The fundamental physical properties of doped ${\mathrm{LaMnO}}_3,$ generically termed “manganites,” and much of the underlying physics, were known more than 40 years ago. This article first reviews progress made at that time, the concept of double exchange in particular, and points out the missing elements that have led to a massive resurgence of interest in these and related materials. More recent research is then described, treating first the ground states that emerge as divalent atoms are substituted for trivalent La. A wide range of ground states appear, including ferromagnetic metals, orbital- and charge-ordered antiferromagnets, and more complex stripe and spin-glass states. Because of the interest in so-called colossal magnetoresistance that occurs in the ferromagnetic/metallic composition range, a section is devoted to reviewing the atypical properties of that phase. Next the high-temperature phase is examined, in particular, evidence for the formation of self-trapped small polarons and the importance of Jahn-Teller coupling in this process. The transitions between the high-temperature polaronic phase and the ferromagnetic and charge-ordered states are treated in a fourth section. In each section, the authors stress the competition among charge, spin, and lattice coupling and review the current state of theoretical understanding. They conclude with some comments on the impact that research on these materials has on our understanding of doped oxides and other strongly correlated electronic materials.

This article reviews experimental and theoretical work on Bose-Einstein condensation in quantum magnets. These magnets are natural realizations of gases of interacting bosons whose relevant parameters such as dimensionality, lattice geometry, amount of disorder, nature of the interactions, and particle concentration can vary widely between different compounds. The particle concentration can be easily tuned by applying an external magnetic field which plays the role of a chemical potential. This rich spectrum of realizations offers a unique possibility for studying the different physical behaviors that emerge in interacting Bose gases from the interplay between their relevant parameters. The plethora of other bosonic phases that can emerge in quantum magnets, of which the Bose-Einstein condensate is the most basic ground state, is reviewed. The compounds discussed in this review have been intensively studied in the last two decades and have led to important contributions in the area of quantum magnetism. In spite of their apparent simplicity, these systems often exhibit surprising behaviors. The possibility of using controlled theoretical approaches has triggered the discovery of unusual effects induced by frustration, dimensionality, or disorder.

Low temperature specific heat and thermal conductivity measurements on the ambient pressure heavy fermion superconductors ${\mathrm{CeIrIn}}_5$ and ${\mathrm{CeCoIn}}_5$ reveal power law temperature dependences of these quantities below $T_c$. The low temperature specific heat in both ${\mathrm{CeIrIn}}_5$ and ${\mathrm{CeCoIn}}_5$ includes $T^2$ terms, consistent with the presence of nodes in the superconducting energy gap. The thermal conductivity data present a $T$-linear term consistent with the universal limit $\left({\mathrm{CeIrIn}}_5\right)$, and a low temperature $T^3$ variation in the clean limit $\left({\mathrm{CeCoIn}}_5\right)$, also in accord with prediction for an unconventional superconductor with lines of nodes.

Thermoelectric power, electrical resistivity, and magnetization experiments, performed in the paramagnetic phase of ${\mathrm{La}}_{2/3}$ ${\mathrm{Ca}}_{1/3}$ ${\mathrm{MnO}}_3$, provide evidence for polaron-dominated conduction in colossal magnetoresistance materials. At high temperatures, a large, nearly-field-independent difference between the activation energies for resistivity ρ and thermopower S, a characteristic of Holstein polarons, is observed, and lnρ ceases to scale with the magnetization. On approaching ${\mathit{T}}_{\mathit{c}}$, both energies become field dependent, indicating that the polarons are magnetically polarized. Below ${\mathit{T}}_{\mathit{c}}$, the thermopower follows a law S(H)∼1/ρ(H) as in nonsaturated ferromagnetic metals. © 1996 The American Physical Society.