Gr{ü}neisen parameter of quantum magnets with spin gap

Abstract

Using Hartree-Fock-Bogoliubov (HFB) approach we obtained analytical expressions for thermodynamic quantities of the system of triplons in spin gapped quantum magnets such as magnetization, heat capacity and the magnetic Gr{ü}neisen parameter ${\Gamma }_H$. Near the critical temperature, ${\Gamma }_H$ is discontinuous and changes its sign upon the Bose-Einstein condensation (BEC) of triplons. On the other hand, in the widely used Hartree-Fock-Popov (HFP) approach there is no discontinuity neither in the heat capacity nor in the Gr{ü}neisen parameter. We predict that in the low-temperature limit and near the critical magnetic field $H_c$, ${\Gamma }_H$ diverges as ${\Gamma }_H\sim 1/T^2$, while it scales as ${\Gamma }_H\sim 1/(H-H_c)$ as the magnetic field approaches the quantum critical point at $H_c$.

Extended by comparision of HFB and HFP approximations

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• Critical behavior of Tan's contact for bosonic systems with a fixed chemical potential
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