Mazin and Singh argue that the observed peaks in the Fourier transformed spectroscopic maps in Fe(Se,Te) (1) may not be related to the quasi-particle interference (QPI) but would be attributed to the Bragg peaks associated with underlying chalcogen lattice and surface-induced spin-density wave (SDW) (2). They point out that: (i) the observed peaks at q 2 and q 3 are too sharp to be ascribed to the QPI, (ii) q 3 is located at the Bragg point of the chalcogen lattice, (iii) if SDW is induced at the surface and if such an SDW triggers a surface reconstruction, Bragg peak would appear at q 2 , (iv) magnetic field would suppress both superconductivity and SDW, giving rise to the enhancement of the Bragg peak at q 3 at the superconducting (SC) gap energy and suppression of the Bragg peak at q 2 , respectively. We show that these arguments are not relevant in the present case.First, the observed peaks which have been discussed in Ref. 1 are not as sharp as Bragg peak. It is true that q 3 is located at the Bragg point of the chalcogen lattice but the QPI signal is distinct from the lattice Bragg peak. In Fig. 1, we show linecuts from the Fourier-transformed conductance-ratio map Z(q, E), in which QPI peaks appear (1), along the line which passes both q 2 and q 3 . Linecut from the Fourier-transformed topographic image (Fig. 1A of Ref. 1) is also shown to give an idea of the sharpness of the Bragg peak. In the absence of magnetic field (black lines), both peaks at q 2 and q 3 in Z(q, E) are much broader than the Bragg peak. Bragg-like sharp feature emerges at q 3 at high energies but near the SC-gap energy (1 ~ 3 meV), only broad feature dominates. Indeed, the widths of the peaks are comparable to 20 % of the Brillouin zone dimension of 2π/a where a is the inter-chalcogen distance (an arrow in Fig. 1A), as suggested by Mazin and Singh (2).When magnetic field is applied (red lines in Fig. 1A), Bragg-like sharp feature grows at q 3 . Note that the field enhancement of this Bragg-like peak persists well above the SC-gap energy, which clearly suggests that the enhancement can not be explained by the suppression of the SC quasi-particle peak alone. On the contrary, pre-existing broad peak is strongly enhanced only near the SC-gap energy, suggesting that it is related to superconductivity. Namely, features at q 3 consist of two components, a sharp Bragg-like peak and a broad peak. What we ascribed to the QPI peak in Ref. 1 is the latter.Surface reconstruction triggered by surface-induced SDW is an interesting proposal. However, there is no evidence that such a reconstruction or SDW are really induced at the

The crystal and magnetic structures of polycrystalline BiCoO 3 have been determined by the Rietveld method from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO 3 (space group P4mm; Z ) 1; a ) 3.72937(7) Å and c ) 4.72382(15) Å at room temperature; tetragonality c/a ) 1.267) is isotypic with BaTiO 3 and PbTiO 3 in the whole temperature range. BiCoO 3 is an insulator with a Ne ´el temperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagation vector of k ) ( 1 / 2 , 1 / 2 , 0). In this model, magnetic moments of Co 3+ ions are parallel to the c direction and align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagnetically along the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300 K are 3.24(2)µ B and 2.93(2)µ B , respectively. The structure refinements revealed no deviation from stoichiometry in BiCoO 3 . BiCoO 3 decomposed in air above 720 K to give Co 3 O 4 and sillenite-like Bi 25 -CoO 39 .

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Neutron diffraction experiments are reported on Ca(3)CoRhO(6) which consists of ferromagnetic Ising spin chains on a triangular lattice. It was first confirmed from temperature dependence of the (110) peak intensity that Ca(3)CoRhO(6) realizes a partially disordered antiferromagnetic state, where 2/3 of the ferromagnetic chains order antiferromagnetically with each other and the remaining 1/3 are left incoherent with the other chains. The 1/3 incoherent ferromagnetic Ising chains freeze to maintain a disordered state at lower temperatures. This compound is successfully discussed as a candidate of a nonequilibrium one-dimensional Ising model.

Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe0.6Se0.4(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV (~8 K) above EF at the Γ-point, which shows a sharp superconducting coherence peak with gap formation below Tc. The estimated superconducting gap Δ and Fermi energy indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.

The crystal structure change of the solid solution BiCo1-xFexO3 was investigated in order to determine the phase boundary between tetragonal BiCoO3 and rhombohedral BiFeO3. It was found that BiCo1-xFexO3 with x = 0 to 0.6 had tetragonal BiCoO3 structures, while those with x = 0.8 to 1 had rhombohedral BiFeO3 structures at room temperature. The monoclinic √2a ×√2a ×a phase was found for the x = 0.7 sample. The tetragonal-to-cubic phase transition was first observed at around 700–850 °C in Bi-based perovskite for the x = 0.8 sample.

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We investigate LiVS2 and LiVSe2 with a triangular lattice as itinerant analogues of LiVO2, known for the formation of valence bond solid (VBS) state out of S = 1 frustrated magnet. LiVS2, which is located at the border between a metal and a correlated insulator, shows a first ordered transition from a paramagnetic metal to a VBS insulator at Tc ∼ 305 K upon cooling. The presence of VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of VBS state. We argue that the high temperature metallic phase of LiVS2 has a pseudo-gap, likely originating from the VBS fluctuation. LiVSe2 was found to be a paramagnetic metal down to 2 K. A question that arises is whether or not similar melting of the VBS state and appearance of exotic metallic phases can occur in inorganic frustrated systems. In the inorganic systems, however, application of an external pressure is expected not to melt but to stabilize VBS due to a predominant volume effect. In CuIr 2 S 4 , the lattice shrinks appreciably in the VBS perhaps due to the formation of strongly bonded singlet molecules and the VBS can be stabilized through -pV (p : pressure, V : volume) term in the corresponding free energy [11][12]. Effects of negative pressure on the VBS states of inorganic systems, on the other hand, have not been investigated so far.The inorganic LiVO 2 in which the magnetic V 3+ ions (3d 2 , S = 1) form a triangular lattice is known to be a paramagnetic insulator with strong antiferromagnetic interactions between the localized S = 1 moments at high temperatures. Upon cooling, at T c ∼ 500 K, LiVO 2 exhibits a first ordered phase transition to a VBS state with a characteristic spin gap of ∼ 1600 K, evidenced by the formation of vanadium trimers. With this system, one can apply "negative" pressure by replacing oxygens with larger anions such as S and Se [13,14,16]. More over, the negative pressure may increase the overlap between V 3d and p-orbital (O 2p, S 3p, and Se 4p), and increase the electronic band width. Thus, this vanadium-based triangular system provides a good opportunity to study effects of negative pressure on VBS states in inorganic materials.In this Letter, we demonstrate that LiVS 2 is indeed an itinerant analogue of LiVO 2 with suppressed VBS. We found that in LiVS 2 a phase transition from a paramagnetic metal to a trimer VBS insulator occurs at T c ∼ 305 K that is lower than that of LiVO 2 . In LiVSe 2 with highest negative pressure, the phase transition is suppressed down to 2 K. In the high temperature metallic phase of LiVS 2 , strong temperature dependence of the bulk susceptibility, χ, was observed, which is similar to the pseudo-gap behavior found in underdoped superconducting cuprates. We argue this is an evidence for a pseudo-gap formation by short-range spin singlet fluctuations in the paramagnetic metallic phase of LiVS 2 .Powder samples of LiVS 2 , LiVSe 2 and their solid solution LiVS 2−x Se x were prepared by a soft-chemical method followed by a solid-state reactio...