We predict that the recently discovered quasi-one dimensional superconductors, A2Cr3As3(A=K,Rb), possess strong frustrated magnetic fluctuations and are nearby a novel in-out co-planar magnetic ground state. The frustrated magnetism is very sensitive to c-axis lattice constant and can thus be suppressed by increasing pressure. Our results qualitatively explain strong non-Fermi liquid behaviors observed in the normal state of the superconductors as the intertwining between the magnetism and superconductivity can create a large quantum critical region in quasi-one dimensional systems and also suggest that the materials share similar phase diagrams and superconducting mechanism with other unconventional superconductors, such as cuprates and iron-based superconductors. 74.25.Ha, 74.20.Pq, 74.20.Rp One of major challenges in condensed matter physics is to understand the role of electron-electron correlation in unconventional superconductors. The effect of electron-electron interaction becomes more important as the dimension of a system is lowered. Indeed, many unconventional superconductors discovered in the past are quasi-two dimensional(Q2D) electron systems. The superconductivity in these unconventional superconductors appears in a vicinity to a magnetically ordered state. Magnetic fluctuations which are caused by electron-electron interaction have been widely considered to be responsible for superconductivity and many non-Fermi liquid behaviors in normal states.While there are many representatives of Q2D unconventional superconductors, it has been difficult to find one in quasi-one dimensional(Q1D) systems even if the effect of the electron-electron correlation is expected to be enhanced further. The Q1D superconductors discovered previously, including Bechgaard salts [1,2] , Tl 2 Mo 6 Se 6 [3] and Li 0.9 Mo 6 O 17 [4][5][6][7], are not attributed to 3d-orbital electrons which can exhibt strong electron-electron interaction.Very recently, two novel Q1D materials K 2 Cr 3 As 3 [8] and Rb 2 Cr 3 As 3 [9] have been synthesized and found to be superconducting below the transition temperature 6.1 K and 4.8 K respectively. The structure of A 2 Cr 3 As 3 (A=K,Rb) is characterized by one-dimensional (Cr 3 As 3 ) chains ( Fig.1(a)), which contain Cr 6 distorted octahedral clusters. The alkali metal ions are intercalated between the (Cr 3 As 3 ) chains. Both new materials show strong non-fermi liquid behaviors in normal states, as well as unconventional superconducting properties in superconducting (SC) states. Moreover, just like cuprates and iron-based superconductors, the electronic physics in these new materials are likely attributed to 3d-oribtals of Cr atoms. Therefore the material may exhibit strong magnetism and electron-electron interaction.In this paper, we show that the new materials can be a critical representative of Q1D unconventional superconductors * Electronic address: jphu@iphy.ac.cn where the superconductivity emerges in a vicinity to a novel magnetically ordered state. We predict that the materials ...

We construct minimum effective models to investigate the pairing symmetry in the newly discovered quasione-dimensional superconductor K2Cr3As3. We show that a minimum three-band model based on the d z 2 , dxy and d x 2 −y 2 orbitals of one Cr sublattice can capture the band structures near Fermi surfaces. In both weak and strong coupling limits, the standard random phase approximation (RPA) and mean-field solutions consistently yield the triplet pz-wave pairing as the leading pairing symmetry for physically realistic parameters. The triplet pairing is driven by the ferromagnetic fluctuations within the sublattice. The gap function of the pairing state possesses line gap nodes on the kz = 0 plane on the Fermi surfaces.

The new discovered iron-based superconductors have chain-like As layers. These layers generate an additional 3-dimensional hole pocket and cone-like electron pockets. The former is attributed to the Ca d and As1 pz orbitals and the latter are attributed to the anisotropic Dirac cone, contributed by As1 px and py orbitals. We find that large gaps on these pockets open in the collinear antiferromagnetic ground state of CaFeAs2, suggesting that the chain-like As layers are strongly coupled to FeAs layers. Moreover due to the low symmetry crystal induced by the As layers, the bands attributed to FeAs layers in ky = π plane are two-fold degenerate but in kx = π plane are lifted. This degeneracy is protected by a hidden symmetryΥ =TRy. Ignoring the electron cones, the materials can be well described by a six-band model, including five Fe d and As1 pz orbitals. We suggest that these new features may help us to identify the sign change and pairing symmetry in iron based superconductors.

A large anomalous Nernst effect (ANE) is crucial for thermoelectric energy conversion applications because the associated unique transverse geometry facilitates module fabrication. Topological ferromagnets with large Berry curvatures show large ANEs; however, they face drawbacks such as strong magnetic disturbances and low mobility due to high magnetization. Herein, we demonstrate that YbMnBi2, a canted antiferromagnet, has a large ANE conductivity of ~10 A m−1 K−1 that surpasses large values observed in other ferromagnets (3–5 A m−1 K−1). The canted spin structure of Mn guarantees a non-zero Berry curvature, but generates only a weak magnetization three orders of magnitude lower than that of general ferromagnets. The heavy Bi with a large spin–orbit coupling enables a large ANE and low thermal conductivity, whereas its highly dispersive px/y orbitals ensure low resistivity. The high anomalous transverse thermoelectric performance and extremely small magnetization make YbMnBi2 an excellent candidate for transverse thermoelectrics.

Half-Heusler compounds with a valence electron count of 18, including ZrNiSn, ZrCoSb, and NbFeSb, are good thermoelec-tric materials owing to favorable electronic structures. Previous computational studies had predicted a high...