Optical spectroscopy of plasmons and excitons in cuprate superconductors

An introduction is given to collective modes in layered, high Tc superconductors. An experimental demonstration is treated of the mechanism proposed by Anderson whereby photons travelling inside the superconductor become massive, when the U(1) gauge symmetry is broken in the superconductor to which the photons are coupled. Using the Ferrell-Tinkham sumrule the photon mass is shown to have a simple relation to the spectral weight of the condensate. Various forms of Josephson plasmons can exist in single-layer, and bi-layecuprates. In the bi-layer cuprates a transverse optical plasma mode can be observed as a peak in the c-axis optical conductivity. This mode appears as a consequence of the existence of two different intrinsic Josephson couplings between the CuO2 layers. It is strongly related to a collective oscillation corresponding to small fluctuations of the relative phases of the two condensates, which has been predicted in 1966 by A.J. Leggett for superconductors with two bands of charge carriers. A description is given of optical data of the high Tc cuprates demonstrating the presence of these and similar collective modes.Comment: Article for a special issue of the Journal of Superconductivity celebrating the 75th birthday of Michael Tinkham. Revtex4, 15 pages, 16 figures encapsulated postscrip

Short-range spin- and pair-correlations: a variational wave-function

A many-body wavefuction is postulated, which is sufficiently general to describe superconducting pair-correlations, and/or spin-correlations, which can occur either as long-range order or as finite-range correlations. The proposed wave-function appears to summarize some of the more relevant aspects of the rich phase-diagram of the high-Tc cuprates. Some of the states represented by this wavefunction are reviewed: For superconductivity in the background of robust anti-ferromagnetism, the Cooper-pairs are shown to be a superposition of spinquantum numbers S=0 and S=1. If the anti-ferromagnetism is weak, a continuous super-symmetric rotation is identified connecting s-wave superconductivity to anti-ferromagnetism.Comment: LaTeX, 11 pages, 3 figures in eps format references update

Treatment of International Human Rights Violations in the United States

In our day and age, the violation of human rights has become a matter of international concern. This article is focused on the sharing of those concerns by the United States, in particular as manifested by the treatment of human rights violations in the United States. Following introductory observations in Part I highlighting the special commitment of the United States to the protection of international human rights, the article will show, in Part II thereof, that in virtue of Article 6, Clause [2] of the American Constitution (the Supremacy Clause), human rights conventions are in principle self-executing in the United States.1 However, the United States invariably adds a reservation to its instruments of ratification of such conventions proclaiming that they will not be self-executing in the United States. Incorporating the provisions of human rights conventions ratified by the United States into the country’s municipal legal system therefore requires Congressional implementation legislation, which will be exemplified in Part III with reference to the Torture Convention Implementation Act of 1994. Part IV of the article is devoted to the exercise of universal jurisdiction by federal courts, in virtue of Article 1, Section (8), Clause [10] of the Constitution, to bring to justice those responsible for piracies and felonies on the High Seas and offences against the law of nations.2 In the United States, universal jurisdiction of federal courts is not confined to criminal prosecutions but has also been extended by the Alien Tort Statute to civil actions by foreign victims of a tort that constitutes a violation of the law of nations or of a treaty entered into by the United States.3 The treatment of human rights violations under the Alien Tort Statute and similar legislation is the subject-matter of Part V of this article. Some concluding observations to evaluate the above manifestations of the American commitment to human rights, notably in view of considerations based on the national interests of the United States and a perception of American exceptionalism, will bring the article to a close in Part VI thereof.http://dflsc.law.duke.edu/am201