Keisuke Katayama

Temperature-induced structural phase transitions in a two-dimensional self-assembled network.

Two-dimensional (2D) supramolecular self-assembly at liquid-solid interfaces is a thermodynamically complex process producing a variety of structures. The formation of multiple network morphologies from the same molecular building blocks is a common occurrence. We use scanning tunnelling microscopy (STM) to investigate a structural phase transition between a densely packed and a porous phase of an alkylated dehydrobenzo[12]annulene (DBA) derivative physisorbed at a solvent-graphite interface. The influence of temperature and concentration are studied and the results combined using a thermodynamic model to measure enthalpy and entropy changes associated with the transition. These experimental results are compared to corresponding values obtained from simulations and theoretical calculations. This comparison highlights the importance of considering the solvent when modeling porous self-assembled networks. The results also demonstrate the power of using structural phase transitions to study the thermodynamics of these systems and will have implications for the development of predictive models for 2D self-assembly.

Solvent-Induced Homochirality in Surface-Confined Low-Density Nanoporous Molecular Networks

Induction of chirality in achiral monolayers has garnered considerable attention in the recent past not only due to its importance in chiral resolutions and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. In this contribution, we demonstrate the emergence of macroscopic chirality in multicomponent supramolecular networks formed by achiral molecules at the interface of a chiral solvent and an achiral substrate. The solvent-mediated chiral induction provides a simple, efficient, and versatile approach for the fabrication of homochiral surfaces using achiral building blocks.

Heavy Fermion State in YbIr2Zn20

We measured the high-field magnetization and de Haas–van Alphen (dHvA) oscillations for YbIr 2 Zn 20 with a cubic crystal structure, together with the electrical resistivity and magnetic susceptibility. The magnetic susceptibility χ with an effective magnetic moment of Yb 3+ becomes temperature-independent at low temperatures, with a broad peak at T χmax =7.4 K for H ∥ . The corresponding magnetization indicates a metamagnetic transition at H m =120 kOe, consistent with a T χmax vs H m relation in the Ce- and U-based heavy fermion compounds. The large cyclotron masses of 4–27 m 0 are detected in the dHvA experiment, and are found to be reduced at magnetic fields higher than H m =120 kOe. The resistivity follows the Fermi liquid relation ρ=ρ 0 + A T 2 under magnetic field, and the \(\sqrt{A}\) value is also found to have a maximum at H m as a function of magnetic field. From the present experimental results, together with the results of 4 f -itinerant energy band calculations, the 4 f electrons are fou...

Metamagnetic Behavior in Heavy-Fermion Compound YbIr2Zn20

The metamagnetic behavior in the heavy-fermion compound YbIr 2 Zn 20 with a cubic structure was studied by magnetization, de Haas–van Alphen (dHvA) oscillation, magnetoresistance, specific heat, thermal expansion, and magnetostriction measurements in single-crystalline samples. A metamagnetic anomaly at H m ≃100 kOe was found to exist in all field directions in the cubic crystal structure. The cyclotron effective mass m c * , the coefficient A in the Fermi liquid relation of electrical resistivity ρ=ρ 0 + A T 2 , and the electronic specific heat coefficient C / T indicate a peak at the metamagnetic field H m . The negative thermal expansion and negative volume magnetostriction suggest that the valence of the Yb ion gradually changes from a 4 f -itinerant state to a trivalent state with increasing magnetic field, and an almost trivalent state is realized above the metamagnetic field H m . On the other hand, the topology of the Fermi surface is approximately unchanged below and above H m in the dHvA experiment.

Field-Induced Antiferromagnetic State in Non-centrosymmetric Superconductor CeIrSi3

We have carried out the electrical resistivity and ac specific heat measurements under pressure P and magnetic field H in a pressure-induced superconductor CeIrSi 3 with the noncentrosymmetric tetragonal crystal structure. Superconductivity is observed in a wide pressure region from 1.9 GPa to about 3.5 GPa. The antiferromagnetic state disappears at P c =2.25 GPa under H =0, but in magnetic field we have found an antiferromagnetic state. The corresponding electrical resistivity in constant magnetic field decreases rather steeply below the Neel temperature T N under pressures up to about 2.4 GPa, while it shows an upturn anomaly at T N under pressures larger than 2.4 GPa. The ac specific heat also indicates a clear jump at T N in magnetic field. When the antiferromagnetic phase exists in magnetic field, the superconducting transition becomes broad, possessing a transition width Δ T sc =0.2–0.5 K. On the other hand, it becomes extremely sharp, with Δ T sc =0.03 K even at 17 T under P =2.55 GPa, for example,...

Low-Temperature Magnetic Orderings and Fermi Surface Properties of LaCd11, CeCd11, and PrCd11 with a Caged Crystal Structure

We succeeded in growing single crystals of cage-structure compounds RCd11 (R: La, Ce, and Pr) and precisely studied their low-temperature magnetic and electronic properties by measuring electrical resistivity, magnetic susceptibility, magnetization, specific heat, and the de Haas–van Alphen (dHvA) effect. We found antiferromagnetic ordering at 0.44 and 0.39 K in CeCd11 and PrCd11, respectively, and clarified the magnetic phase diagrams of the compounds. In addition, low-lying crystalline electric field (CEF) schemes were proposed from the specific heat results of both compounds. From the present study, the antiferromagnetic ordering in PrCd11 is found to be of the exchange-induced type with a singlet ground state. From the dHvA experiment, we detected small dHvA branches ranging from 7 � 10 5 to 2 � 10 7 Oe, which correspond to small Fermi surfaces. This is mainly due to a small Brillouin zone based on a large unit cell. Moreover, the dHvA frequencies and cyclotron masses are approximately the same among RCd11, revealing a localized character of 4f electrons in CeCd11 and PrCd11.

Two-Dimensional Fermi Surfaces in LaRuPO and LaFePO versus Three-Dimensional Fermi Surfaces in LaFe2P2

We succeeded in observing the de Haas–van Alphen (dHvA) effect in LaRuPO, which is a sister compound of iron-based oxypnictide superconductors. All the detected dHvA frequencies, which correspond to the maximum or minimum cross-sectional areas of Fermi surfaces, approximately follow the 1/cos θ dependence, where θ is a field-tilted angle from the tetragonal [001] direction to the [100] and [110] directions. The Fermi surfaces are found to consist of two cylindrical hole Fermi surfaces and two cylindrical electron Fermi surfaces on the basis of the similar cylindrical Fermi surfaces in LaFePO and the result of energy band calculations. The cyclotron effective mass in LaRuPO is light, ranging from 0.55 to 0.86 m 0 , which is compared with a large cyclotron mass in LaFePO. These two-dimensional Fermi surfaces in LaRuPO and LaFePO are also compared with the three-dimensional Fermi surfaces in LaFe 2 P 2 .