Metallicity without quasi-particles in room-temperature strontium titanate

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 T 3 behavior before becoming T 2 in the lowtemperature 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 T 3 -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. npj Quantum Materials (2017)2:41 ; doi:10.1038/s41535-017-0044-5 INTRODUCTIONThe 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. But in "bad" 2 or "strange" 3 metals, it continues to increase. 4 It is indeed strange when the mean-freepath persists to fall after attaining its shortest conceivable magnitude and often unexpected behavior is considered bad.In most cases, bad metals present a linear temperature dependence beyond the MIR limit. Bruin et al. 5 recently noticed that the T-linear scattering rate in numerous metals, either ordinary or strange, has a similar magnitude. This observation suggests the relevance of a universal Planck timescale (τ P $

Charge transport in a polar metal

“…α in µ ∼ n −α is close to unity). Second, this mobility is strongly temperature dependent and passes from a room-temperature value of 5 cm 2 V −1 s −1 to 20000 cm 2 V −1 s −1 at liquid He temperature [40,41]. This latter value implies that the low-temperature carrier mean-free-path becomes much longer than the interdopant distance (l ee = n −1/3 ) in contrast to the ionized-impurity-scattering scenario.…”

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

“…On the other hand, Spinelli et al [251] estimated values for a H of 200 nm at RT and as large as 10 µm for low temperatures, where ε is enhanced by two orders of magnitude. To cope with the very low value of the carrier concentration limit in the case of the classical interpretation of the insulator-to-metal transition for SrTiO 3 other authors have suggested resolving the contradiction by applying, e.g., the Mott-Ioffe-Regel (MIR) limit [252]. This model can be used when the mean-free-path of a carrier falls below its Fermi wavelength or the length is smaller than the lattice constant (interatomic distance).…”

Novel Metal-Insulator Transition at the SmTiO3/SrTiO3 Interface

“…Thus, the two features are independent phenomena. Bulk SrTiO 3 has an antiferrodistortive transition at ∼110 K, and resistance anomalies have been observed to be associated with it [21][22][23], although their precise origin remains to be determined. Figure 3 shows T MIT as a function of the sheet carrier density (n s ), determined at room temperature from the Hall measurements (shown in Fig.…”