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Register a new userSpin-charge-lattice coupling near the metal-insulator transition in Ca3Ru2O7
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We report x-ray scattering studies of the c-axis lattice parameter in Ca3Ru2O7 as a function of temperature and magnetic field. These structural studies complement published transport and magnetization data, and therefore elucidate the spin-charge-lattice coupling near the metal-insulator transition. Strong anisotropy of the structural change for field applied along orthogonal in-plane directions is observed. Competition between a spin-polarized phase that does not couple to the lattice, and an antiferromagnetic metallic phase, which does, gives rise to rich behavior for B $parallel$ b.
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We use Ru $L_3$-edge resonant inelastic x-ray scattering (RIXS) to study the full range of excitations in Ca$_3$Ru$_2$O$_7$ from meV-scale magnetic dynamics through to the eV-scale interband transitions. This bilayer $4d$-electron correlated metal expresses a rich phase diagram, displaying long range magnetic order below 56 K followed by a concomitant structural, magnetic and electronic transition at 48 K. In the low temperature phase we observe a magnetic excitation with a bandwidth of $sim$30 meV and a gap of $sim$8 meV at the zone center, in excellent agreement with inelastic neutron scattering data. The dispersion can be modeled using a Heisenberg Hamiltonian for a bilayer $mathrm{S}=1$ system with single ion anisotropy terms. At a higher energy loss, $dd$-type excitations show heavy damping in the presence of itinerant electrons, giving rise to a fluorescence-like signal appearing between the $t_{2g}$ and $e_g$ bands. At the same time, we observe a resonance originating from localized $t_{2g}$ excitations, in analogy to the structurally related Mott-insulator Ca$_2$RuO$_4$. But whereas Ca$_2$RuO$_4$ shows sharp separate spin-orbit excitations and Hunds-rule driven spin-state transitions, here we identify only a single broad asymmetric feature. These results indicate that local intra-ionic interactions underlie the correlated physics in Ca$_3$Ru$_2$O$_7$, even as the excitations become strongly mixed in the presence of itinerant electrons.
By using the cluster perturbation theory, we investigate the effects of the local electron-phonon interaction in the quantum spin Hall topological insulator described by the half-filled Kane-Mele model on an honeycomb lattice. Starting from the topological non trivial phase, where the minimal gap is located at the two inequivalent Dirac points of the Graphene, $text{K}$ and $text{K}$, we show that the coupling with quantum phonons induces a topological-trivial quantum phase transition through a gap closing and reopening in the $text{M}$ point of the Brillouin zone. The average number of fermions in this point turns out to be a direct indicator of the quantum transition pointing out a strong hybridization between the two bare quasiparticle bands of the Kane-Mele model. By increasing the strength of charge-lattice coupling, the phonon Greens propagator displays a two peak structure: the one located at the lowest energy exhibits a softening that is maximum around the topological transition. Numerical simulations provide also evidence of several kinks in the quasiparticle dispersion caused by the coupling of the electrons with the bosonic lattice mode.
It has been proposed that an extended version of the Hubbard model which potentially hosts rich possibilities of correlated physics may be well simulated by the transition metal dichalcogenide (TMD) moir{e} heterostructures. Motivated by recent reports of continuous metal insulator transition (MIT) at half filling, as well as correlated insulators at various fractional fillings in TMD moir{e} heterostructures, we propose a theory for the potentially continuous MIT with fractionalized electric charges. The charge fractionalization at the MIT will lead to experimental observable effects, such as a large universal resistivity jump and interaction driven bad metal at the MIT, as well as special scaling of the quasi-particle weight with the tuning parameter. These predictions are different from previously proposed theory for continuous MIT.
In this article, we discuss the non-trivial collective charge excitations (plasmons) of the extended square-lattice Hubbard model. Using a fully non-perturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly-correlated phase. The momentum-resolved charge susceptibility is also computed on the basis of the Euclidean charge density-density correlator. In agreement with previous EDMFT studies, we find that at large strength of the electron-electron interaction, the plasmon dispersion develops two branches.
The electrodynamics near the metal-to-insulator transitions (MIT) induced, in V3O5 single crystals, by both temperature (T) and pressure (P) has been studied by infrared spectroscopy. The T- and P-dependence of the optical conductivity may be explained within a polaronic scenario. The insulating phase at ambient T and P corresponds to strongly localized small polarons. Meanwhile the T-induced metallic phase at ambient pressure is related to a liquid of polarons showing incoherent dc transport, in the P-induced metallic phase at room T strongly localized polarons coexist with partially delocalized ones. The electronic spectral weight is almost recovered, in both the T and P induced metallization processes, on an energy scale of 1 eV, thus supporting the key-role of electron-lattice interaction in the V3O5 metal-to-insulator transition.
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