LOW-TEMPERATURE THERMAL-PROPERTIES OF AMORPHOUS ASXSE1-X

We have measured the low-temperature specific heat C and thermal conductivity kappa (1.5 K less-than-or-equal-to T less-than-or-equal-to 30 K) of amorphous AsxSe1-x in the concentration range of 0 less-than-or-equal-to x less-than-or-equal-to 0.72. The maximum in C/T3 and the plateau in kappa display consistent but nonmonotonic concentration dependences, similar to the earlier specific-heat results for the same samples below 1 K. Our results give unambiguous evidence that the behavior below 1 K (attributed to tunneling states) and the intermediate-temperature anomalies are intimately related, hence, they might have a common structural origin. Possible microscopic mechanisms are discussed, suggesting two different types of low-energy excitations. The specific-heat maximum in C/T3 can be scaled by two parameters, and this feature can be generalized to other amorphous systems. Finally, our results are discussed in terms of current theoretical models.