Significance Modest magnetic fields above ≈ 22 T in the underdoped cuprates were argued to destroy superconductivity and reveal a conventional metallic pseudogap ground state that hosts quantum oscillations. We perform high-magnetic field electrical resistivity and magnetic torque measurements using low temperatures and small applied measurement currents to reveal instead an unconventional quantum vortex matter ground state that persists beyond the highest static magnetic fields. An alternative model is required to explain the coexistence of quantum oscillations with a robust d -wave superconducting gap in the newly uncovered quantum vortex matter ground state.

In most strongly correlated electron systems superconductivity appears nearby a magnetic quantum critical point (QCP) which is believed to cause unconventional behaviors. In order to explore this physics, we present here a study of the heavy-fermion superconductors CeIrSi3 and CeRhSi3 carried out using a newly developed system for high-resolution magnetic penetration-depth measurements under pressure. Superconductivity in CeIrSi3 shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi3 does not possess a T = 0 quantum phase transition and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that in these compounds unconventional superconducting behaviors are rather connected with the coexisting antiferromagnetic order. This study provides another viewpoint on the interplay of superconductivity, magnetism, and quantum criticality in CeIrSi3 and CeRhSi3 and maybe in other heavy fermions.

Superconductivity and magnetism are mutually exclusive in most alloys and elements, so it is striking that superconductivity emerges around a magnetic quantum critical point (QCP) in many strongly correlated electron systems (SCES). In the latter case superconductivity is believed to be unconventional and directly influenced by the QCP. However, experimentally unconventional superconductivity has neither been established nor directly been linked to any mechanism of the QCP. Here we report measurements in the heavy-fermion superconductors CeIrSi$_3$ and CeRhSi$_3$. The measurements were performed with a newly developed system, first of its kind, that allows high-resolution studies of the superconducting gap structure under pressure. Superconductivity in CeIrSi$_3$ shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi$_3$ does not possess an obvious pressure-tuned QCP and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that unconventional behaviours may be connected with the coexisting antiferromagnetic order. This study provides a new viewpoint on the interplay of superconductivity and magnetism in SCES.

We present a magnetic-penetration-depth study on polycrystalline and granular samples of SrPtAs, a pnictide superconductor with a hexagonal structure containing PtAs layers that individually break inversion symmetry (local noncentrosymmetry). Compact samples show a clear-cut $s$-wave-type BCS behavior, which we consider to be the intrinsic penetration depth of SrPtAs. Granular samples display a sample-dependent second diamagnetic drop, attributed to the intergrain coupling. Our experimental results point to a nodeless isotropic superconducting energy gap in SrPtAs, which puts strong constraints on the driven mechanism for superconductivity and the order parameter symmetry of this compound.

We measured the temperature dependence of the magnetic penetration depth of La3Pd4Si4 down to 0.02 T-c. We observe a temperature- independent behaviour below 0.25 T-c, which is firm evidence for a nodeless superconducting gap in this material. The data display a very small anomaly around 1 K which we attribute to the possible presence of a superconducting impurity phase. The superfluid density is well described by a two- phase model, considering La3Pd4Si4 and the impurity phase. The present analysis suggests that the superconducting energy gap of La3Pd4Si4 is isotropic, as expected for conventional BCS superconductors.

There are estimated to be more than 20,000 species of plants in Venezuela, of which more than 1500 are used for medicinal purposes by indigenous and local communities. Only a relatively small proportion of these have been evaluated in terms of their potential as antitumor agents. In this study, we screened 308 extracts from 102 species for cytostatic and cytotoxic activity against a panel of six tumor cell lines using a 24‐h sulphorhodamine B assay. Extracts from Clavija lancifolia , Hamelia patens , Piper san‐vicentense , Physalis cordata , Jacaranda copaia , Heliotropium indicum , and Annona squamosa were the most cytotoxic, whereas other extracts from Calotropis gigantea , Hyptis dilatata , Chromolaena odorata , Siparuna guianensis , Jacaranda obtusifolia , Tapirira guianensis , Xylopia aromatica , Protium heptaphyllum , and Piper arboreum showed the greatest cytostatic activity. These results confirm previous reports on the cytotoxic activities of the abovementioned plants as well as prompting further studies on others such as C. lancifolia and H. dilatata that have not been so extensively studied. Copyright © 2012 John Wiley & Sons, Ltd.