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The transport and thermodynamic properties of $\beta$-ReO$_{2}$ crystallizing in a nonsymmorphic structure were studied using high-quality single crystals. An extremely large magnetoresistance (XMR) reaching 22,000 $\%$ in a transverse magnetic field of 10 T at 2 K was observed. However, distinguished from other topological semimetals with low carrier densities that show XMR, $\beta$-ReO$_{2}$ has a high electron carrier density of 1 $\times$ $10^{22}$ cm$^{-3}$ as determined by Hall measurements and large Fermi surfaces in the electronic structure. In addition, a small Fermi surface with a small effective mass was evidenced by de Haas-van Alphen oscillation measurements. The previous band structure calculations [S. S. Wang, et al., Nat. Commun. 8, 1844 (2017)] showed that two kinds of loops made of Dirac points of hourglass-shaped dispersions exist and are connected to each other by a point to form a string of alternating loops, called the Dirac loop chain (DLC), which are protected by the multiple glide symmetries. Our first-principles calculations revealed the complex Fermi surfaces with the smallest one corresponding to the observed small Fermi surface, which is just located near the DLC. The XMR of $\beta$-ReO$_{2}$ is attributed to the small Fermi surface and thus is likely caused by the DLC., Comment: 9 pages, 7 figures, 1 Table

We investigate the finite temperature properties of the extended Hubbard model with a nearest-neighbor Coulomb repulsion on the square lattice. Solving the self-consistent equations obtained using ...

Realization of magnetic atomic layers exhibiting strong magnetic anisotropy is desired for future magnetic memory applications. Here, the magnetocrystalline anisotropy of Co-based 3d transition-met...

A highly insulating bulk state and a tunable Dirac cone surface state are required for future spintronics device applications of spin-polarized surface states in three-dimensional topological insul...

By means of first-principles calculations, we study electronic and spectroscopic properties of NaFeSO4F, which has been expected recently to be a candidate cathode material for Na-ion batteries. Th...

The extended Hubbard model with a nearest-neighbor Coulomb repulsion on the square lattice is studied to obtain insight into the phase diagram of cuprate high $T_c$ superconductors (HTS). To pursue the hidden-order scenario proposed in [S. Chakravarty et al., Phys. Rev. B 63, 094503 (2001)], we derive an effective Hamiltonian by using the canonical transformation and develop a mean-field theory. The calculated phase diagrams are qualitatively consistent with the experimental phase diagrams of HTS, and we thus conclude that the pseudogap can be interpreted as the order parameter of the $d_{x^2-y^2}$-wave density wave (DDW) state, and the $d_{x^2-y^2}$-wave superconducting (DSC) rises based on the DDW order. Furthermore, the analytical representation of the density of states is obtained and, near the optimal doping of the DSC, the van Hove singular point of the density of states is located at the Fermi level., Comment: 26 pages, 7 figures

We study the cathode properties of Li2MTiO4 (M = V, Cr, Mn, Fe, Co, and Ni) for Li-ion batteries by performing first-principles calculations. Formation energies and voltages for Li2−xMTiO4 (0 ≤ x ≤ 2) models with rock-salt-based structures considering several Li concentrations (2 − x) are calculated. Two dominant charge/discharge reaction mechanisms associated with redox reactions of M and O are found mainly in the ranges of lower and higher x, respectively. In the higher-x region, the O redox reactions can destabilize atomic structures, because the electron removal from O-p states produces high peaks at the fermi level in the density of states. The structural stability of O using the models with O deficiency is calculated, and the result shows that O can dissociate much more easily than Li in the higher-x region. The critical Li concentration at which the vacancy formation energy of O becomes lower than that of Li is estimated, and the critical x value decreases with increasing number of 3d electrons as ...

Structural parameters of β-ZrNCl with SmSI and YOF types are determined by first-principles total-energy and atomic-force calculations. Obtained structural parameters for SmSI-type ZrNCl are in good agreement with the experimental ones. Differences between the optimized parameters for YOF-type ZrNCl and experimental ones for YOF-type Li 0.16 ZrNCl show significant Li-doping effects on distances of the nearest N–N and Zr–Cl atoms and flatness of double Zr–N layers. Electronic band structures for the optimized crystal structure as well as the observed one are compared and discussed in conjunction to the structural difference. A 1 g phonon modes are evaluated from the force constants calculated and found to be rather insensitive to structural type and Li doping.

We have performed first-principles band structure calculation for CeRhAs and its isostructural Ce compounds. Calculated insulating and metallic or semimetallic ground states are consistent with recent experimental observations. We discussed projected density of states on Ce 4 f | J , J Z > states, which is a clue to understand the anisotropic effects to realize the ground state and gap formation. Band gap and pseudogaps are opened mainly due to Ce 4 f |5/2, ±5/2> states. These states are very sensitive to lattice deformation. Gap formation and structural instability in CeRhAs may be understood by orientations of Ce 4 f orbitals.

An antiferromagnetic Ising model on the Δ chain, with a macroscopic ground state degeneracy and exponentially decaying spin correlation functions, is studied. By introducing transverse magnetic fields Γ on spins at tips of the triangles and λΓ on spins on the bottom chain, we study the ground state as a function of λ and Γ. The λ=0 problem is exactly solved and the ground state has a staggered magnetization on the bottom chain for any Γ>0. Because the transverse field on the bottom chain with finite λ destroys the staggered order, the order–disorder transition occurs as λ is increased. We calculate the transition point λ c (Γ/ J ) as a function of Γ/ J , where J denotes the magnitude of the exchange interaction, by using the series expansion method around the λ=0 limit and conclude that λ c (Γ/ J =+0)≃0.9459. It is shown that states in the degenerate ground state manifold at Γ=0 are crucial in getting a finite value of λ c (+0).

Surface properties of antiferromagnetic MnO(001) and NiO(001) are investigated by means of first-principles electronic structure calculations. It is shown that the surface O sites have finite spin magnetic moments of 0.04 µ B and 0.07 µ B for MnO and NiO surfaces, respectively. Because of non-zero energy gap even at the surface, the spin magnetic moment of Mn and Ni sites are almost the same as those in bulk. At the surface O sites, calculated spin density shows asymmetric distribution comparing with that of the bulk. These results are explained in detail from calculated partial density of states. By surface structural optimization, stable surface structure of O inward rumpled relaxation is obtained for both monoxides.

Systematic trend in lattice constants and heats of formation is studied for AlB 2 -type diborides from first principles. Observed trend in the lattice constants and the c / a ratio can be interpret...

A coadsorbed system of Li and Mg on a Cu(001) surface is studied by means of first-principles total-energy calculations within the local density approximation. It is proved that a hybrid phase in which Mg atoms are located at substitutional sites by kicking out Cu row along the [010] direction and Li atoms occupy hollow sites is the most stable geometry in the coadsorption system. Mechanism of structural stability of this coadsorption surface is discussed by comparing optimized structure, adsorption energies and electron density distribution between related coadsorbed and adsorbed surface systems.

We study spin-1/2 Heisenberg antiferromagnets on a diamond-like-decorated square lattice perturbed by two kinds of further neighbor couplings. In our previous study [J. Phys. Soc. Jpn. 85, 094002 (2016)], the second-order effective Hamiltonian for the Heisenberg model perturbed by a further neighbor coupling was found to be a square-lattice quantum-dimer model with a finite hopping amplitude, t>0, and no dimer-dimer interaction, v=0. In this study, we introduce another kind of further neighbor coupling and show that it leads to an attractive interaction between dimers, which suggests the stabilization of the columnar phase of the square-lattice quantum-dimer model. The calculated v/t is presented as a function of the ratio of the two exchange parameters in the Heisenberg model., 29 pages, 10 figures

Ferroelectricity in sodium nitrite NaNO 2 has been studied from first principles. The spontaneous polarization calculated with Berry-phase theory is 0.116 C/m 2 , being in excellent agreement with experimental values, 0.117 C/m 2 and 0.119 C/m 2 . In order to discuss the phase transitions, we have estimated coupling parameters J 1 and J 2 in the axial next-nearest-neighbor Ising model from total-energy and force calculations. As results, J 1 and J 2 are quite sensitive to relative displacement of NO 2 molecules. The transition temperature and a role of molecular displacement in the phase transitions are discussed in detail.

We treat the organic system m M P Y N N - B F 4 as a network of hexagons. Each hexagon contains six S =1/2 spins coupled alternately with ferro- and antiferromagnetic interactions. The antiferromagnetic coupling between hexagons is treated as a perturbation term. We obtain the ferro- and antiferromagnetic coupling constants in the hexagon and the antiferromagnetic coupling constant between hexagons. The susceptibility calculated by the second-order perturbation method for m M P Y N N - B F 4 agrees well with the experimental results. The ground state energy is also calculated.

The magnetization process in the Shastry-Sutherland system is studied by using the third-order perturbation expansion. It is shown that the 1/3-plateau is realized by the second-order perturbation, which is not prevented by the off-diagonal part. In each subspace whose magnetization per dimer is less than 1/3, the lowest energy state is determined by a small but finite energy-gain due to the third-order correlated flip terms and there exists no plateau originating from the third-order effect. Our results are compared with those of the exact diagonalization method to discuss the validity of truncation of states in our perturbation theory.

A local-density electronic-band-structure calculation was performed for pyrochlore ruthenium oxides A 2 Ru 2 O 7 ( A = Bi, Tl and Y). As a general feature, these pyrochlores have band structure com...

Magnetization process in the S =1/2 Heisenberg antiferromagnet with plaquette structure and up to second neighbor couplings on the 1/5-depleted square lattice is studied by using perturbation expansion and exact diagonalization methods. This model describes the magnetism of CaV 4 O 9 for an adequate choice of the exchange parameters. Within first order calculations it is shown that plateaus at m =1/8, 1/4 and 3/8 appear for some parameter region of the exchange interactions, where m denotes magnetization per a spin. The magnetization curve for CaV 4 O 9 is calculated, which shows that the 1/4-plateau is clearly observed and CaV 4 O 9 is almost right at the quantum critical point of the 3/8-plateau. Critical behavior of the 1/4-plateau is also discussed.

We have studied the electronic structures of ternary Ce compounds CePdX (X=As, Sb) by means of high resolution 4 d -4 f resonance photoemission spectroscopy. In the Ce 4 f spectra, the relative int...

Magneto-optical Kerr effect (MOKE) of magnetic metallic multilayers, Fe/Pt, Co/Pt, Fe/Au and Co/Au, is investigated based on first-principles electronic structure calculations by using the FLAPW method. The MOKE spectrum of these systems can be classified into two photon-energy ranges, below and above 7 eV, along the final-state character in the optical transition. We have found that the spin-orbit splitting at the noble-metal site dominates the shape of the MOKE spectrum. This is because the spin-orbit splitting of the bands which are involved in the magneto-optical transition is mainly determined at the noble-metal site. Hence, the most important contribution to the dipole-transition matrix elements comes from the noble-metal site. Especially, d to p transitions with the majority spin at the noble-metal site are crucial for the MOKE spectrum below 7 eV. The large spin-orbit interaction at the noble-metal site induces the orbital splitting also at the 3 d transition-metal site through the band hybridizat...

The uniform susceptibility and triplet excitation spectrum of the Heisenberg antiferromagnet on the one-fifth depleted square lattice are calculated using the third-order perturbation expansion method from the viewpoint of the weakly coupled meta-plaquette picture. Both the susceptibility and triplet excitation spectrum data for CaV 4 O 9 are simultaneously explained. The origin of the relatively large spin gap in this compound is discussed.

The stability of Cu(001)-(2×1)-Li and Al(001)-c(2×2)-Na systems, in which the adatoms (Li or Na) occupy substitutional sites are investigated based on first-principles electronic structure calculations. The total energies of the systems are calculated and compared, by considering some related surface structures and optimizing the structural parameters involved. The stability is discussed in terms of vacancy-formation and binding energies. Change in work function by adsorption is also discussed.

The 7 Li and 6 Li nuclear spin-lattice relaxation rates, ( 7 T 1 ) -1 and ( 6 T 1 ) -1 , have been measured for LiCoO 2 as a function of temperature. Comparison between 7 Li- and 6 Li-rich samples shows that the ratio ( 6 T 1 ) -1 /( 7 T 1 ) -1 =0.06 is considerably larger than the value expected for quadrupolar relaxation processes. Furthermore ( 7 T 1 ) -1 decreases significantly as 7 Li is replaced by 6 Li. These observations indicate that ( 7 T 1 ) -1 is dominated by the nuclear magnetic dipole-dipole interaction between the 7 Li nuclei. The substitution of Cr for Co has no effect on ( 7 T 1 ) -1 in the range below 200 K, whereas the substitution of Na for Li enhances ( 7 T 1 ) -1 . The substitution effect supports the view that the two-dimensional Li ion motion is dominant in LiCoO 2 . The weak dependence of ( 7 T 1 ) -1 upon temperature and frequency suggests the presence of a broad distribution of barrier heights for ionic motion in LiCoO 2 .