Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence of unconventional superconductivity in the Ni-doped NbB2 system   In this paper, a comprehensive study of the effects of Ni-doping on
structural, electrical, thermal and magnetic properties of the NbB2 is
presented. Low amounts (\leq 10 %) of Ni substitution on Nb sites cause
structural distortions and induce drastic changes in the physical properties,
such as the emergence of a bulk superconducting state with anomalous behaviors
in the critical fields (lower and upper) and in the specific heat. Ni-doping at
the 9 at.% level, for instance, is able to increase the critical temperature
(TC) in stoichiometric NbB2 (< 1.3 K) to approximately 6.0 K. Bulk
superconductivity is confirmed by magnetization, electronic transport, and
specific heat measurements. Both Hc1 and Hc2 critical fields exhibit a linear
dependence with reduced temperature (T/TC), and the specific heat deviates
remarkably from the conventional exponential temperature dependence of the
single-band BCS theory. These findings suggest multiband superconductivity in
the composition range from 0.01 \leq x \leq 0.10.

12
The categories of this paper are: nucl-th
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con