CC BY 4.0 UnportedShipulin, IlyaStegani, NadiaMaccari, IlariaKihou, KunihiroLee, Chul-HoHu, QuanxinZheng, YuYang, FazhiLi, YongweiYim, Chi-MingHühne, RubenKlauss, Hans-HenningPutti, MarinaCaglieris, FedericoBabaev, EgorGrinenko, Vadim2024-05-102024-05-102023https://oa.tib.eu/renate/handle/123456789/14593https://doi.org/10.34657/13624Materials that break multiple symmetries allow the formation of four-fermion condensates above the superconducting critical temperature (T c). Such states can be stabilized by phase fluctuations. Recently, a fermionic quadrupling condensate that breaks the Z 2 time-reversal symmetry was reported in Ba1−xKxFe2As2. A phase transition to the new state of matter should be accompanied by a specific heat anomaly at the critical temperature where Z 2 time-reversal symmetry is broken (TcZ2>Tc). Here, we report on detecting two anomalies in the specific heat of Ba1−xKxFe2As2 at zero magnetic field. The anomaly at the higher temperature is accompanied by the appearance of a spontaneous Nernst effect, indicating the breakdown of Z 2 symmetry. The second anomaly at the lower temperature coincides with the transition to a zero-resistance state, indicating the onset of superconductivity. Our data provide the first example of the appearance of a specific heat anomaly above the superconducting phase transition associated with the broken time-reversal symmetry due to the formation of the novel fermion order.enghttps://creativecommons.org/licenses/by/4.0500phase-diagramsuperconductivityvorticesfluxheatArticle