31 research outputs found
Direct observation of spin-polarised bulk bands in an inversion-symmetric semiconductor
Methods to generate spin-polarised electronic states in non-magnetic solids
are strongly desired to enable all-electrical manipulation of electron spins
for new quantum devices. This is generally accepted to require breaking global
structural inversion symmetry. In contrast, here we present direct evidence
from spin- and angle-resolved photoemission spectroscopy for a strong spin
polarisation of bulk states in the centrosymmetric transition-metal
dichalcogenide WSe. We show how this arises due to a lack of inversion
symmetry in constituent structural units of the bulk crystal where the
electronic states are localised, leading to enormous spin splittings up to
eV, with a spin texture that is strongly modulated in both real and
momentum space. As well as providing the first experimental evidence for a
recently-predicted `hidden' spin polarisation in inversion-symmetric materials,
our study sheds new light on a putative spin-valley coupling in
transition-metal dichalcogenides, of key importance for using these compounds
in proposed valleytronic devices.Comment: 6 pages, 4 figure
The economics of Theocracy
This paper models theocracy as a regime where the clergy in power retains knowledge of the cost of political production but which is potentially incompetent or corrupt. This is contrasted with a secular regime where government is contracted out to a secular ruler, and hence the church loses the possibility to observe costs and creates for itself a hidden-information agency problem. The church is free to choose between regimes – a make-or-buy choice – and we look for the range of environmental parameters that are most conducive to the superiority of theocracy and therefore to its occurrence and persistence, despite its disabilities. Numerical solution of the model indicates that the optimal environment for a theocracy is likely to be one in which the “bad” (high-cost) state is disastrously bad but the probability of its occurrence is not very high. A broad review of the historical evidence yields some suggestive support to the predictions of the model. Finally, the model is shown to be applicable to the make-or-buy-government choices of other groups, such as organized labor and the military