Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the superconducting state of the organic conductor $(TMTSF)_2ClO_4$   $(TMTSF)_2ClO_4$ is a quasi-one dimensional organic conductor and
superconductor with $T_c=1.4$K, and one of at least two Bechgaard salts
observed to have upper critical fields far exceeding the paramagnetic limit.
Nevertheless, the $^{77}$Se NMR Knight shift at low fields reveals a decrease
in spin susceptibility $\chi_s$ consistent with singlet spin pairing. The field
dependence of the spin-lattice relaxation rate at 100mK exhibits a sharp
crossover (or phase transition) at a field $H_s\sim15$kOe, to a regime where
$\chi_s$ is close to the normal state value, even though \hc2 $\gg H_s$.

1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ