Hiroyasu Matsuura

Effect of Spin–Orbit Interaction on (4d)3- and (5d)3-Based Transition-Metal Oxides

The effects of a spin–orbit interaction on transition-metal ions of \((4d)^{3}\)- and \((5d)^{3}\)-based oxides in which three electrons occupy t\text{2g orbitals are studied. The amplitude of the magnetic moment of \(d\) electrons on the \(5d\) and \(4d\) orbitals is estimated by numerical diagonalization. It is found that the magnetic moment is reduced by the spin–orbit interaction. It is suggested that \((4d)^{3}\)- and \((5d)^{3}\)-based oxides are located in the middle of the \(L\)–\(S\) and \(J\)–\(J\) coupling schemes.

Theory of Defect-Induced Kondo Effect in Graphene: Numerical Renormalization Group Study

An effective model that describes the Kondo effect due to a point defect in graphene is developed, taking account of the electronic state and the lattice structure of the defect. It is shown that this model can be transformed into a single-channel pseudogap Anderson model with a finite chemical potential. On the basis of the numerical renormalization group method, it is clarified that the experimentally observed gate-voltage dependence of the Kondo temperature is understood in this framework.

Theory on Softening of Elastic Constants in Non-Doped and B-Doped Si with a Vacancy

Softening of elastic constants in non-doped and B-doped Si with a vacancy is discussed theoretically on the basis of a numerical diagonalization study. To explain the difference of the magnetic fie...

Theory of Charge Kondo Effect on Pair Hopping Mechanism

A new microscopic model of the charge Kondo effect is proposed and is studied on the basis of numerical renormalization group calculations. It is shown that the charge Kondo effect is caused by the pair hopping interaction between the conduction band and the localized band. It is found that the formation of a charge Kondo–Yosida singlet due to its mechanism corresponds to the appearance of a valence skipping phenomenon, and that the charge Kondo–Yosida singlet and the spin Kondo–Yosida singlet state coexist for a tuned parameter set, because the charge and spin degrees of freedom are separated in this model. It is also found that the Sommerfeld coefficient is enhanced by the competition between these two singlet states.

Magnetically Robust Non-Fermi Liquid Behavior in Heavy Fermion Systems with f2-Configuration: Competition between Crystalline-Electric-Field and Kondo–Yosida Singlets

In f 2 -based heavy fermion systems with a crystalline-electric-field (CEF) singlet ground state, the non-Fermi liquid (NFL) arises around the quantum critical point (QCP) due to the competition between the CEF singlet and the Kondo–Yosida singlet states. In such a case, the characteristic temperature T F * at which the entropy starts to decrease toward zero is suppressed by the effect of the competition, compared to both energy scales characterizing each singlet state, the lower Kondo temperature ( T K2 ) and the CEF splitting (Δ). We show that in the case of tetragonal symmetry T F * is not affected by the magnetic field up to H z * which is determined by the distance from the QCP or characteristic energy scales of each singlet states, not by T F * itself. As a result, in the vicinity of QCP, there are parameter regions where the NFL is robust against the magnetic field, at an observable temperature range T > T F * , up to H z * which is far larger than T F * and less than min ( T K2 ,Δ). Our result sug...

Temperature Dependent f-Electron Valence of Ion in Two-Level Kondo System

Theory for temperature dependent valence of Sm ion in magnetically robust heavy fermion system SmOs 4 Sb 12 is presented on the basis of the two-level (or double-well) Kondo model. It is shown that the conduction electrons with f-symmetry accumulate on the ion tunneling between double well potential when the temperature is decreased across the Kondo temperature.

Theory of Room Temperature Ferromagnet V(TCNE)x (1.5 < x < 2): Role of Hidden Flat Bands

Theoretical studies on the possible origin of room temperature ferromagnetism (ferromagnetic once crystallized) in the molecular transition metal complex, V(TCNE) x (1.5 < x < 2) have been carried out. For this family, there have been no definite understanding of crystal structure so far because of sample quality, though the effective valence of V is known to be close to +2. Proposing a new crystal structure for the stoichiometric case of x = 2, where the valence of each TCNE molecule is -1 and resistivity shows insulating behavior, exchange interaction among d -electrons on adjacent V atoms has been estimated based on the cluster with 3 vanadium atoms and one TCNE molecule. It turns out that Hunds coupling among d orbitals within the same V atoms and antiferromagnetic coupling between d oribitals and LUMO of TCNE (bridging V atoms) due to hybridization result in overall ferromagnetism (to be precise, ferrimagnetism). This view based on localized electrons is supplemented by the band picture, which indic...

Theory of Orbital Susceptibility on Excitonic Insulator

We study the temperature dependence of the orbital susceptibility of an excitonic insulator on the basis of a two-band model. It is shown that a drastic change (an anomalous enhancement) in susceptibility as a function of temperature occurs owing to the occurrence of additional orbital susceptibility due to the excitonic gap. We calculate explicitly the temperature dependence of orbital susceptibility for a model of Ta2NiSe5, and show that the result is consistent with experimental results.

Theory of Orbital Susceptibility in the Tight-Binding Model: Corrections to the Peierls Phase

An extended formula for orbital susceptibility including corrections of the Peierls phase is introduced. By using the new developed formula, the orbital susceptibility of benzene is estimated analytically on the basis of the

Deformation of the Fermi Surface and Anomalous Mass Renormalization by Critical Spin Fluctuations through Asymmetric Spin-Orbit Interaction

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