Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pressure-induced quantum critical point in a heavily hydrogen-doped
  iron-based superconductor LaFeAsO   An iron-based superconductor LaFeAsO$_{1-x}$H$_x$ (0 $\leq x \leq$ 0.6)
undergoes two antiferromagnetic (AF) phases upon H doping. We investigated the
second AF phase ($x$=0.6) using NMR techniques under pressure. At pressures up
to 2 GPa, the ground state is a spin-density-wave state with a large gap;
however, the gap closes at 4.0 GPa, suggesting a pressure-induced quantum
critical point. Interestingly, the gapped excitation coexists with gapless
magnetic fluctuations at pressures between 2 and 4 GPa. This coexistence is
attributable to the lift up of the $d_{xy}$ orbital to the Fermi level, a
Lifshitz transition under pressure.

11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th