Abstract
Cooling oxygen-deficient strontium titanate to liquid-helium temperature leads to a decrease in its electrical resistivity by several orders of magnitude. The temperature dependence of resistivity follows a rough T3 behavior before becoming T2 in the low-temperature limit, as expected in a Fermi liquid. Here, we show that the roughly cubic resistivity above 100 K corresponds to a regime where the quasi-particle mean-free-path is shorter than the electron wave-length and the interatomic distance. These criteria define the Mott-Ioffe-Regel limit. Exceeding this limit is the hallmark of strange metallicity, which occurs in strontium titanate well below room temperature, in contrast to other perovskytes. We argue that the T3-resistivity cannot be accounted for by electron-phonon scattering à la Bloch–Gruneisen and consider an alternative scheme based on Landauer transmission between individual dopants hosting large polarons. We find a scaling relationship between carrier mobility, the electric permittivity and the frequency of transverse optical soft mode in this temperature range. Providing an account of this observation emerges as a challenge to theory.
Highlights
The existence of well-defined quasi-particles is taken for granted in the Boltzmann–Drude picture of electronic transport
The Mott-Ioffe-Regel (MIR) limit is attained when the mean-free-path of a carrier falls below its Fermi wavelength or the interatomic distance.[1]
We show here that n-doped SrTiO3 is an unnoticed case of strange or bad metallicity
Summary
The existence of well-defined quasi-particles is taken for granted in the Boltzmann–Drude picture of electronic transport. In this picture, carriers of charge or energy are scattered after traveling a finite distance. The Mott-Ioffe-Regel (MIR) limit is attained when the mean-free-path of a carrier falls below its Fermi wavelength or the interatomic distance.[1] In most metals, resistivity saturates when this limit is approached. In “bad”[2] or “strange”[3] metals, it continues to increase.[4] It is strange when the mean-freepath persists to fall after attaining its shortest conceivable magnitude and often unexpected behavior is considered bad
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