Possible Spin-Density Wave on Fermi Arc of Edge State in Single-Component Molecular Conductors [Pt(dmdt)₂] and [Ni(dmdt)₂]

Abstract

We construct three-orbital tight-binding models describing single-component molecular conductors [Pt(dmdt)2] and [Ni(dmdt)2] using first-principles calculations. We show that [Ni(dmdt)2] is a Dirac nodal line system with highly one-dimensional edge states at the (001) edge, similar to [Pt(dmdt)2], as demonstrated in prior studies. To investigate possible edge magnetism, we calculate longitudinal and transverse spin susceptibilities using real-space-dependent random-phase approximation (RPA) in three-orbital Hubbard models in the presence of spin-orbit coupling. We find that the edge spin-density wave (SDW) is induced by the Coulomb repulsion and incommensurate nestings of the Fermi arcs. We also find that the magnetic structure of the edge SDW can be changed via extremely small carrier doping, which is controllable in molecular conductors.

Fragment-orbital-dependent spin fluctuations in the single-component molecular conductor [Ni(dmdt)$_2$]

“…They are obtained using Wannier fitting to three isolated energy bands near E F , which were previously obtained using first-principles calculations. 54 The Wannier fitting and first-principles calculations were performed using the programs respack 65 and Quantum Espresso 66 , respectively. 54 respack was also used for calculating the Coulomb interaction and other factors.…”

“…By contrast, if the electron hopping perpendicular to the main conducting layer were coherent, the Dirac point would be connected and draw lines (rings) in the three-dimensional momentum space, which are called the Dirac nodal lines (rings). [33][34][35][36] Such kinds of Dirac nodal line (ring) systems have indeed been found in graphite, 37 transitionmetal monophosphates, 38 Cu 3 N, 39 antiperovskites, 40 perovskite iridates, 41 and hexagonal pnictides with the composition CaAgX (X = P, As), 42 as well as in the single-component molecular conductors [Pd(dddt) 2 ], [43][44][45][46][47][48][49][50] [Pt(dmdt) 2 ], [51][52][53][54][55] and [Ni(dmdt) 2 ]. 54,55 The Dirac nodal line (ring) systems exhibit not only the properties in common with two-dimensional Dirac electron systems, e.g., the in-plane conductivity 51 , but also the characteristic electronic properties such as non-dispersive Landau levels, 56 Kondo effect, 57 quasi-topological electromagnetic responses, 58 and edge magnetism 54 because of the three-dimensionality.…”

“…In previous studies, the electronic properties of [M(dmdt) 2 ] were studied using density functional theory (DFT), and tightbinding models were constructed on the basis of the extended Hückel method and DFT. [51][52][53][54] These investigations showed that [M(dmdt) 2 ] is a Dirac nodal line system. Furthermore, electronic resistivity measurements using conventional four-probe methods were performed and showed that the resistivity of [M(dmdt) 2 ] hardly depends on the temperature (T ), which is consistent with the property of the Dirac electron system.…”

“…59 In addition, we previously suggested that the nesting between the Fermi arcs localized at the edge and the electronic correlation induce a helical spin density wave (SDW) at the edge. 54 Recently, the spin-lattice relaxation rate 1/T1T, probing the low-energy spin dynamics, and the Knight shift, scaling to the spin susceptibility, of [Ni(dmdt) 2 ] were observed in a 13 C nuclear magnetic resonance ( 13 C-NMR) experiment. 60 At high temperature, 1/T 1T decreases with cooling and is almost proportional to T 2 .…”

“…The electronic states of singlecomponent molecular conductors, e.g., [M(tmdt) 2 ] (M = Ni, Au, Cu) and [M(dmdt) 2 ] (M = Pt, Ni), are described by multiple molecular orbitals localized in a part of the molecule. 53,54,[61][62][63] These molecular orbitals are the energy eigenstates obtained using first-principles calcula-tions and are called "fragment orbitals". The fragment orbitals are transformed into HOMO and LUMO by a high-symmetry unitary transform.…”