arXiv subjects

Nicolas Delnour

Publications and source records attributed to Nicolas Delnour.

4 recordsLinked to original sources

arXiv2026

Coexisting Large and Small Polarons in Photoexcited CeO$_2$

Time-resolved terahertz (THz) spectroscopy is used to probe polaron formation in CeO$_2$. The ultrafast THz photoconductivity is dominated by contributions from large hole and small electron polarons. Delocalized large hole polarons are formed on a $820 \pm 50$ fs time scale and are of Fr\"ohlich type, with optical conductivity well described by a simple Drude model and a transient hole mobility of $100$ cm$^2$/Vs. Small electron polarons form via localized coupling to Ce lattice sites, revealed by reduction in the lattice Born effective charge causing a transient phonon softening. These results establish the dual polaron nature of CeO$_2$ and provide a basis for understanding charge transfer dynamics in metal oxide photocatalysts.

cond-mat.mtrl-sci↗

arXiv2023

Boundary-induced topological transition in an open SSH model

We consider a Su-Schrieffer-Heeger chain to which we attach a semi-infinite undimerized chain (lead) to both ends. We study the effect of the openness of the SSH model on its properties. A representation of the infinite system using an effective Hamiltonian allows us to examine its low-energy states in more detail. We show that, as one would expect, the topological edge states hybridize as the coupling between the systems is increased. As this coupling grows, these states are suppressed, while a new type of edge state emerges from the trivial topological phase. These new states, referred to as phase-inverted edge states, are localized low-energy modes very similar to the edge states of the topological phase. Interestingly, localization occurs on a new shifted interface, moving from the first (and last) site to the second (and second to last) site. This suggests that the topology of the system is strongly affected by the leads, with three regimes of behavior. For very small coupling the system is in a well-defined topological phase; for very large coupling it is in the opposite phase; in the intermediate region, the system is in a transition regime.

cond-mat.mes-hall↗

arXiv2023

Scanning qubit probe of edge states in a topological insulator

In this work, we propose a novel qubit-based sensor with the ability to characterize topological edge states in low-dimensional systems. A composite system is studied, consisting of a qubit coupled to a topologically nontrivial Su-Schrieffer-Heeger chain between semi-infinite lead channels. This qubit probe utilizes decoherence dynamics which, under a weak-coupling framework, are related to the environment's local density of states. Qubit decoherence rate measurements along a sample therefore provide the means to extract edge state profiles. The environment's influence on the qubit's subspace is captured by an effective projective treatment, leading to an analytical decoherence rate expression. We demonstrate that the scanning qubit probe identifies and yields a complete spatial characterization of the topological edge states within the composite system.

cond-mat.mes-hall↗

arXiv2020

Detecting topological edge states with the dynamics of a qubit

We consider the Su-Schrieffer-Heeger (SSH) chain, which has 0, 1, or 2 topological edge states depending on the ratio of the hopping parameters and the parity of the chain length. We couple a qubit to one edge of the SSH chain and a semi-infinite undimerized chain to the other, and evaluate the dynamics of the qubit. By evaluating the decoherence rate of the qubit we can probe the edge states of the SSH chain. The rate shows strong even-odd oscillations with the number of sites reflecting the presence or absence of edge states. Hence, the qubit acts as an efficient detector of the topological edge states of the SSH model. This can be generalized to other topological systems.

cond-mat.mes-hall↗