The present study develops a general framework for weak antilocalization (WAL) in a three-dimensional (3D) system, which can be applied for a consistent description of longitudinal resistivity $$\rho_{xx} \left( B \right)$$ ρ xx B and Hall resistivity $$\rho_{xy} \left( B \right)$$ ρ xy B over a wide temperature (T) range. Compared to the previous approach Vu et al. (Phys Rev B 100:125162, 2019), which assumes infinite phase coherence length (lϕ) and a zero spin–orbit scattering length (lSO), the present framework is more general, covering high T and the intermediate spin–orbit coupling strength. Based on the new approach, the $$\rho_{xx} \left( B \right)$$ ρ xx B and $$\rho_{xy} \left( B \right)$$ ρ xy B of the Dirac semimetal Bi0.97Sb0.03 was analyzed over a wide T range from 1.7 to 300 K. The present framework not only explains the main features of the experimental data but also enables one to estimate lϕ and lSO at different temperatures. The lϕ has a power-law T dependence at high T and saturates at low T. In contrast, the lSO shows negligible T dependence. Because of the different T dependence, a crossover occurs from the lSO-dominant low-T to the lϕ-dominant high-T regions. Accordingly, the hallmark features of weak antilocalization (WAL) in $$\rho_{xx} \left( B \right)$$ ρ xx B and $$\rho_{xy} \left( B \right)$$ ρ xy B are gradually suppressed across the crossover with increasing T. The present theory describes both low-T and high-T regions successfully, which is impossible in the previous approximate approach. This work offers insights for understanding quantum electrical transport phenomena and their underlying physics, particularly when multiple WAL length scales are competing.

Oxide perovskite materials with heterointerfaces are important structures with applications such as electronic devices. The functionality of these materials depends on many factors, such as the charge, structure, and presence of defects at the interface. Thus, understanding the properties of interfaces and their effects on material function is important in the design and optimization of functional materials. In this study, the interplay among the Mn oxidation state distribution, the presence of oxygen vacancies (VOs), and the structure of the interface is investigated in the heterointerface between CaMnO3−δ and La0.7Ca0.3MnO3 layers by using electron energy loss spectroscopy combined with scanning transmission electron microscopy. Unlike the expectation that the Mn oxidation state distribution is controlled by the distribution of cations intermixing at the interface, it is dominantly influenced by the presence of VOs when the substrate gives tensile stress to it. As a result, the tensile-strained heterointerface shows an anomalously sharp reduction in the Mn oxidation state at the interface. This result suggests that VOs and strain are two essential ingredients to consider for the understanding of oxidation state distribution at interfaces. This study provides insights into the nature of various oxide heterointerfaces.

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Three-dimensional (3D) topological semimetals (TSMs) are a new class of Dirac materials that can be viewed as 3D graphene and are referred to as Dirac semimetals (DSMs) or Weyl semimetals (WSMs) depending on whether time reversal symmetry and/or inversion symmetry are protected, respectively. Despite some interesting results on Dirac- to Weyl-semimetal phase transitions under conditions of low temperature or strong magnetic field (B), all of them are reversible phenomena. Here, we report for the first time a possible permanent transition in a single TSM by ion implantation. A Dirac- to Weyl-semimetal phase transition in a Bi0.96Sb0.04 DSM results from inversion-symmetry breaking induced by implantation with nonmagnetic Au ions for implant fluences (ϕG) ≥ 3.2 × 1016 Au cm−2. This phenomenon is evidenced by the ϕG-dependent behavior of the Raman spectra and quantum-oscillation parameters extracted from magnetoresistance (MR) measurements, which show abrupt changes at ϕG ≥ 3.2 × 1016 Au cm−2. The verification of the transition is further supported by observations of negative MR in the longitudinal B // electric field orientation, indicating the existence of a chiral anomaly in Weyl fermions induced by implantation with nonmagnetic Au ions. In contrast, implantation with magnetic Mn ions exhibits no such particular behavior. Our findings demonstrate the first realization of a possible permanent DSM-to-WSM phase transition in a single material by the simple approach of implantation using nonmagnetic elements.

Magnetotransport studies have established the existence of exotic electronic properties in materials of technological and fundamental interest. However, measurements of the Shubnikov–de Haas oscillations, intended to reveal information about Fermi surfaces (FSs), have mostly been carried out in magnetic fields perpendicular to the applied currents. Here, using magnetic fields not only perpendicular but also parallel to the applied currents in a given contact configuration, we investigated the anisotropic magnetotransport and the anisotropic FS properties of Bi2−x Sn x Te3 (0 ⩽ x ⩽ 0.0075) and Bi2Se3. While the magnetotransport properties of Bi2Te3 and Bi2Se3 were nearly isotropic, Bi1.995Sn0.005Te3 exhibited quite anisotropic features. These observations are attributed to the nonparabolicity of the associated bands, which evolved to more anisotropic band structures with Sn concentration. This sensitivity of the band anisotropy was rather unexpected because only a small number of dopants are known to increase disorder levels in the degenerate region. Our approach, using two different magnetic field directions in the measurements of the Shubnikov–de Haas oscillations, is a simple and easily adoptable method for shedding more light on the FSs of functional materials.