No abstract

Proximity of a topological insulator (TI) surface with a magnetic insulator (MI) can open an exchange gap at the Dirac point leading to exploration of surface quantum anomalous Hall effect. An important requirement to observe the above effect is to prevent the topological breakdown of the surface states (SSs) due to various interface coupling effects and to tune the Fermi level at the interface near the Dirac point. In this work, we demonstrate the growth of high-quality c-axis oriented strain-free layered films of TI, Bi2Se3, on amorphous SiO2 substrate in proximity to an MI, europium sulfide (EuS), that show stronger weak anti-localization response from the surface than previous studies with epitaxially interfaced heterostructures. Importantly, we find gate and magnetic field cooling modulated localization effects in the SSs, attributed to the position of interface Fermi level within the band gap that is also corroborated from our positron annihilation spectroscopy measurements. Furthermore, our experiments provide a direct evidence of gate-controlled enhanced interface magnetism in EuS arising from the carrier mediated Ruderman–Kittel–Kasuya–Yosida interactions across the Bi2Se3/EuS interface. These findings demonstrate the existence of complex interfacial phenomena affecting the localization response of the SSs that might be important in proximity engineering of the TI surface to observe surface quantum Hall effects.

Proximity‐induced tuning of spin–orbit coupling (SOC) is of paramount importance in emerging magnetic materials and in spintronics. Probing the above SOC via light–matter interaction assisted methods provides a novel route to investigate interesting material phenomena. Here, the proximity studies in a heterostructure of monolayer molybdenum disulfide (MS) and iron (Fe) to enhance and tune the interfacial SOC are reported. The augmented SOC of the MSFe heterostructure arises due to interfacial charge transfer, and is probed using magneto‐optic Kerr effect and a novel optical technique utilizing the spin Hall effect of light. Measuring the changes in the state of polarization of light reflected from the sample via weak measurement provides direct access to the real and imaginary parts of the complex weak value and, hence, the underlying SOC and induced magnetic effects from a single experiment. The results obtained are confirmed using other experimental and simulation tools.

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 Bi 2 Se 3 films. 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 SiO 2 substrate rather than on crystalline Al 2 O 3 (0001), can lead to stronger decoupling between the top and bottom surface states of the film.

Simultaneous extraction of the magnetic and spin‐orbit coupling (SOC) information of an interface using the weak measurement assisted spin‐Hall effect of light (SHEL) is demonstrated as a novel probe to characterize materials' magnetic properties, see article number 2000042 by Karthik V. Raman, Tharangattu N. Narayanan, Nirmal K. Viswanathan, and co‐workers. A heterostructure of Fe and MoS2 monolayers is shown for enhanced SOC due to the proximity effect, which is proven via SHEL method and then confirmed using magneto‐optic Kerr effect (MOKE) studies.