Specific heat study of the field-induced magnetic ordering in the spin-gap system<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">TlCuCl</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Specific heat measurements have been performed in the coupled dimer system ${\mathrm{TlCuCl}}_{3},$ which has a singlet ground state with the excitation gap $\ensuremath{\Delta}\ensuremath{\simeq}7.5$ K. The cusplike anomaly indicative of the three-dimensional magnetic ordering was clearly observed in magnetic fields higher than the critical field ${H}_{\mathrm{g}}$ corresponding to the gap $\ensuremath{\Delta}.$ The phase boundary determined by the present specific heat measurements coincides with that determined by previous magnetization measurements. The phase boundary can be described by the power law $[{H}_{\mathrm{c}}(T)\ensuremath{-}{H}_{\mathrm{g}}]\ensuremath{\propto}{T}^{\ensuremath{\varphi}}$ with $\ensuremath{\varphi}=2.1(1).$ This result supports the magnon Bose condensation picture for the field-induced magnetic ordering in ${\mathrm{TlCuCl}}_{3}$ [Nikuni et al., Phys. Rev. Lett. 84, 5868 (2000)].

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