title: Frustrated cuprate route from antiferromagnetic to ferromagnetic spin-1/2 Heisenberg chains: Li2ZrCuO4 as a missing link near the quantum critical point.
abstract: From thermodynamics, local spin density approximation+Hubbard U studies and exact diagonalizations of a five-band Hubbard model on CuO2 stripes we find that Li2ZrCuO4 (Li2CuZrO4 in traditional notation) is close to a ferromagnetic critical point. Analyzing its susceptibility chi(T) and specific heat cp(T,H) within a Heisenberg model, we show that the ratio of the 2nd to the 1st neighbor exchange integrals alpha=-J2/J1 approximately 0.3 is close to the critical value alphac=1/4. Comparing with related chain cuprates we explain the rather strong field dependence of cp, the monotonic downshift of the peak of chi(T), and its increase for alpha-->alphac+0.
authors.affiliation: Leibniz-Institut für Festkörper-und Werkstoffforschung (IFW) Dresden, P.O. Box 270116, D-01171 Dresden, Germany. s.l.drechsler@ifw-dresden.de
authors.forename: S-L
authors.initials: SL
authors.lastname: Drechsler
authors.forename: O
authors.initials: O
authors.lastname: Volkova
authors.forename: A N
authors.initials: AN
authors.lastname: Vasiliev
authors.forename: N
authors.initials: N
authors.lastname: Tristan
authors.forename: J
authors.initials: J
authors.lastname: Richter
authors.forename: M
authors.initials: M
authors.lastname: Schmitt
authors.forename: H
authors.initials: H
authors.lastname: Rosner
authors.forename: J
authors.initials: J
authors.lastname: Málek
authors.forename: R
authors.initials: R
authors.lastname: Klingeler
authors.forename: A A
authors.initials: AA
authors.lastname: Zvyagin
authors.forename: B
authors.initials: B
authors.lastname: Büchner