Back gating of a two-dimensional hole gas in a SiGe quantum well

A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8 × 1011 cm–2 down to a measurement-limited value of 4 × 1011 cm–2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3

Scaling and the Metal-Insulator Transition in Si/SiGe Quantum Wells

The existence of a metal-insulator transition at zero magnetic field in two- dimensional electron systems has recently been confirmed in high mobility Si-MOSFETs. In this work, the temperature dependence of the resistivity of gated Si/SiGe/Si quantum well structures has revealed a similar metal- insulator transition as a function of carrier density at zero magnetic field. We also report evidence for a Coulomb gap in the temperature dependence of the resistivity of the dilute 2D hole gas confined in a SiGe quantum well. In addition, the resistivity in the insulating phase scales with a single parameter, and is sample independent. These results are consistent with the occurrence of a metal-insulator transition at zero magnetic field in SiGe square quantum wells driven by strong hole-hole interactions.Comment: 3 pages, 3 figures, LaTe

QUANTITATIVE NON-DESTRUCTIVE NEUTRON ACTIVATION ANALYSIS OF SILVER IN COINS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65909/1/j.1475-4754.1967.tb00617.x.pd

IDENTIFICATION OF THE GEOLOGIC ORIGINS OF ARCHAEOLOGICAL ARTIFACTS: AN AUTOMATED METHOD OF Na and Mn NEUTRON ACTIVATION ANALYSIS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66345/1/j.1475-4754.1967.tb00618.x.pd

Coexistence of Weak Localization and a Metallic Phase in Si/SiGe Quantum Wells

Magnetoresistivity measurements on p-type Si/SiGe quantum wells reveal the coexistence of a metallic behavior and weak localization. Deep in the metallic regime, pronounced weak localization reduces the metallic behavior around zero magnetic field without destroying it. In the insulating phase, a positive magnetoresistivity emerges close to B=0, possibly related to spin-orbit interactions.Comment: 4 pages, 3 figure

Cr-spinel Seam Petrogenesis in the Rum Layered Suite, NW Scotland:Cumulate Assimilation and <em>in situ</em> Crystallization in a Deforming Crystal Mush

Laterally extensive (∼2 mm thick) Cr-spinel seams in the Rum Layered Suite, NW Scotland, occur at the bases of several of the coupled peridotite–troctolite macro-rhythmic units that form the bulk of the eastern part of the intrusion. Detailed petrography, mineral chemical analyses and quantitative textural measurements of the rocks above and below two of these seams suggest that existing models for seam petrogenesis involving early crystallization and gravitational settling of Cr-spinel from a newly emplaced body of magma need to be reassessed. We argue for assimilation of troctolitic cumulate by a new influx of picrite magma at the crystal mush–magma interface, and subsequent in situ crystallization of the Cr-spinel seams. The bases of seams are characterized by Mg- and Al-rich Cr-spinel, with slightly more Fe-rich crystals toward the tops. These seams crystallized from a superheated hybrid magma generated by the initial assimilation and dissolution of the plagioclase-rich cumulate floor by the picrite. Coeval syn-magmatic deformation of the crystal mush at the unit boundary between peridotite and troctolite caused localized expulsion of Cr-spinel seed crystals several centimetres upward into the peridotite mush, resulting in the formation of overlying supra-seams as well as possibly developing a distinctive texture comprising chains of Cr-spinel around cumulus olivine crystals immediately above unit boundaries. The mineral compositional and textural evidence collected from the Rum Cr-spinel seams also indicates that they exhibit varying degrees of postcumulus chemical and textural equilibration