Crystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo2As2

TitleCrystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo2As2
Publication TypeJournal Article
Year of Publication2013
AuthorsPandey A, Quirinale DG, Jayasekara W, Sapkota A, Kim MG, Dhaka RS, Lee Y, Heitmann TW, Stephens PW, Ogloblichev V, Kreyssig A, McQueeney RJ, Goldman AI, Kaminski A, Harmon BN, Furukawa Y, Johnston DC
Journal TitlePhysical Review B
Date Published07
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberWOS:000322223400003
KeywordsANTIFERROMAGNET, arsenides, ba, feas, frustrated magnets, high-temperature superconductivity, LIV2O4, metals, state, Ternary

In tetragonal SrCo2As2 single crystals, inelastic neutron scattering measurements demonstrated that strong stripe-type antiferromagnetic (AFM) correlations occur at a temperature T = 5 K [Jayasekara et al., arXiv:1306.5174] that are the same as in the isostructural AFe(2)As(2) (A = Ca, Sr, Ba) parent compounds of high-T-c superconductors. This surprising discovery suggests that SrCo2As2 may also be a good parent compound for high-T-c superconductivity. Here structural and thermal expansion, electrical resistivity rho, angle-resolved photoemission spectroscopy (ARPES), heat capacity C-p, magnetic susceptibility chi, As-75 NMR, and neutron diffraction measurements of SrCo2As2 crystals are reported together with LDA band structure calculations that shed further light on this fascinating material. The c-axis thermal expansion coefficient alpha(c) is negative from 7 to 300 K, whereas alpha(a) (the a-axis thermal expansion coefficient) is positive over this T range. The rho(T) shows metallic character. The ARPES measurements and band theory confirm the metallic character and in addition show the presence of a flat band near the Fermi energy E-F. The band calculations exhibit an extremely sharp peak in the density of states D(E approximate to E-F) arising from a flat d(x2-y2) band, where the x and y axes are along the a and b axes of the Co square lattice, respectively. A comparison of the Sommerfeld coefficient of the electronic specific heat with chi(T -> 0) suggests the presence of strong ferromagnetic itinerant spin correlations, which on the basis of the Stoner criterion predicts that SrCo2As2 should be an itinerant ferromagnet, in conflict with the magnetization data. The chi(T) does have a large magnitude, but also exhibits a broad maximum at approximate to 115 K suggestive of dynamic short-range AFM spin correlations, in agreement with the neutron scattering data. The measurements show no evidence for any type of phase transition between 1.3 and 300 K and we suggest that metallic SrCo2As2 has a gapless quantum spin-liquid ground state.

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