Chi-Te Liang

We report the magnetotransport properties of zirconium pentatelluride (ZrTe5) in the Dirac semimetal phase, focusing on its magnetoresistance behavior at low temperatures. Pronounced Shubnikov–de Haas oscillations were observed in the low magnetic field regime. In the quantum limit, linear magnetoresistance and behavior consistent with a topological phase transition emerge. In-depth analyses of these phenomena and their temperature dependences suggest that both the chemical potential and the Fermi velocity may play an important role in determining the transport properties of ZrTe5 in the quantum limit. Our findings highlight the importance of band parameters in topological transport and provide insights for future studies of topological materials and the design of quantum devices.

Aluminum (Al) has attracted considerable attention for uses in photonic, electronic, and quantum devices. Its grain architecture governs surface roughness, electron and light scattering, and quantum decoherence, all of which critically affect device performance. Enhancing crystalline domain size and refining granularity control remain an ongoing research focus for producing ultraclean nanofilms. This study investigates the crystallinity of epitaxial Al grown on miscut GaAs substrates and examines its influence on Al superconductivity. The introduction of a substrate miscut alters Al growth kinetics, enabling the formation of twinned grains, polycrystalline structures, and micrometer‐scale single crystal. Variations in grain architecture result in approximately 10%, 100%, and 1000% modulation of the superconducting critical temperature, current, and magnetic field, respectively, while maintaining constant channel geometries. Reducing macroscopic grain boundaries decreases the Al nanofilm resistivity but enhances strain‐induced crystallinity deterioration, driving a transition from type‐I to type‐II‐like superconducting behavior. We suggest that preparing Al nanofilms, which approach an ultraclean limit in terms of surface quality, crystallinity, and transport properties, requires careful control of substrate miscut as well as the grain architecture. These findings highlight a tunable approach to controlling Al granularity and superconductivity via miscut, lattice‐mismatched substrates.

We study the electronic transport properties of W ₅ N ₆ by vacuum gentle heating methods, which are useful ways to probe the electronic transport properties in highly sensitive 2D materials. Importantly, we found stable nearest-neighbor hopping behavior and Efros–Shklovskii variable range hopping behavior by accumulating vacuum gentle heating time, which is highly consistent with previous results in paramagnetic W ₅ N ₆ to pave the way for applying to future magnetic sensing devices in industrial production aspects due to its highly stable atmospheric chemical doping on the surface, large-scale, ultra-thin, and resilient properties.

Two-dimensional (2D) transition metal nitrides (TMNs), which are members of the family of 2D materials, may find practical applications in electronics and optoelectronics because of their superior physical properties. Recently, wafer-scale, single-unit-cell height P62m W5N6, which was difficult to be synthesized in the past, has been grown using a restricted vapor–liquid–solid method. Here, we report experimental evidence for hysteretic magnetoresistance (MR) mediated by temperature in paramagnetic W5N6. Surprisingly, hysteretic MR is weak or even non-existent at millikelvin temperatures where hysteresis is expected to be most pronounced. With increasing temperature, hysteretic behavior becomes the strongest at around 9 K. With further increase in temperature, hysteresis becomes weaker and undetectable at around 26 K. The observed paramagnetism in the Efros–Shklovskii variable range hopping (E–S VRH) regime, where Coulomb interactions are important, provides a paradigm for probing magnetism in 2D TMNs. Importantly, such paramagnetism in TMNs in the E–S VRH regime, which is supported by density functional theory calculations, may find applications in medical imaging, magnetic refrigeration, and magnetic sensing.

In electrical metrology, the quantum Hall effect is accessed at the Landau level filling factor ν = 2 plateau to define and disseminate the unit of electrical resistance (ohm). The robustness of the plateau is only exhibited at this Landau level filling factor and thus places a constraint on the quantized resistances that are accessible when constructing quantized Hall array resistance standards (QHARSs) using epitaxial graphene on SiC. To overcome device constraints by using Hall elements in series or in parallel, this work approaches the fabrication of a cross–square network configuration, which is similar to but departs slightly from conventional wye–delta designs and achieves significantly higher effective quantized resistance outputs. Furthermore, the use of pseudofractal-like recursion amplifies the ability to reach high resistances. QHARS devices designed as the ones here are shown to achieve an effective resistance of 55.81 MΩ in one configuration and 27.61 GΩ in another, with a hypothetically projected 317.95 TΩ that could be accessed with more specialized equipment. Teraohmmeter measurements reveal the limits of conventional wet cryogenic systems due to resistance leakage. Ultimately, this work builds on the capability of realizing exceptionally high-value quantum resistance standards.