Probing the Dilute Metallic State in SrTiO3

This work reported on the first detailed, systematic study of low temperature electronic specific heat in doped SrTiO3. This was done over a wide doping range, in Nb-doped single crystals. The electronic specific heat was shown to be typical of a Fermi liquid, using both experimental and theoretical approaches. The density-of-states effective mass extracted from the data were also shown to be quantitatively consistent with quantum transport data, revealing an increase to as high as 5 free electron masses with filling. Critically, this was shown to be reconcilable with theoretical band structure, revealing a notably filling-independent mass enhancement factor. Moreover, with a complete data set on both electronic specific heat and resistivity available for the first time, Kadowaki-Woods scaling between the T2 resistivity pre-factor (A) and the electronic specific heat (g) was tested. Massive, even qualitative, violations of the behavior expected for Fermi liquids was found (see Figure), highlighting the highly unusual nature of the T2 resistivity in SrTiO3. Whether this T2 resistivity even reflects Fermi liquid behavior in this material remains a major open question. This work will no doubt stimulate further work in this important direction.