Heavy-fermion systems have attracted extensive attention as platforms for investigating exotic quantum phenomena, ranging from quantum criticality to unconventional superconductivity. Substantial efforts have focused on modulating quantum phases by dimensional reduction, representing a long-standing challenge for conventional heavy-fermion compounds with three-dimensional crystal and electronic structures. Here, we report the transport properties of bulk and nanoflake samples of CeSiI, a van der Waals antiferromagnet that has been established as a heavy-fermion metal. Magnetic torque and magnetoresistance measurements reveal two metamagnetic transitions at ${\mu }_{0}H\approx 2.4$ and $4.2\mathrm{T}$. Zero-field out of plane and in-plane electronic transport measurements indicate a heavy-fermion behavior with $T^2$-linear dependence on resistivity in the antiferromagnetic state. As the magnetic field increases, the antiferromagnetic state is gradually suppressed, and the resistivity deviates from the $T^2$-linear relationship simultaneously; this suggests a deeper underlying coupling between the heavy-fermion behavior and the antiferromagnetic order. These two features persist down to the nanoflakes, but the metamagnetic transitions are suppressed by proton gating. Our work establishes CeSiI as an ideal platform for investigating the interplay between Kondo screening and magnetic order in bulk crystals and as a potential building block for engineering two-dimensional heterostructures.

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• Antiferromagnetism
• Kondo effect
• 2-dimensional systems
• Layered crystals
• Two-dimensional electron system
• Resistivity measurements
• Transport techniques