Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

We investigate out-of-equilibrium dynamics in an excitonic insulator (EI) with a finite momentum pairing perturbed by a laser-pulse excitation and a sudden coupling to fermionic baths. The transient dynamics of the excitonic order parameter is resolved using the full nonequilibrium Green's function approach and the generalized Kadanoff-Baym ansatz (GKBA) within the second-Born approximation. The comparison between the two approaches after a laser pulse excitation shows a good agreement in the weak and the intermediate photo-doping regime. In contrast, the laser-pulse dynamics resolved by the GKBA does not show a complete melting of the excitonic order after a strong excitation. Instead we observe persistent oscillations of the excitonic order parameter with a predominant frequency given by the renormalized equilibrium bandgap. This anomalous behavior can be overcome within the GKBA formalism by coupling to an external bath, which leads to a transition of the EI system towards the normal state. We analyze the long-time evolution of the system and distinguish decay timescales related to dephasing and thermalization.Comment: 13 pages, 12 figure

Adiabatic preparation of a correlated symmetry‐broken initial state with the generalized Kadanoff–Baym Ansatz

A fast time propagation method for nonequilibrium Green's functions (NEGF) based on the generalized Kadanoff–Baym Ansatz (GKBA) is applied to a lattice system with a symmetry‐broken equilibrium phase, namely an excitonic insulator (EI). The adiabatic preparation of a correlated symmetry‐broken initial state from a Hartree– Fock wave function within GKBA is assessed by comparing with a solution of the imaginary‐time Dyson equation. It is found that it is possible to reach a symmetry‐ broken correlated initial state with nonzero excitonic order parameter by the adiabatic switching (AS) procedure. It is discussed under which circumstances this is possible in practice within reasonably short switching times

The effect of orthodontic tooth movement on the sensitivity of dental pulp: A systematic review and meta-analysis

Objectives: Orthodontic tooth movement (OTM) is a process that's initiated by orthodontic forces. As a consequence, the forces could restrict pulpal blood supply, possibly affecting dental pulp. The study aimed to review the available evidence on the short and long-term effects of orthodontic tooth movement on dental pulp sensitivity and to identify clinically relevant risk factors. Sources: PubMed, Embase, Scopus, and Web of Science were searched for papers from 1990 to the end of December 2021. Study selection: The studies that evaluated dental pulp sensitivity of teeth undergoing OTM were included in the systematic review. Randomized, nonrandomized and case-controlled studies were included in the analysis. Risk of bias in each study was assessed using the ROBINS-I tool. Data: The systematic search yielded an initial sample of 1110 studies, 17 were included in qualitative analysis. Most studies were classified as moderate risk of bias, however only limited long-term evidence with a higher risk of bias exists. Electric pulp test (EPT) sensitivity threshold during active OTM was increased by 4.25 SD (P < 0.001) and the relative risk (RR) of pulpal non-sensitivity was 13.27 (P < 0.001) higher compared to pre-orthodontic baseline status. Significant differences were between subgroups associated with the type of OTM. A positive relationship between pulpal non-sensitivity and mean patient age was discovered (P = 0.041). After OTM the risk of pulpal non-sensitivity remained 5.76 times higher (P < 0.001) in the long term. Conclusions: Evidence showed that OTM could affect dental pulp sensitivity. The type of OTM and patients' age were identified as clinically relevant risk factors. Clinical significance: Orthodontic tooth movement negatively impacts the sensitivity of dental pulp during active treatment and to a lesser degree in the long term. Pulpal sensitivity tests during active OTM should therefore be interpreted with caution. Data indicates younger patients have a lower risk of negative pulpal sensitivity during orthodontic treatment

Imaging the coherent propagation of collective modes in the excitonic insulator Ta₂NiSe₅ at room temperature.

Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator Ta2NiSe5 Below 328 K, we observe the anomalous micrometer-scale propagation of coherent modes at velocities of ~105 m/s, which we attribute to the hybridization between phonon modes and the phase mode of the condensate. We develop a theoretical framework to support this explanation and propose that electronic interactions provide a substantial contribution to the ordered phase in Ta2NiSe5 These results allow us to understand how the condensate's collective modes transport energy and interact with other degrees of freedom. Our study provides a unique paradigm for the investigation and manipulation of these properties in strongly correlated materials

Snapshots of the retarded interaction of charge carriers with ultrafast fluctuations in cuprates

One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive as electronic correlations are expected to greatly accelerate the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and frequency range of transient reflectivity measurements up to an unprecedented level, enabling us to directly observe the ∼16 fs build-up of the effective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations