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The authors investigated the low-temperature transport and thermodynamic behavior of AB-stacked twisted bilayer MoS$_2$ at twist angles of $4.1^\circ$ and $3.9^\circ$ under fractional filling factors $\nu = 1/3$ and $\nu = 1/4$. Rather than observing conventional thermal melting, warming the system from ultra-low temperatures drives a counterintuitive transition from a conducting Fermi-liquid state into an insulating generalized Wigner crystal marked by a steep rise in longitudinal resistivity. This provides direct experimental evidence of an electronic Pomeranchuk effect driven by isospin entropy, revealing how flat bands can stabilize highly degenerate magnetic phases in two-dimensional moiré lattices.
Heating electrons in twisted MoS$_2$ counterintuitively freezes an itinerant quantum liquid into a localized Wigner crystal, proving that isospin entropy can invert conventional thermodynamic melting in moiré flat bands.
Moire superlattices in transition metal dichalcogenides provide a highly tunable platform for exploring strongly correlated electronic phases, such as generalized Wigner crystals. While these crystalline states typically melt with increasing thermal fluctuations, an electronic analogue of the Pomeranchuk effect can stabilize the localized solid phase at elevated temperature through isospin entropy. Here, we report the observation of an electronic Pomeranchuk effect at the fractional filling factors of $\nu = 1/3$ and $\nu = 1/4$ in AB-stacked twisted bilayer MoS$_2$ with twist angles of 4.1$^\circ$ and 3.9$^\circ$, respectively. At ultra-low temperature, the system exhibits a highly conducting, itinerant behavior at these fractional fillings, characteristic of a compressible Fermi-liquid ground state. Upon heating, the system exhibits a counterintuitive increase in the longitudinal resistivity, signaling an isospin-entropy-driven transition into a localized generalized Wigner crystal state. Our findings highlight the unique capacity of flat bands in twisted bilayer MoS$_2$ for stabilizing highly degenerate magnetic configurations, offering new insights into the thermodynamic phase diagrams of low-dimensional correlated systems.