Polaron-mediated spin correlations in metallic and insulating La1−xAx_{1-x}A_{x}MnO3_{3} (AA=Ca, Sr, or Ba)

Neutron spectroscopy measurements reveal short-range spin correlations near and above the ferromagnetic-paramagnetic phase transition in manganite materials of the form La$_{1-x}A_{x}$MnO$_{3}$, including samples with an insulating ground state as well as colossal magnetoresistive samples with a metallic ground state. Quasielastic magnetic scattering is revealed that forms clear ridges running along the [100]-type directions in momentum space. A simple model consisting of a conduction electron hopping between spin polarized Mn ions that becomes self-trapped after a few hops captures the essential physics of this magnetic component of the scattering. We associate this scattering component with the magnetic part of diffuse polarons, as we observe a temperature dependence similar to that of the diffuse structural scattering arising from individual polarons.Comment: 8 pages, 6 figure

Beyond the Fermi Liquid Paradigm: Hidden Fermi Liquids

An intense investigation of possible non-Fermi liquid states of matter has been inspired by two of the most intriguing phenomena discovered in the past quarter century, namely high temperature superconductivity and the fractional quantum Hall effect. Despite enormous conceptual strides, these two fields have developed largely along separate paths. Two widely employed theories are the resonating valence bond theory for high temperature superconductivity and the composite fermion theory for the fractional quantum Hall effect. The goal of this "perspective" article is to note that they subscribe to a common underlying paradigm: they both connect these exotic quantum liquids to certain ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation yields numerous nontrivial experimental consequences, exposing these theories to rigorous and definitive tests.Comment: perspective articl

Effects of Cognitive Fatigue on High Intensity Circuit Exercise: Preliminary study

Please refer to the pdf version of the abstract located adjacent to the title

A Cu2+ (S = 1/2) Kagom\'e Antiferromagnet: MgxCu4-x(OH)6Cl2

Spin-frustrated systems are one avenue for inducing macroscopic quantum states in materials. However, experimental realization of this goal has been difficult because of the lack of simple materials and, if available, the separation of the unusual magnetic properties arising from exotic magnetic states from behavior associated with chemical disorder, such as site mixing. Here we report the synthesis and magnetic properties of a new series of magnetically frustrated materials, MgxCu4-x(OH)6Cl2. Because of the substantially different ligand-field chemistry of Mg2+ and Cu2+, site disorder within the kagom\'e layers is minimized, as directly measured by X-ray diffraction. Our results reveal that many of the properties of these materials and related systems are not due to disorder of the magnetic lattice but rather reflect an unusual ground state.Comment: Accepted for publication in J. Am. Chem. Soc

Can Quantum de Sitter Space Have Finite Entropy?

If one tries to view de Sitter as a true (as opposed to a meta-stable) vacuum, there is a tension between the finiteness of its entropy and the infinite-dimensionality of its Hilbert space. We invetsigate the viability of one proposal to reconcile this tension using $q$-deformation. After defining a differential geometry on the quantum de Sitter space, we try to constrain the value of the deformation parameter by imposing the condition that in the undeformed limit, we want the real form of the (inherently complex) quantum group to reduce to the usual SO(4,1) of de Sitter. We find that this forces $q$ to be a real number. Since it is known that quantum groups have finite-dimensional representations only for $q=$ root of unity, this suggests that standard $q$-deformations cannot give rise to finite dimensional Hilbert spaces, ruling out finite entropy for q-deformed de Sitter.Comment: 10 pages, v2: references added, v3: minor corrections, abstract and title made more in-line with the result, v4: published versio

Magnetic structure of Yb2Pt2Pb: Ising moments on the Shastry-Sutherland lattice.

Neutron diffraction measurements were carried out on single crystals and powders of Yb2Pt2Pb, where Yb moments form two interpenetrating planar sublattices of orthogonal dimers, a geometry known as Shastry-Sutherland lattice, and are stacked along the c axis in a ladder geometry. Yb2Pt2Pb orders antiferromagnetically at TN=2.07K, and the magnetic structure determined from these measurements features the interleaving of two orthogonal sublattices into a 5×5×1 magnetic supercell that is based on stripes with moments perpendicular to the dimer bonds, which are along (110) and (−110). Magnetic fields applied along (110) or (−110) suppress the antiferromagnetic peaks from an individual sublattice, but leave the orthogonal sublattice unaffected, evidence for the Ising character of the Yb moments in Yb2Pt2Pb that is supported by point charge calculations. Specific heat, magnetic susceptibility, and electrical resistivity measurements concur with neutron elastic scattering results that the longitudinal critical fluctuations are gapped with ΔE≃0.07meV