A symmetric van der Pauw disk of homogeneous nonmagnetic indium antimonide with an embedded concentric gold inhomogeneity is found to exhibit room-temperature geometric magnetoresistance as high as 100, 9100, and 750,000 percent at magnetic fields of 0.05, 0.25, and 4.0 teslas, respectively. For inhomogeneities of sufficiently large diameter relative to that of the surrounding disk, the resistance is field-independent up to an onset field above which it increases rapidly. These results can be understood in terms of the field-dependent deflection of current around the inhomogeneity.

Bulk Bi2Te3 is known to be a topological insulator. We investigate surface states of Bi2Te3(111) thin films of one to six quintuple layers using density-functional theory including spin-orbit coupling. We construct a method to identify topologically protected surface states of thin film topological insulators. Applying this method to Bi2Te3 thin films, we find that the topological nature of the surface states remains robust with the film thickness and that the films of three or more quintuple layers have topologically nontrivial surface states, which agrees with experiments.

We report the noise characteristics of quantum point contacts between 100 Hz and 100 kHz at 4.2 K. The noise consists of a 111 component on top of a white background. The 1I/noise increases as the contact width decreases and shows peaks between the quantized resistance plateaus. The white noise background increases with current but is much lower than the fuB shot noise level, suggesting that shot noise is not generated in an ideal quantum point oontact, where the electrons do not suffer backscattering as they enter and traverse the contact.

The magnetoresistance at temperatures below 20 K in an n-InSb/ In 0.85 Al 0.15 Sb two-dimensional electron system is studied and described in terms of antilocalization due to quantum interference under strong spin-orbit interaction. The spin-orbit interaction coefficients are extracted by fitting the magnetoresistance data to an antilocalization theory distinguishing the Rashba and Dresselhaus contributions. A good agreement between magnetoresistance data and theory suggests a Rashba coefficient ͉␣͉Ϸ0.03 eV Å and a Dresselhaus coefficient ␥ Ϸ 490 eV Å 3 . A strong contribution from the Dresselhaus term leads to pronounced anisotropy in the energy splitting induced by spin-orbit interaction in the two-dimensional electron dispersion.

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The filling fraction limitation (FFL) in n-type CoSb3 skutterudites is far below that of p-type (Fe,Co)­Sb3-based skutterudites, and it is critical to increase FFL for accomplishing high thermoelectric figure of merit (ZT max). Here, a series of Yb x Co4–y Fe y Sb12 alloys with x = 0.25–0.5 and y = 0.1–0.5 were synthesized, which demonstrate a clear increase of the FFL of Yb from ∼0.3 in CoSb3 to 0.5. Ultralow thermal conductivities of 2.0–2.5 W/m·K at 300 K and 1.75 W/m·K at ∼600 K have been achieved, which are the lowest values reported among skutterudite materials and comparable with p-type skutterudites. These ultralow thermal conductivities result from the combination of secondary phase scattering and phonon scattering from dynamic electron exchange between Fe2+ and Co3+. High ZT max values of 1.28 at 740 K and 1.34 at 780 K are obtained, which are among the best values reported in the temperature range of 740–800 K. The temperature at which maximum ZT max appears is shifted below 850 K. These results are highly exciting toward the development of multistage segmented and cascade thermoelectric power generators for in-air operations.

We have measured the low-temperature mobility of high-quality two-dimensional hole systems confined at the (311)A GaAs/AlxGa1−xAs interface. Variables were the thickness of the spacer layer separating the carriers from the Si dopants, and the carrier sheet density. A large anisotropy in mobility is found between the [2̄33] and [011̄] directions. While the high mobility [2̄33] direction yields results analogous to the two-dimensional electron case, we conclude that transport along [011̄] is almost entirely determined by anisotropic interface roughness scattering.

We present a method to create spin-polarized beams of ballistic electrons in a twodimensional electron system in the presence of spin-orbit interaction. Scattering of a spinunpolarized injected beam from a lithographic barrier leads to the creation of two fully spin-polarized side beams, in addition to an unpolarized specularly reflected beam.Experimental magnetotransport data on InSb/InAlSb heterostructures demonstrate the spin-polarized reflection in a mesoscopic geometry, and confirm our theoretical predictions.