Fragment-orbital-dependent spin fluctuations in the single-component molecular conductor [Ni(dmdt)_2]
arxiv(2022)
摘要
Motivated by recent nuclear magnetic resonance experiments, we calculated the
spin susceptibility, Knight shift, and spin-lattice relaxation rate
(1/T_1T) of the single-component molecular conductor [Ni(dmdt)_2] using
the random phase approximation in a multi-orbital Hubbard model describing the
Dirac nodal line electronic system in this compound. This Hubbard model is
composed of three fragment orbitals and on-site repulsive interactions obtained
using ab initio many-body perturbation theory calculations. We found
fragment-orbital-dependent spin fluctuations with the momentum
q=0 and an incommensurate value of the wavenumber
q=Q at which a diagonal element of the spin
susceptibility is maximum. The q=0 and Q
responses become dominant at low and high temperatures, respectively, with the
Fermi-pocket energy scale as the boundary. We show that 1/T_1T decreases
with decreasing temperature but starts to increase at low temperature owing to
the q=0 spin fluctuations, while the Knight shift keeps
monotonically decreasing. These properties are due to the intra-molecular
antiferromagnetic fluctuations caused by the characteristic wave functions of
this Dirac nodal line system, which is described by an n-band (n≥ 3)
model. We show that the fragment orbitals play important roles in the magnetic
properties of [Ni(dmdt)_2].
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