We have found that by extensive current injection along the c-axis, the superconducting properties of Bi2Sr2CaCu2O8+δ can be changed effectively. We show that critical temperature, c-axis resistivity, and critical current of intrinsic Josephson junctions can be tuned in a large range from underdoping to extreme overdoping. This effect is reversible and persistent. Our results can be explained by trapping charges in the insulating layers, which induce a change of carrier concentration in superconducting planes. This floating gate concept can be a general property of layered materials where the insulating charge reservoir layers are separated from the conducting planes.

The characteristics of Fe-based superconductors are manifested in their electronic, magnetic properties, and pairing symmetry of the Cooper pair, but the latter remain to be explored. Usually in these materials, superconductivity coexists and competes with magnetic order, giving unconventional pairing mechanisms. We report on the results of the bulk magnetization measurements in the superconducting state and the low-temperature specific heat down to 0.4 K for BaFe 2−x Ni x As 2 single crystals. The electronic specific heat displays a pronounced anomaly at the superconducting transition temperature and a small residual part at low temperatures in the superconducting state. The normal-state Sommerfeld coefficient increases with Ni doping for x = 0.092, 0.096, and 0.10, which illustrates the competition between magnetism and superconductivity. Our analysis of the temperature dependence of the superconducting-state specific heat and the London penetration depth provides strong evidence for a two-band s-wave order parameter. Further, the data of the London penetration depth calculated from the lower critical field follow an exponential temperature dependence, characteristic of a fully gapped superconductor. These observations clearly show that the superconducting gap in the nearly optimally doped compounds is nodeless.

X-ray diffraction measurements as well as electron (scanning and transmission), optical, and atomic force microscopies are used to study the thermally induced stress relief mechanisms in coimplanted H+ and He+ ions into (001) Si substrates at moderate energies, resulting in damage layers located at ≈1.5 μm underneath the surface. By changing the implantation fluence rate from 0.25 to 1.5 μA cm−2, two distinct phenomena take place: localized blistering/exfoliations or complete surface delamination, resulting into freestanding 1.5 μm thick single crystalline Si films. The results are discussed on the basis of linear fracture mechanics arguments. Localized exfoliation is explained by means of distinct coarsening processes linking the initially formed gas filled nanosized platelets to crack structures of several micrometers in diameter. The delamination behavior is explained in terms of unstable crack propagation process triggered at a single nucleation site.

We introduce a refractive radiative transfer equation to the graphics community for the physically based rendering of participating media that have a spatially varying index of refraction. We review principles of geometric nonlinear optics that are crucial to discuss a more generic light transport equation. In particular, we present an optical model that has an integral form suitable for rendering. We show rigorously that the continuous bending of light rays leads to a nonlinear scaling of radiance. To obtain physically correct results, we build on the concept of basic radiance—known from discontinuous refraction—to conserve energy in such complex media. Furthermore, the generic model accounts for the reduction in the speed of light due to the index of refraction to render transient effects like the propagation of light echoes. We solve the refractive volume rendering equation by extending photon mapping with transient light transport in a refractive, participating medium. We demonstrate the impact of our approach on the correctness of rendered images of media that are dominated by spatially continuous refraction and multiple scattering. Furthermore, our model enables us to render visual effects like the propagation of light echoes or time-of-flight imagery that cannot be produced with previous approaches.

At any pressure sensitive quantum critical point (QCP) the thermal expansion is more singular than the specific heat leading to a divergence of the Grüneisen parameter. For a magnetic field sensitive QCP, the complementary property is the magnetic Grüneisen ratio which equals the magnetocaloric effect. Here we use both properties to investigate magnetic QCPs in different heavy fermion (HF) metals starting from CeNi 2 Ge 2 . The influence of dimensionality on quantum criticality is addressed by the comparison of cubic CeIn 3−x Sn x with layered CeMIn 5−x Sn x (M = Co, Rh) systems, in which Sn doping both acts as tuning parameter and introduces slight disorder. Near the field-tuned QCP in undoped CeCoIn 5 a crossover scale T is discovered which separates 2D (at T > T ) from 3D (at T < T ) quantum criticality. Disorder, introduced by Sn-doping, is found to increase T , stabilizing 3D behavior. We also compare the magnetic Grüneisen ratio in the approach of the field-tuned QCP in YbRh 2 Si 2 with zero-field Grüneisen parameter data on YbRh 2 (Si 1−x Ge x ) 2 (x = 0, x = 0.05). Both properties indicate quantum criticality incompatible with the predictions of the itinerant theory.