Restoration of isotropy on fractals

We report a new type of restoration of macroscopic isotropy (homogenization) in fractals with microscopic anisotropy. The phenomenon is observed in various physical setups, including diffusions, random walks, resistor networks, and Gaussian field theories. The mechanism is unique in that it is absent in spaces with translational invariance, while universal in that it is observed in a wide class of fractals.Comment: 11 pages, REVTEX, 3 postscript figures. (Compressed and encoded figures archived by "figure" command). To appear in Physical Review Letter

Non-Fermi liquid, unscreened scalar chirality and parafermions in a frustrated tetrahedron Anderson model

We investigate a four-impurity Anderson model where localized orbitals are located at vertices of a regular tetrahedron and find a novel fixed point in addition to the ordinary Fermi liquid phase. That is characterized by unscreened scalar chirality of a tetrahedron. In this phase, parafermions emerges in the excitation spectrum and quasiparticle mass diverges as 1/|T log^3 T| at low temperatures (T). The diverging effective mass is a manifestation of singular Fermi liquid states as in the underscreened Kondo problem. Between the two phases, our Monte Carlo results show the existence of a non Fermi liquid critical point where the Kondo effects and the intersite antiferromagnetic interactions are valanced. Singular behaviors are prominent in the dynamics and we find that the frequency (omega) dependence of the self-energy (Sigma) is the marginal Fermi liquid like, -Im Sigma \sim |omega|.Comment: 7 pages, 4 figures, 1 table, published versio

Electron Mass Enhancement due to Anharmonic Local Phonons

In order to understand how electron effective mass is enhanced by anharmonic local oscillation of an atom in a cage composed of other atoms, i.e., {\it rattling}, we analyze anharmonic Holstein model by using a Green's function method. Due to the evaluation of an electron mass enhancement factor $Z$, we find that $Z$ becomes maximum when zero-point energy is comparable with potential height at which the amplitude of oscillation is rapidly enlarged. Cooperation of such quantum and rattling effects is considered to be a key issue to explain the electron mass enhancement in electron-rattling systems.Comment: 3 pages, 3 figures, to appear in J. Phys. Soc. Jpn. Suppl. (Proceedings for International Conference on Heavy Electrons

Effective Hamiltonian of Three-orbital Hubbard Model on Pyrochlore Lattice: Application to LiV_2O_4

We investigate heavy fermion behaviors in the vanadium spinel LiV_2O_4. We start from a three-orbital Hubbard model on the pyrochlore lattice and derive its low-energy effective Hamiltonian by an approach of real-space renormalization group type. One important tetrahedron configuration in the rochlore lattice has a three-fold orbital degeneracy and spin S=1, and correspondingly, the effective Hamiltonian has spin and orbital exchange interactions of Kugel-Khomskii type as well as correlated electron hoppings. Analyzing the effective Hamiltonian, we find that ferromagnetic double exchange processes compete with antiferromagnetic superexchange processes and various spin and orbital exchange processes are competing to each other. These results suggest the absence of phase transition in spin and orbital spaces down to very low temperatures and their large fluctuations in the low-energy sector, which are key issues for understanding the heavy fermion behavior in LiV_2O_4.Comment: 26 pages, 26 figure

Perception and production of English /r/-/l/ by adult Japanese speakers

This dissertation examines perception and production of English /r/-/l/ by adult Japanese speakers. This programme of research is organized into three sections, termed Study 1, Study2, and Study 3. The first study examined whether category assimilation between English /r/-/l/ and Japanese /ɾ/ was predictive of /r/-/l/ identification accuracy using an individual difference approach. Japanese speakers were assessed in terms of /r/-/l/ identification and assimilation of English /r/-/l/ into Japanese /ɾ/, /r/-/l/ production, and perceptual best exemplars for /r/, /l/, and /ɾ/. The results demonstrated that, although Japanese speakers strongly assimilated /l/ to /ɾ/, category assimilation was not predictive of English /r/-/l/ identification accuracy, and that only Japanese speaker’s representations for F3 in /r/ and /l/ was predictive of /r/-/l/ identification ability. The second study similarly took an individual difference approach and examined whether there is a relationship between perception and production of /r/-/l/ measuring perception accuracies (i.e., identification, discrimination, and perceptual best exemplars) and production accuracies (i.e., acoustic measurements, and recognition accuracy by English speakers). The results demonstrated that perception and production of /r/-/l/ were moderately related. However, not all aspects of /r/-/l/ perception were incorporated into /r/-/l/ production. The third study examined whether one-to-one pronunciation training leads to improvement in production and perception of English /r/-/l/ using a multipronged approach (i.e., explicit instructions, real-time spectrograms, and feedback with signal-processed versions of their own productions). The results demonstrated that Japanese speakers could be trained to produce native-like English /r/-/l/, improving to the point that they approached a 100% accuracy ceiling in terms of how well native speakers could identify their productions. However, the training did not improve their English /r/-/l/ perception at all