Insulator–metal transitions in Pr0.7Ca0.3MnO3 induced by a magnetic field

A magnetic field induced insulator to metal transition has been observed in both polycrystalline and single crystals samples of Pr0.7Ca0.3MnO3. Application of a magnetic field leads to a first-order phase transition from an insulating to a conducting state at low temperatures. The hysteresis associated with this transition allows the resistivity at 4 K to be varied by more than eight orders of magnitude depending on the field history of the sample

Probing the superconducting ground state of the rare-earth ternary boride superconductors RRRuB2_2 (RR = Lu,Y) using muon-spin rotation and relaxation

The superconductivity in the rare-earth transition metal ternary borides $R$RuB$_2$ (where $R$ = Lu and Y) has been investigated using muon-spin rotation and relaxation. Measurements made in zero-field suggest that time-reversal symmetry is preserved upon entering the superconducting state in both materials; a small difference in depolarization is observed above and below the superconducting transition in both compounds, however this has been attributed to quasistatic magnetic fluctuations. Transverse-field measurements of the flux-line lattice indicate that the superconductivity in both materials is fully gapped, with a conventional s-wave pairing symmetry and BCS-like magnitudes for the zero-temperature gap energies. The electronic properties of the charge carriers in the superconducting state have been calculated, with effective masses $m^*/ m_\mathrm{e} =$ $9.8\pm0.1$ and $15.0\pm0.1$ in the Lu and Y compounds, respectively, with superconducting carrier densities $n_\mathrm{s} =$ ($2.73\pm0.04$) $\times 10^{28}$ m$^{-3}$ and ($2.17\pm0.02$) $\times 10^{28}$ m$^{-3}$. The materials have been classified according to the Uemura scheme for superconductivity, with values for $T_\mathrm{c}/T_\mathrm{F}$ of $1/(414\pm6)$ and $1/(304\pm3)$, implying that the superconductivity may not be entirely conventional in nature.Comment: 8 pages, 8 figure

Crystal growth and properties of the non-centrosymmetric superconductor, Ru7B3

We describe the crystal growth of high quality single crystals of the non-centrosymmetric superconductor, Ru7B3 by the floating zone technique, using an optical furnace equipped with xenon arc lamps. The crystals obtained are large and suitable for detailed measurements, and have been examined using x-ray Laue patterns. The superconducting properties of the crystals obtained have been investigated by magnetisation and resistivity measurements. Crystals have also been grown starting with enriched 11B isotope, making them suitable for neutron scattering experiments.Comment: 4 pages, 5 figures. Accepted for publication in Journal of Crystal Growt

Using negative muons as a probe for depth profiling silver Roman coinage

Debasement of silver Roman coins is a well-known phenomenon and understanding the quality of ancient silver coinages can provide an idea about the underlying fiscal condition of the issuing states. These coins are made from a silver-copper alloy, the surfaces of which were deliberately enhanced at the mints by a process of surface-enrichment to give them the appearance of being made of pure silver. Therefore, any surface analysis would provide a composition of the silver-copper alloy that would not be representative of the original alloy from which the coin blank was made; the result would be too high in silver. However, the bulk of the sample, the interior, should provide a composition that is true to the original alloy. Elemental analysis using negative muons has been used to provide a depth dependent compositional, completely non-destructive analysis of a silver-copper alloy denarius of the empress Julia Domna datable to 211–217 CE. The composition of the coin, beyond the surface enrichment layer, is 51 ± 1.8 % copper and 49 ± 1.9% silver, taken at a muon depth of 402 ± 61 µm. The surface enrichment layer is approximately 190 µm thick

Structure and superconductivity of two different phases of Re3W

Two superconducting phases of Re(3)W have been found with different physical properties. One phase crystallizes in a noncentrosymmetric cubic (alpha-Mn) structure and has a superconducting transition temperature T(c) of 7.8 K. The other phase has a hexagonal centrosymmetric structure and is superconducting with a T(c) of 9.4 K. Switching between the two phases is possible by annealing the sample or remelting it. The properties of both phases of Re(3)W have been characterized by powder neutron diffraction, magnetization, and resistivity measurements. The temperature dependences of the lower and upper critical fields have been measured for both phases. These are used to determine the penetration depths and the coherence lengths for these systems

Evidence for a hybridization gap in noncentrosymmetric CeRuSi3

Inelastic neutron scattering (INS) and specific heat measurements have been performed on the intermediate valence compound CeRuSi3, which is isostructural to the noncentrosymmetric pressure-induced superconductors CeRhSi3, CeIrSi3, and CeCoGe3. INS measurements at 7 K reveal a broad peak at (58.5 ± 1.4) meV, while at 300 K, broad quasielastic scattering is observed. This indicates a large Kondo temperature of TK ~ 680 K. The magnetic contribution to the specific heat (Cmag) has a value of γ = 62.5(1) mJ/molK2 at low temperatures and above about 100 K can be well accounted for by the Coqblin-Schrieffer model with a characteristic temperature of T0 = 680 K, which is further evidence that CeRuSi3 is in the intermediate valence regime

Unconventional superconductivity in La7Ir3 revealed by muon spin relaxation : introducing a new family of noncentrosymmetric superconductor that breaks time-reversal symmetry

The superconductivity of the noncentrosymmetric compound La7Ir3 has been investigated using muon spin rotation and relaxation (μSR). Zero-field measurements reveal the presence of spontaneous static or quasi-static magnetic fields below the superconducting transition temperature Tc = 2:25 K - a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic, and that the pairing symmetry of the superconducting electrons is predominantly s-wave with an enhanced binding strength. The results indicate that the superconductivity in La7Ir3 may be unconventional, and paves the way for further studies of this family of materials

Suppression of magnetic excitations near the surface of the topological Kondo insulator SmB6

We present a detailed investigation of the temperature and depth dependence of the magnetic properties of 3D topological Kondo insulator SmB6 , in particular near its surface. We find that local magnetic field fluctuations detected in the bulk are suppressed rapidly with decreasing depths, disappearing almost completely at the surface. We attribute the magnetic excitations to spin excitons in bulk SmB6 , which produce local magnetic fields of about ~1.8 mT fluctuating on a time scale of ~60 ns. We find that the excitonic fluctuations are suppressed when approaching the surface on a length scale of 40-90 nm, accompanied by a small enhancement in static magnetic fields. We associate this length scale to the size of the excitonic state.Comment: 5 pages, 5 figures, accepted for publication as a Rapid Communication in Phys. Rev.

Coexistence of type-I and type-II superconductivity signatures in ZrB12 probed by muon spin rotation measurements

Superconductors usually display either type-I or type-II superconductivity and the coexistence of these two types in the same material, for example, at different temperatures, is rare in nature. We employed the muon spin rotation (μSR) technique to unveil the superconducting phase diagram of the dodecaboride ZrB12 and obtained clear evidence of both type-I and type-II characteristics. Most important, we found a region showing unusual behavior where the usually mutually exclusive μSR signatures of type-I and type-II superconductivity coexist. We reproduced that behavior in theoretical modeling that required taking into account multiple bands and multiple coherence lengths, which suggests that material has one coherence length larger and another smaller than the magnetic field penetration length (the type-1.5 regime). At stronger fields, a footprint of the type-II mixed state showing square flux-line lattice was also obtained using neutron diffraction

High quality single crystals of the SrR2O4 family of frustrated magnets

Large high quality single crystals of several compounds of the new family of frustrated magnetic oxides SrR2O4 where R = Dy, Er, Ho and their nonmagnetic analogues with R = Lu, Y have been synthesized by the floating zone technique. The magnetic rare earth ions in these compounds are linked to each other through a network of hexagons and triangles reminiscent of the honeycomb lattice. Initial characterization measurements show that geometrical frustration plays an important role in the formation of the magnetic ground states in these systems. The single crystals grown are suitable for more detailed investigations, especially those using neutron scattering techniques