arXiv subjects

Chun-Hui Lv

Publications and source records attributed to Chun-Hui Lv.

3 recordsLinked to original sources

arXiv2026

Electronic Nematicity Revealed by Polarized Ultrafast Spectroscopy in Bilayer La$_3$Ni$_2$O$_7$

We report a polarized ultrafast pump-probe study of the normal-state electronic dynamics in bilayer La$_3$Ni$_2$O$_7$ and trilayer La$_4$Ni$_3$O$_{10}$ single crystals at ambient pressure. While both nickelates exhibit density-wave (DW) transitions accompanied by the opening of a quasiparticle relaxation bottleneck, their electronic responses display strikingly different symmetry properties. La4Ni3O10 maintains an isotropic optical response across the entire temperature range. In contrast, La$_3$Ni$_2$O$_7$ exhibits a pronounced twofold ($C_2$) anisotropy in its lowtemperature electronic dynamics. This electronic nematicity, evident in both the relaxation dynamics and the polarization-dependent effective bottleneck energy scales, is strongly modified below 115 K, suggesting coupling or competition with a secondary DW-like instability reported by complementary probes. The presence of macroscopic electronic anisotropy in the bilayer system, and its absence in the trilayer system, suggests a possible relation between electronic nematic correlations and the superconducting normal state in a$_3$Ni$_2$O$_7$ that deserves further exploration.

cond-mat.str-el↗

arXiv2025

Nonthermal melting and density wave instability coupled to the lattice in La$_4$Ni$_3$O$_{10}$

The recent discovery of high-temperature superconductivity in pressurized nickelates has renewed interest in the broken-symmetry states of their ambient-pressure parent phases, where a density-wave (DW) order emerges and competes with superconductivity, but its microscopic origin remains unresolved. Using ultrafast optical spectroscopy, we track quasiparticle relaxation dynamics across the DW transition at $T_{\rm DW} \approx$ 136 K in trilayer nickelate {\LNO} single crystals, revealing the opening of an energy gap of $\sim$52 meV. Multiple coherent phonons, including $A_g$ modes near 3.88, 5.28, and 2.09 THz, display pronounced mode-selective anomalies across the transition, indicating that the DW is strongly coupled to lattice degrees of freedom and suggesting an important role of electron-phonon coupling. At higher excitation densities, the DW is nonthermally suppressed, producing a temperature-fluence phase diagram that parallels pressure-tuned behavior. These results establish the DW in {\LNO} as a lattice-entangled instability involving multiple phonon modes, and highlight ultrafast optical excitation as a nonequilibrium tuning parameter for suppressing density-wave order in nickelates.

cond-mat.str-el↗

arXiv2025

Ultrafast Optical Evidence of Coexisting Density Waves in Bilayer Nickelate La$_3$Ni$_2$O$_7$

Utilizing ultrafast optical pump-probe spectroscopy, we investigate the coexistence and competition of electronic orders in the bilayer nickelate La$_3$Ni$_2$O$_7$. Our results reveal two coexisting density waves that can be selectively manipulated with light. We directly identify a spin-density wave (SDW) with electronic nematicity emerging below $T_{\rm SDW}$ $\approx$ 140 K by measuring its spin dynamics, and discover a distinct, nonmagnetic charge order appearing below $T_{\rm DW}$ $\approx$ 115 K. The central finding is the demonstration of differential optical control: the charge order is fragile, completely suppressed by a pump fluence of approximately 40 $\mu$J/cm$^2$, while the SDW is remarkably robust, persisting to 200 $\mu$J/cm$^2$. This work establishes a clear hierarchy in the stability of competing electronic orders and provides a powerful method for disentangling their interplay in quantum materials.

cond-mat.str-el↗