We study the out-of-equilibrium scaling behavior of two-dimensional and three-dimensional Ising systems, when they are slowly driven across their magnetic first-order transitions at low temperature T<T_{c}, where T_{c} is the temperature of their continuous transition. We consider Kibble-Zurek (KZ) protocols in which a spatially homogenous magnetic field h varies as h(t)=t/t_{s} with a timescale t_{s}. The KZ dynamics starts from negatively magnetized configurations equilibrated at h_{i}<0 and stops at a positive value of h where the configurations acquire a positive average magnetization. We consider the Metropolis and the heat-bath dynamics, which are two specific examples of a purely relaxational dynamics. We focus on two different dynamic regimes. We consider the out-equilibrium finite-size scaling (OFSS) limit in which the system size L and the timescale t_{s} diverge simultaneously, keeping an appropriate combination fixed. Then, we analyze the KZ dynamics in the thermodynamic limit (TL), obtained by taking first the L→∞ limit at fixed t and t_{s}, and then considering the scaling behavior in the large-t_{s} limit. Our numerical results provide evidence of OFSS, as predicted by general scaling arguments. The results in the TL show the emergence of spinodal-like behaviors: The passage from the negatively magnetized phase to the positively magnetized one occurs at positive values h_{*}>0 of the magnetic field, which decrease as h_{*}∼1/(lnt_{s})^{κ}, with κ=2 and κ=1 in two and three dimensions, respectively, for t_{s}→∞. We identify σ≡t(lnt)^{κ}/t_{s} as the relevant scaling variable associated with the KZ dynamics in the TL.
We show that an out-of-equilibrium percolation transition occurs after quenching ferromagnetic Ising-like systems across their magnetic first-order transitions. As a paradigmatic example, we consider a two-dimensional Ising system driven across its low-temperature first-order transition line by a quench of the magnetic field
h from
hi<0 to
h>0. In the thermodynamic limit and for finite values of
h, the post-quench evolution under a purely relaxational dynamics is characterized by a dynamic transition at a finite critical time
tc(h) from the metastable negatively magnetized phase to the positive one, marked by the percolation of the largest clusters of positive and negative spins. This out-of-equilibrium percolation transition displays a finite-size scaling behavior as in the standard random-percolation case. However, while the fractal dimension of the percolating clusters is consistent with the random-percolation value, the exponent controlling the approach to criticality differs and depends on
h. We also show that the percolation critical behavior is related to the spinodal-like behavior of the magnetization in the small-
h limit, which implies that the percolation time
tc(h) exhibits a spinodal-like exponential dependence on
h.
We analyze the out-of-equilibrium relaxational dynamics of ferromagnetic Ising-like systems driven across their low-temperature magnetic first-order transition (FOT) line, by sudden and slow variations of an external homogenous magnetic field
h. As a paradigmatic example, we consider a two-dimensional Ising system driven across its low-temperature FOT line by suddently quenching
h from
hi<0 to
h>0, inducing a transition from the negatively to the positively magnetized phase. We show the emergence of a dynamic percolation transition at a finite critical time
tc(h) along the post-quench evolution for finite (sufficiently small) values of
h, which is marked by the percolation of the largest positive-spin cluster and the antipercolation of the largest negative-spin cluster. This out-of-equilibrium percolation transition displays a finite-size scaling behavior as in the standard random-percolation case. However, while the fractal dimension of the percolating clusters is consistent with the random-percolation value, the exponent controlling the approach to criticality differs and depends on
h. We also show that the percolation transition marks the passage from the metastable negatively-magnetized phase to the stable positively-magnetized one. Therefore, in the small-
h limit, the percolation critical behavior is related to the spinodal-like behavior of the magnetization, implying that the percolation time
tc(h) exhibits a spinodal-like exponential dependence on
h. The existence of percolation transitions is likely a generic phenomenon at magnetic Ising-like FOTs. For example, we observe an analogous behavior in dynamic (Kibble-Zurek-like) protocols entailing slow variations of the magnetic field driving the crossing of the FOT line.
We study the out-of-equilibrium dynamics of one-dimensional quantum Ising models in a transverse field
g, driven by a time-dependent longitudinal field
h across their {\em magnetic} first-order quantum transition at
h=0, for sufficiently small values of
∣g∣. We consider nearest-neighbor Ising chains of size
L with periodic boundary conditions. We focus on the out-of-equilibrium behavior arising from Kibble-Zurek protocols, in which
h is varied linearly in time with time scale
ts, i.e.,
h(t)=t/ts. The system starts from the ground state at
hi≡h(ti)<0, where the longitudinal magnetization
M is negative. Then it evolves unitarily up to positive values of
h(t), where
M(t) becomes eventually positive. We identify several scaling regimes characterized by a nontrivial interplay between the size
L and the time scale
ts, which can be observed when the system is close to one of the many avoided level crossings that occur for
h≥0. In the
L→∞ limit, all these crossings approach
h=0+, making the study of the thermodynamic limit, defined as the limit
L→∞ keeping
t and
ts constant, problematic. We study such limit numerically, by first determining the large-
L quantum evolution at fixed
ts, and then analyzing its behavior with increasing
ts. Our analysis shows that the system switches from the initial state with
M<0 to a positively magnetized state at
h=h∗(ts)>0, where
h∗(ts) decreases with increasing
ts, apparently as
h∗∼1/lnts. This suggests the existence of a scaling behavior in terms of the rescaled time
Ω=tlnts/ts. The numerical results also show that the system converges to a nontrivial stationary state in the large-
t limit, characterized by an energy significantly larger than that of the corresponding homogeneously magnetized ground state.
We study the out-of-equilibrium Kibble-Zurek (KZ) dynamics in quantum Ising chains in a transverse field, driven by a time-dependent longitudinal field
h(t)=t/ts (
ts is the time scale of the protocol), across their first-order quantum transitions (FOQTs) at
h=0. The KZ protocol starts at time
ti<0 from the negatively magnetized ground state for
hi=ti/ts<0. Then, the system evolves unitarily up to a time
tf>0, such that the magnetization of the state at time
tf is positive. In finite-size systems, the KZ dynamics develops out-of-equilibrium finite-size scaling (OFSS) behaviors. Their scaling variables depend either exponentially or with a power law on the size, depending on the boundary conditions (BC). The OFSS functions can be computed in effective models restricted to appropriate low-energy (magnetized and/or kink) states. The KZ scaling behavior drastically changes in the thermodynamic limit (TL), defined as the infinite-size limit keeping
t and
ts fixed, which appears substantially unrelated with the OFSS regime, because it involves higher-energy multi-kink states, which are irrelevant in the OFSS limit. The numerical analyses of the KZ dynamics in the TL show the emergence of a quantum spinodal-like scaling behavior at the FOQTs for all considered BC, which is independent of the BC. The longitudinal magnetization changes sign at
h(t)=h∗>0, where
h∗ decreases with increasing
ts, as
h∗∼1/lnts. Moreover, in the large-
ts limit, the time-dependence of the magnetization is described by a universal function of
Ω=t/τs, with
τs=ts/lnts.
We investigate the out-of-equilibrium dynamics of a relativistic
Z2-symmetric scalar field theory with Langevin dynamics in two and three spatial dimensions under linear driving across magnetic first-order phase transitions, close to and far below the critical temperature
Tc. Using classical-statistical lattice simulations, we find that if the driving timescale is sufficiently fast, the system exhibits finite-time scaling behavior independent of temperature and dimensionality, identical to that observed in mean-field simulations. In slow quenches near
Tc this mean-field behavior crosses over to critical Kibble-Zurek scaling behavior, while for temperatures
T≪Tc nucleation and growth dominate the transition dynamics, resulting in corrections to scaling. Near the transition point where the order parameter changes sign, the crossover between mean-field and critical out-of-equilibrium dynamics is found to be well described by the leading algebraic correction to Kibble-Zurek scaling. We find that universal non-equilibrium scaling behavior can be observed for
T≲Tc, provided the driving is fast enough to avoid nucleation but slow enough for correlations to form, and compute the associated universal scaling functions for the order parameter.