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(3) sigma modelJimmenez, S.*; Oka, Makoto; Sasaki, Kiyoshi*
Physical Review D, 97(11), p.114506_1 - 114506_28, 2018/06
Times Cited Count：0 Percentile：0.01(Astronomy & Astrophysics)We nonperturbatively calculate the wave-function renormalization in the two-dimensional (3) sigma model. It is evaluated in a box with a finite spatial extent. We determine the anomalous dimension in the finite-volume scheme through an analysis of the step-scaling function. Results are compared with a perturbative evaluation, and reasonable behavior is observed.
Kobayashi, Keita*; Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko; Aoki, Hideo*
Physical Review B, 94(21), p.214501_1 - 214501_7, 2016/12
Times Cited Count：56 Percentile：89.32(Materials Science, Multidisciplinary)no abstracts in English
-electron systemsOnishi, Hiroaki; Hotta, Takashi
Journal of the Physical Society of Japan, 75(Suppl.), p.266 - 269, 2006/08
In order to clarify multipole correlations in -electron systems, we investigate a one-dimensional -electron model based on a 
- coupling scheme by exploiting a density-matrix renormalization group method. We discuss the effect of a crystalline electric field and the dependence on the change of -electron numbers in detail.
Hotta, Takashi
Physica B; Condensed Matter, 378-380, p.51 - 53, 2006/05
Times Cited Count：4 Percentile：22.76(Physics, Condensed Matter)In order to clarify what types of spin and orbital fluctuations dominate over low-temperature electronic properties of Pr-based filled skutterudites, we evaluate multipole susceptibility based on a multiorbital Anderson model constructed from a - coupling scheme. It is found that magnetic and quadrupole fluctuations are dominant at low temperatures. When we further include the effect of rattling as dynamical Jahn-Teller phonons, there remain quadrupole and octupole fluctuations, which may induce exotic superconducting pairing.
-orbital Hubbard modelXavier, J. C.*; Onishi, Hiroaki; Hotta, Takashi; Dagotto, E.*
Physical Review B, 73(1), p.014405_1 - 014405_9, 2006/01
Times Cited Count：9 Percentile：41.55(Materials Science, Multidisciplinary)We present the zero-temperature phase diagram of the one-dimensional -orbital Hubbard model, by using the density-matrix renormalization group and Lanczos techniques. Emphasis is given to the case for the electron density 
=5, of relevance to Co-based compounds. Several other cases for electron densities between =3 and 6 are also studied. At =5, our results indicate a first-order transition between a paramagnetic (PM) insulator phase and a ferromagnetic (FM) state by tuning the Hund's coupling. The results also suggest a transition from the =5 PM insulator phase to a metallic regime by changing the electron density. The behavior of the spin, charge, and orbital correlation functions in the FM and PM states are discussed.
Hotta, Takashi
Journal of the Physical Society of Japan, 74(9), p.2425 - 2429, 2005/09
Times Cited Count：26 Percentile：73.62(Physics, Multidisciplinary)In order to clarify exotic multipole properties of filled skutterudites, we evaluate multipole susceptibility for =1
5, where is the local -electron number, on the basis of a multiorbital Anderson model constructed using the - coupling scheme. For =1, magnetic fluctuations dominate over low-temperature electronic properties, while for =2 and 4, electronic states are dominated by both magnetic and quadrupole fluctuations. For =3 and 5, octupole fluctuations are found to be significant, depending on the crystalline electric field potential. We discuss possible relevance of the results to actual materials.
Onishi, Hiroaki; Hotta, Takashi
Physical Review B, 71(18), p.180410_1 - 180410_4, 2005/05
Times Cited Count：5 Percentile：26.14(Materials Science, Multidisciplinary)In order to clarify a crucial role of orbital degree of freedom in geometrically frustrated systems, we investigate both ground- and excited-state properties of the 
-orbital degenerate Hubbard model on two kinds of lattices, ladder and zigzag chain, by using numerical techniques. In the ladder, spin correlation extends on the whole system, while the zigzag chain is decoupled to a double chain and spin excitation is confined in one side of the double chain due to the selection of a specific orbital. We envision a kind of self-organization phenomenon that the geometrically frustrated multi-orbital system is spontaneously reduced to a one-orbital model to suppress the spin frustration.
-electron systems with filled skutterudite structureHotta, Takashi
Journal of the Physical Society of Japan, 74(4), p.1275 - 1288, 2005/04
Times Cited Count：25 Percentile：72.91(Physics, Multidisciplinary)In order to understand electronic properties of filled skutterudite materials, the Anderson model is analyzed by using the numerical renormalization group method to evaluate magnetic susceptibility and entropy of electron for each case of =113, where is the number of electrons per rare-earth ion. For the 
-electron system corresponding to the Pr-based filled skutterudite, it is found that magnetic fluctuations significantly remain at low temperatures, even when the ground state is 
singlet, if 
triplet is the excited state with small excitation energy. By analyzing an orbital degenerate Hubbard model constructed based on the - coupling scheme, we find that anisotropic Cooper-pair mediated by magnetic fluctuations appears in a limited region in which the singlet and triplet ground states are interchanged.
-electron systemsHotta, Takashi
Physica B; Condensed Matter, 359-361, p.1003 - 1005, 2005/04
Times Cited Count：1 Percentile：6.23(Physics, Condensed Matter)In order to understand magnetic properties of filled skutterudite materials, we evaluate magnetic susceptibility of the Anderson model with orbital degeneracy by using the numerical renormalization group method. Even when the local ground state is , magnetic fluctuations significantly remain, if is the excited state with small excitation energy, as experimentally proposed for Pr-based filled skutterudite compounds.
Hotta, Takashi
Physical Review Letters, 94(6), p.067003_1 - 067003_4, 2005/02
Times Cited Count：15 Percentile：62.72(Physics, Multidisciplinary)In order to clarify magnetic properties of filled skutterudites, we analyze the Anderson model including seven orbitals hybridized with an 
conduction band using a numerical technique. For =2 corresponding to Pr-based filled skutterudites, where is the local -electron number, even if the ground state is a singlet, there remain significant magnetic fluctuations from a triplet state with a small excitation energy. This result can be understood by the fact that -electron states are clearly distinguished as itinerant and localized ones in the filled skutterudite structure. This picture also explains the complex results for -electron magnetic susceptibility and entropy for =113.
Itakura, Mitsuhiro
JAERI-Review 99-009, p.40 - 44, 1999/03
no abstracts in English
Tanaka, A.*; Machida, Masahiko
Physical Review Letters, 81(8), p.1746 - 1747, 1998/08
Times Cited Count：1 Percentile：44.08(Physics, Multidisciplinary)no abstracts in English
