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Geometrical frustration is known to significantly modify the properties of many materials. Pyrochlore spin ice and hexagonal water ice are canonical systems that show the effects of frustration in both heat capacity and dynamical response. In both instances, microscopic ordering principles on the lattice lead to a macroscopic degeneracy of configurations. This degeneracy in spin ice may also be modified or lifted by lattice imperfections, external pressure, or magnetic field. Unfortunately, these effects are difficult to model or predict, because existing experimental techniques cannot directly observe the local ordering, near lattice defects or otherwise. To address this long outstanding problem, recent interest has focused on fabricating systems that allow the effects of frustration to be physically modeled and the resulting local ...
Geometric frustration is a phenomenon where a crystalline material cannot satisfy all of its competing interactions, which can drastically change the behavior of a material. When water freezes into solid ice, the hydrogen atom positions are geometrically frustrated due to different interactions among neighboring oxygen atoms. Frustration is not limited to electrostatic interactions, though. Magnetic spin ice mimics the crystal structure and, therefore, the frustration of water ice. However, a problem with the spin ices is that the details of the magnetic state cannot be imaged which makes the dynamics difficult to probe. In 2006, a model system known as “artificial” spin ice was created to alleviate these problems. The artificial spin ices are also geometrically frustrated, but they are easier to fabricate, and the intera...
Silicon-based anode materials are an attractive candidate to replace today's widely-utilized graphitic electrodes for lithium-ion batteries because of their high gravimetric energy density (3572 mAh/g vs. 372 mAh/g for carbon) and relatively low working potential (~ 0.5V vs. Li/Li+). However, their commercial realization is still far away because of the structural instabilities associated with huge volume changes of ~300% during charge-discharge cycles. Recently, it has been proposed that silicon nanowires and other related one-dimensional nanostructures could be used as lithium storage materials with greatly enhanced storage capacities over that for graphite in the next generation of lithium-ion batteries. However, the studies to date have shown that the nanomaterials, while better, are still not good enough to withstand a large numb...
Since early days of their discovery, it has been realized that Carbon Nanotubes (CNTs) have an unusually high thermal conductivity. Unfortunately, the amount of heat they can transfer from one medium to another can be limited by their thermal contact resistance, Rc, which in the worst case can result in thermally insulating bulk materials. Prior studies on individual nanotubes have reached various disparate conclusions, partly because many techniques employed for measuring such small samples rely on uncharacterized heat sources thus leaving fundamental uncertainties in the measurements. This has caused concerns that the true potential of these extraordinary thermal conductors will remain untapped. Relying on solid to liquid phase transition of sub-200nm Indium islands for thermometry, we report direct measurement of Rc by employing a...
The ability to tune the thermal resistance of carbon nanotube mechanical supports from insulating to conducting could permit the next generation of thermal management devices. Here, we demonstrate fabrication techniques for carbon nanotube supports that realize either weak or strong thermal coupling, selectively. Direct imaging by in-situ electron thermal microscopy shows that the thermal contact resistance of a nanotube weakly-coupled to its support is greater than 250 K*m/W and that this value can be reduced to 4.2(+5.6/-2.1) K*m/W by imbedding the nanotube in metal contacts.
Artificial spin ice has become a valuable tool for understanding magnetic interactions on a microscopic level. The strength in the approach lies in the ability of a synthetic array of nanoscale magnets to mimic crystalline materials, composed of atomic magnetic moments. Unfortunately, these nanoscale magnets, patterned from metal alloys, can show substantial variation in relevant quantities such as coercive field, with deviations up to 6%. By carefully studying the reversal process of artificial kagome ice, we can directly measure the distribution of coercivities, and by switching from disconnected islands to a connected structure, we find that the coercivity distribution can achieve a deviation of only 3.3%. These narrow deviations should allow the observation of behavior that mimics canonical spin-ice materials more closely.
Comment: 10 pp., 5 fig. cond-mat/0606258 was split into two papers to clarify their separate stories. cond-mat/0606258v2 treats the effect of C60 intercalation on transport in nanotubes. 0704.3641 is on Kondo physics in a nanotube in B-field. We now note: the splitting of Kondo resonances with B-field is sub-linear at low field, in qualitative agreement with theories
Comment: 1 PDF file, incl. 17 pages manuscript plus 6 pages Supplementary Discussion v2: Add corresponding author asterisk and acknowledgement
Comment: 19 pages, focus issue of New J. Phys. on artificial frustrated systems, minor clarifications requested by referee
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