  The recent discovery of superconductivity in doped infinite-layer nickelates
has stimulated intensive interest, especially for similarities and differences
compared to that in cuprate superconductors. In contrast to cuprates, although
earlier magnetization measurement reveals a Curie-Weiss-like behavior in
undoped infinite-layer nickelates, there is no magnetic ordering observed by
elastic neutron scattering down to liquid helium temperature. Until now, the
nature of the magnetic ground state in undoped infinite-layer nickelates was
still elusive. Here, we perform a nuclear magnetic resonance (NMR) experiment
through 139La nuclei to study the intrinsic spin susceptibility of
infinite-layer LaNiO2. First, the signature for magnetic ordering or freezing
is absent in the 139La NMR spectrum down to 0.24 K, which unambiguously
confirms a paramagnetic ground state in LaNiO2. Second, a pseudogap-like
behavior instead of Curie-Weiss-like behavior is observed in both the
temperature-dependent Knight shift and nuclear spin-lattice relaxation rate
(1/T1), which is widely observed in both underdoped cuprates and iron-based
superconductors. Furthermore, the scaling behavior between the Knight shift and
1/T1T has also been discussed. Finally, the present results imply a
considerable exchange interaction in infinite-layer nickelates, which sets a
strong constraint for the proposed theoretical models.
