In chalcogenide topological insulator materials, two types of magneto-resistance (MR) effects are widely discussed: a positive MR dip around zero magnetic field associated with the weak antilocalization (WAL) effect and a linear MR effect which gener
ally persists to high fields and high temperatures. We have studied the MR of topological insulator Bi2Te3 films from the metallic to semiconducting transport regime. While in metallic samples, the WAL is difficult to identify due to the smallness of the WAL compared to the samples conductivity, the sharp WAL dip in the MR is clearly present in the samples with higher resistivity. To correctly account for the low field MR by the quantitative theory of WAL according to the Hikami-Larkin-Nagaoka (HLN) model, we find that the classical (linear) MR effect should be separated from the WAL quantum correction. Otherwise the WAL fitting alone yields an unrealistically large coefficient $alpha$ in the HLN analysis.
The structure of low-lying excitation states of even-even $N=40$ isotones is studied using a five-dimensional collective Hamiltonian with the collective parameters determined from the relativistic mean-field plus BCS method with the PC-PK1 functional
in the particle-hole channel and a separable paring force in the particle-particle channel. The theoretical calculations can reproduce not only the systematics of the low-lying states along the isotonic chain but also the detailed structure of the spectroscopy in a single nucleus. We find a picture of spherical-oblate-prolate shape transition along the isotonic chain of $N=40$ by analyzing the potential energy surfaces. The coexistence of low-lying excited $0^+$ states has also been shown to be a common feature in neutron-deficient $N=40$ isotones.
