Interactions and non-magnetic fractional quantization in one-dimension

ABSTRACT In this Perspective article, we present recent developments on interaction effects on the carrier transport properties of one-dimensional (1D) semiconductor quantum wires fabricated using the GaAs/AlGaAs system, particularly the emergence of the long predicted fractional quantization of conductance in the absence of a magnetic field. Over three decades ago, it was shown that transport through a 1D system leads to integer quantized conductance given by N·2e2/h, where N is the number of allowed energy levels (N = 1, 2, 3, …). Recent experiments have shown that a weaker confinement potential and low carrier concentration provide a testbed for electrons strongly interacting. The consequence leads to a reconfiguration of the electron distribution into a zigzag assembly which, unexpectedly, was found to exhibit quantization of conductance predominantly at 1/6, 2/5, 1/4, and 1/2 in units of e2/h. These fractional states may appear similar to the fractional states seen in the Fractional Quantum Hall Effect; however, the system does not possess a filling factor and they differ in the nature of their physical causes. The states may have promise for the emergent topological quantum computing schemes as they are controllable by gate voltages with a distinct identity

Research in COVID-19 times: The way forward

The COVID-19 pandemic has had a major impact on research at universities. Universities around the world, including in South Africa, have been or are still closed as part of national lockdown strategies. Students have not been attending classes or doing hands-on experimental work, and students and academics have been working from home. Many thousands of students have had their university education interrupted, and for them, the resumption of learning programmes online, and where possible in research laboratories, is critically important. There is no question that as we emerge from lockdown we will not be entering a world that resembles a ‘norm’ as lived in the pre-COVID-19 era, and many changes will be required. Here we discuss the importance of research, the urgency to get things up and running again, and strategies that will need to be implemented to ensure that research activities continue. At the same time, it is necessary to ensure that students and staff are not exposed to risk in their research endeavours, which will require the development and implementation of risk management plans

Quantum phase transition detected through one-dimensional ballistic conductance

A quantum phase transition is an unequivocal signature of strongly correlated many-body physics. Signatures of such phenomena are yet to be observed in ballistic transport through quantum wires. Recent developments in quantum wires have made it possible to enhance the interaction between the electrons. Here we show that hitherto unexplained anticrossing between conduction energy subbands, observed in such experiments, can be explained through a simple yet effective discretized model which undergoes a second-order quantum phase transition within the Ising universality class. Accordingly, we observe how the charge distribution, transverse to the direction of the wire, will vary across the phase transition. We show that data coming from three different samples with differing electron densities and gate voltages show a remarkable universal scaling behavior, determined by the relevant critical exponent, which is only possible near a quantum phase transition

Quantum phase transition detected through one-dimensional ballistic conductance

A quantum phase transition is an unequivocal signature of strongly correlated many-body physics. Signatures of such phenomena are yet to be observed in ballistic transport through quantum wires. Recent developments in quantum wires have made it possible to enhance the interaction between the electrons. Here we show that hitherto unexplained anticrossing between conduction energy subbands, observed in such experiments, can be explained through a simple yet effective discretized model which undergoes a second-order quantum phase transition within the Ising universality class. Accordingly, we observe how the charge distribution, transverse to the direction of the wire, will vary across the phase transition. We show that data coming from three different samples with differing electron densities and gate voltages show a remarkable universal scaling behavior, determined by the relevant critical exponent, which is only possible near a quantum phase transition

The legal position on the classification of human tissue in South Africa: Can tissues be owned?

The ownership of tissue samples donated for medical research is an ongoing subject of dispute. Some advocates assert that patients have ongoing ownership rights in their tissues, including an unfettered right to determine what happens to their tissue sample. Researchers argue that giving patients property rights in their samples will turn the human body and body parts into a commodity and bring research to a halt. The question of the human body as property involves complex and philosophical dimensions. The law displays an uneasiness in making sense of the human body in the context of ownership and property, as the notion of owning oneself (and one’s tissues) implies that persons are able to objectify their selves, and in the process become susceptible to objectification by others. The creation of commercial products from human tissue has generated very difficult legal and ethical questions that have no clear, universally accepted answers

Rapid evolution of our understanding of the pathogenesis of COVID-19: Implications for therapy

COVID-19 severity appears to lie in its propensity to cause a hyperinflammatory response, attributed to the cytokine release syndrome (CRS) or ‘cytokine storm’, although the exact role of the CRS remains to be fully elucidated. Hyperinflammation triggers a hypercoagulable state, also thought to play a key role in COVID-19 pathogenesis. Disease severity is linked to age, sex and comorbid conditions, which in turn may be linked to oxidative stress and pre-existing depletion of nicotinamide adenine dinucleotide (NAD+). There is increasing evidence that the host genome may determine disease outcome. Since most information pertaining to COVID-19 has thus far been extrapolated from the ‘global North’, similar studies in African populations are warranted. Many studies are aimed at finding a therapeutic strategy based on scientific rationale. Some promising results have emerged, e.g. the use of corticosteroids in severe acute respiratory distress syndrome (ARDS)

The impact of obesity on the cellular and molecular pathophysiology of COVID-19

Emerging evidence reveals a strong association between COVID-19 and obesity in terms of disease severity, need for hospitalisation and risk of mortality. In this review, we discuss cellular and molecular mechanisms potentially contributing to the pathophysiology of COVID-19 in obese patients. Understanding the relationship between COVID-19 and obesity is pertinent for the clinical management of these patients

The effects of heat stress on the development of the foetal lamb

Environmental heat stress in tropical sheep suppressed lamb birth weight, but the animals which did not experience hyperthermia under natural environmental conditions gave birth to significantly heavicr (P<0.01) lambs than their less adapted counterparts. Climate chamber studies designed to simulate the rectal temperature patterns of tropical sheep demonstrated that, without nutritional intervention, heat stress during the last month of pregnancy significantly retarded foetal growth (birth weight 2.3 kg v. 3.4 kg; P< 0.01) and maturation of wool follicles (P< 0.01). By comparison, severe nutritional restrictions during the last 3 months of pregnancy also caused a significant reduction in lamb birth weight (3.2 kg v. 3.9 kg; P<O.01), but this difference was not so marked