Surface acoustic wave-driven valley current generation in intervalley coherent states

Abstract

Recent experiments have reported valley-gauge-symmetry-broken phases, identified as intervalley coherent (IVC) states. Exploration of anomalous responses, particularly those analogous to superconductivity, has become an urgent theoretical issue. In this study, we show that the IVC order gives rise to anomalous valley-current generation driven by surface acoustic waves (SAWs). The anomalous valley current exhibits a characteristic power-law dependence for low-frequency SAWs. Furthermore, we demonstrate by numerical analysis that the IVC order significantly enhances valley-current generation in rhombohedral graphene. These results open a pathway toward exploring exotic phenomena emerging from valley-gauge-symmetry breaking, in close analogy with gauge-symmetry breaking in superconductors.

Figures (4)

• Figure 1: (a) Schematic of the IVC state under the SAWs. The SAWs induce the pseudogauge field $\bm{A}_{s}$. (b) The unit cell and the interlayer hopping process in R3G. Here, $A_j$ and $B_j$ represent the sublattice on the layer $j=1,2,3$. The hopping integrals are denoted by $\gamma_i$. (c) The valley charge is assumed to be well-defined in the shaded domain $D$ around the K/K' points. We parameterize the size of the domain $D$ by $\Delta k$.
• Figure 2: Frequency dependence of the VAG conductivity, which stems from the Drude term $\sigma_{\mathrm{s, Drude}}$, the Berry connection polarizability term $\sigma_{\mathrm{s, BCP}}$, and the NRSF term $\sigma_{\mathrm{s, NRSF}}$. We set (a) $\Delta=30\,\mathrm{meV}$ (IVC state) and (b) $\Delta=0\,\mathrm{meV}$ (normal state).
• Figure 3: The NRPSF $f^{x;xx}_{\mathrm{s}}$ as a function of $r$ for the IVC order parameter $\Delta=20\,$meV and $30\,$meV.
• Figure 4: The NRPSF $f^{x;xx}_{s}$ for various $\Delta k$, a parameter specifying the integral domain $D$. We plot the $r$ dependence in (a) the normal state ($\Delta=0\,$meV) and (b) the IVC state ($\Delta=30\,$meV).