Exciton bound states in solids between electrons and holes are predicted to form a superfluid at high temperatures. We show that by employing atomically thin crystals such as a pair of adjacent bilayer graphene sheets, equilibrium superfluidity of electron-hole pairs should be achievable for the first time. The transition temperatures are well above liquid helium temperatures. Because the sample parameters needed for the device have already been attained in similar graphene devices, our work suggests a new route toward realizing high-temperature superfluidity in existing quality graphene samples.

SynopsisSeveral previous studies have reported increased rates of schizophrenia among Afro-Caribbean immigrants, although doubt has been cast upon the value of case-note diagnoses and retrospective case-finding. A prospective study was therefore undertaken, including all patients of Afro-Caribbean ethnic origin with a first onset psychosis presenting to the psychiatric services from a defined catchment area. Utilizing several diagnostic classifications, rates for schizophrenia were found to be substantially increased in the Afro-Caribbean community, and especially in the ‘second generation’ British born. Mode of onset and symptom profiles of psychoses suggest that atypical syndromes, and by implication ‘misdiagnoses’, do not account for reported higher rates of schizophrenic illness in these patients.

We study the occurrence of excitonic superfluidity in electron-hole bilayers at zero temperature. We not only identify the crossover in the phase diagram from the BCS limit of overlapping pairs to the BEC limit of nonoverlapping tightly bound pairs but also, by varying the electron and hole densities independently, we can analyze a number of phases that occur mainly in the crossover region.With different electron and hole effective masses, the phase diagram is asymmetric with respect to excess electron or hole densities. We propose, as the criterion for the onset of superfluidity, the jump of the electron and hole chemical potentials when their densities cross