Author
Roger W. Cohen
Bio: Roger W. Cohen is an academic researcher from Princeton University. The author has contributed to research in topics: Superconductivity & Electrical resistivity and conductivity. The author has an hindex of 11, co-authored 16 publications receiving 1221 citations.
Papers
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470 citations
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186 citations
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153 citations
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152 citations
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TL;DR: In this article, the experimental results for superconductivity in single-crystal lattice-transformation lattices were compared with the predictions of simple one-dimensional band models.
Abstract: The elastic moduli ${c}_{11}$, ${c}_{12}$, and ${c}_{44}$ and the magnetic susceptibility $\ensuremath{\chi}$ of single-crystal ${\mathrm{Nb}}_{3}$Sn have been measured as a function of temperature below 300 K. Detailed comparison is made between the experimental results and the predictions of simple one-dimensional band models. It is found that the behavior of the elastic moduli ${c}_{11}$ and ${c}_{12}$ above and below the cubic-tetragonal transformation at 45 K is well accounted for by the band model with an effective Fermi temperature of 80 K. Unlike the case of ${\mathrm{V}}_{3}$Si, the modulus ${c}_{44}$ is observed to undergo a considerable softening at low temperatures. This softening is not predicted by the theory. The susceptibility displays the predicted maximum near the lattice-transformation temperature. However, the decrease of $\ensuremath{\chi}$ in the tetragonal state, associated with a drop in the electronic density of states, is not nearly as large as expected. Furthermore, the cubic-state $\ensuremath{\chi}$ data indicate a much larger Fermi temperature (230 K) than is obtained from the ${c}_{11}$ and ${c}_{12}$ data. We review these anomalies in terms of available band-structure calculations. The implications of our experimental results for superconductivity in ${\mathrm{Nb}}_{3}$Sn are discussed.
87 citations
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TL;DR: This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskiteOxides, metal nitrides, silicides, germanides, and 2D materials such as graphene.
Abstract: Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.
1,836 citations
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TL;DR: In this article, stand-off interferometric imaging and sensing for the detection of explosives, weapons and drugs is emphasized, and future prospects of terahertz technology are discussed.
Abstract: Over the past 5 years, there has been a significant interest in employing terahertz (THz) technology, spectroscopy and imaging for security applications. There are three prime motivations for this interest: (a) THz radiation can detect concealed weapons since many non-metallic, non-polar materials are transparent to THz radiation; (b) target compounds such as explosives and illicit drugs have characteristic THz spectra that can be used to identify these compounds and (c) THz radiation poses no health risk for scanning of people. In this paper, stand-off interferometric imaging and sensing for the detection of explosives, weapons and drugs is emphasized. Future prospects of THz technology are discussed.
1,604 citations
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TL;DR: Transparent conductors (TCs) have a multitude of applications for solar energy utilization and for energy savings, especially in buildings as discussed by the authors, which leads naturally to considerations of spectral selectivity, angular selectivity, and temporal variability of TCs, as covered in three subsequent sections.
1,471 citations
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TL;DR: In this article, the transition from the metallic regime to the dielectric regime (10−50 A size isolated metal particles in an insulator continuum) is associated with the breaking up of a metal, where the volume fraction of metal, x, was varied from x = 1 to x = 0.05.
Abstract: Granular metal films (50–200,000 A thick) were prepared by co-sputtering metals (Ni, Pt, Au) and insulators (SiO2, Al2O3), where the volume fraction of metal, x, was varied from x = 1 to x = 0.05. The materials were characterized by electron micrography, electron and X-ray diffraction, and measurements of composition, density and electrical resistivity at electric fields e up to 106 V/cm and temperatures T in the range of 1.3 to 291 K. In the metallic regime (isolated insulator particles in a metal continuum) and in the transition regime (metal and insulator particles in a metal continuum) and in the transition regime (metal and insulator labyrinth structure) the conduction is due to percolation with a percolation threshold at x⋍0.5. Tunnelling measurements on superconductor-insulator-granular metal junctions reveals that the transition from the metallic regime to the dielectric regime (10–50 A size isolated metal particles in an insulator continuum) is associated with the breaking up of a metal ...
1,088 citations
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922 citations