Criticality and thermodynamic geometry of quantum BTZ black holes

Within the framework of extended black hole thermodynamics, where the cosmological constant acts as the thermodynamic pressure and its conjugate as the thermodynamic volume, we analyze the phase structure and thermodynamic geometry of the three-dimensional quantum Bañados-Teitelboim-Zanelli (qBTZ) black hole. Our results uncover two-phase transitions in the T−S plane across all pressures except at a critical value. Numerical analysis reveals continuous critical phenomena along the coexistence curve, with critical exponents of 2 and 3 for the heat capacity at constant pressure and the new thermodynamic geometry (NTG) curvature, respectively. Importantly, these values notably deviate from the well-known critical exponents observed in mean-field van der Waals (vdW) fluids, where the NTG curvature and heat capacity demonstrate discontinuous criticality. To our knowledge, our investigation is the first exploration of critical behavior in black holes incorporating consistent semiclassical backreaction.