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T Tayama

Publications and source records attributed to T Tayama.

14 recordsLinked to original sources
PubMed2006

Metallic spin-liquid behavior of the geometrically frustrated Kondo lattice.

Strongly frustrated magnetism of the metallic pyrochlore oxide Pr2Ir2O7 has been revealed by single crystal study. While Pr 4f moments have an antiferromagnetic RKKY interaction energy scale of /T*/ = 20 K mediated by Ir 5d-conduction electrons, no magnetic long-range order is found except for partial spin freezing at 120 mK. Instead, the Kondo effect, including a lnT dependence in the resistivity, emerges and leads to a partial screening of the moments below /T*/. Our results indicate that the underscreened moments show spin-liquid behavior below a renormalized correlation scale of 1.7 K.

Journal Article↗
PubMed2005

Metamagnetic quantum criticality revealed by 17O-NMR in the itinerant metamagnet Sr3Ru2O7.

We have investigated the spin dynamics using 17O-NMR in the bilayered perovskite Sr3Ru2O7, which sits close to a metamagnetic quantum critical point. The nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced on approaching the metamagnetic critical field of approximately 7.9 T, and at the critical field 1/T1T continues to increase and does not show Fermi-liquid behavior down to 0.3 K. The temperature dependence of T1T in this region suggests the critical temperature Theta to be approximately 0 K, which is strong evidence that the spin dynamics possesses a quantum critical character. Comparison between uniform susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of two-dimensional ferromagnetic fluctuations dominate the spin fluctuation spectrum at the critical field, which is unexpected for itinerant metamagnetism.

Journal Article↗
PubMed2004

Disorder-sensitive phase formation linked to metamagnetic quantum criticality.

Condensed systems of strongly interacting electrons are ideal for the study of quantum complexity. It has become possible to promote the formation of new quantum phases by explicitly tuning systems toward special low-temperature quantum critical points. So far, the clearest examples have been appearances of superconductivity near pressure-tuned antiferromagnetic quantum critical points. We present experimental evidence for the formation of a nonsuperconducting phase in the vicinity of a magnetic field-tuned quantum critical point in ultrapure crystals of the ruthenate metal Sr3Ru2O7, and we discuss the possibility that the observed phase is due to a spin-dependent symmetry-breaking Fermi surface distortion.

Journal Article↗
PubMed2003

Magnetic field induced sign reversal of the anomalous Hall effect in a pyrochlore ferromagnet Nd2Mo2O7: evidence for a spin chirality mechanism.

The anisotropic Hall effect and magnetization have been investigated for single crystals of Nd2Mo2O7 under high magnetic fields up to 27 T and at low temperatures down to 50 mK. The magnetization curves indicate that the Nd moments with strong Ising anisotropy are coupled antiferromagnetically with the Mo spins and show field-induced flipping on the respective sites. The Hall resistivity changes its sign with increasing field applied along the [111] direction, while it monotonously approaches zero with the field applied along the [100] or [110] direction. This behavior is in accord with the prediction by the Berry phase theory and is interpreted in terms of the field-induced reversal of spin chirality on the pyrochlore lattice.

Journal Article↗
PubMed2003

Observation of a liquid-gas-type transition in the pyrochlore spin ice compound Dy2Ti2O7 in a magnetic field.

Low temperature magnetization measurements on the pyrochlore spin ice compound Dy2Ti2O7 reveal that the ice-rule breaking spin flip, appearing at H approximately 0.9 T applied parallel to the [111] direction, turns into a novel first-order transition for T<0.36 K which is most probably of a liquid-gas type. T-linear variation of the critical field observed down to 0.03 K suggests the unusual situation that the entropy release across the transition remains finite [approximately 0.5 (J/K) x mol-Dy] as T-->0, in accordance with a breaking of the macroscopic degeneracy in the intermediate "kagomé ice" state.

Journal Article↗
PubMed2002

Magnetic-field induced quantum critical point in YbRh(2)Si(2).

We report low-temperature calorimetric, magnetic, and resistivity measurements on the antiferromagnetic (AF) heavy-fermion metal YbRh(2)Si(2) ( T(N)=70 mK) as a function of magnetic field B. While for fields exceeding the critical value B(c0) at which T(N)-->0 the low-temperature resistivity shows an AT2 dependence, a 1/(B-B(c0)) divergence of A(B) upon reducing B to B(c0) suggests singular scattering at the whole Fermi surface and a divergence of the heavy quasiparticle mass. The observations are interpreted in terms of a new type of quantum critical point separating a weakly AF ordered from a weakly polarized heavy Landau-Fermi liquid state.

Journal Article↗
PubMed2000

The minimum temporal thresholds for motion detection of grating patterns.

The minimum temporal thresholds for absolute motion detection were measured for sinusoidal grating patterns in foveal vision. Test patterns of relatively low temporal frequencies and low velocities were examined. The thresholds clearly decreased with test velocities rather than with test temporal frequencies. Modified velocity-time reciprocity was observed (i.e. the relationship between test velocity and temporal thresholds was described by a simple equation including two constants which indicate temporal and spatial limits). The temporal constant was about 35 ms and the spatial constant was about 1 min of arc. These constants are thought to provide the basic constraints on motion detection.

Humans↗
PubMed1995

Familial thrombocytosis.

Four cases of thrombocytosis in three successive generations of a family are described. High peripheral platelet count was found incidentally in the proband with cutaneous malignant lymphoma. Bone marrow examination showed megakaryocytic hyperplasia. Neither Philadelphia chromosome nor chimaeric bcr/abl junction was detected in marrow cells. In this family, thrombocytosis was thought to be transmitted by an autosomal dominant mode of inheritance.

Child, Preschool↗
PubMed1989

Microinjection of endogenous and exogenous proteins into primary cultures of rat hepatocytes and the degradation of the injected proteins.

1. A method to microinject proteins into cells through packaging proteins to erythrocyte ghosts (erythrocyte-mediated microinjection) was modified partially in order to apply the method to primary cultures of rat hepatocytes. 2. Degradation of the microinjected proteins was examined employing the improved method. The mean half-life of the injected endogenous liver protein was 20 hr. The data suggested that the injected proteins are degraded through both lysosomal and non-lysosomal proteolytic pathways probably depending on their structure. 3. The present method to microinject exogenous proteins into primary cultures of rat hepatocytes can be employed usefully for the investigations of protein metabolism in liver.

Animals↗
PubMed1986

[The diminution of spatial effects upon duration estimation with focused attention].

The purpose of this study is to investigate the influence of spatial attributes of stimuli upon the estimation of duration time. Using magnitude estimation method, three tasks were imposed on seven undergraduate students. C (control) task was to estimate the duration of a static small circle, MF (moving-free) task was that of a moving pattern of randomly located luminous spots, both with free regard, and MX (moving-fixed) task was that of the small circle superimposed on the moving pattern, with focused attention. In the MF task, there was found a velocity effect, i.e. the higher the velocity was, the larger was the estimated duration. In the MX task, the velocity effect was also found but in a small amount. The estimated durations in the C task were larger than those for the lowest velocity conditions in the other two tasks. These results were discussed in terms of two hypothetical cognitive processing systems in prospective time estimation.

Adult↗
PubMed1984

[Global matching and local matching in perceiving velocity changes].

Two experiments were conducted to examine the processes of perceiving velocity changes of visual stimuli which were gradually accelerated. In Exp. I, using a rotating pattern of luminous spots as moving stimuli, the time required of the subject to perceive a velocity change was measured in slow, medium and fast positively accelerating conditions. Irrespective of the accelerating rates, subjects tended to respond at the time the velocity difference attained to a constant value. In Exp. II, with the same moving pattern but presented only for a predetermined duration, subjects were asked to judge if there was a velocity change or not. The results showed that the slower was the acceleration, the larger were the velocity differences required of the subject to notice the velocity change. Based upon these results, the velocity change perception was discussed in terms of global and local matching processes.

Acceleration↗