The complexity of the cuprate phase diagram is one of the main challenges in developing a microscopic understanding of high-temperature superconductivity. Recent work has suggested that part of this complexity may originate from disorder effects, motivating the study of “clean” cuprates such as YBCO, Hg1201, and Tl2201 in order to isolate intrinsic features of the phase diagram.

Tl2201 is a key candidate system, as multiple experimental probes—including specific heat, transport, quantum oscillations, and ARPES—are consistent with a simple Fermi-liquid-like normal state with a large cylindrical Fermi surface. However, thermodynamic studies have largely been limited by the small size of available single crystals, and have therefore relied on powder samples. Specific heat measurements on these samples suggest a suppression of the superconducting anomaly with increased overdoping.

Here, we present membrane-based AC nanocalorimetry measurements of microgram-scale single crystals, enabling precise determination of the absolute specific heat. We find that the superconducting specific heat anomaly is significantly sharper and larger than previously reported, approaching the value expected in the absence of disorder effects.

These results indicate that disorder plays a dominant role in the previously observed suppression of the superconducting anomaly. Our findings further suggest that modeling the intrinsic evolution of superconductivity in heavily overdoped Tl2201 may provide key insight into the mechanism of high-temperature superconductivity.