Showing papers in "Journal of the Physical Society of Japan in 2012"
TL;DR: In this paper, a new type of BiS 2 -based layered superconductor LaO 1- x F x BiS2, with a T c as high as 10.6 K, was reported.
Abstract: Layered superconductors have provided some interesting fields in condensed matter physics owing to the low dimensionality of their electronic states. For example, the high- T c (high transition temperature) cuprates and the Fe-based superconductors possess a layered crystal structure composed of a stacking of spacer (blocking) layers and conduction (superconducting) layers, CuO 2 planes or Fe-Anion layers. The spacer layers provide carriers to the conduction layers and induce exotic superconductivity. Recently, we have reported superconductivity in the novel BiS 2 -based layered compound Bi 4 O 4 S 3 . It was found that superconductivity of Bi 4 O 4 S 3 originates from the BiS 2 layers. The crystal structure is composed of a stacking of BiS 2 superconducting layers and the spacer layers, which resembles those of high- T c cuprate and the Fe-based superconductors. Here we report a discovery of a new type of BiS 2 -based layered superconductor LaO 1- x F x BiS 2 , with a T c as high as 10.6 K.
396 citations
TL;DR: In this paper, the symmetry properties of the pairing, i.e., the parity and spin-singlet/spin-triplet, determine the physical properties of superconducting state.
Abstract: Superconductivity is a phenomenon where the macroscopic quantum coherence appears due to the pairing of electrons. This offers a fascinating arena to study the physics of symmetry breaking, i.e., broken gauge symmetry. However, the important symmetries in superconductors are not only the gauge invariance. Especially, the symmetry properties of the pairing, i.e., the parity and spin-singlet/spin-triplet, determine the physical properties of the superconducting state. Recently it has been recognized that there is the important third symmetry of the pair amplitude, i.e., even or odd parity with respect to the frequency. The conventional uniform superconducting states correspond to the even-frequency pairing, but the recent finding is that the odd-frequency pair amplitude arises in the spatially non-uniform situation quite ubiquitously. Especially, this is the case in the Andreev bound state (ABS) appearing at the surface/interface of the sample. The other important recent development is on the nontrivial top...
362 citations
TL;DR: In this article, a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2 RuO 4 as they were known in the autumn of 2011 are presented.
Abstract: This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2 RuO 4 as they are known in the autumn of 2011. This paper appends the main progress th...
356 citations
TL;DR: In this paper, the anisotropic magnetoresistance (AMR) effects of bcc Fe (+), fcc Co (+, fcc Ni (+), Fe 4 N (-), and a half-metallic ferromagnet (-) were theoretically analyzed.
Abstract: We theoretically analyze the anisotropic magnetoresistance (AMR) effects of bcc Fe (+), fcc Co (+), fcc Ni (+), Fe 4 N (-), and a half-metallic ferromagnet (-). The sign in each parenthesis represents the sign of the AMR ratio observed experimentally. We here use the two-current model for a system consisting of a spin-polarized conduction state and localized d states with spin–orbit interaction. From the model, we first derive a general expression of the AMR ratio. The expression consists of a resistivity of the conduction state of the σ spin (σ= ↑ or ↓), ρ s σ , and resistivities due to s–d scattering processes from the conduction state to the localized d states. On the basis of this expression, we next find a relation between the sign of the AMR ratio and the s–d scattering process. In addition, we obtain expressions of the AMR ratios appropriate to the respective materials. Using the expressions, we evaluate their AMR ratios, where the expressions take into account the values of ρ s ↓ /ρ s ↑ of the res...
150 citations
TL;DR: In this paper, an isotope of the 113th element, i.e., 278 113, was produced in a nuclear reaction with a 70 Zn beam on a 209 Bi target, and six consecutive α-decays following the implantation of a heavy particle in nearly the same position in the semiconductor detector under an extremely low background condition.
Abstract: An isotope of the 113th element, i.e., 278 113, was produced in a nuclear reaction with a 70 Zn beam on a 209 Bi target. We observed six consecutive α-decays following the implantation of a heavy particle in nearly the same position in the semiconductor detector under an extremely low background condition. The fifth and sixth decays are fully consistent with the sequential decays of 262 Db and 258 Lr in both decay energies and decay times. This indicates that the present decay chain consisted of 278 113, 274 Rg ( Z =111), 270 Mt ( Z =109), 266 Bh ( Z =107), 262 Db ( Z =105), and 258 Lr ( Z =103) with firm connections. This result, together with previously reported results from 2004 and 2007, conclusively leads to the unambiguous production and identification of the isotope 278 113 of the 113th element.
142 citations
TL;DR: In this paper, the electrical resistivity measurements under pressure for the recently discovered BiS 2 -based layered superconductors Bi 4 O 4 S 3 and La(O,F)BiS 2 were reported.
Abstract: We report the electrical resistivity measurements under pressure for the recently discovered BiS 2 -based layered superconductors Bi 4 O 4 S 3 and La(O,F)BiS 2 . In Bi 4 O 4 S 3 , the transition temperature T c decreases monotonically without a distinct change in the metallic behavior in the normal state. In La(O,F)BiS 2 , on the other hand, T c initially increases with increasing pressure and then decreases above ∼1 GPa. The semiconducting behavior in the normal state is suppressed markedly and monotonically, whereas the evolution of T c is nonlinear. The strong suppression of the semiconducting behavior without doping in La(O,F)BiS 2 suggests that the Fermi surface is located in the vicinity of some instability. In the present study, we elucidate that the superconductivity in the BiS 2 layer favors the Fermi surface at the boundary between the semiconducting and metallic behaviors.
139 citations
TL;DR: In this article, the elastic properties of the iron-based superconductor Ba(Fe 1- x Co x ) 2 As 2 with eight Co concentrations were investigated and the results are similar to those of unconventional superconductors, where the properties are governed by quantum fluctuations associated with the zero-temperature critical point of long-range order.
Abstract: We investigated the elastic properties of the iron-based superconductor Ba(Fe 1- x Co x ) 2 As 2 with eight Co concentrations. The elastic constant C 66 shows a large elastic softening associated with structural phase transition. C 66 was analyzed on the basis of the localized and itinerant pictures of Fe-3d electrons, which shows a strong electron–lattice coupling and a possible mass enhancement in this system. The results are similar to those of unconventional superconductors, where the properties of the system are governed by quantum fluctuations associated with the zero-temperature critical point of long-range order, namely, the quantum critical point (QCP). In this system, the inverse of C 66 behaves just like the magnetic susceptibility in magnetic QCP systems. Although the QCPs of these existing superconductors are all ascribed to antiferromagnetism, our systematic studies on the canonical iron-based superconductor Ba(Fe 1- x Co x ) 2 As 2 have revealed that there is a signature of “structural quan...
130 citations
TL;DR: In this article, the nature of the magnetic spectrum and variations in magnetic spectral weight with doping were discussed. And the behavior of hole-doped superconductivity was compared with the trends found in the electron-Doped superconductor, and connections with the phenomena of charge and spin stripe order were made.
Abstract: Neutron scattering experiments continue to improve our knowledge of spin fluctuations in layered cuprates, excitations that are symptomatic of the electronic correlations underlying high-temperature superconductivity. Time-of-flight spectrometers, together with new and varied single crystal samples, have provided a more complete characterization of the magnetic energy spectrum and its variation with carrier concentration. While the spin excitations appear anomalous in comparison with simple model systems, there is clear consistency among a variety of cuprate families. Focusing initially on hole-doped systems, we review the nature of the magnetic spectrum, and variations in magnetic spectral weight with doping. We consider connections with the phenomena of charge and spin stripe order, and the potential generality of such correlations as suggested by studies of magnetic-field and impurity induced order. We contrast the behavior of the hole-doped systems with the trends found in the electron-doped supercond...
118 citations
TL;DR: In this article, the superconductivity (SC) peacefully coexists with the ferromagnetism (FM), forming the spin-triplet state of Cooper pairs, and the striking new phenomena such as SC reinforced by the magnetic field are associated with Ising-type ferromagnetic fluctuations.
Abstract: Recent advances on ferromagnetic superconductors, UGe 2 , URhGe and UCoGe are presented. The superconductivity (SC) peacefully coexists with the ferromagnetism (FM), forming the spin-triplet state of Cooper pairs. The striking new phenomena, such as SC reinforced by the magnetic field, are associated with Ising-type ferromagnetic fluctuations. A variety of ferromagnetic ordered moments between UGe 2 , URhGe and UCoGe affords to understand the relation between FM, tricriticality and SC.
112 citations
TL;DR: Ce115 and related Ce compounds are particularly suited to detailed studies of the interplay of antiferromagnetic order, unconventional superconductivity and quantum criticality due to their availability as high quality single crystals and their tunability by chemistry, pressure and magnetic field as mentioned in this paper.
Abstract: Ce115 and related Ce compounds are particularly suited to detailed studies of the interplay of antiferromagnetic order, unconventional superconductivity and quantum criticality due to their availability as high quality single crystals and their tunability by chemistry, pressure and magnetic field. Neutron-scattering, NMR and angle-resolved thermodynamic measurements have deepened the understanding of this interplay. Very low temperature experiments in pure and lightly doped CeCoIn 5 have elaborated the FFLO-like magnetic state near the field-induced quantum-critical point. New, related superconducting materials have broadened the phase space for discovering underlying principles of heavy-fermion superconductivity and its relationship to nearby states. © 2012 The Physical Society of Japan.
112 citations
TL;DR: In this article, powder neutron diffraction and inelastic scattering measurements of frustrated pyrochlore Nd 2 Ir 2 O 7, which exhibits a metal-insulator transition at a temperature T MI of 33 K.
Abstract: In this study, we performed powder neutron diffraction and inelastic scattering measurements of frustrated pyrochlore Nd 2 Ir 2 O 7 , which exhibits a metal–insulator transition at a temperature T MI of 33 K. The diffraction measurements revealed that the pyrochlore has an antiferromagnetic long-range structure with propagation vector q 0 of (0,0,0) and that it grows with decreasing temperature below 15 K. This structure was analyzed to be of the all-in all-out type, consisting of highly anisotropic Nd 3+ magnetic moments of magnitude 2.3±0.4µ B , where µ B is the Bohr magneton. The inelastic scattering measurements revealed that the Kramers ground doublet of Nd 3+ splits below T MI . This suggests the appearance of a static internal magnetic field at the Nd sites, which probably originates from a magnetic order consisting of Ir 4+ magnetic moments. Here, we discuss a magnetic structure model for the Ir order and the relation of the order to the metal–insulator transition in terms of frustration.
TL;DR: In this article, the authors reviewed recent developments in research into superconductivity in organic materials and provided good evidence for magnetically-mediated pairing in BEDT-TTF and BETS superconductors.
Abstract: Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with T c ∼1 K, T c decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde–Ferrel–Larkin–Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice....
TL;DR: In this article, it was shown that the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the appearance of a structural critical point in the T = 0 limit at x(c) similar or equal to 0.035.
Abstract: IrTe2, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. This transition is characterized by the formation of Ir-Ir bonds along the b-axis. We found that the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the appearance of a structural critical point in the T = 0 limit at x(c) similar or equal to 0.035. Although both IrTe2 and PtTe2 are paramagnetic metals, superconductivity at T-c = 3.1 K is induced by the bond breaking in a narrow range of x >= x(c) in Ir1-xPtxTe2. This result indicates that structural fluctuations can be involved in the emergence of superconductivity.
TL;DR: In this paper, the intrinsic phase diagram of antiferromagnetic magnetism and high-temperature superconductivity for a disorder-free CuO 2 plane with hole carriers was uncovered.
Abstract: High-temperature superconductivity (HTSC) in copper oxides emerges on a layered CuO 2 plane when an antiferromagnetic Mott insulator is doped with mobile hole carriers. We review extensive studies of multilayered copper oxides by site-selective nuclear magnetic resonance (NMR), which have uncovered the intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a disorder-free CuO 2 plane with hole carriers. We present our experimental findings such as the existence of the AFM metallic state in doped Mott insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of d -wave SC with a maximum T c just outside a critical carrier density, at which the AFM moment on a CuO 2 plane disappears. These results can be accounted for by the Mott physics based on the t – J model. The superexchange interaction J in among spins plays a vital role as a glue for Cooper pairs or mobile spin-singlet pairs, in contrast to the phonon-mediated attractive interaction among electrons established in the Bardeen...
TL;DR: In this article, an analytical representation for the rogue waves of the Fokas-Lenells (FL) equation is presented by deriving an appropriate Darboux transformation (DT) and utilizing a Taylor series expansion of the associated breather solution.
Abstract: The Fokas–Lenells (FL) equation arises as a model equation which describes for nonlinear pulse propagation in optical fibers by retaining terms up to the next leading asymptotic order [in the leading asymptotic order the nonlinear Schrodinger (NLS) equation results]. Here we present an explicit analytical representation for the rogue waves of the FL equation. This representation is constructed by deriving an appropriate Darboux transformation (DT) and utilizing a Taylor series expansion of the associated breather solution. When certain higher-order nonlinear effects are considered, the propagation of rogue waves in optical fibers is given.
TL;DR: In this paper, the authors present an overview of angle-resolved photoemission spectroscopy (ARPES) studies of high-temperature cuprate superconductors aiming at elucidating the relationship between the superconductivity, the pseudogap, and the Fermi arc.
Abstract: We present an overview of angle-resolved photoemission spectroscopy (ARPES) studies of high-temperature cuprate superconductors aiming at elucidating the relationship between the superconductivity, the pseudogap, and the Fermi arc. ARPES studies of underdoped samples show a momentum dependence of the energy gap below T c which deviates from a simple d -wave form, suggesting the coexistence of multiple energy scales in the superconducting state. Hence, two distinct energy scales have been introduced, namely, the gap near the node (characterized by Δ 0 ) and in the anti-nodal region (characterized by Δ * ). Dichotomy between them has been demonstrated from the material, doping, and temperature dependence of the energy gap. While Δ * at the same doping level is approximately material independent, Δ 0 shows a strong material dependence tracking the magnitude of T cmax . The anti-nodal gap does not close at T c in contrast to the gap near the node which follows something closer to a BCS-like temperature depend...
TL;DR: In this paper, the behavior of perfect fluid and massless scalar field for homogeneous and anisotropic Bianchi type I universe model in f ( R, T ) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor.
Abstract: In this paper, we study the behavior of perfect fluid and massless scalar field for homogeneous and anisotropic Bianchi type I universe model in f ( R , T ) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor. We assume the variation law of mean Hubble parameter to obtain exact solutions of the modified field equations. The physical and kinematical quantities are discussed for both models in future evolution of the universe. We check the validity of null energy condition and conclude that our perfect fluid solution can behave like phantom model. Finally, we find that perfect fluid solutions correspond to massless scalar field models.
TL;DR: The cubic compound PrTi 2 Al 20 exhibits type-II superconductivity at T c = 200 mK in the nonmagnetic ferro-quadrupolar state as discussed by the authors.
Abstract: The cubic compound PrTi 2 Al 20 is a quadrupolar Kondo lattice system that exhibits quadrupolar ordering due to the non-Kramers Γ 3 ground doublet and has strong hybridization between 4 f and conduction electrons. Our study using high-purity single crystals reveals that PrTi 2 Al 20 exhibits type-II superconductivity at T c = 200 mK in the nonmagnetic ferroquadrupolar state. The superconducting critical temperature and field phase diagram indicates clean limit superconductivity with moderately enhanced effective mass of m * / m 0 ∼16.
TL;DR: In this article, a two-dimensional oxyantimonide, BaTi 2 Sb 2 O, was presented, which showed a superconducting transition at 1.2 K, representing the first superconductivity in a system with Ti 3+ (d 1 ) in a square lattice.
Abstract: We prepared a new two-dimensional oxyantimonide, BaTi 2 Sb 2 O, which shows a superconducting transition at 1.2 K, representing the first superconductivity in a system with Ti 3+ ( d 1 ) in a square lattice. The TiO 2 Sb 4 mixed anionic coordination stabilizes a unique half-filled Ti d x y orbital configuration in Ti 2 O plane, which is analogous to Cu 2+ ( d 9 ) in the high- T c superconductors. A charge density wave (CDW)- or spin density wave (SDW)-like anomaly appears at 50 K, which is significantly reduced compared with 200 K for the isostructural and non-superconducting BaTi 2 As 2 O.
TL;DR: In this article, the authors report a novel and new types of rogue optical wave propagation in an erbium-doped fiber system governed by the nonlinear Schrodinger and the Maxwell-Bloch equation.
Abstract: We report a novel and new types of rogue optical wave propagation in an erbium-doped fibre system governed by the nonlinear Schrodinger and the Maxwell–Bloch equation. The breather solutions of the three fields, namely field envelop, polarization and population inversion, are used to generate the rogue waves. For the first time, we report bright and, in particular, dark rogue waves in a coupled nonlinear optical systems. The distinction between bright and dark rogue waves are discussed in detail through figures. The rogue wave formation in our model can also be connected to the generation of supercontinuum generation in resonant optical fibre.
TL;DR: In this article, the superconductivity in multilayer models exhibiting inhomogeneous Rashba spin-orbit coupling is investigated and it is shown that the spin susceptibility is determined by the phase difference of the order parameter between layers and is nearly independent of the parity mixing of order parameters.
Abstract: Although multilayer systems possess global inversion symmetry, some of the layers lack local inversion symmetry because no global inversion centers are present on such layers. Such locally non-centrosymmetric systems exhibit spatially modulated Rashba spin–orbit coupling. In this study, the superconductivity in multilayer models exhibiting inhomogeneous Rashba spin–orbit coupling is investigated. We study the electronic structure, superconducting gap, and spin susceptibility in the superconducting state with mixed parity order parameters. We show the enhancement of the spin susceptibility by Rashba spin–orbit coupling and interpret it on the basis of the crossover from a centrosymmetric superconductor to a non-centrosymmetric superconductor. It is also shown that the spin susceptibility is determined by the phase difference of the order parameter between layers and is nearly independent of the parity mixing of order parameters. An intuitive understanding is given on the basis of the analytic expression of...
TL;DR: In this paper, the dispersive Bogoliubov quasiparticles of a homogeneous d-wave superconductor were observed in both the dSC and pseudogap phases of underdoped cuprates using SI-STM.
Abstract: One of the key motivations for the development of atomically resolved spectroscopic imaging scanning tunneling microscopy (SI-STM) has been to probe the electronic structure of cuprate high temperature superconductors. In both the d -wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates, two distinct classes of electronic states are observed using SI-STM. The first class consists of the dispersive Bogoliubov quasiparticles of a homogeneous d -wave superconductor. These are detected below a lower energy scale | E |=Δ 0 and only upon a momentum space ( k -space) arc which terminates near the lines connecting k =±(π/ a 0 ,0) to k =±(0,π/ a 0 ). Below optimal doping, this “nodal” arc shrinks continuously with decreasing hole density. In both the dSC and PG phases, the only broken symmetries detected in the | E |≤Δ 0 states are those of a d -wave superconductor. The second class of states occurs at energies near the pseudogap energy scale | E |∼Δ 1 which is associated conventionally w...
TL;DR: In this paper, the Ginzburg-Landau free energy of three-band superconductors was derived from the BCS microscopic theory, and a chirality and fractional quantum flux vortices were obtained in the chiral region of the double sine-Gordon model.
Abstract: We investigate some significant properties of multi-band superconductors. They are time-reversal symmetry breaking, chirality and fractional quantum flux vortices in three-band superconductors. The Bardeen–Cooper–Schrieffer (BCS) gap equation has a solution with time-reversal symmetry breaking in some cases. We derive the Ginzburg–Landau free energy from the BCS microscopic theory. The frustrating pairing interaction among Fermi surfaces leads to a state with broken time-reversal symmetry, that is, a chiral solution. The Ginzburg–Landau equation for three-component superconductors leads to a double sine-Gordon model. A kink solution exists to this equation as in the conventional sine-Gordon model. In the chiral region of the double sine-Gordon model, an inequality of Bogomol'nyi type holds, and fractional-π kink solutions exist with the topological charge Q . This yields multi-vortex bound states in three-band superconductors.
TL;DR: In this paper, the magnetocrystalline anisotropy energy and orbital magnetic moment in L 1 0 -type transition metal alloys such as FePt, FePd, FeNi, CoPt and MnAl are evaluated while continuously varying the degree of order.
Abstract: The magnetocrystalline anisotropy energy and orbital magnetic moment in L 1 0 -type transition metal alloys such as FePt, FePd, FeNi, CoPt, CoPd, and MnAl are evaluated while continuously varying the degree of order. The electronic structure with spin–orbit interaction is calculated by employing the tight-binding linear muffin-tin orbital method based on the local spin-density approximation. To control the degree of order, we consider a substitutional disorder and then adopt the coherent potential approximation. The magnetocrystalline anisotropy energy Δ E is roughly proportional to the power of the long-range order parameter S , i.e., Δ E ∝ S n ( n ∼1.6–2.4). We also discuss the relationship between the magnetocrystalline anisotropy energy and the orbital magnetic moment. In the same compositional system with different degrees of order, the difference between the orbital magnetic moment in the magnetic easy axis and that in the hard one is proportional to Δ E . However, the coefficient corresponding to t...
TL;DR: In this article, the authors present a summary of experimental and theoretical investigations on the rattling and superconductivity of the β-pyrochlore osmium oxides AOs 2 O 6 (A = Cs, Rb, and K), after these oxides were found in 2004.
Abstract: In this review, we present a summary of experimental and theoretical investigations on the rattling and superconductivity of the β-pyrochlore osmium oxides AOs 2 O 6 (A = Cs, Rb, and K), after these oxides were found in 2004. First, we provide the background of our research, a brief history of rattling, and the characteristics of cage compounds thus far studied in terms of rattling. Then we show the structural properties of β-pyrochlore oxides, focusing on the rattling of an A ion in an oversized cage made of oxide ions. After the chemical trends of the normal and superconducting states are summarized, the role of rattling, which is a local, essentially anharmonic oscillation with a large atomic excursion, is discussed. Furthermore, two recent topics, i.e., an isomorphic structural transition and peculiar behavior under high pressure, are addressed. We conclude that rattling vibrations markedly affect the structural and electronic properties of β-pyrochlore oxides and even induce or enhance superconductiv...
TL;DR: In this article, a BaFe 2 (As 1-x P x ) 2, As 3 /Ba 2 P 3 self-flux method was employed to grow large single crystals (∼7×7 mm 2 ) using a quartz tube, the P content of which is systematically controlled by tuning the As/P mixture ratio of the starting compositions.
Abstract: Sizable single crystals of iron-based high-transition-temperature superconductors, BaFe 2 (As 1- x P x ) 2 , have been synthesized over an entire x range from 0 to 1. The employment of a Ba 2 As 3 /Ba 2 P 3 self-flux method enables us to grow large single crystals (∼7×7 mm 2 ) using a quartz tube, the P content of which is systematically controlled by tuning the As/P mixture ratio of the starting compositions. The post-annealing of the as-grown crystals results in sample quality improvement, evidenced by the increase in superconducting and antiferromagnetic-orthorhombic (AFO) transition temperatures as well as the significant reduction in residual resistivity in the AFO phase in the underdoped regime.
TL;DR: In this paper, the authors examined the physical properties of EuRh 2 Si 2 under external pressure and showed that the valence change associated with valence transition is roughly estimated to be ∼0.19 from the thermal expansion anomaly.
Abstract: Considering the unique properties of EuRh 2 Si 2 from the viewpoint of the Eu valence, we have examined its physical properties under external pressure. At ambient pressure, EuRh 2 Si 2 is an antiferromagnet with a Neel temperature T N of 25 K, and the Eu ion is in the divalent state. The application of pressure up to 0.84 GPa slightly shifts T N toward higher values. Under pressures higher than 1.00 GPa, an abrupt first-order valence transition emerges simultaneously with the disappearance of antiferromagnetism. For P =1.17 GPa, the valence change associated with valence transition is roughly estimated to be ∼0.19 from the thermal expansion anomaly. The valence transition temperature T v increases rapidly with increasing pressure. The temperature–pressure phase diagram of EuRh 2 Si 2 is very similar to those of the other systems showing pressure-induced valence transition.
TL;DR: In this paper, the authors explore the bulk-edge correspondence for topological insulators (superconductors) without time-reversal symmetry from the viewpoint of the index theorem for open spaces and show the equivalence between the spectral flow of the edge states and the Chern numbers specifying the bulk systems.
Abstract: We explore the bulk-edge correspondence for topological insulators (superconductors) without time-reversal symmetry from the viewpoint of the index theorem for open spaces. We assume generic Hamiltonians not only with a linear dispersion but also with higher order derivatives arising from generic band structures. Using a generalized index theorem valid for such systems, we show the equivalence between the spectral flow of the edge states and the Chern numbers specifying the bulk systems.
TL;DR: In this paper, the band structure of Ca 3 PbO, which possesses a three-dimensional massive Dirac electron at the Fermi energy, is investigated in detail.
Abstract: The band structure of Ca 3 PbO, which possesses a three-dimensional massive Dirac electron at the Fermi energy, is investigated in detail. Analysis of the orbital weight distributions on the bands obtained in the first-principles calculation reveals that the bands crossing the Fermi energy originate from the three Pb- p orbitals and three Ca- d x 2 - y 2 orbitals. Taking these Pb- p and Ca- d x 2 - y 2 orbitals as basis wave functions, a tight-binding model is constructed. With the appropriate choice of hopping integrals and the strength of the spin–orbit coupling, the constructed model successfully captures important features of the band structure around the Fermi energy obtained in the first-principles calculation. By applying a suitable basis transformation and expanding the matrix elements in the series of the momentum measured from a Dirac point, the low-energy effective Hamiltonian of this model is explicitly derived and proved to be a Dirac Hamiltonian. The origin of the mass term is also discussed...
TL;DR: Hirama et al. as discussed by the authors reviewed progress in thin film research on iron-based superconductors since their discovery for each of five material systems with an emphasis on growth, physical properties, device fabrication, and relevant bulk material properties.
Abstract: Iron-based superconductors have received much attention as a new family of high-temperature superconductors owing to their unique properties and distinct differences from cuprates and conventional superconductors. This paper reviews progress in thin film research on iron-based superconductors since their discovery for each of five material systems with an emphasis on growth, physical properties, device fabrication, and relevant bulk material properties. (*) E-mail address: h-hirama@lucid.msl.titech.ac.jp