ABSTRACT
A combination of out-of-plane (OOP) and in-plane (IP) magnetoconductance (MC) study in topological insulators (TI) is often used as an experimental technique to probe weak anti-localization (WAL) response of the topological surface states (TSSs). However, in addition to the above WAL response, weak localization (WL) contribution from conducting bulk states are also known to coexist and contribute to the overall MC; a study that has so far received limited attention. In this article, we accurately extract the above WL contribution by systematically analyzing the temperature and magnetic field dependency of conductivity in Bi2Se3films. For accurate analysis, we quantify the contribution of electron-electron interactions to the measured MC which is often ignored in the WAL studies. Moreover, we show that the WAL effect arising from the TSSs with finite penetration depth, for OOP and IP magnetic field can together explain the anisotropic magnetoconductance (AMC) and, thus, the investigated AMC study can serve as a useful technique to probe the parameters like phase coherence length and penetration depth that characterise the TSSs in 3D TIs. We also demonstrate that increase in bulk-disorder, achieved by growing the films on amorphous SiO2substrate rather than on crystalline Al2O3(0001), can lead to stronger decoupling between the top and bottom surface states of the film.
ABSTRACT
Understanding and tuning of metal-insulator transition (MIT) in oxide systems is an interesting and active research topics of condensed matter physics. We report thickness dependent MIT in Ga-doped ZnO (Ga:ZnO) thin films grown by pulsed laser deposition technique. From the electrical transport measurements, we find that while the thinnest film (6 nm) exhibits a resistivity of 0.05 Ω cm, lying in the insulating regime, the thickest (51 nm) has resistivity of 6.6 × 10-4 Ω cm which shows metallic type of conduction. Our analysis reveals that the Mott's variable range hopping model governs the insulating behavior in the 6 nm film whereas the 2D weak localization (WL) phenomena is appropriate to explain the electron transport in the thicker Ga:ZnO films. Magnetoresistance study further confirms the presence of strong localization in 6 nm film while WL is observed in 20 nm and above thicker films. From the density functional calculations, it is found that due to surface reconstruction and Ga doping, strong crystalline disorder sets in very thin films to introduce localized states and thereby, restricts the donor electron mobility.
ABSTRACT
The availability of Human Umbilical Cord-derived Mesenchymal Stem Cells (HUCMSCs) from a single sex being a major limitation for the utilization of a potential stem cell, it is highly desirable to utilize, an autogenous pluripotent cell with desirable biological and mechanical properties in clinical situations. Comparison of Human Gingival Mesenchymal Stem Cells (HGMSCs) with HUCMSCs demonstrates; MSCs derived from gingiva have higher proliferation rate and higher population doubling time than Umbilical Cord. Unlike HUCMSCs, immunofluorescence studies showed the presence of pluripotency markers OCT-4 and NANOG predominantly in the cytoplasm of HGMSCs which was confirmed by Western blot. The mechanical property, such as modulus of elasticity of HGMSCs, is on par with HUCMSCs, but the surface roughness found to be lesser in HGMSCs, which may suggest HGMSCs greater adhesive property to the extracellular matrix. There is a marginal difference in the neuronal differentiation rate between HGMSCs and HUCMSCs; both the cells expressed positivity for several neuronal lineage markers. Hence, HGMSCs represent an autogenous source of mesenchymal stem cells, which are easy to procure with least morbidity, multipotent in nature with desirable biological, and mechanical properties, probably an ideal candidate for clinical applications. J. Cell. Biochem. 118: 2000-2008, 2017. © 2017 Wiley Periodicals, Inc.
