High-pressure resistance of PuTe up to 25 GPa

The electrical resistance of a single crystal of PuTe has been measured up to similar to 25 GPa and as a function of temperature down to 1.3 K. At low pressure, the resistance R displays the expected activated behavior, i.e., an upturn at low temperature and a change of curvature at similar to 200 K as at ambient pressure. Surprisingly, the resistance at 1.5 K is enhanced by increasing pressure. For the NaCl phase, we propose a model where the conductivity sigma is composed of three contributions; a constant 0 K term sigma (0) as expected in a semimetal, the Mott's law sigma (proportional to) exp-(T-0/T)(1/4) indicating variable-range hopping conductivity below 100 K, and an exponential term exp(-E-g/2k(B)T) due to a band gap. At 0.2 GPa, the activation energies T-0 and E-g equal 23 meV and 0.185 eV, and increase up to 110 meV and similar to0.4 eV at 4.2 GPa, respectively. As a possible origin of the Mott's law behavior, we suggest a mechanism of hopping conduction involving the 5f states of the Pu ions. Between 10.7 GPa and 12.7 GPa, R strongly decreases over the whole temperature range. We attribute this collapse to the NaCl-CsCl structural transition. This effect indicates a strong increase of the state density and is in agreement with theoretical predictions. Above 12.7 GPa, the upturn tends to disappear and the temperature variation of R progressively approaches that of a metal. Our data suggest a magnetic transition below 15 K in the CsCl phase.