The 12%-S doped FeSe system has a high Tc of 30 K at a pressure of 3.0 GPa. We have successfully investigated its microscopic properties for the first time via 77 Se-NMR measurements under pressure. The antiferromagnetic (AFM) fluctuations at the optimal pressure (∼ 3 GPa) exhibited unexpected suppression compared with the AFM fluctuations at ambient pressure, even though the optimal pressure is close to the phase boundary of the AFM phase induced at the high-pressure region. In addition, we revealed that the SC phase at an applied field of 6.02 T exhibited a remarkable double-dome structure in the pressure-temperature phase diagram, unlike the SC phase at zero field.
An experimental approach was proposed for the measurement of the surface potential (SP) induced on an insulator surface during ion irradiation by ion scattering spectroscopy (ISS). The resultant ISS spectra obtained for a MgO thin film of 600nm thickness on a Si substrate under 950eV He+ irradiation revealed that the surface is positively charged by approximately 230V. In addition, the onset energy of a secondary ion peak indicated a SP of approximately 205V. The present results confirmed that ISS is an effective technique for measuring the SP during ion irradiation.
An iron-based superconductor LaFeAsO1−xHx (0 ≤ x ≤ 0.6) undergoes two antiferromagnetic (AF) phases upon H doping. We investigated the second AF phase (x=0.6) using NMR techniques under pressure. At pressures up to 2 GPa, the ground state is a spin-density-wave state with a large gap; however, the gap closes at 4.0 GPa, suggesting a pressure-induced quantum critical point. Interestingly, the gapped excitation coexists with gapless magnetic fluctuations at pressures between 2 and 4 GPa. This coexistence is attributable to the lift up of the dxy orbital to the Fermi level, a Lifshitz transition under pressure.PACS numbers:
We performed [Formula: see text]-nuclear magnetic resonance measurements on [Formula: see text] ([Formula: see text] = 0.12 and 0.23). We found from the relaxation time [Formula: see text] that nematicity and antiferromagnetic fluctuations show cooperative coupling.
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