  The entire magnetization process of TlCuCl$_3$ has been experimentally
investigated up to 100 T employing the single-turn technique. The upper
critical field $H_{c2}$ is observed to be 86.1 T at 2 K. A convex slope of the
$M$-$H$ curve between the lower and upper critical fields ($H_{c1}$ and
$H_{c2}$) is clearly observed, which indicates that a particle-hole symmetry is
broken in TlCuCl$_3$. By quantum Monte Carlo simulation and the bond-operator
theory method, we find that the particle-hole symmetry breaking results from
strong inter-dimer interactions.

Strongly Correlated Electrons