Estudo da supercondutividade no SrTiO3 dopado com Nb, em ultrabaixas temperaturas sob pressão

Abstract

In this work, we determined experimentally the performance of the superconducting critical temperature versus pressure for Nb-doped SrTiO3. Pure SrTiO3 at low temperatures is a paraelectric near a quantum critical point to a ferroelectric phase at negative pressure. Under small electron doping, the material becomes the superconductor with the lowest charge carrier density known. The motivation of this work is a proposed electron pairing mechanism based on the exchange of virtual polar phonons. To understand the features of the material, we have performed transport, specific heat and Hall effect measurements on three Nb-doped SrTiO3 samples with different doping levels (explicitly, 1%, 0.2% and 0.02%). The two doped samples show a critical temperature above 100mK. The electrical transport measurements were made under pressure using a hydrostatic pressure cell type. Low temperatures have been achieved by using an adiabatic demagnetization refrigerator. The sample with 0.2% Nb doping showed a rapid decrease of its critical superconducting temperature under pressure. This suggests a probable relationship of the emergence of superconductivity to the ferroelectric quantum critical point. The specific heat measurements suggest that electron-electron scattering at low temperature is not a relevant mechanism in the samples.