Steven Wolgast

Low-temperature surface conduction in the Kondo insulator SmB6

We study the transport properties of the Kondo insulator SmB6 with a specialized configuration designed to distinguish bulk-dominated conduction from surface-dominated conduction. We find that as the material is cooled below 4 K, it exhibits a crossover from bulk to surface conduction with a fully insulating bulk. We take the robustness and magnitude of the surface conductivity, as is manifest in the literature of SmB6, to be strong evidence for the topological insulator metallic surface states recently predicted for this material.

Magnetotransport measurements of the surface states of samarium hexaboride using Corbino structures

Utilizing Corbino disc structures, we have examined the magnetic field response of resistivity for the surface states of SmB6 on different crystalline surfaces at low temperatures. Our results reveal a hysteretic behavior whose magnitude depends on the magnetic field sweep rate and temperature. Although this feature becomes smaller when the field sweep is slower, a complete elimination or saturation is not observed in our slowest sweep-rate measurements, which is much slower than a typical magnetotransport trace. These observations cannot be explained by quantum interference corrections such as weak anti-localization. Instead, they are consistent with behaviors of glassy surface magnetic ordering, whose magnetic origin is most likely from samarium oxide (Sm2O3) forming on the surface during exposure to ambient conditions.The recent conjecture of a topologically protected surface state in

Hot-spot detection and calibration of a scanning thermal probe with a noise thermometry gold wire sample

{\mathrm{SmB}}_{6}

Influence of helical spin structure on the magnetoresistance of an ideal topological insulator

and the verification of robust surface conduction below 4 K have prompted a large effort to understand surface states. Conventional Hall transport measurements allow current to flow on all surfaces of a topological insulator, so such measurements are influenced by contributions from multiple surfaces of varying transport character. Instead, we study magnetotransport of

Reduction of the low-temperature bulk gap in samarium hexaboride under high magnetic fields

{\mathrm{SmB}}_{6}

Hysteretic Magnetotransport in SmB6 at Low Magnetic Fields

using a Corbino geometry, which can directly measure the conductivity of a single, independent surface. Both (011) and (001) crystal surfaces show a strong negative magnetoresistance at all magnetic field angles measured. The (011) surface has a carrier mobility of

High Field Magnetoresistance Measurements on the Surface States of Samarium Hexaboride using Corbino Structures

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Discovery of the First Topological Kondo Insulator: Samarium Hexaboride

with a carrier density of

Measuring Transport Properties of Thin Films Under Isotropic and Anisotropic Strain Using Piezoelectric Substrates

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Magnetotransport Measurements on SmB

, which are significantly lower than indicated by Hall transport studies. This mobility value can explain the failure so far to observe Shubnikov--de Haas oscillations. Analysis of the angle dependence of conductivity on the (011) surface suggests a combination of a field-dependent enhancement of the carrier density and a suppression of Kondo scattering from native oxide layer magnetic moments as the likely origin of the negative magnetoresistance. Our results also reveal a hysteretic behavior whose magnitude depends on the magnetic field sweep rate and temperature. Although this feature becomes smaller when the field sweep is slower, it does not disappear or saturate during our slowest sweep-rate measurements, which is much slower than a typical magnetotransport trace. These observations cannot be explained by quantum interference corrections such as weak antilocalization but are more likely due to an extrinsic magnetic effect such as the magnetocaloric effect or glassy ordering.