Very low-temperature search for superconductivity in semiconducting KTaO3

Abstract

A series of attempts have been made to detect the presence of superconductivity in semiconducting potassium tantalate (KTaO3) single crystals. Semiconducting potassium tantalate has a number of properties in common with semiconducting SrTiO3, which is superconducting below ∼0.3 K, with a critical temperatureT c that varies as a function of the carrier concentration. Both KTaO3 and SrTiO3 are perovskite-structure oxides and both materials are so-called incipient ferroelectrics that are characterized by high dielectric constants at low temperature. These common properties suggest that superconductivity might also be observed in semiconducting potassium tantalate. In the temperature ange from 0.01 to 4.0 K, however, no evidence was found for superconductivity in KTaO3 in the presence of magnetic fields of 10−5–10−4 T (i.e., 0.1–1 Oe). Below 1.5 K, the search for superconductivity in KTaO3 was carried out using a3He-4He dilution refrigerator equipped with a SQUID magnetometer and an ac magnetometer. The system response was verified by measuring the paramagnetic susceptibility of Dy2O3-doped KTaO3. The failure to observe superconductivity in KTaO3, while SrTiO3 is an established superconducting material, may be related to the fact that the latter substance assumes a tetragonal symmetry phase at 105 K, while KTaO3 remains cubic to low temperatures.