We report a strategy to induce superconductivity in the BiS2-based compound LaOBiS2. Instead of substituting F for O, we increase the charge-carrier density (electron dope) via substitution of tetravalent Th +4 , Hf +4 , Zr +4 , and Ti +4 for trivalent La +3 . It is found that both the LaOBiS2 and ThOBiS2 parent compounds are bad metals and that superconductivity is induced by electron doping with Tc values of up to 2.85 K. The superconducting and normal states were characterized by electrical resistivity, magnetic susceptibility, and heat capacity measurements. We also demonstrate that reducing the charge-carrier density (hole doping) via substitution of divalent Sr +2 for La +3 does not induce superconductivity.
A quantum spin liquid is a state of matter where unpaired electrons' spins, although entangled, do not show magnetic order even at the zero temperature. The realization of a quantum spin liquid is a long-sought goal in condensed-matter physics. Although neutron scattering experiments on the two-dimensional spin-1/2 kagome lattice ZnCu 3 (OD) 6 Cl 2 and triangular lattice YbMgGaO 4 have found evidence for the hallmark of a quantum spin liquid at very low temperature (a continuum of magnetic excitations), the presence of magnetic and non-magnetic site chemical disorder complicates the interpretation of the data. Recently, the three-dimensional Ce 3+ pyrochlore lattice Ce 2 Sn 2 O 7 has been suggested as a clean, effective spin-1/2 quantum spin liquid candidate, but evidence of a spin excitation continuum is still missing. Here, we use thermodynamic, muon spin relaxation and neutron scattering experiments on single crystals of Ce 2 Zr 2 O 7 , a compound isostructural to Ce 2 Sn 2 O 7 , to demonstrate the absence of magnetic ordering and the presence of a spin excitation continuum at 35 mK. With no evidence of oxygen deficiency and magnetic/non-magnetic ion disorder seen by neutron diffraction and diffuse scattering measurements, Ce 2 Zr 2 O 7 may be a three-dimensional pyrochlore lattice quantum spin liquid material with minimum magnetic and non-magnetic chemical disorder.
Thermal expansion, electrical resistivity, magnetization, and specific heat measurements were performed on URu 2−x FexSi 2 single crystals for various values of Fe concentration x in both the hidden-order (HO) and large-moment antiferromagnetic (LMAFM) regions of the phase diagram. Our results show that the paramagnetic (PM) to HO and LMAFM phase transitions are manifested differently in the thermal expansion coefficient. The uniaxial pressure derivatives of the HO/LMAFM transition temperature T 0 change dramatically when crossing from the HO to the LMAFM phase. The energy gap also changes consistently when crossing the phase boundary. In addition, for Fe concentrations at xc ≈ 0.1, we observe two features in the thermal expansion upon cooling, one that appears to be associated with the transition from the PM to the HO phase and another one at lower temperature that may be due to the transition from the HO to the LMAFM phase.hidden order | URu 2 Si 2 | thermal expansion T he search for the order parameter of the hidden-order (HO) phase in URu2Si2 has attracted an enormous amount of attention for the past three decades (1-4). The small antiferromagnetic moment of only ∼0.03 µB /U found in the HO phase is too small to account for the entropy of ∼ 0.2Rln(2) derived from the second-order mean-field Bardeen-Copper-Schrieffer (BCS)-like specific heat anomaly associated with the HO transition that occurs below T0 = 17.5 K (2, 5). A first-order transition from the HO phase to a large-moment antiferromagnetic (LMAFM) phase occurs under pressure at a critical pressure Pc that lies in the range 0.5-1.5 GPa (6-9). Many studies suggest that the HO and LMAFM phases are intimately related and that a comprehensive investigation of both phases will be useful in unraveling the nature of the order parameter of the HO phase (10). Although the order parameters are presumably different in the HO and LMAFM phases, the two phases exhibit almost indistinguishable transport and thermodynamic properties. This behavior has been referred to as "adiabatic continuity" (11).We have recently demonstrated that tuning URu2Si2 by substitution of Fe for Ru affords an opportunity to study both the HO and LMAFM phases and the HO-LMAFM phase transition at atmospheric pressure (12)(13)(14). Specifically, the substitution of the smaller Fe ions for Ru ions in URu2Si2 appears to act as a chemical pressure such that the temperature vs. Fe concentration (T − x) phase diagram for the URu2−x FexSi2 system resembles the temperature vs. applied pressure (T − P) phase diagram for URu2Si2. In a previous study, neutron diffraction measurements on single-crystal samples of URu2−x FexSi2 for various values of x (13) revealed that the magnetic moment increases abruptly to a maximum value at x = 0.1, above which it then decreases slowly with x, supporting the interpretation that tuning by Fe substitution acts as a chemical pressure.On the other hand, the phase boundary between the HO and LMAFM phases has not been definitively determined for the URu2−x FexSi2 system. ...
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