Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: YBa2Cu3O7 grain boundary junctions and low-noise superconducting quantum
  interference devices patterned by a focused ion beam down to 80 nm linewidth   YBa$_2$Cu$_3$O$_7$ 24$^\circ$ (30$^\circ$) bicrystal grain boundary junctions
(GBJs), shunted with 60\,nm (20\,nm) thick Au, were fabricated by focused ion
beam milling with widths $80\,{\rm nm} \le w \le 7.8\,\mu$m. At 4.2\,K we find
critical current densities $j_c$ in the $10^5\,{\rm A/cm^2}$ range %\dkc{\#1}
(without a clear dependence on $w$) and an increase in resistance times
junction area $\rho$ with an approximate scaling $\rho\propto w^{1/2}$. For the
narrowest GBJs $j_c\rho\approx 100\,\mu$V, which is promising for the
realization of sensitive nanoSQUIDs for the detection of small spin systems. We
demonstrate that our fabrication process allows the realization of sensitive
nanoscale dc SQUIDs; for a SQUID with $w\approx 100$\,nm wide GBJs we find an
rms magnetic flux noise spectral density of $S_\Phi^{1/2}\approx
4\,\mu\Phi_0/{\rm Hz}^{1/2}$ in the white noise limit. We also derive an
expression for the spin sensitivity $S_\mu^{1/2}$, which depends on
$S_\Phi^{1/2}$, on the location and orientation of the magnetic moment of a
magnetic particle to be detected by the SQUID, and on the SQUID geometry. For
the not optimized SQUIDs presented here, we estimate
$S_\mu^{1/2}=390\,\mu_B/\sqrt{\rm{Hz}}$, which could be further improved by at
least an order of magnitude.

30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th