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Proc Natl Acad Sci U S A ; 116(23): 11201-11206, 2019 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-30975759


The magnetoresistance (MR) of a material is typically insensitive to reversing the applied field direction and varies quadratically with magnetic field in the low-field limit. Quantum effects, unusual topological band structures, and inhomogeneities that lead to wandering current paths can induce a cross-over from quadratic to linear MR with increasing magnetic field. Here we explore a series of metallic charge- and spin-density-wave systems that exhibit extremely large positive linear MR. By contrast to other linear MR mechanisms, this effect remains robust down to miniscule magnetic fields of tens of Oersted at low temperature. We frame an explanation of this phenomenon in a semiclassical narrative for a broad category of materials with partially gapped Fermi surfaces due to density waves.

J Phys Chem B ; 118(47): 13453-7, 2014 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-25157644


Neutron diffraction patterns for deuterated poly-N,N,-dimethylacrylamide (PDMAA) hydrogels were measured from 10 to 300 K to investigate the structure and properties of water in the gels. Diffraction peaks observed below 250 K indicate the existence of ice in the hydrogels. Some diffraction peaks from the ice are at lower diffraction angles than those in ordinary hexagonal ice (Ih). These shifts in peaks indicate that the lattice constants of the a and c axes in the ice are about 0.29 and 0.3% higher than those in ice Ih, respectively. The results show that bulk low-density ice can exist in PDMAA hydrogels. The distortions in the lattice structure of ice imply significant interactions between water molecules and the surrounding polymer chains, which play an important role in the chemical and mechanical properties of the hydrogel.

Phys Rev Lett ; 109(26): 267208, 2012 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-23368614


Spin dynamics in the new Kondo insulator compound CeRu2Al10 has been studied using unpolarized and polarized neutron scattering on single crystals. In the unconventional ordered phase forming below T0=27.3 K, two excitation branches are observed with significant intensities, the lower one of which has a gap of 4.8±0.3 meV and a pronounced dispersion up to ≈8.5 meV. Comparison with random-phase approximation magnon calculations assuming crystal-field and anisotropic exchange couplings captures major aspects of the data, but leaves unexplained discrepancies, pointing to a key role of direction-specific hybridization between 4f and conduction band states in this compound.