Understanding the competition between superconductivity and other ordered states (such as antiferromagnetic or charge-density-wave (CDW) state) is a central issue in condensed matter physics. The recently discovered layered kagome metal AV3Sb5 (A = K, Rb, and Cs) provides us a new playground to study the interplay of superconductivity and CDW state by involving nontrivial topology of band structures. Here, we conduct high-pressure electrical transport and magnetic susceptibility measurements to study CsV3Sb5 with the highest Tc of 2.7 K in AV3Sb5 family. While the CDW transition is monotonically suppressed by pressure, superconductivity is enhanced with increasing pressure up to P1 ≈ 0.7 GPa, then an unexpected suppression on superconductivity happens until pressure around 1.1 GPa, after that, Tc is enhanced with increasing pressure again. The CDW is completely suppressed at a critical pressure P2 ≈ 2 GPa together with a maximum Tc of about 8 K. In contrast to a common dome-like behavior, the pressure-dependent Tc shows an unexpected double-peak behavior. The unusual suppression of Tc at P1 is concomitant with the rapidly damping of quantum oscillations, sudden enhancement of the residual resistivity and rapid decrease of magnetoresistance. Our discoveries indicate an unusual competition between superconductivity and CDW state in pressurized kagome lattice.

The observation of quantized anomalous Hall conductance in the forced ferromagnetic state of MnBi2Te4 thin flakes has attracted much attentions. However, strong magnetic field is needed to fully polarize the magnetic moments due to the large antiferromagnetic interlayer exchange coupling. Here, we reported the magnetic and electrical transport properties of the magnetic van der Waals MnBi2Te4(Bi2Te3)n (n=1,2) single crystals, in which the interlayer antiferromagnetic exchange coupling is greatly suppressed with the increase of the separation layers Bi2Te3. MnBi4Te7 and MnBi6Te10 show weak antiferromagnetic transition at 12.3 and 10.5 K, respectively. The ferromagnetic hysteresis was observed at low temperature for both of the crystals, which is quite crucial for realizing the quantum anomalous Hall effect without external magnetic field. Our work indicates that MnBi2Te4(Bi2Te3)n (n=1,2) provide ideal platforms to investigate the rich topological phases with going to their 2D limits.

A novel fulleride Sm 6 C 60 has been synthesized using high temperature solid state reaction. The Rietveld refinement on high resolution synchrotron Xray powder diffraction data shows that Sm 6 C 60 is isostructural with bodycentered cubic A 6 C 60 (A=K, Ba). Raman spectrum of Sm 6 C 60 is similar to that of Ba 6 C 60 , and the frequencies of two A g modes in Sm 6 C 60 are nearly the same as that of Ba 6 C 60 , suggesting that Sm is divalent and hybridization between C 60 molecules and the Sm atom could exist in Sm 6 C 60 . Resistivity measurement shows a weak T-linear behavior above 180 K, the transport at low temperature is mainly dominated by granular-metal theory.PACS numbers: 71.20. Tx, 67.57.Hi Alkali intercalation into the C 60 host lattice is a successful technique for synthesizing new fullerides.1 Hereafter, an extensive research has been concentrated on the intercalation of a wide variety of atoms or molecules in the C 60 solids. Intercalation of alkali metals in the C 60 solids yields various structural compounds A x C 60 (x=1, 3, 4, 6) with different physical property.2-6 Among these, the superconducting compounds, A 3 C 60 , has attracted considerable interest.3 In this system, the fcc lattice parameter and band filling are tunable by changing the intercalants, T c goes up with increasing lattice parameter, 7 while it rapidly decreases when the nominal valence ( n ) shifts from the half-filling n=3 of t 1u band. 8The study was then extended to the alkali-earth series of AE x C 60 , 9-12 the electrons are introduced by intercalation of alkali-earth metals into the next lowest unoccupied molecular orbital with t 1g symmetry. The superconducting compounds with various structures and critical temperatures were prepared (Ca 5 C 60 , Ba 4 C 60 , Sr 4 C 60 ).9,13 Such tolerance for the C 60 molecular valence in t 1g superconductors makes a striking contrast with the strict constraint for the valence state in the case of t 1u superconductors.The rare-earth metals were also intercalated into the C 60 solids, but only one phase RE 2.75 C 60 (RE=Yb, Sm) was discovered so far.14,15 In this system, the basic structure of 1

A series of new stable fullerides A 3 C 70 (A ) Sm, Ba) has been synthesized using solid-state reactions. The structure of Sm 3 C 70 has been identified to be monoclinic by simulation of synchrotron powder diffraction data. The structure of Ba 3 C 70 is derived from the A15 structure adopted by Ba 3 C 60 . The low symmetry relative to C 60 fullerides could be an important factor in the absence of superconductivity in C 70 fullerides. The electronic transport can be explained by a variable-range hopping mechanism for A 3 C 70 (A ) Ba, Sm) samples, while the transport for Sm x C 70 (x > 3) samples appears to be dominated by weak localization (WL) theory.