Studies on the [4 + 2] cycloaddition and allylic substitution of indole-fused zwitterionic π-allylpalladium.

The zwitterionic π-allylpalladium species, also known as dipoles, are important synthons widely used in various reactions including cycloaddition and allylic substitution. This study reported the development of a new indole-fused zwitterionic π-allylpalladium precursor compound and its application in [4 + 2] cycloaddition and allylic substitution reactions. As a result, the synthesis of pyrrolo[3,2,1-ij]quinazolin-3-one and 7-vinyl indole compounds was achieved with moderate to good yields. Notably, the allylic substitution reaction exhibited excellent regio- and stereoselectivity.

Large Anomalous Nernst Effects at Room Temperature in Fe3 Pt Thin Films.

Heat current in ferromagnets can generate a transverse electric voltage perpendicular to magnetization, known as anomalous Nernst effect (ANE). ANE originates intrinsically from the combination of large Berry curvature and density of states near the Fermi energy. It shows technical advantages over the conventional longitudinal Seebeck effect in converting waste heat to electricity due to its unique transverse geometry. However, materials showing giant ANE remain to be explored. Herein,  a large ANE thermopower of Syx ≈ 2 µV K-1 at room temperature in ferromagnetic Fe3 Pt epitaxial films is reported, which also show a giant transverse thermoelectric conductivity of αyx ≈ 4 A K-1  m-1 and a remarkable coercive field of 1300 Oe. The theoretical analysis reveals that the strong spin-orbit interaction in addition to the hybridization between Pt 5d and Fe 3d electrons leads to a series of distinct energy gaps and large Berry curvature in the Brillouin zone, which is the key for the large ANE. These results highlight the important roles of both Berry curvature and spin-orbit coupling in achieving large ANE at zero magnetic field, providing pathways to explore materials with giant transverse thermoelectric effect without an external magnetic field.

Unusual upper critical fields of the topological nodal-line semimetal candidate SnxNbSe2-δ.

We report superconductivity in SnxNbSe2-δ, a topological nodal-line semimetal candidate with a noncentrosymmetric crystal structure. The superconducting transition temperatureTcof this compound is extremely sensitive to Sn concentrationxand Se deficiencyδ, 5.0 K for Sn0.13NbSe1.70and 8.6 K for Sn0.14NbSe1.71and Sn0.15NbSe1.69. In all samples, the temperature dependence of the upper critical fieldHc2(T) differs from the prediction of the Werthamer-Helfand-Hohenberg theory. While the zero-temperature value of the in-plane upper critical field of SnxNbSe2-δwith the higherTcis lower than the BCS Pauli paramagnetic limitHP, that of the lowerTcsample exceedsHPby a factor of ∼2. Our observations suggest that a possible odd-parity contribution dominates the superconducting gap function of SnxNbSe2-δ, and it can be fine-tuned by the Sn concentration and Se deficiency.

Fermi surfaces of the topological semimetal CaSn3probed through de Haas van Alphen oscillations.

In the search of topological superconductors, nailing down the Fermiology of the normal state is as crucial a prerequisite as unraveling the superconducting pairing symmetry. In particular, the number of time-reversal-invariant momenta (TRIM) in the Brillouin zone enclosed by Fermi surfaces is closely linked to the topological class of time-reversal-invariant systems, and can experimentally be investigated. We report here a detailed study of de Haas van Alphen quantum oscillations in single crystals of the topological semimetal CaSn3with torque magnetometry in high magnetic fields up to 35 T. In conjunction with density functional theory based calculations, the observed quantum oscillations frequencies indicate that the Fermi surfaces of CaSn3enclose an odd number of TRIM, satisfying one of the proposed criteria to realize topological superconductivity. Nonzero Berry phases extracted from the magnetic oscillations also support the nontrivial topological nature of CaSn3.