Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Stiffnessometer, a magnetic-field-free superconducting stiffness meter
  and its application   We provide a detailed account for a new method to measure superconducting
stiffness $\rho_{s}$, critical current density $j_c$, and coherence length
$\xi$, in one apparatus, without subjecting the sample to magnetic field or
attaching leads. The method is based on the London equation
$\mathbf{j}=-\rho_{s}\mathbf{A}$, where ${\bf j}$ is the current density and
${\bf A}$ is the vector potential. Using a rotor free $\bf{A}$ and a
measurement of $\bf{j}$ via the magnetic moment of a superconducting ring, we
determine $\rho_{s}$. By increasing $\mathbf{A}$ until the London equation
fails we determine $j_c$ and $\xi$. The method is sensitive to very small
stiffness, which translates to penetration depth $\lambda \lesssim 1$~mm. It is
also sensitive to low critical current density $j_c \sim 10^3$ Amm$^{-2}$ or
long coherence length $\xi \sim 1$~$\mu$m. Naturally, the method does not
suffer from demagnetization factor complications, the presence of vortices, or
out-of-equilibrium conditions. Therefore, the absolute values of the different
parameters can be determined. We demonstrate the application of this method to
La$_{2-x}$Sr$_{x}$CuO$_{4}$ with $x=0.17$.

24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ