J. Appl. Cryst.の発刊に際して

Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.

Weyl and Dirac semimetals in three-dimensional solids

Frustrated magnets are materials in which localized magnetic moments, or spins, interact through competing exchange interactions that cannot be simultaneously satisfied, giving rise to a large degeneracy of the system ground state. Under certain conditions, this can lead to the formation of fluid-like states of matter, so-called spin liquids, in which the constituent spins are highly correlated but still fluctuate strongly down to a temperature of absolute zero. The fluctuations of the spins in a spin liquid can be classical or quantum and show remarkable collective phenomena such as emergent gauge fields and fractional particle excitations. This exotic behaviour is now being uncovered in the laboratory, providing insight into the properties of spin liquids and challenges to the theoretical description of these materials.

Spin liquids in frustrated magnets

We discuss phenomena arising from the combined influence of electron correlation and spin-orbit coupling (SOC), with an emphasis on emergent quantum phases and transitions in heavy transition metal compounds with 4d and 5d elements. A common theme is the influence of spin-orbital entanglement produced by SOC, which influences the electronic and magnetic structure. In the weak-to-intermediate correlation regime, we show how nontrivial band-like topology leads to a plethora of phases related to topological insulators (TIs). We expound these ideas using the example of pyrochlore iridates, showing how many novel phases, such as the Weyl semimetal, axion insulator, topological Mott insulator, and TIs, may arise in this context. In the strong correlation regime, we argue that spin-orbital entanglement fully or partially removes orbital degeneracy, reducing or avoiding the normally ubiquitous Jahn-Teller effect. As we illustrate for the honeycomb-lattice iridates and double perovskites, this leads to enhanced qu...

Correlated Quantum Phenomena in the Strong Spin-Orbit Regime

Within the past 20 years or so, there has occurred an explosion of interest in the magnetic behavior of pyrochlore oxides of the type $A_{2}^{3+}$$B_{2}^{4+}$O$_{7}$ where $A$ is a rare-earth ion and $B$ is usually a transition metal. Both the $A$ and $B$ sites form a network of corner-sharing tetrahedra which is the quintessential framework for a geometrically frustrated magnet. In these systems the natural tendency to form long range ordered ground states in accord with the Third Law is frustrated, resulting in some novel short range ordered alternatives such as spin glasses, spin ices and spin liquids and much new physics. This article attempts to review the myriad of properties found in pyrochlore oxides, mainly from a materials perspective, but with an appropriate theoretical context.

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Magnetic Pyrochlore Oxides

Strongly frustrated magnetism of the metallic pyrochlore oxide ${\mathrm{Pr}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ has been revealed by single crystal study. While Pr $4f$ moments have an antiferromagnetic RKKY interaction energy scale of $|{T}^{*}|=20\text{ }\text{ }\mathrm{K}$ 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 $\mathrm{ln}﻿T$ 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.

/pdf/metallic-spin-liquid-behavior-of-the-geometrically-2t5d5t3v5s.pdf

Metallic Spin-Liquid Behavior of the Geometrically Frustrated Kondo Lattice Pr 2 Ir 2 O 7

Crystal growth and structure of R2Ir2O7 (R = Pr, Eu) using molten KF

https://escholarship.org/content/qt1nd7m4j0/qt1nd7m4j0.pdf?t=oapvvj

A comparison of the structure and localized magnetism in Ce2PdGa12 with the heavy fermion CePdGa6

Our interests lie in studying and understanding the structure-property relationships in novel ternary intermetallics synthesized by metallic flux-growth methods. This review highlights the synthesis, structures and physical properties of ternary lanthanide – transition metal – main group element intermetallics (Ln – T – X), where T = Co, Rh, Ir, Ni, Pd, and Pt, and X = Ga, In, Sb and Sn. Several phases will be discussed, including Ln n TIn3 n +2 (n = 1, 2, ∞), CePdGa6, Ce2PdGa12, Ce2PdGa10, LnNiSb3, LnNi1−x Sb2 (x ∼ 0.4) and Ln 3Co4Sn13. In addition, we report the synthesis, structure characterization, and magnetic behavior from single crystals of Ln 3Co4Sn13 (Ln = Pr, Nd, Sm, Gd, Tb).

Crystal growth and the search for highly correlated intermetallics

The effect of cobalt doping on the thermopower of the superconductor FeSe is investigated through electrical and thermal transport measurements Our results point to the destruction of superconductivity at very low Co concentrations Thermopower data suggest negative charge carriers along with a large enhancement of the Seebeck coefficient, S, on the order of ≈−80 μV/K near T=100 K

Jasmine N. Millican

Papers

Metallic Spin-Liquid Behavior of the Geometrically Frustrated Kondo Lattice Pr 2 Ir 2 O 7

Crystal growth and structure of R2Ir2O7 (R = Pr, Eu) using molten KF

A comparison of the structure and localized magnetism in Ce2PdGa12 with the heavy fermion CePdGa6

Crystal growth and the search for highly correlated intermetallics

Thermopower of Co-doped FeSe