Abstract
Magnetostriction and thermal expansion of the spin-ladder compound piperidinium copper bromide are analyzed in detail. We find perfect agreement between experiments and the theory of a two-leg spin-ladder Hamiltonian for more than a decade in temperature and in a wide range of magnetic fields. Relating the magnetostriction along different crystallographic directions to two static spin-spin correlation functions, which we compute with quantum Monte Carlo, allows us to reconstruct the magnetoelastic couplings of . We especially focus on the quantum critical behavior near the two critical magnetic fields and , which is characterized by strong singularities rooted in the low dimensionality of the critical spin system. Extending our discussion in Lorenz [ et al. Phys. Rev. Lett. 100, 067208 (2008)], we show explicitly that the thermal expansion near the upper critical field is quantitatively described by a parameter-free theory of one-dimensional, nonrelativistic fermions. We also point out that there exists a singular quantum critical correction to the elastic moduli. This correction is proportional to the magnetic susceptibility , which diverges as at the critical fields and thus leads to a strong softening of the crystal.
1 More- Received 7 March 2008
DOI:https://doi.org/10.1103/PhysRevB.77.235113
©2008 American Physical Society