Effect of long-range hopping on dynamic quantum phase transitions of an exactly solvable free-fermion model: Nonanalyticities at almost all times

Abstract

In this work, we investigate quenches in a free-fermion chain with long-range hopping which decay with the distance with an exponent $\nu$ and has range $D$. By exploring the exact solution of the model, we found that the dynamic free energy is non-analytical, in the thermodynamic limit, whenever the sudden quench crosses the equilibrium quantum critical point. We were able to determine the non-analyticities of dynamic free energy $f(t)$ at some critical times $t^{c}$ by solving nonlinear equations. We also show that the Yang-Lee-Fisher (YLF) zeros cross the real-time axis at those critical times. We found that the number of nontrivial critical times, $N_{s},$ depends on $\nu$ and $D$. In particular, we show that for small $\nu$ and large $D$ the dynamic free energy presents non-analyticities in any time interval $\Delta t\sim1/D\ll1$, i.e., there are \emph{non-analyticities at almost all times}. For the spacial case $\nu=0$, we obtain the critical times in terms of a simple expression of the model parameters and also show that $f(t)$ is non-analytical even for finite system under anti-periodic boundary condition, when we consider some special values of quench parameters. We also show that, generically, the first derivative of the dynamic free energy is discontinuous at the critical time instant when the YLF zeros are non-degenerate. On the other hand, when they become degenerate, all derivatives of $f(t)$ exist at the associated critical instant.