Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Efficient fluctuation exchange approach to low-temperature spin
  fluctuations and superconductivity: from the Hubbard model to
  Na$_x$CoO$_2\cdot y$H$_2$O   Superconductivity arises mostly at energy and temperature scales that are
much smaller than the typical bare electronic energies. Since the computational
effort of diagrammatic many-body techniques increases with the number of
required Matsubara frequencies and thus with the inverse temperature, phase
transitions that occur at low temperatures are typically hard to address
numerically. In this work, we implement a fluctuation exchange (FLEX) approach
to spin fluctuations and superconductivity using the "intermediate
representation basis" (IR) [Shinaoka et al., PRB 96, 2017] for Matsubara Green
functions. This FLEX+IR approach is numerically very efficient and enables us
to reach temperatures on the order of $10^{-4}$ in units of the electronic band
width in multi-orbital systems. After benchmarking the method in the doped
repulsive Hubbard model on the square lattice, we study the possibility of
spin-fluctuation-mediated superconductivity in the hydrated sodium cobalt
material Na$_x$CoO$_2\cdot y$H$_2$O reaching the scale of the experimental
transition temperature $T_{\mathrm{c}}=4.5$ K and below.

1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex