Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An unexplored MBE growth mode reveals new properties of superconducting
  NbN   Accessing unexplored conditions in crystal growth often reveals remarkable
surprises and new regimes of physical behavior. In this work, performing
molecular beam epitaxy of the technologically important superconductor NbN at
temperatures greater than 1000$^\circ$C, higher than in the past, is found to
reveal persistent RHEED oscillations throughout the growth, atomically smooth
surfaces, normal metal resistivities as low as 37$\mu\Omega$-cm and
superconducting critical temperatures in excess of 15 K. Most remarkably, a
reversal of the sign of the Hall coefficient is observed as the NbN films are
cooled, and the high material quality allows the first imaging of Abrikosov
vortex lattices in this superconductor.

5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an