Magnetic Breakdown and Topology in the Kagome Superconductor CsV_{3}Sb_{5} under High Magnetic Field.

The recently discovered layered kagome metals of composition AV_{3}Sb_{5} (A=K, Rb, Cs) exhibit a complex interplay among superconductivity, charge density wave order, topologically nontrivial electronic band structure and geometrical frustration. Here, we probe the electronic band structure underlying these exotic correlated electronic states in CsV_{3}Sb_{5} with quantum oscillation measurements in pulsed fields up to 86 T. The high-field data reveal a sequence of magnetic breakdown orbits that allows the construction of a model for the folded Fermi surface of CsV_{3}Sb_{5}. The dominant features are large triangular Fermi surface sheets that cover almost half the folded Brillouin zone. These sheets have not yet been detected in angle resolved photoemission spectroscopy and display pronounced nesting. The Berry phases of the electron orbits have been deduced from Landau level fan diagrams near the quantum limit without the need for extrapolations, thereby unambiguously establishing the nontrivial topological character of several electron bands in this kagome lattice superconductor.

Evidence for unconventional superconductivity and nontrivial topology in PdTe.

PdTe is a superconductor with Tc ~ 4.25 K. Recently, evidence for bulk-nodal and surface-nodeless gap features has been reported in PdTe. Here, we investigate the physical properties of PdTe in both the normal and superconducting states via specific heat and magnetic torque measurements and first-principles calculations. Below Tc, the electronic specific heat initially decreases in T3 behavior (1.5 K < T < Tc) then exponentially decays. Using the two-band model, the superconducting specific heat can be well described with two energy gaps: one is 0.372 meV and another 1.93 meV. The calculated bulk band structure consists of two electron bands (α and ß) and two hole bands (γ and η) at the Fermi level. Experimental detection of the de Haas-van Alphen (dHvA) oscillations allows us to identify four frequencies (Fα = 65 T, Fß = 658 T, Fγ = 1154 T, and Fη = 1867 T for H // a), consistent with theoretical predictions. Nontrivial α and ß bands are further identified via both calculations and the angle dependence of the dHvA oscillations. Our results suggest that PdTe is a candidate for unconventional superconductivity.

Coexistence of Bulk-Nodal and Surface-Nodeless Cooper Pairings in a Superconducting Dirac Semimetal.

The interplay of nontrivial topology and superconductivity in condensed matter physics gives rise to exotic phenomena. However, materials are extremely rare where it is possible to explore the full details of the superconducting pairing. Here, we investigate the momentum dependence of the superconducting gap distribution in a novel Dirac material PdTe. Using high resolution, low temperature photoemission spectroscopy, we establish it as a spin-orbit coupled Dirac semimetal with the topological Fermi arc crossing the Fermi level on the (010) surface. This spin-textured surface state exhibits a fully gapped superconducting Cooper pairing structure below T_{c}∼4.5 K. Moreover, we find a node in the bulk near the Brillouin zone boundary, away from the topological Fermi arc. These observations not only demonstrate the band resolved electronic correlation between topological Fermi arc states and the way it induces Cooper pairing in PdTe, but also provide a rare case where surface and bulk states host a coexistence of nodeless and nodal gap structures enforced by spin-orbit coupling.

Mn-induced spin glass behavior in metallic Ir3Sn7-xMnx.

Transition metal stannides are usually semiconductors with a narrow band gap. We report experimental investigation on metallic Ir3Sn7-xMnx(x= 0 and 0.56). Single crystal x-ray diffraction refinement indicates that Ir3Sn7-xMnxcrystals form a cubic structure (space groupIm3̄m) with the lattice parametera= 9.362(4) Å forx= 0 and 9.328(6) Å forx= 0.56. The electrical resistivity shows metallic behavior between 2 K and 300 K withT2dependence atT< 30 K forx= 0, reflecting the Fermi-liquid ground state. While Ir3Sn7exhibits weak diamagnetism, partial substitution of Sn by Mn results in spin glass behavior in Ir3Sn7-xMnxbelowTg∼ 13 K forx= 0.56. Remarkably, an upturn in the resistivity is observed inx= 0.56 below ∼2Tg, suggesting strong spin fluctuation. This fluctuation is suppressed by the application of magnetic field, which is reflected in the observation of negative magnetoresistance. The unusual properties that emerge due to Mn doping are discussed.

Quantum oscillations with angular dependence in PdTe2single crystals.

The layered transition-metal dichalcogenide PdTe2has been discovered to possess bulk Dirac points as well as topological surface states. By measuring the magnetization (up to 7 T) and magnetic torque (up to 35 T) in single crystalline PdTe2, we observe distinct de Haas-van Alphen (dHvA) oscillations. Eight frequencies are identified withH||c, with two low frequencies (Fα= 8 T andFß= 117 T) dominating the spectrum. The effective masses obtained by fitting the Lifshitz-Kosevich (LK) equation to the data aremα*=0.059m0andmß*=0.067m0wherem0is the free electron mass. The corresponding Landau fan diagrams allow the determination of the Berry phase for these oscillations resulting in values of ∼0.67πfor the 3D α band (hole-type) (down to the 1st Landau level) and ∼0.23π-0.73πfor the 3D ß band (electron-type) (down to the 3rd Landau level). By investigating the angular dependence of the dHvA oscillations, we find that the frequencies and the corresponding Berry phase (ΦB) vary with the field direction, with a ΦB∼ 0 whenHis 10°-30° away from theabplane for both α and ß bands. The multiple band nature of PdTe2is further confirmed from Hall effect measurements.

Imidazolium-dysprosium-based magnetic NanoGUMBOS for isolation of hemoglobin.

A novel imidazolium-dysprosium-based magnetic nanomaterial, i.e. [C16mim]5[Dy(SCN)8] nanoGUMBOS (nanomaterials fabricated from a group of uniform material based on organic salts), was prepared using a facile method for selective hemoglobin (Hb) isolation. In this nanomaterial, the imidazolium cation serves as a selective Hb affinity group, while dysprosium contributes paramagnetic properties. Through a combination of the advantages of ionic liquids, magnetic adsorbent, and nanoscale solid phase extraction, [C16mim]5[Dy(SCN)8] nanoGUMBOS exhibit great selectivity toward Hb and a favorable extraction efficiency of 95.4% when 1 mL of 100 µg/mL Hb solution is processed with 0.6 mg of [C16mim]5[Dy(SCN)8] nanoGUMBOS. As the Hb concentration increased to 800 µg/mL, the adsorption capacity approached ∼840 µg/mg. The adsorbed protein is recovered with an elution efficiency of 87% by using 1% SDS solution. This novel nanoGUMBOS solid-phase extraction procedure was successfully applied to selective isolation of Hb from human whole blood and verified using SDS-PAGE. This simple strategy is a novel approach towards fabrication and use of a nanoadsorbent for selective isolation of proteins.