Recent Studies in Superconductivity at Extreme Pressures

Studies of the effect of high pressure on superconductivity began in 1925 with the seminal work of Sizoo and Onnes on Sn to 0.03 GPa and have continued up to the present day to pressures in the 200 - 300 GPa range. Such enormous pressures cause profound changes in all condensed matter properties, including superconductivity. In high pressure experiments metallic elements, Tc values have been elevated to temperatures as high as 20 K for Y at 115 GPa and 25 K for Ca at 160 GPa. These pressures are sufficient to turn many insulators into metals and magnetics into superconductors. The changes will be particularly dramatic when the pressure is sufficient to break up one or more atomic shells. Recent results in superconductivity to Mbar pressures wll be discussed which exemplify the progress made in this field over the past 82 years.Comment: Proceedings of the 21st AIRAPT and 45th EHPRG International Conference on High Pressure Science and Technology, Catania, Italy, Sept. 17-21, 200

NASA-FAA helicopter Microwave Landing System curved path flight test

An ongoing series of joint NASA/FAA helicopter Microwave Landing System (MLS) flight tests was conducted at Ames Research Center. This paper deals with tests done from the spring through the fall of 1983. This flight test investigated and developed solutions to the problem of manually flying curved-path and steep glide slope approaches into the terminal area using the MLS and flight director guidance. An MLS-equipped Bell UH-1H helicopter flown by NASA test pilots was used to develop approaches and procedures for flying these approaches. The approaches took the form of Straight-in, U-turn, and S-turn flightpaths with glide slopes of 6 deg, 9 deg, and 12 deg. These procedures were evaluated by 18 pilots from various elements of the helicopter community, flying a total of 221 hooded instrument approaches. Flying these curved path and steep glide slopes was found to be operationally acceptable with flight director guidance using the MLS

Studies of superconductivity and structure for CaC6 to pressures above 15 GPa

The dependence of the superconducting transition temperature Tc of CaC6 has been determined as a function of hydrostatic pressure in both helium-loaded gas and diamond-anvil cells to 0.6 and 32 GPa, respectively. Following an initial increase at the rate +0.39(1) K/GPa, Tc drops abruptly from 15 K to 4 K at 10 GPa. Synchrotron x-ray measurements to 15 GPa point to a structural transition near 10 GPa from a rhombohedral to a higher symmetry phase

Pressure-Induced Superconductivity in Sc to 74 GPa

Using a diamond anvil cell with nearly hydrostatic helium pressure medium we have significantly extended the superconducting phase diagram Tc(P) of Sc, the lightest of all transition metals. We find that superconductivity is induced in Sc under pressure, Tc increasing monotonically to 8.2 K at 74.2 GPa. The Tc(P) dependences of the trivalent d-electron metals Sc, Y, La, and Lu are compared and discussed within a simple s-d charge transfer framework.Comment: to be published in Phys. Rev. B (Brief Reports

Evolution of the Fermi surface of BiTeCl with pressure

We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeCl under applied pressures up to ~2.5 GPa. We observe two distinct oscillation frequencies, corresponding to the Rashba-split inner and outer Fermi surfaces. BiTeCl has a conduction band bottom that is split into two sub-bands due to the strong Rashba coupling, resulting in two spin-polarized conduction bands as well as a Dirac point. Our results suggest that the chemical potential lies above this Dirac point, giving rise to two Fermi surfaces. We use a simple two-band model to understand the pressure dependence of our sample parameters. Comparing our results on BiTeCl to previous results on BiTeI, we observe similar trends in both the chemical potential and the Rashba splitting with pressure.Comment: 6 pages, 5 figure

Probing the strength of infants' preference for helpers over hinderers: two replication attempts of Hamlin and Wynn (2011)

Several studies indicate that infants prefer individuals who act prosocially over those who act antisocially toward unrelated third parties. In the present study, we focused on a paradigm published by Kiley Hamlin and Karen Wynn in 2011. In this study, infants were habituated to a live puppet show in which a protagonist tried to open a box to retrieve a toy placed inside. The protagonist was either helped by a second puppet (the “Helper”), or hindered by a third puppet (the “Hinderer”). At test, infants were presented with the Helper and the Hinderer, and encouraged to reach for one of them. In the original study, 75% of 9-month-olds selected the Helper, arguably demonstrating a preference for prosocial over antisocial individuals. We conducted two studies with the aim of replicating this result. Each attempt was performed by a different group of experimenters. Study 1 followed the methods of the published study as faithfully as possible. Study 2 introduced slight modifications to the stimuli and the procedure following the guidelines generously provided by Kiley Hamlin and her collaborators. Yet, in our replication attempts, 9-month-olds’ preference for helpers over hinderers did not differ significantly from chance (62.5% and 50%, respectively, in Studies 1 and 2). Two types of factors could explain why our results differed from those of Hamlin and Wynn: minor methodological dissimilarities (in procedure, materials, or the population tested), or the effect size being smaller than originally assumed. We conclude that fine methodological details that are crucial to infants’ success in this task need to be identified to ensure the replicability of the original result