title: Effects of two energy scales in weakly dimerized antiferromagnetic quantum spin chains.
abstract: By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)(2)P(2)O(7), the effects of two energy scales of the weakly dimerized antiferromagnetic S=1/2 Heisenberg chain are explored. The low-energy scale, given by the spin gap Delta, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing the density-matrix renormalization-group approach for transfer matrices calculations, shows that this feature originates from changes in the magnetic entropy with respect to Delta, partial differentialS(m)/partial differentialDelta. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit, where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in Delta.
authors.affiliation: Physikalisches Institut, Universität Frankfurt, D-60438 Frankfurt(M), Germany.
authors.forename: A
authors.initials: A
authors.lastname: Brühl
authors.forename: B
authors.initials: B
authors.lastname: Wolf
authors.forename: V
authors.initials: V
authors.lastname: Pashchenko
authors.forename: M
authors.initials: M
authors.lastname: Anton
authors.forename: C
authors.initials: C
authors.lastname: Gross
authors.forename: W
authors.initials: W
authors.lastname: Assmus
authors.forename: R
authors.initials: R
authors.lastname: Valenti
authors.forename: S
authors.initials: S
authors.lastname: Glocke
authors.forename: A
authors.initials: A
authors.lastname: Klümper
authors.forename: T
authors.initials: T
authors.lastname: Saha-Dasgupta
authors.forename: B
authors.initials: B
authors.lastname: Rahaman
authors.forename: M
authors.initials: M
authors.lastname: Lang