Phase diagram of Na x CoO 2 ͑x տ 0.71͒ has been reinvestigated using electrochemically fine-tuned single crystals. Both phase-separation and staging phenomena as a result of sodium multivacancy cluster ordering have been found. Phase-separation phenomenon is observed in the narrow ranges of 0.76Շ x Շ 0.82 and 0.83Շ x Շ 0.86. While x = 0.820 shows A-type antiferromagnetic ͑A-AF͒ ordering below 22 K, x = 0.833 is confirmed to have a magnetic ground state of A-AF ordering below ϳ8 K and is only reachable through slow cooling. In addition, x = 0.859 is found to be responsible for the highest A-AF transition temperature at about 29 K. Staging model based on ordered stacking of multivacancy layers is proposed to explain the hysteretic behavior and A-AF correlation length for x ϳ0.82-0.86.

We report a detailed characterization of the noncentrosymmetric superconductor Re 24 Ti 5 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 Re 24 Ti 5 crystallizes in the α-Mn structure. All measured quantities demonstrate a bulk superconducting transition at T c = 5.8 K. Our low-temperature specific heat data measured down to 0.5 K yield a Sommerfeld coefficient γ = 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 gap /k B = 10.6 K. This value gives a ratio of 2 /k B T c = 3.68, higher than the value of 3.5 predicted from BCS theory. On this basis, we conclude that the noncentrosymmetric Re 24 Ti 5 compound can be characterized as a moderately coupled BCS-type superconductor. Furthermore, the obtained parameters from the present study of Re 24 Ti 5 were compared to those of the isostructural compound Re 23.8 Nb 5.2 , indicating the similarity between both systems.

Erratum: NbS 3 : A unique quasi-one-dimensional conductor with three charge density wave transitions [Phys. Rev. B 95, 035110 (2017)]

We report an observation of a first-order phase transition in Ce 3 Co 4 Sn 13 by means of the specific heat, electrical resistivity, Seebeck coefficient, and thermal conductivity, as well as 59 Co nuclear magnetic resonance (NMR) measurements. The phase transition has been evidenced by marked features near T o 155 K in all measured physical quantities except for magnetic susceptibility. This excludes a magnetic origin for the observed phase transition. In addition, x-ray diffraction results below and above T o confirm the absence of a structural change, suggesting that the peculiar phase transition is possibly related to an electronic origin and/or electron-lattice coupling such as the formation of a charge density wave (CDW). As a matter of fact, the disappearance of the double-peak feature of 59 Co NMR central lines below T o can be realized as the spatial modulation of the electric field gradient due to incommensurate CDW superlattices. Also, a distinct peak found in the spin-lattice relaxation rate near T o manifests a phase transition and its feature can be accounted for by the thermally driven normal modes of the CDW. From the NMR analyses, we obtained a consistent picture that the change of electronic structures below T o is mainly due to the weakening of p-d hybridization. Such an effect could result in possible electron-lattice instability and, thus, the formation of a CDW state in Ce 3 Co 4 Sn 13 .

Through transport, compositional and structural studies, we review the features of the chargedensity wave (CDW) conductor of NbS3 (phase II). We highlight three central results: 1) In addition to the previously reported CDW transitions at TP 1 = 360 K and TP 2 = 150 K, another CDW transition occurs at a much higher temperature TP 0 = 620-650 K; evidence for the non-linear conductivity of this CDW is presented. 2) We show that CDW associated with the TP 2 -transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. 3) We show exceptional coherence of the TP 1-CDW at room-temperature. Additionally, we report on the effects of uniaxial strain on the CDW transition temperatures and transport.