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Search Results: 1 - 10 of 2426 matches for " Hiroaki Ikeda "
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Interplay of crystal field structures with $f^2$ configuration to heavy fermions
Hiroaki Kusunose,Hiroaki Ikeda
Physics , 2004, DOI: 10.1143/JPSJ.74.405
Abstract: We examine a relevance between characteristic of crystal field structures and heavily renormalized quasiparticle states in the $f^0$-$f^1$-$f^2$ Anderson lattice model. Using a slave-boson mean-field approximation, we find that for $f^2$ configurations two or three quasiparticle bands are formed near the Fermi level depending on the number of the relevant $f^1$ orbitals in the $f^2$ crystal field ground state. The inter-orbital correlations characterizing the crystal field ground state closely reflect in inter-band residual interactions among quasiparticles. Particularly in the case of a singlet crystal field ground state, resulting residual antiferromagnetic exchange interactions among the quasiparticles lead to an anomalous suppression of the quasiparticle contribution of the spin susceptibility, even though the quasiparticle mass is strongly enhanced.
A Theory of Anisotropic Semiconductor of Heavy Fermions
Hiroaki Ikeda,Kazumasa Miyake
Physics , 1996, DOI: 10.1143/JPSJ.65.1769
Abstract: It is demonstrated that a {\veck}-dependence of the hybridization matrix element between $f$- and conduction electrons can give rise to an anisotropic hybridization gap of heavy fermions if the filling of electrons corresponds to that of the band insulator. The most interesting case occurs when the hybridization vanishes along some symmetry axis of the crystal reflecting a particular symmetry of the crystal field. The results of a model calculation are consistent with wide range of anomalous properties observed in CeNiSn and its isostructural compounds, the anisotropic semiconductor of heavy fermions. In particular, highly sensitive effect of impurity scattering on the residual density of states for zero energy excitation and the anisotropic temperature dependence of the resistivity are well explained. It is also discussed that a weak semimetallic behavior arises through the weak $\veck$-dependence of the $f$-electron self-energy $\Sigma_{f}(\veck,0)$.
Impurity Effects in Strongly Correlated Metals: Large Pressure Dependence of Residual Resistivity of Heavy Fermions
Hiroaki Ikeda,Kazumasa Miyake
Physics , 1996,
Abstract: It is shown on the basis of the Fermi liquid theory that the s-wave scattering potential due to nonmagnetic impurity is strongly enhanced by the mass enhancement factor $1/z$. As a result the impurity potential with moderate strength, of the order of the bandwidth of conduction electrons, gives scattering in the unitarity limit in strongly correlated metals as heavy fermions. This effect is embodied by large pressure dependence of residual resistivities in heavy fermion systems, since the pressure decreases the degree of correlations, which makes the Kondo temperature increase rapidly. This accounts for the large pressure dependence of the residual resistivity observed in heavy fermion metals, such as CeInCu$_{2}$, CeCu$_{6}$, CeAl$_{3}$.
Effect of magnetic criticality and Fermi-surface topology on the magnetic penetration depth
Takuya Nomoto,Hiroaki Ikeda
Physics , 2013, DOI: 10.1103/PhysRevLett.111.167001
Abstract: We investigate the effect of anti-ferromagnetic (AF) quantum criticality on the magnetic penetration depth $\lambda(T)$ in line-nodal superconductors, including the cuprates, the iron pnictides, and the heavy-fermion superconductors. The critical magnetic fluctuation renormalizes the current vertex and drastically enhances zero-temperature penetration depth $\lambda(0)$, which is more remarkable in the iron-pnictide case due to the Fermi-surface topology. Additional temperature ($T$) dependence of the current renormalization makes the expected $T$-linear behavior at low temperatures approaching to $T^{1.5}$ asymptotically. These anomalous behaviors are well consistent with experimental observations. We stress that $\lambda(T)$ is a good probe to detect the AF quantum critical point in the superconducting state.
Reply to the Comment by Kiselev and Bouis
Hiroaki Ikeda,Yoji Ohashi
Physics , 1999,
Abstract: The possibility of the ferromagnetic state modifies the phase diagram in Phys.Rev.Lett.81,3723(1998), as Kiselev and Bouis have pointed out. However, the unconventional SDW that has been proposed in the letter above is still a candidate for the curious magnetism in URu_2Si_2.
Theory of Unconventional Spin Density Wave: A Possible Mechanism of the Micromagnetism in U-based Heavy Fermion Compounds
Hiroaki Ikeda,Yoji Ohashi
Physics , 1999, DOI: 10.1103/PhysRevLett.81.3723
Abstract: We propose a novel spin density wave (SDW) state as a possible mechanism of the anomalous antiferromagnetism, so-called the micromagnetism, in URu_2Si_2 below 17.5[K]. In this new SDW, the electron-hole pair amplitude changes its sign in the momentum space as in the case of the unconventional superconductivity. It is shown that this state can be realized in an extended Hubbard model within the mean field theory. We also examine some characteristic properties of this SDW to compare with the experimental results. All these properties well explain the unsolved problem of the micromagnetism.
Is Fermi-surface nesting the origin of superconductivity in iron pnictides?: A fluctuation-exchange-approximation study
Ryotaro Arita,Hiroaki Ikeda
Physics , 2009, DOI: 10.1143/JPSJ.78.113707
Abstract: We study whether Fermi-surface (FS) nesting can give rise to high-temperature superconductivity in iron pnictides. Starting with ab initio construction of an effective four-orbital model, we employ the fluctuation-exchange approximation to show that FS does not necessarily favor the stripe antiferromagnetic order observed in experiments, especially for realistic electronic correlations. If superconductivity in iron pnictides is magnetically mediated and has fully-gapped sign-reversing s-wave symmetry, our results suggest that the pairing interaction does not arise only from FS nesting and exchange interactions between local moments in the Fe 3d orbitals may play a crucial role.
Integrating Psychiatric Services into Comprehensive Dementia Care in the Community  [PDF]
Hiroto Ito, Hideyuki Hattori, Hiroaki Kazui, Masamoto Taguchi, Manabu Ikeda
Open Journal of Psychiatry (OJPsych) , 2015, DOI: 10.4236/ojpsych.2015.52014
Abstract: Purpose: This study was conducted to clarify the utility of patient-held records as an integrated care approach for patients with dementia in the community. Method: We analyzed the family-held/patient-held records of patients with dementia in the community. The inclusion criteria in the study were as follows: 1) patient-held/family member-held records of patients with dementia in the community; 2) patient-held records designed to share information across different professionals, direct-care staff members, and local government staff; and 3) the continuous participation of psychiatrists in the development and use of the patient-held records. Results: We identified eight sets of family-held/patient-held records in Japanese communities of various sizes, all of which were aimed at integrating information from various services, including information provided by medical and psychiatric professionals to the family and patient. Innovative tools have been available in the areas of the hopes and preferences of the patient, medication and monitoring, sharing information, and the use of information technology. Conclusion and Discussion: Family-held/patient-held records have potential as a tool to enhance the integrated care of people with dementia in the community.
Multipole order and global/site symmetry in the hidden order phase of URu2Si2
Michi-To Suzuki,Hiroaki Ikeda
Physics , 2014, DOI: 10.1103/PhysRevB.90.184407
Abstract: On the basis of group theory and the first-principles calculations, we investigate high-rank multipole orderings in URu2Si2, which have been proposed as a genuine primary order parameter in the hidden order phase below 17.5K. We apply Shubnikov group theory to the multipole ordered states characterized by the wave vector Q = (0, 0, 1) and specify the global/site symmetry and the secondary order parameters, such as induced dipole moments and change in charge distribution. We find that such antiferroic magnetic multipole orderings have particularly advantageous to conceal the primary order parameter due to preserving high symmetry in charge distribution. Experimental observations of the inherent low-rank multipoles, which are explicitly classified in this paper, will be key pieces to understand the puzzling hidden order phase.
Doping dependence of spin fluctuations and electron correlations in iron pnictides
Hiroaki Ikeda,Ryotaro Arita,Jan Kune?
Physics , 2010, DOI: 10.1103/PhysRevB.82.024508
Abstract: Doping dependence of the spin fluctuations and the electron correlations in the effective five-band Hubbard model for iron pnictides is investigated using the fluctuation-exchange approximation. For a moderate hole doping, we find a dominant low-energy spin excitation at Q=(\pi,0), which becomes critical at low temperature. The low-energy spin excitations in the heavily hole-doped region are characterized by weak Q dependence. The electron doping leads to an appearance of a pseudogap in spin excitation spectrum. Correspondingly, the NMR-1/T1 relaxation rate is strongly enhanced on the hole-doped side and suppressed on the electron-doped side of the phase diagram. This behavior can be to large extent understood by systematic changes of the Fermi-surface topology.
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