Quantum criticality within Dirac fermions harbors a plethora of exotic phenomena, attracting sustained attention in the past decades. Here, we explore the imaginary-time relaxation dynamics in a typical Dirac quantum criticality belonging to chiral Heisenberg universality class. Performing large-scale quantum Monte Carlo simulation, we unveil rich nonequilibrium critical phenomena from different initial states. In particular, we identify a nonstationary initial slip evolution characterized by an unconventional negative critical exponent $\theta =-0.84(4)$, corroborating the significant impact of fermionic critical fluctuations. Furthermore, we generalize the nonequilibrium scaling theory to incorporate both fermionic and bosonic critical modes, capturing their distinct relaxation behaviors. Armed with the scaling theory, we establish a new framework to investigate fermionic quantum criticality based on short-time dynamics, paving a promising avenue to fathoming quantum criticality in diverse fermionic systems with high efficiency.

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• Critical exponents
• Critical phenomena
• Dirac fermions
• Dynamic critical phenomena
• Nonequilibrium statistical mechanics
• Phase transitions
• Quantum criticality
• Quantum quench
• Honeycomb lattice
• Finite-size scaling
• Hubbard model
• Quantum Monte Carlo
• Scaling methods