arXiv subjects

Quynh Le Nguyen

Publications and source records attributed to Quynh Le Nguyen.

2 recordsLinked to original sources

arXiv2026

Emergent Antiphase Stacking in a Transient Charge Density Wave

Photoexcitation can induce novel states in materials that are inaccessible in equilibrium, a recent example being the light-induced charge density wave (CDW) observed in $\text{LaTe}_3$. Here, we investigate this transient CDW using infrared-pump x-ray-probe scattering at a free-electron laser, with high momentum and time resolution. We find that the transient CDW Bragg peak is broad in reciprocal space, indicating a highly disordered state. The ordering wavevector of the transient state is different from the equilibrium orders that develop in this class of materials - the transient peak appears near (2/7, 0, 0) reciprocal lattice units, whereas the equilibrium $a$ order and $c$ order occur at $\approx (5/7, 0, 0)$ and $(0, 0, 2/7)$, respectively. The transient CDW is therefore distinct from the equilibrium $a$ order, differing in the relative phase of the CDW displacement between the two equivalent nearly-square Te-Te nets in the conventional unit cell. Our work highlights how photoexcitation can access states with no equilibrium analog, and how x-ray scattering can provide microscopic insight into such elusive phases.

cond-mat.str-el↗

arXiv2024

Dynamical Scaling Reveals Topological Defects and Anomalous Evolution of a Photoinduced Phase Transition

Nonequilibrium states of quantum materials can exhibit exotic properties and enable unprecedented functionality and applications. These transient states are inherently inhomogeneous, characterized by the formation of topologically protected structures, requiring nanometer spatial resolution on femtosecond timescales to resolve their evolution. Using ultrafast total x-ray scattering at a free electron laser and a sophisticated scaling analysis, we gain unique access to the dynamics on the relevant mesoscopic lengthscales. Our results provide direct evidence that ultrafast excitation of LaTe$_3$ leads to formation of topological vortex strings of the charge density wave. These dislocations of the charge density wave exhibit anomalous, subdiffusive dynamics, slowing the equilibration process, providing rare insight into the nonequilibrium mesoscopic response in a quantum material. Our findings establish a general framework to investigate properties of topological defects, which are expected to be ubiquitous in nonequilibrium phase transitions and may arrest equilibration and enhance competing orders.

cond-mat.mtrl-sci↗