C. N. Kuo

Weakly-correlated nodeless superconductivity in single crystals of Ca3Ir4Sn13 and Sr3Ir4Sn13 revealed by critical fields, Hall effect, and magnetoresistance measurements

We report a study of single crystal Ca3Ir4Sn13 (CIS) and Sr3Ir4Sn13 (SIS) by measuring the longitudinal and Hall resistivities, upper and lower critical fields and magnetoresistance, as well as the magnetization. The sign change in the Hall coefficient observed on both the CIS and SIS provides direct evidence for the Fermi surface reconstructing during the superlattice phase transition. Both materials are of current interest due to indications of superconductivity associated with charge-density-wave (CDW) ordering. Observations of the diamagnetic feature and the lower critical field Hc1(T) in both CIS and SIS can be realized by means of the nodeless single-gap BCS theory. In addition, a weak electronic correlation in both systems has been revealed by the small values of the spin exchange energy, upper critical field and Δ(0)/kBTc ratio, derived respectively from the normal-state Hall effect, resistive transition and temperature-dependent Hc1. It is noticeable that the magnetoresistance of SIS shows a rapid increase below T′xa0∼xa040 K, following Kohler’s scaling rule. The results of the magnetic susceptibility and Hall coefficient also exhibit anomalous features near T′. With respect to these observations, this suggests that the existence of an additional phonon mode with energy of about 4.0 meV in SIS is responsible for the presence of lattice instability toward a phase transition.

Investigation of normal and superconducting states in noncentrosymmetric Re24Ti5

We report a detailed characterization of the noncentrosymmetric superconductor Re24Ti5 using powder x-ray diffraction (XRD), magnetic susceptibility, electrical resistivity, thermal conductivity, Seebeck coefficient, and specific heat measurements. Rietveld refinement of powder XRD data confirms that Re24Ti5 crystallizes in the -Mn structure. All measured quantities demonstrate a bulk superconducting transition at TcD 5:8 K. Our low-temperature specific heat data measured down to 0.5 K yield a Sommerfeld coefficient D 111:8 mJ mol 1 K 2 , which implies a high density of states at the Fermi level. Moreover, the electronic specific heat in the superconducting state was found to obey a typical s-wave expression, revealing a single gap1=kBD 10:6 K. This value gives a ratio of 21=kBTcD 3:68, higher than the value of 3.5 predicted from BCS theory. On this basis, we conclude that the noncentrosymmetric Re24Ti5 compound can be characterized as a moderately coupled BCS-type superconductor. Furthermore, the obtained parameters from the present study of Re24Ti5 were compared to those of the isostructural compound Re23:8Nb5:2, indicating the similarity between both systems. (Some figures may appear in colour only in the online journal)

Dynamics of phonons in Sr3Ir4Sn13: an experimental study by ultrafast spectroscopy measurements

We report a study of ultrafast dynamics of photoexcited electrons and phonons in Sr3Ir4Sn13 using dual-color transient reflectivity change () measurements. Time resolved optical spectroscopy of collective excitations reveal the marked features near its structural phase transition temperature K. Two distinctive oscillatory timescales in have been clearly resolved. The rapid THz-range oscillations are attributed to the dynamics of the optical phonons which strongly correlate to the structural phase transition. The slow GHz-range oscillatory phenomenon which only occurs below about 150 K is associated with the dynamic response of the longitudinal-acoustic phonons. These low-energy phonons show a softening feature on approaching the transition temperature, also indicating a strong relevance to the structural phase transition. The information that we demonstrated would provide a deeper understanding of the structural phase transition in Sr3Ir4Sn13.

Spin gap behavior inCu2Sc2Ge4O13studied usingSc45nuclear magnetic resonance

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Electronic and atomic structures of the Sr 3 Ir 4 Sn 13 single crystal: A possible charge density wave material

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Electrical and thermal transport properties of Nb- and Ru-substituted Mo3Al2C superconducting compounds

Sc nuclear magnetic resonance (NMR) study on the quasi-one-dimensional compound Cu

Effect of partial La filling on the local electronic properties of LaxCo4Sb12 studied using 59Co NMR

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First-order phase transition in the ternary sulfide NiV2S4

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Optical spectroscopy study of charge density wave order in Sr3Rh4Sn13 and (Sr0.5Ca0.5)3Rh4Sn13

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Nodeless superconducting gap in the caged-type superconductors Y5Rh6Sn18 and Lu5Rh6Sn18

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