In this study, the metamagnetic transitions in the novel spin-triplet superconductor UTe2 are investigated based on the recently developed simultaneous measurements of magnetization and sample temperature for the applied field along the orthorhombic b-axis and close to the  direction, where reentrant superconductivity (RSC) is detected below and above the first-order metamagnetic transition field Hm. Combining Maxwell’s relation and the Clausius–Clapeyron equation, we obtain the field dependence of the Sommerfeld coefficient γ through the first-order metamagnetic transition. A significant enhancement in the effective mass toward Hm is detected in both field directions. In contrast, above Hm, the effective mass discontinuously decreases for H ∥ b, while it discontinuously increases for H ∥ ∼, which plays a crucial role in the RSC.
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