The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide superconductors whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers in a unit cell. When n=3 (the 10-3-8 ...phase), the undoped compound is an antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the undoped compound is a superconductor with the transition temperature of 26K. Here we report the results of high-pressure studies on the 10-3-8 compound obtained through a combination of in-situ resistance, magnetic susceptibility, and Hall coefficient measurements. We find that its AFM order can be suppressed completely at 3.5 GPa and then superconducting state appears in the pressure range of 3.5-7 GPa. The pressure dependence of superconducting transition temperature displays a dome-like shape.
We report experimental evidence for the connection between superconductivity and antiferromagnetism in Rb sub(0.8)Fe sub(2-y)Se sub(2-x)Te sub(x) single crystals under negative chemical pressure ...introduced by the lattice expansion of substituting Se with isovalent Te atoms. Electrical resistance and magnetic measurements in the temperature range from 4 to 600 K demonstrate that both superconducting transition temperature (T sub(c)) and the Neel temperature (T sub(N)) are suppressed continuously with the lattice expansion. When the Te concentration x in Rb sub(0.8)Fe sub(2-y)Se sub(2-x)Te sub(x) approaches 0.4, the superconductivity is completely suppressed, and the sample behaves like a semiconductor; meanwhile, the features for antiferromagnetic transition on resistance and magnetization curves disappear. Our observation suggests that the effect of negative-pressure-induced lattice expansion can be used to tune the correlativity of superconductivity and antiferromagnetism in the studied system.
A unique platform for investigating the correlation between the antiferromagnetic (AFM) and superconducting (SC) states in high temperature superconductors is created by the discovery of alkaline ...iron selenide superconductors which are composed of an AFM insulating phase and a SC phase separated spatially. Our previous studies showed that pressure can fully suppress the superconductivity of ambient-pressure superconducting phase (SC-I) and AFM order simultaneously, then induce another superconducting phase (SC-II) at higher pressure. Consequently, the connection between the two superconducting phases becomes an intriguing issue. In this study, on the basis of observing pressure-induced reemergence of superconductivity in Rb0.8Fe2-ySe2-xTex (x=0, 0.19 and 0.28) superconductors, we find that the superconductivity of the SC-I and SC-II phases as well as the AFM ordered state can be synchronously tuned by Te doping and disappear together at the doping level of x=0.4. We propose that the two superconducting phases are connected by the AFM phase, in other words, the state of long-ranged AFM order plays a role in giving rise to superconductivity of the SC-I phase, while the fluctuation state of the suppressed AFM phase drives the emergence of SC-II phase. These results comprehensively demonstrate the versatile roles of AFM states in stabilizing and developing superconductivity in the alkaline iron selenide superconductors.
We report the first observation of a pressure-induced breakdown of the 3D-DSM state in Cd3As2, evidenced by a series of in-situ high-pressure synchrotron X-ray diffraction (XRD) and single crystal ...transport measurements. We find that Cd3As2 undergoes a structural phase transition from a metallic tetragonal (T) phase in space group I41/acd to a semiconducting monoclinic (M) phase in space group P21/c at critical pressure 2.57 GPa, above this pressure, an activation energy gap appears, accompanied by distinct switches in Hall resistivity slope and electron mobility. These changes of crystal symmetry and corresponding transport properties manifest the breakdown of the 3D-DSM state in pressurized Cd3As2.
The emergence of superconductivity in the iron pnictide and cuprate high temperature superconductors usually accompanies the suppression of an antiferromagnetically (AFM) ordered state in a ...corresponding parent compound through the use of chemical doping or external pressure1-5. A great deal of effort has been made to find superconductivity in Mn-based compounds6-14, which are thought to bridge the gap between the two families of high temperature superconductors7,15,16, but long-ranged AFM order was not successfully suppressed via chemical doping in these investigations. Here we report the first observation of the pressure-induced elimination of long-ranged AFM order in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor15,17. By combining in-situ high pressure resistance and ac susceptibility measurements, we found that LaMnPO undergoes a crossover from an AFM insulating to an AFM metallic state at a pressure ~20 GPa and that the long-ranged AFM order collapses at a higher pressure ~32 GPa. Our findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.
Here, we report that K-doped BaMn2Bi2 shows no experimental evidence of superconductivity down to 1.5 K under pressures up to 35.6 GPa, however, a tetragonal to an orthorhombic phase transition is ...observed at pressure of 20 GPa. Theoretical calculations for the tetragonal and orthorhombic phases, on basis of our high-pressure XRD data, find that the AFM order is robust in both of the phases in pressurized Ba0.61K0.39Mn2Bi2. Our experimental and theoretical results suggest that the K-doped BaMn2Bi2 belongs to a strong Hunds AFM metal with a hybridization of localized spin electrons and itinerant electrons, and that its robust AFM order essentially prevents the emergence of superconductivity.
Here we show that a pressure of about 8 GPa suppresses both the vacancy order and the insulating phase, and a further increase of the pressure to about 18 GPa induces a second transition or ...crossover. No superconductivity has been found in compressed insulating 245 phase. The metallic phase in the intermediate pressure range has a distinct behavior in the transport property, which is also observed in the superconducting sample. We interpret this intermediate metal as an orbital selective Mott phase (OSMP). Our results suggest that the OSMP provides the physical pathway connecting the insulating and superconducting phases of these iron selenide materials.
We report the first experimental evidence for the intimate connection between superconductivity and antiferromagnetism in Rb0.8Fe2Se2-xTex single crystal under negative chemical pressure by ...substituting Se with isovalent Te atoms. Electrical resistance measurements in the temperature range from 4 K to 550 K demonstrate that both superconducting transition temperature (Tc) and Neel temperature (TN) were suppressed continuously with the lattice expansion. When the Te concentration x in Rb0.8Fe2Se2-xTex approaches 0.3, the superconducting transition temperature Tc is completely suppressed and the sample behaves like a semiconductor, meanwhile the characteristic peak of antiferromagnetic transition on resistance curve disappears. Our observation suggests that the pressure-induced lattice expansion can be used to tune the correlativity of superconductivity and antiferromagnetism.
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