We report the discovery of bulk superconductivity (SC) at 6.1 K in a quasi-one-dimensional (Q1D) chromium pnictide K2Cr3As3 which contains [(Cr3As3) 2− ]∞ double-walled subnano-tubes with face-sharing Cr 6/2 (As 6/2 ) octahedron linear chains in the inner (outer) wall. The material has a large electronic specific-heat coefficient of 70∼75 mJ K −2 mol −1 , indicating significantly strong electron correlations. Signature of non-Fermi liquid behavior is shown by the linear temperature dependence of resistivity in a broad temperature range from 7 to 300 K. Unconventional SC is preliminarily manifested by the estimated upper critical field exceeding the Pauli limit by a factor of three to four. The title compound represents a rare example that possibly unconventional SC emerges in a Q1D system with strong electron correlations.

Since the discovery of high-temperature superconductivity (SC) in quasi-two-dimensional copper oxides, a few layered compounds, which bear similarities to the cuprates, have also been found to host the unconventional SC. Our recent observation of SC at 6.1 K in correlated electron material K2Cr3As3 represents an obviously different paradigm, primarily because of its quasi-one-dimensional ( The revolutionary discovery of high-temperature SC in cuprates in the 1980s [1] has inspired the unprecedented enthusiasm to explore new superconductors, especially in transition-metal compounds. The continuous efforts over a quarter century have led to the discoveries of unconventional SC in a few classes of materials including iron pnictides [2], which bear two fundamental similarities to the cuprates -strong electron correlations and quasi two dimensionality. It is of great interest to explore possible unconventional SC in a Q1D material with significant electron correlations.Our recent observation of SC at T c = 6.1 K in K 2 Cr 3 As 3 realized the above possibility [3]. Unconventional SC was preliminarily evidenced by the peculiar properties including linear temperature dependence of resistivity in the normal state and extremely high upper critical field exceeding the Pauli limit by a factor of four [3] [7][8][9][10][11] in the normal state is evidenced by the NQR measurements [6]. So far, all the investigations [3-6] consistently point to the unconventional SC in the Q1D Crbased material.It is known that Peierls transition easily occurs in Q1D metallic systems [11,12], which prevents the appearance of SC [13]. The interchain coupling serves as a crucial control parameter, thus it is of interest to explore other possible analogues with varying interchain coupling strength. By the replacement of K + with Rb +

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We report the physical properties and electronic structure calculations of a layered chromium oxypnictide, Sr2Cr3As2O2, which crystallizes in a Sr2Mn3As2O2-type structure containing both CrO2 planes and Cr2As2 layers. The newly synthesized material exhibits a metallic conduction with a dominant electron-magnon scattering. Magnetic and specific-heat measurements indicate at least two intrinsic magnetic transitions below room temperature. One is an antiferromagnetic transition at 291 K, probably associated with a spin ordering in the Cr2As2 layers. Another transition is broad, occurring at around 38 K, and possibly due to a short-range spin order in the CrO2 planes. Our first-principles calculations indicate predominant two-dimensional antiferromagnetic exchange couplings, and suggest a KG-type (i.e. K2NiF4 type for CrO2 planes and G type for Cr2As2 layers) magnetic structure, with reduced moments for both Cr sublattices. The corresponding electronic states near the Fermi energy are mostly contributed from Cr-3d orbitals which weakly (modestly) hybridize with the O-2p (As-4p) orbitals in the CrO2 (Cr2As2) layers. The bare bandstructure density of states at the Fermi level is only ∼1/4 of the experimental value derived from the lowtemperature specific-heat data, consistent with the remarkable electron-magnon coupling. The title compound is argued to be a possible candidate to host superconductivity.