Positive magnetoresistance ͑MR͒ in La 0.7 Pb 0.3 MnO 3 single crystals was observed between temperatures 4.2 and 50 K, in addition to the negative colossal magnetoresistance ͑CMR͒ at higher temperatures. The positive MR increases with temperature lowered and reaches 20% at Tϭ4.2 K in a magnetic field of Hϭ8 T. From temperature and field dependences of the resistivity, it follows that the positive MR at low temperatures arise from quantum interference effects ͑QIE͒. The QIE-induced MR observed in the CMR manganites indicates that the Coulomb interaction and disorder may play an important role in their transport properties.Magnetoelectronics is a hot topic in the condensed matter physics with wide technological applications. 1 An imbalance of electron spins can lead to spin-polarized transport; this in turn leads to the idea of electronic devices based not on electrons and holes driven by electric fields, but on spin-up and spin-down electrons biased and controlled by magnetic fields. Negative giant magnetoresistance ͑GMR͒ has been successively observed in magnetic multilayers and magnetic granular systems. 2,3 Such GMR effects are attributed to spindependent scattering at interfaces and in bulk ferromagnets. In a two-channel ͑spin up and down͒ current model, an applied magnetic field can induce a low-resistance or shortcircuit channel, resulting in a big drop in resistance. On the other hand, a negative CMR observed in perovskite-type ferromagnetic manganites 4,5 arises from the magnetic field suppressing the scattering of carriers by localized moments. Recently, Manyala et al. 6 found an anomalous positive MR in ferromagnet Fe 1Ϫy Co y Si and argued that it can arise by a different mechanism-the quantum interference effects ͑QIE͒ rather than simple scattering. It was emphasized that the Fe 1Ϫy Co y Si ferromagnets are disordered, low-carrierdensity magnets where the same electrons are responsible for both magnetic properties and electrical conduction. They are quite different from the CMR manganites in which the e g electrons are carriers responsible for the electrical conduction, while t 2g electrons form the local spins responsible for the magnetism and act as scattering sites for the conduction electrons. This argument seems to exclude the possibility of the QIE-induced positive MR occurring in the CMR manganites. In this paper, however, we find a QIE-induced positive MR in La 0.7 Pb 0.3 MnO 3 single crystals between temperatures 4.2 and 50 K, providing an interesting reverse example.The parent compound LaMnO 3 is an A-type antiferromagnetic insulator which consists of ferromagnetic ͑FM͒ planes ordered antiferromagnetically in the third direction. The insulating behavior of LaMnO 3 stems from the fact that there appears at most one e g electron at each Mn 3ϩ ion due to strong on-site Coulomb interactions. Upon doping with Pb 2ϩ ions on La 3ϩ sites, La 1Ϫx Pb x MnO 3 (0.25ϽxϽ0.4) becomes a mixed-valence oxide due to introduction of Mn 4ϩ and exhibits an FM metal ground state. 7 This manganite undergoes an FM me...

Summary Inorganic halide perovskites have emerged as a promising platform in a wide range of applications from solar energy harvesting to computing and light emission. The recent advent of epitaxial thin film growth of halide perovskites has made it possible to investigate low-dimensional quantum electronic devices based on this class of materials. This study leverages advances in vapor-phase epitaxy of halide perovskites to perform low-temperature magnetotransport measurements on single-domain cesium tin iodide (CsSnI 3 ) epitaxial thin films. The low-field magnetoresistance carries signatures of coherent quantum interference effects and spin-orbit coupling. These weak anti-localization measurements reveal a micron-scale low-temperature phase coherence length for charge carriers in this system. The results indicate that epitaxial halide perovskite heterostructures are a promising platform for investigating long coherent quantum electronic effects and potential applications in spintronics and spin-orbitronics.