Chiral Superconductivity in Periodically Driven Altermagnet/Superconductor Heterostructures

Abstract

The interplay between magnetism and superconductivity provides a fertile ground for engineering exotic topological phases, while dynamical control via periodic driving offers a unique avenue to access quantum states that are inaccessible in static equilibrium. Here, we propose a strategy to achieve the Floquet chiral topological superconductivity in an altermagnet-superconductor heterostructure driven by elliptically polarized light. We show that for $s$-wave pairing, the system undergoes a transition from a trivial to a chiral topological superconducting phase. More strikingly, with the introduction of mixed $s+d$-wave pairing, we find that the system can access Floquet chiral topological superconducting phases with highly tunable Chern numbers up to N=4. These exotic phases are attributed to the intertwining of altermagnetism, superconducting pairing, and the periodic driving field. Our work establishes the light-driven altermagnetic heterostructure as a versatile platform for exploring and manipulating high-Chern-number chiral topological superconductivity.

Figures (4)

• Figure 1: Schematic of the light-driven 2D AM-SC heterostructure, where the red and blue arrows denote spin-up and spin-down, respectively.
• Figure 2: (a) Topological phase diagram characterized by Chern numbers in the $\theta$-$A$ parameter plane for an $s$-wave/AM heterojunction at $J_\text{AM} = 0.245$. The red dashed line indicates $A=0.8$. As $\theta$ varies along this dashed line, the system undergoes phase transitions between two distinct strong FCTSC phases and a topologically trivial phase. (b) Topological phase diagram in the $\theta$-$A$ parameter plane for an $s$-wave/AM heterojunction at $J_\text{AM} = 0.26$. As $A$ varies along the dashed line, the system evolves from a weak TSC state into an FCTSC state, and ultimately transitions into a topologically trivial state. The gray regions represent the topologically trivial phase. The yellow and green regions correspond to strong TSC states with Chern numbers $\mathcal{N} = \pm 1$, while the blue regions indicate a weak topological superconducting state with a Chern number of $\mathcal{N} = 0$.
• Figure 3: Edge states and topological phase transitions in an AM/s-wave SC system. (a)--(e) Edge state spectra along the $-\bar{\text{Y}} -\bar{\Gamma}-\bar{\text{Y}}$ path for fixed AM strength $J_\text{AM}=0.245$ and light amplitude $A=0.8$. The polarization angles correspond to $\theta = 0.1\pi$, $0.31\pi$, $0.25\pi$, $0.18\pi$, and $0.10\pi$, respectively. The corresponding Chern numbers are $\mathcal{N}=1$, gap closing, $\mathcal{N}=0$, gap closing, and $\mathcal{N}=-1$. (f)--(g) Edge state spectra for fixed AM strength $J_\text{AM}=0.26$ and polarization angle $\theta=0.225\pi$. The light amplitudes are $A=0.3$, $0.46$, $0.55$, $0.72$, and $0.9$, respectively. The corresponding Chern numbers are $\mathcal{N}=0$, gap closing, $\mathcal{N}=1$, gap closing, and $\mathcal{N}=0$. Notably, in (f), two opposite chirality Majorana edge modes are present, resulting in a net Chern number of $\mathcal{N}=0$
• Figure 4: Topological phases in an AM/$s+d$-wave SC system. (a) Spin-resolved band structures along the high-symmetry path $\text{Y}$-$\Gamma$-$\text{X}$ in the static limit ($A_x = 0, J_\text{AM} = 0.3$). (b) Illustration of the distribution of bulk nodes in the Brillouin zone. (c)-(f) Topological edge state spectra of the AM/$s+d$-wave SC heterostructure along the surface Brillouin zone path $\bar{\text{Y}}$-$\bar{\Gamma}$-$\bar{\text{Y}}$, driven by an EPL with a varying light amplitude $A_x$ and exchange strength $J_\text{AM}$. The specific parameters and resulting phases are: (c) $\mathcal{N} = -1$ with $J_\text{AM} = 0.6$ and $A_x = 0.98$; (d) $\mathcal{N} =- 2$ with $J_\text{AM} = 0.4$ and $A_x = 1.05$; (e) High-Chern-number state $\mathcal{N} = -3$ with $J_\text{AM} = 0.4$ and $A_x = 0.7$; and (f) $\mathcal{N} =- 4$ with $J_\text{AM} = 0.4$ and $A_x = 0.90$. Other model parameters are fixed at $\mu = 0, \lambda_\text{R} = 0.3$, and $t = 1$ for all plots.