Article
Using magnetostriction to measure the spinspin correlation function and magnetoelastic coupling in the quantum magnet NiCl$_2$4SC(NH$_2$)$_2$
06/2007;
Source: arXiv

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ABSTRACT: Magnetostriction and thermal expansion of the spinladder compound piperidinium copper bromide (C5H12N)2CuBr4 are analyzed in detail. We find perfect agreement between experiments and the theory of a twoleg spinladder 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 spinspin correlation functions, which we compute with quantum Monte Carlo, allows us to reconstruct the magnetoelastic couplings of (C5H12N)2CuBr4 . We especially focus on the quantum critical behavior near the two critical magnetic fields Hc1 and Hc2 , which is characterized by strong singularities rooted in the low dimensionality of the critical spin system. Extending our discussion in Lorenz [ Phys. Rev. Lett. 100, 067208 (2008)], we show explicitly that the thermal expansion near the upper critical field Hc2 is quantitatively described by a parameterfree theory of onedimensional, 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 chi , which diverges as chi˜1/T at the critical fields and thus leads to a strong softening of the crystal.Physical review. B, Condensed matter 06/2008; 77(23). DOI:10.1103/PhysRevB.77.235113 · 3.66 Impact Factor
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