Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of Cooper Pairs in a Mesoscopic 2D Fermi Gas   Pairing is the fundamental requirement for fermionic superfluidity and
superconductivity. To understand the mechanism behind pair formation is an
ongoing challenge in the study of many strongly correlated fermionic systems.
Here, we directly observe Cooper pairs in a mesoscopic two-dimensional Fermi
gas. We apply an imaging scheme that enables us to extract the full in-situ
momentum distribution of a strongly interacting Fermi gas with single particle
and spin resolution. Our ultracold gas allows us to freely tune between a
completely non-interacting, unpaired system and weak attractions, where we find
Cooper pair correlations at the Fermi surface. When increasing the attractive
interactions even further, the pairs gradually turn into deeply bound molecules
breaking up the Fermi surface. Our observables provide new opportunities to
address questions concerning mesoscopic systems that have been raised in
nuclear, atomic and condensed matter physics.

24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
16
The categories of this paper are: stat
1
The categories of this paper are: cs