[en] Correlated electron systems on a honeycomb lattice have emerged as a fertile playground to explore exotic electronic phenomena. Theoretical and experimental work has appeared to realize novel behavior, including quantum Hall effects and valleytronics, mainly focusing on van der Waals compounds, such as graphene, chalcogenides, and halides. Here in this paper, we review our theoretical study on perovskite transition-metal oxides (TMOs) as an alternative system to realize such exotic phenomena. We demonstrate that novel quantum Hall effects and related phenomena associated with the honeycomb structure could be artificially designed by such TMOs by growing their heterostructures along the [111] crystallographic axis. One of the important predictions is that such TMO heterostructures could support two-dimensional topological insulating states. The strong correlation effects inherent to TM d electrons further enrich the behavior.

[en] Neutron diffraction experiments have been carried out to characterize the magnetic structures and order parameters in an intermediate phase of NdB₄ showing the successive phase transitions at T₀ = 17.2 K, T_N1 = 7.0 K, and T_N2 = 4.8 K. We have revealed the antiferromagnetic ordering with the propagation vectors q0=(0,0,0), q0 and qs1=(δ,δ,0.4) (δ ~ 0.14), and q₀ and q_s2=(0.2,0,0.4) in phase II (T_N1 < T < T₀), phase III (T_N2 < T < T_N1), and phase IV (T < T_N2), respectively. The observed patterns in phase II are successfully explained by postulating a coplanar structure with static magnetic moments in the tetragonal ab-plane. We have found that the magnetic structure in phase II can be uniquely determined to be a linear combination of antiferromagnetic “all-in/all-out”-type (Γ₄) and “vortex”-type (Γ₂) structures, consisting of a Γ₄ main component (77%) with a small amplitude of Γ₂ (23%). Finally, we propose that the quadrupolar interaction holds the key to stabilizing the noncollinear magnetic structure and quadrupolar order. Here, the frustration in the Shastry–Sutherland lattice would play an essential role in suppressing the dominance of the magnetic interaction.

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[en] The nonlinear stabilities of resistive MHD modes are investigated in a tokamak configuration by a three dimensional MHD simulation based on a rectangular column model under the fixed boundary condition. The m = 1 internal resistive kink mode is excited for the central safety factor, q₀ < 1, resulting in a sawtooth oscillation of temperature. Only the m = 2 mode is excited for q₀ < 2 and a small resistivity. On the other hand, the several modes of (-m : n) = (2 : 1), (1 : 1) and (3 : 2) appear for q₀ < 2 and a little large resistivity depending on the q-configuration through the variation of toroidal current. The (3 : 2) mode plays an important role on the mode coupling between the (1 : 1) and (2 : 1) modes. As the result, the (2 : 1) mode finally determines the stability and stable configurations of plasma are formed with the condition of q >= 2. (author)

[en] In ¹¹⁷Sn sup(m) an E5 γ transition between the 314.2 keV (11/2^-) and the ground (1/2⁺) states was observed by using a Compton suppression spectrometer. Its branching ratio was found to be (4.9 +- 1.1) x 10^-6. A B(E5) value obtained here is (2.9 +- 0.6) x 10⁴ e²fm¹⁰. An effective charge of the E5 γ transition was deduced to be (0.23 +- 0.03)e in Weisskopf estimate. This is of the same magnitude as those in ¹¹³Cd sup(m) and ¹²³Te sup(m). In the single particle unit the effective charge was obtained to be (0.089 +- 0.010)e by using the 1h sub(11/2) and 3s sub(1/2) wave functions deduced from the Woods-Saxon potential. A core polarization charge due to the 5^- state at 2367 keV in ¹¹⁶Sn was calculated to be 0.11 e, by taking into accounts of the effects due to the pairing. (author)

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[en] The level structure of ¹²⁴Te has been investigated by studying gamma rays emitted following the beta decay of ¹²⁴Sb to the excited states of ¹²⁴Te. The intensities of 70 gamma rays observed in this decay have been measured with a better precision than known earlier. The existence of the gamma rays with energies of 1248.62 and 1731.4 keV has been confirmed, whereas the 159.4, 185.4, 385.9, 476.6, 498.4, 553.8, 997.0, 1163.2, 1388.7, 1505.6, 1557, 1950.4, 2151.5 and 2274.0 keV gamma transitions reported earlier have not been observed in the present investigations. The gamma-gamma angular correlation measurements for nine cascades populated in this decay have been done out of which 791-(646)-603 keV cascade has been attempted for the first time. From these measurements, the multipole admixtures in the 714, 723, 791, 968, 1045, 1368, 1691 and 2091 keV transitions have been obtained. These angular correlation studies have enabled us to assign 2⁺ and 3^- characters to the levels at 2039.5 and 2694.0 keV respectively. (author)

[en] Rapidity correlations among hadrons produced at 200 GeV/c proton-nucleus interactions in emulsion are investigated. A two step mechanism is considered in which cluster of hadrons are produced independently. The analysis of the data shows an evidence for short-range correlations. The average number of particles (pions) emerging out of a cluster is found to be at least three at this energy. (author)