Magnetic Instability of Pr3Ru4Sn13

We report on the quantum criticality of Pr$_3$Ru$_4$Sn$_{13}$ revealed by our new material research. Pr$_3$Ru$_4$Sn$_{13}$ has been synthesized by flux growth and characterized by single X-ray, powder X-ray, and powder neutron diffraction measurements. The compound adopts a Yb$_3$Rh$_4$Sn$_{13}$-type structure with a cubic Pm$\bar{3}$n. From the magnetization at 1 T, the effective magnetic moment was estimated to be 3.58 $\mu _B$ per Pr$^{3+}$, suggesting that the magnetism is mainly contributed by Pr$^{3+}$ ions. The specific heat and magnetization show an anomaly at $T_{N} = 7.5$ ~ K owing to the phase transition. The muon spin rotation and relaxation ($\mu$SR) time spectra exhibit clear oscillations below $T_N$. This suggests that the phase is magnetically ordered. The volume fraction of the magnetic phase estimated from the initial asymmetry is around ten percent. In addition, spin fluctuations were observed at low temperatures. These results provide microscopic evidence that the material is closest to the antiferromagnetically quantum critical point with a partial order among Pr$_3$$T_4$Sn$_{13}$ ($T=$ Co, Ru, Rh).Comment: 14 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp

Direct spectroscopic evidence for phase competition between the pseudogap and superconductivity in Bi2_{2}Sr2_{2}CaCu2_{2}O8+δ_{8+{\delta}}

In the high-temperature ($T_{c}$) cuprate superconductors, increasing evidence suggests that the pseudogap, existing below the pseudogap temperature $T$*, has a distinct broken electronic symmetry from that of superconductivity. Particularly, recent scattering experiments on the underdoped cuprates have suggested that a charge ordering competes with superconductivity. However, no direct link of this physics and the important low-energy excitations has been identified. Here we report an antagonistic singularity at $T_{c}$ in the spectral weight of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+{\delta}}$ as a compelling evidence for phase competition, which persists up to a high hole concentration $p$ ~ 0.22. Comparison with a theoretical calculation confirms that the singularity is a signature of competition between the order parameters for the pseudogap and superconductivity. The observation of the spectroscopic singularity at finite temperatures over a wide doping range provides new insights into the nature of the competitive interplay between the two intertwined phases and the complex phase diagram near the pseudogap critical point.Comment: 17 pages with 4 figures and supplementary information with 18 pages with 1 table and 4 figure

Possible future upgrades of the direct-geometry chopper spectrometer 4SEASONS

4SEASONS is a direct geometry time-of-flight spectrometer installed in the Materials and Life Science Experimental Facility, the Japan Proton Accelerator Research Complex. It is used to study atomic and spin dynamics in the energy range of 100 meV to 102 meV. Since more than a decade has crossed after the first inelastic scattering experiment, it is essential to consider upgrading the instrument to improve its flexibility and performance. In this paper, we discuss the possible medium-term upgrades of key components of the instrument like the chopper system, which are achievable with the current technology and at reasonable cost. Herein, we demonstrated that 4SEASONS can improve the energy resolution by a factor of two, remove frame overlap of adjacent incident energies, significantly improve the asymmetry in the pulse shape, and increase the flux by a factor of ∼1.5, without major technical difficulties

Q Dependence of Magnetic Resonance Mode on FeTe0.5Se0.5 Studied by Inelastic Neutron Scattering

Inelastic neutron scattering measurements have been performed on a superconducting single crystal FeTe 0.5 Se 0.5 to examine the Q -dependent enhancement of the dynamical structure factor, S ( Q , E ) , from Q = (0, 0) to ( π , π ), including ( π , 0) in the superconducting state. In most of iron-based superconductors, S ( Q , E ) is enhanced at Q = ( π , 0), where the “magnetic resonance mode” is commonly observed in the unfolded Brillouin zone. Constant-E cuts of S ( Q , E ) suggest that the enhancement is not uniform in the magnetic excitation, and limited around Q = ( π , 0). This result is consistent with the theoretical simulation of the magnetic resonance mode due to the Bardeen–Cooper–Schrieffer coherence factor with the sign-reversing order parameter of s ± wave

Evidence of electronic polarization of the As ion in the superconducting phase of F-doped LaFeAsO

Understanding the nature of superconductivity in iron-based compounds is essential in the development of new strategies to increase Tc. Using a charge density analysis based on synchrotron radiation X-ray powder diffraction data, we found that the charge carriers only accumulated in the iron layer of the superconducting phase of LaFeAsO1 − xFx at low temperatures. Analysis of the electrostatic potential distribution revealed the concerted enhancement of the electronic polarization of the As ions and the carrier redistribution. This suggests that the enhanced electronic polarization of the As ion plays an important role in inducing high Tc superconductivity, and that the polaron concept, which has been previously regarded as an untenable mechanism, should be reconsidered for the description of the iron–arsenide superconducting phase