Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Heavy non-degenerate electrons in doped strontium titanate   Room-temperature metallicity of lightly doped SrTiO$_3$ is puzzling, because
the combination of mobility and the effective mass would imply a mean-free-path
(mfp) below the Mott Ioffe Regel (MIR) limit and a scattering time shorter than
the Planckian time ($\tau_P=\hbar/k_BT$). We present a study of electric
resistivity, Seebeck coefficient and inelastic neutron scattering extended to
very high temperatures, which deepens the puzzle. Metallic resistivity persists
up to 900 K and is accompanied by a large Seebeck coefficient whose magnitude
(as well as its temperature and doping dependence) indicates that carriers are
becoming heavier with rising temperature. Combining this with neutron
scattering data, we find that between 500 K and 900 K, the Bohr radius and the
electron wave-length become comparable to each other and twice the lattice
parameter. According to our results, between 100 K and 500 K, metallicity is
partially driven by temperature-induced amplification of the carrier mass. We
contrast this mass amplification of non-degenerate electrons with the
better-known case of heavy degenerate electrons. Above 500 K, the
mean-free-path continues to shrink with warming in spite of becoming shorter
than both the interatomic distance and the thermal wavelength of the electrons.
The latter saturates to twice the lattice parameter. Available theories of
polaronic quasi-particles do not provide satisfactory explanation for our
observations.

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The categories of this paper are: q-fin
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th