Enhancement and Discontinuity of Effective Mass through the First-Order Metamagnetic Transition in UTe₂

Metamagnetic transitions in the novel spin-triplet superconductor UTe$_2$ were investigated through newly developed simultaneous measurements of magnetization and sample temperature for field along orthorhombic $b$-axis close to [011] direction, where reentrant superconductivity (RSC) is detected below above first-order metamagnetic transition $H_{\rm m}$. Combining Maxwell's relation Clausius-Clapeyron equation, we obtained dependence Sommerfeld coefficient $\gamma$ transition. A significant enhancement effective mass toward m}$ both directions. On other hand, m}$, discontinuously decreases $H~||~b$, while it increases $H~||~\sim [011]$, which seems make a crucial role RSC.