No abstract

No abstract

We have investigated the inert gases Ar, Xe, and He for suitability as pressure media in a diamond anvil cell at liquid-helium temperature, from 0 to 30 kbar, and compared these with a 4:1 methanol/ethanol mixture. Xe gives severe nonhydrostaticity and is of no value as a low-temperature medium. Ar gives much less nonhydrostaticity, but little improvement over the 4:1 methanol/ethanol mixture. He gives no observable nonhydrostaticity even when the pressure is changed at low temperature. A technique for loading with He is presented.

We have measured the photoluminescence (PL) of HgTe/CdTe superlattices under high hydrostatic pressures up to 30 kbar at liquid-nitrogen temperature. We observed several photoluminescence peaks with energies ranging from -130 to -700 meV. The most prominent peak at -130 meV, which has been attributed to the recombination across the superlattice band gap, moves higher in energy with a pressure coefficient of 1 meV/kbar. Other peaks, whose origins are not well established, have higher energies and their pressure coefficients are in the range of 0 -2 meV/kbar. A calculation based on the envelope-function approximation gives a pressure coefficient of at least -6.5 meV/kbar for the superlattice band gap. This is far outside the error bars of the measured pressure dependence of the main peak, 1 meV/kbar. Varying the input parameters for the calculation, including the valence-band offset, changes the result of the calculation by less than 10%. Possible explanations for this disagreement, including a modification of the current model of HgTe/CdTe superlattice bands and a reinterpretation of the PL peaks, are examined.

No abstract