Electrical resistivity measurements as a function of temperature between 1 K and 300 K were performed at various pressures up to 3 GPa on the superconducting layered compounds LnO0.5F0.5BiS2 (Ln = La, Ce). At atmospheric pressure, LaO0.5F0.5BiS2 and CeO0.5F0.5BiS2 have superconducting critical temperatures, Tc, of 3.3 K and 2.3 K, respectively. For both compounds, the superconducting critical temperature Tc initially increases, reaches a maximum value of 10.1 K for LaO0.5F0.5BiS2 and 6.7 K for CeO0.5F0.5BiS2, and then gradually decreases with increasing pressure. Both samples also exhibit transient behavior in the region between the lower Tc phase near atmospheric pressure and the higher Tc phase. This region is characterized by a broadening of the superconducting transition, in which Tc and the transition width ∆Tc are reversible with increasing and decreasing pressure. There is also an appreciable pressure-induced and hysteretic suppression of semiconducting behavior up to the pressure at which the maximum value of Tc is found. At pressures above the value at which the maximum in Tc occurs, there is a gradual decrease of Tc and further suppression of the semiconducting behavior with pressure, both of which are reversible.
Abstract. Measurements of electrical resistivity were performed between 3 and 300 K at various pressures up to 2.8 GPa on the BiS 2 -based superconductors LnO 0.5 F 0.5 BiS 2 (Ln = Pr, Nd).At lower pressures, PrO 0.5 F 0.5 BiS 2 and NdO 0.5 F 0.5 BiS 2 exhibit superconductivity with critical temperatures T c of 3.5 and 3.9 K, respectively. As pressure is increased, both compounds undergo a transition at a pressure P t from a low T c superconducting phase to a high T c superconducting phase in which T c reaches maximum values of 7.6 and 6.4 K for PrO 0.5 F 0.5 BiS 2 and NdO 0.5 F 0.5 BiS 2 , respectively. The pressure-induced transition is characterized by a rapid increase in T c within a small range in pressure of ∼0.3 GPa for both compounds. In the normal state of PrO 0.5 F 0.5 BiS 2 , the transition pressure P t correlates with the pressure where the suppression of semiconducting behaviour saturates. In the normal state of NdO 0.5 F 0.5 BiS 2 , P t is coincident with a semiconductor-metal transition. This behaviour is similar to the results recently reported for the LnO 0.5 F 0.5 BiS 2 (Ln = La, Ce) compounds. We observe that P t and the size of the jump in T c between the two superconducting phases both scale with the lanthanide element in LnO 0.5 F 0.5 BiS 2 (Ln = La, Ce, Pr, Nd).
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. ...
a b s t r a c tWe discuss several classes of conventional magnetic superconductors including the ternary rhodium borides and molybdenum chalcogenides (or Chevrel phases), and the quaternary nickel-borocarbides. These materials exhibit some exotic phenomena related to the interplay between superconductivity and long-range magnetic order including: the coexistence of superconductivity and antiferromagnetic order; reentrant and double reentrant superconductivity, magnetic field induced superconductivity, and the formation of a sinusoidally-modulated magnetic state that coexists with superconductivity. We introduce the article with a discussion of the binary and pseudobinary superconducting materials containing magnetic impurities which at best exhibit short-range ''glassy'' magnetic order. Early experiments on these materials led to the idea of a magnetic exchange interaction between the localized spins of magnetic impurity ions and the spins of the conduction electrons which plays an important role in understanding conventional magnetic superconductors. These advances provide a natural foundation for investigating unconventional superconductivity in heavy-fermion compounds, cuprates, and other classes of materials in which superconductivity coexists with, or is in proximity to, a magnetically-ordered phase.
Measurements of electrical resistivity, ρ(T ), were performed under quasi-hydrostatic pressure up to P ∼ 2.2 GPa to determine the pressure dependence of the so called "hidden order" (HO) and largemoment antiferromagnetic (LMAFM) phases for the URu2−xFexSi2 system with x = 0.025, 0.05, 0.10, 0.15, and 0.20. As the Fe concentration (x) is increased, we observed that a smaller amount of external pressure, Pc, is required to induce the HO → LMAFM phase transition. A critical pressure of Pc ∼ 1.2 GPa at x = 0.025 reduces to Pc ∼ 0 at x = 0.15, suggesting the URu2−xFexSi2 system is fully expressed in the LMAFM phase for x ≥ x * c = 0.15, where x * c denotes the ambient pressure critical concentration of Fe. Using a bulk modulus calculation to convert x to chemical pressure, P ch (x), we consistently found that the induced HO → LMAFM phase transition occurred at various combinations of xc and Pc such that P ch (xc) + Pc ≈ 1.5 GPa, where xc denotes those critical concentrations of Fe that induce the HO → LMAFM phase transition for the URu2−xFexSi2 compounds under pressure. We performed exponential fits of ρ(T ) in the HO and LMAFM phases in order to determine the pressure dependence of the energy gap, ∆, that opens over part of the Fermi surface in the transition from the paramagnetic (PM) phase to the HO/LMAFM phase at the transition temperature, T0. The change in the pressure variation of ∆(P ) at the HO → LMAFM phase transition is consistent with the values of Pc determined from the T0(P ) phase lines at the PM → HO/LMAFM transition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.