Single-hole transistor in p-type GaAs/AlGaAs heterostructures

A single-hole transistor is patterned in a p-type, C-doped GaAs/AlGaAs heterostructure by AFM oxidation lithography. Clear Coulomb blockade resonances have been observed at T=300 mK. A charging energy of ~ 1.5 meV is extracted from Coulomb diamond measurements, in agreement with the lithographic dimensions of the dot. The absence of excited states in Coulomb diamond measurements, as well as the temperature dependence of Coulomb peak heights indicate that the dot is in the multi-level transport regime. Fluctuations in peak spacings larger than the estimated mean single-particle level spacing are observed.Comment: 4 pages, 5 figure

Hysteretic magnetotransport in p-type AlGaAs heterostructures with In/Zn/Au ohmic contacts

The two-terminal magneto-conductance of a hole gas in C-doped AlGaAs/GaAs heterostructures with ohmic contacts consisting of alloyed In/Zn/Au displays a pronounced hysteresis of the conductance around zero magnetic field. The hysteresis disappears above magnetic fields of around 0.5 T and temperatures above 300 mK. For magnetic fields below 10 mT we observe a pronounced dip in the magneto-conductance. We tentatively discuss these experimental observations in the light of superconductivity of the ohmic contacts.Comment: 4+ pages, 3 figures

Occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in New Hampshire Biosolids

Per- and polyfluoroalkyl substances (PFAS) are a group of over 4,000 compounds used in the manufacturing of products including aqueous film forming foams for firefighting, stain repellents, waterproofing agents, and nonstick cookware since their initial development in the 1940s. The long fluorinated carbon chain structure of PFAS causes chemical and thermal stability, and thus resistance to biodegradation. Biosolids produced at wastewater facilities for uses such as agricultural land-applied compost and fertilizer for lawns and athletic fields, as well as sludge disposed in landfills can cause contamination of groundwater and surface water. This poses a significant threat to human and environmental health. This research looks at presence and concentration of various PFAS in biosolids samples collected by the New Hampshire Department of Environmental Services (NHDES) from 2019 to 2022. An additional focus is placed on five of the six PFAS targeted by the U.S. Environmental Protection Agency’s recent proposed updated national drinking water standards for PFAS (PFOA, PFOS, PFNA, PFBS, and PFHxS). All biosolids samples were split into eight groups based on production method. Statistical analysis was conducted using the software JMP Pro version 16 to determine (1) if presence of specific PFAS at levels above each sample’s respective reporting limit is independent of the specific PFAS and (2) if there is a difference in central tendency of concentration of each PFAS between each processing group. This research will help inform NHDES of trends in PFAS presence and concentration in biosolids, which may cause facilities to reexamine their processing methods

Waveform sampling using an adiabatically driven electron ratchet in a two-dimensional electron system

We utilize a time-periodic ratchet-like potential modulation imposed onto a two-dimensional electron system inside a GaAs/Al$_x$Ga$_{1-x}$As heterostructure to evoke a net dc pumping current. The modulation is induced by two sets of interdigitated gates, interlacing off center, which can be independently addressed. When the transducers are driven by two identical but phase-shifted ac signals, a lateral dc pumping current $I(\phi)$ results, which strongly depends on both, the phase shift $\phi$ and the waveform $V(t)$ of the imposed gate voltages. We find that for different periodic signals, the phase dependence $I(\phi)$ closely resembles $V(t)$. A simple linear model of adiabatic pumping in two-dimensional electron systems is presented, which reproduces well our experimental findings.Comment: 3 figure

Electrical read-out of the local nuclear polarization in the quantum Hall effect

It is demonstrated that the now well-established `flip-flop' mechanism of spin exchange between electrons and nuclei in the quantum Hall effect can be reversed. We use a sample geometry which utilizes separately contacted edge states to establish a local nuclear spin polarization --close to the maximum value achievable-- by driving a current between electron states of different spin orientation. When the externally applied current is switched off, the sample exhibits an output voltage of up to a few tenths of a meV, which decays with a time constant typical for the nuclear spin relaxation. The surprizing fact that a sample with a local nuclear spin polarization can act as a source of energy and that this energy is well above the nuclear Zeeman splitting is explained by a simple model which takes into account the effect of a local Overhauser shift on the edge state reconstruction.Comment: Submitted to Phys. Rev. Let