topological phase transition in phosphorene and phosphorene nanoribbons

Using the tight-binding (TB) approximation with inclusion of the spin-orbit interaction, we predict a topological phase transition in the electronic band structure of phosphorene in the presence of axial strains. We derive a low-energy TB Hamiltonian that includes the spin-orbit interaction for bulk phosphorene. Applying a compressive biaxial in-plane strain and perpendicular tensile strain in ranges where the structure is still stable leads to a topological phase transition. We also examine the influence of strain on zigzag phosphorene nanoribbons (zPNRs) and the formation of the corresponding protected edge states when the system is in the topological phase. For zPNRs up to a width of 100 nm the energy gap is at least three orders of magnitude larger than the thermal energy at room temperature.Comment: 10 pages, 6 figure

Spin-dependent transmission through a chain of rings: influence of a periodically modulated spin-orbit interaction strength or ring radius

We study ballistic electron transport through a finite chain of quantum circular rings in the presence of spin-orbit interaction of strength \alpha. For a single ring the transmission and reflection coefficients are obtained analytically and from them the conductance for a chain of rings as a function of \alpha and of the wave vector k of the incident electron. We show that due to destructive spin interferences the chain can be totaly opaque for certain ranges of k the width of which depends on the value of \alpha. A periodic modulation of the strength \alpha or of the ring radius widens up the gaps considerably and produces a nearly binary conductance output.Comment: 4 pages, 4 figures. Appl. Phys. Lett., in pres