  The upper critical field is a fundamental measure of the strength of
superconductivity in a material. It is also a cornerstone for the realization
of superconducting magnet applications. The critical field arises because of
the Copper pair breaking at a limiting field, which is due to the Pauli
paramagnetism of the electrons. The maximal possible magnetic field strength
for this effect is commonly known as the Pauli paramagnetic limit given as
$\mu_0 H_{\rm Pauli} \approx 1.86{\rm [T/K]} \cdot T_{\rm c}$ for a
weak-coupling BCS superconductor. The violation of this limit is only rarely
observed. Exceptions include some low-temperature heavy fermion and some
strongly anisotropic superconductors. Here, we report on the superconductivity
at 9.75 K in the centrosymmetric, cubic $\eta$-carbide-type compound
Nb$_4$Rh$_2$C$_{1-\delta}$, with a normalized specific heat jump of $\Delta
C/\gamma T_{\rm c} =$ 1.64. We find that this material has a remarkably high
upper critical field of $\mu_0 H_{\rm c2}{\rm (0)}$ =~28.5~T, which is
exceeding by far its weak-coupling BCS Pauli paramagnetic limit of $\mu_0
H_{\rm Pauli}$~=~18.1 T. Determination of the origin and consequences of this
effect will represent a significant new direction in the study of critical
fields in superconductors.
