Light-Enhanced Spin Fluctuations and $d$-Wave Superconductivity at a Phase Boundary

Time-domain techniques have shown the potential of photomanipulating existing orders and inducing new states of matter in strongly correlated materials. Using time-resolved exact diagonalization, we perform numerical studies of pump dynamics in a Mott-Peierls system with competing charge and spin density waves. A light-enhanced $d$-wave superconductivity is observed when the system resides near a quantum phase boundary. By examining the evolution of spin, charge, and superconducting susceptibilities, we show that a subdominant state in equilibrium can be stabilized by photomanipulating the charge order to allow superconductivity to appear and dominate. This work provides an interpretation of light-induced superconductivity from the perspective of order competition and offers a promising approach for designing novel emergent states out of equilibrium.

Figure 1

(a) Schematics of SDW and CDW insulating states. (b) Average phonon occupancy $⟨n_{\text{ph}}⟩$ at various $\lambda$ and $u$. The dashed lines indicate the phase boundaries in the antiadiabatic limit where $u_{\text{eff}}=0$, while the solid line tracks the numerical boundary where the translational symmetry breaks and the ground state changes from doubly degenerate (Peierls phase) to nondegenerate. The red and orange circles denote the parameters used in Fig. 2, and the boundary-crossing dotted bar shows the parameter space traversed in Fig. 3.

Figure 2

Evolution of (a) $d$-wave pairing correlation $⟨{\mathrm{\Delta }}_d^{†}{\mathrm{\Delta }}_d⟩$ and (b) magnetization $⟨m_z^2⟩$ (in the log scale) during and after the pump, for systems deep [$u=3.9$, $\lambda =4$, bottom] and shallow [$u=7.8$, $\lambda =4$, top] in the Peierls phase, respectively. The darkness of curves denotes the pump strength varying from $A_0=0.1$ to 0.8.

Figure 3

Change of (a) pairing correlation and (b) $d$-wave projected spin fluctuations evaluated in the postpump state ($t=10t_h^{-1}$) for various pump strengths $A_0$ and parameter sets near the phase boundary along two parameters. The cut positions are denoted by the color plains in the inset. (c) The change of pairing correlation with fixed pump strengths, over a wider range of interaction parameter sets. The color maps are plotted in the logarithmic scale. The dashed lines indicate the phase boundary.

Figure 4

(a) Evolution of DOS during the pump. The shaded regions denote occupied states. (b),(c) Comparison of postpump ($t=10t_h^{-1}$) pairing correlation (solid blue circles), spin fluctuations (red squares), and quasiparticle weight (green triangles) as a function of the pump strength from the (b) Peierls phase ($u=7.8$) and (c) Mott phase ($u=8$). The quasiparticle weights are plotted against the right axis.