Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nuclear-order-induced quantum criticality and heavy-fermion
  superconductivity at ultra-low temperatures in YbRh$_2$Si$_2$   The tetragonal heavy-fermion metal YbRh$_2$Si$_2$ orders
antiferromagnetically at $T_{\rm N} = 70$ mK and exhibits an unconventional
quantum critical point (QCP) of Kondo-destroying type at $B_{\rm N} = 60$ mT,
for the magnetic field applied within the basal ($a,b$) plane.
Ultra-low-temperature magnetization and heat-capacity measurements at very low
fields indicate that the 4$f$-electronic antiferromagnetic (AF) order is
strongly suppressed by a nuclear-dominated hybrid order (`A-phase') at $T_{\rm
A} \le 2.3$ mK, such that quantum critical fluctuations develop at $B \approx
0$ (Schuberth et al., Science \textbf{351}, 485 (2016)). This enables the onset
of heavy-fermion superconductivity ($T_{\rm c} = 2$ mK) which appears to be
suppressed by the primary AF order at elevated temperatures. Measurements of
the Meissner effect reveal bulk superconductivity, with $T_{\rm c}$ decreasing
under applied field to $T_{\rm c} < 1$ mK at $B > 20$ mT. The observation of a
weak but distinct superconducting shielding signal at a temperature as high as
10 mK suggests the formation of insulated random islands with emergent A-phase
order and superconductivity. Upon cooling, the shielding signal increases
almost linearly in temperature, indicating a growth of the islands which
eventually percolate at $T \approx 6.5$ mK. Recent electrical-resistivity
results by Nguyen et al. (Nat. Commun. \textbf{12}, 4341 (2021)) confirm the
existence of superconductivity in YbRh$_2$Si$_2$ at ultra-low temperatures. The
combination of the results of Schuberth et al. and Nguyen et al. at ultra-low
temperatures below $B_{\rm N}$, along with those previously established at
higher temperatures in the paramagnetic state, provide compelling evidence that
the Kondo-destruction quantum criticality robustly drives unconventional
superconductivity.

28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci
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The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
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The categories of this paper are: supr-con
9
The categories of this paper are: nlin