Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Insulator-like behavior coexisting with metallic electronic structure in
  strained FeSe thin films grown by molecular beam epitaxy   This paper reports that ~10-nm-thick FeSe thin films exhibit insulator-like
behavior in terms of the temperature dependence of their electrical resistivity
even though bulk FeSe has a metallic electronic structure that has been
confirmed by photoemission spectroscopy and first-principles calculations. This
apparent contradiction is explained by potential barriers formed in the
conduction band. Very thin FeSe epitaxial films with various [Fe]/[Se] were
fabricated by molecular beam epitaxy and classified into two groups with
respect to lattice strain and electrical properties. Lattice parameter a
increased and lattice parameter c decreased with increasing [Fe]/[Se] up to 1.1
and then a levelled off and c began to decrease at higher [Fe]/[Se].
Consequently, the FeSe films had the most strained lattice when [Fe]/[Se] was
1.1, but these films had the best quality with respect to crystallinity and
surface flatness. All the FeSe films with [Fe]/[Se] of 0.8-1.9 exhibited
insulator-like behavior, but the temperature dependences of their electrical
resistivities exhibited different activation energies Ea between the Se-rich
and Fe-rich regions; i.e., Ea were small (a few meV) up to [Fe]/[Se]=1.1 but
jumped up to ~25 meV at higher [Fe]/[Se]. The film with [Fe]/[Se]=1.1 had the
smallest Ea of 1.1 meV and exhibited an insulator-superconducting transition at
35 K with zero resistance under gate bias. The large Ea of the Fe-rich films
was attributed to the unusual lattice strain with tensile in-plane and relaxed
out-of-plane strains. The large Ea of films with [Fe]/[Se]>1.1 resulted in low
mobility with a high potential barrier of ~50 meV in the conduction band for
percolation carrier conduction compared with that of the [Fe]/[Se]=1.1 film
(~17 meV). Therefore, the Fe-rich films exhibited remarkable insulator-like
behavior similar to a semiconductor despite their metallic electronic
structure.

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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: math
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: cs
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The categories of this paper are: cmp-lg
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc