Carrier density independent scattering rate in SrTiO3-based electron liquids

Abstract

We examine the carrier density dependence of the scattering rate in two- and three-dimensional electron liquids in SrTiO3 in the regime where it scales with Tn (T is the temperature and n ≤ 2) in the cases when it is varied by electrostatic control and chemical doping, respectively. It is shown that the scattering rate is independent of the carrier density. This is contrary to the expectations from Landau Fermi liquid theory, where the scattering rate scales inversely with the Fermi energy (EF). We discuss that the behavior is very similar to systems traditionally identified as non-Fermi liquids (n < 2). This includes the cuprates and other transition metal oxide perovskites, where strikingly similar density-independent scattering rates have been observed. The results indicate that the applicability of Fermi liquid theory should be questioned for a much broader range of correlated materials and point to the need for a unified theory.

Kinetic Theory of Electronic Transport in Random Magnetic Fields

“…In many metals including some transition metals and their oxides, heavy fermion metals, and organic charge transfer salts, (i ) or (ii ) are consistent with experiment [2]. Recently, a curious observation of ρ ∝ T 2 was reported in SrTiO 3 [7,8], at electronic carrier densities of n ≈ 10 17 cm −3 . A second band appears in SrTiO 3 when n 10 18 cm −3 ; umklapp is allowed when n 10 20 cm −3 [7].…”

“…(ii ) Letting ρ ≈ ρ 0 + AT 2 , [7] found that A is insensitive to the emergence of a second band of carriers at n ∼ 10 18 cm −3 , as is our toy model of a multi-band metal in Figure 1a. (iii ) The residual resistivity ρ 0 appears unrelated to A [7,8]. In the weak disorder limit, contributions to ρ(T ) from magnetic vs. potential disorder add via Matthiesen's rule.…”

Pseudogaps and Emergence of Coherence in Two-Dimensional Electron Liquids inSrTiO3

“…One may speculate that this may be an indicator of an unconventional metallic phase. Prior transport studies indicate that none of the 2DELs are Fermi liquids, even when n ~ 2 [21,35]. Out of the power-law "backbone DOS" [17] pseudogaps emerge below ~ 5 SrO layers in both types of quantum wells.…”

“…Specifically, the evolution of the pseudogap in the quantum wells in SmTiO 3 is quite typical of correlated electron systems, whereas that in GdTiO 3 appears to be dominated by the transition to a symmetry broken, gapped state, i.e., reflecting a stronger interaction with the lattice. Finally, we wish to again emphasize the incompatibility of all the transport properties of these quantum wells with Fermi liquid theory (carrier-density independent scattering rates, separation of Hall and longitudinal transport lifetimes [21,35]). This supports the idea that the pseudogaps are an intrinsic manifestation of an unusual metallic state in a wider class of correlated electron systems.…”

Charge transport in oxygen-deficient EuTiO3 : The emerging picture of dilute metallicity in quantum-paraelectric perovskite oxides

“…For many systems, the prefactor A of ρ(T ) = ρ 0 + AT 2 is related to the electronic specific heat coefficient γ, since both depend on the Fermi energy E F , as is expressed in the Kadowaki-Woods ratio A/γ 2 [17]. Furthermore, E F itself depends on the carrier density n and one may expect a particular scaling behavior in A(n) as shown for metallic SrTiO 3−δ [16,18].…”