Domain Dynamics in Quantum-Paraelectric SrTiO_{3}

Non-equilibrium quantum domain reconfiguration dynamics in a two-dimensional electronic crystal and a quantum annealer

Relaxation dynamics of complex many-body quantum systems trapped into metastable states is a very active field of research from both the theoretical and experimental point of view with implications in a wide array of topics from macroscopic quantum tunnelling and nucleosynthesis to non-equilibrium superconductivity and energy-efficient memory devices. In this work, we investigate quantum domain reconfiguration dynamics in the electronic superlattice of a quantum material using time-resolved scanning tunneling microscopy and unveil a crossover from temperature to noisy quantum fluctuation dominated dynamics. The process is modeled using a programmable superconducting quantum annealer in which qubit interconnections correspond directly to the microscopic interactions between electrons in the quantum material. Crucially, the dynamics of both the experiment and quantum simulation is driven by spectrally similar pink noise. We find that the simulations reproduce the emergent time evolution and temperature dependence of the experimentally observed electronic domain dynamics.

Dynamic domain boundaries: chemical dopants carried by moving twin walls

Domain walls and specifically ferroelastic twin boundaries are depositaries and fast diffusion pathways for chemical dopants and intrinsic lattice defects. Ferroelastic domain patterns act as templates for chemical structures where the walls are the device and not the bulk. Several examples of such engineered domain boundaries are given. Moving twin boundaries are shown to carry with them the dopants, although the activation of this mechanism depends sensitively on the applied external force. If the force is too weak, the walls remain pinned while too strong forces break the walls free of the dopants and move them independently. Several experimental methods and approaches are discussed.

Temperature-induced surface phonon polaritons dissipation in perovskite SrTiO3

Perovskite SrTiO₃ has emerged as a relevant technological material for nano-photonics that confines light to subdiffraction geometry with remarkably wide spectral tunability. Yet, the influence of lattice vibrations on its surface phonon polaritons (SPhPs) and localized surface phonon resonances (LSPhRs) receives little attention, and the underlying physics still remains elusive. Here, we apply spectroscopic ellipsometry (SE) experiments and multiscale simulations spanning from first-principles to finite-difference time-domain (FDTD), and investigate the temperature influence on infrared dielectric functions, SPhPs and LSPhRs of SrTiO₃. SE measurements find that the width of the Reststrahlen band lying between transverse and longitudinal oxygen-related optical phonons changes slightly, but infrared dielectric functions vary significantly as temperature increases. First-principles calculations confirm the coupling of the motion of oxygen atoms to incident photons, forming quasiparticles of SPhPs. FDTD simulations show that strong LSPhRs exist at 250 K in the SrTiO₃ nanodisks but dissipate as lattice vibration strengthens, mainly due to the reduced phonon relaxation lifetime. This work reveals the underlying physics of temperature influence on SPhPs and LSPhRs of SrTiO₃ and helps explore its potential applications as photonic resonators at high temperatures.

Optical phonon contribution to the thermal conductivity of a quantum paraelectric

Motivated by recent experimental findings, we study the contribution of a quantum critical optical phonon branch to the thermal conductivity of a paraelectric system. We consider the proximity of the optical phonon branch to transverse acoustic phonon branch and calculate its contribution to the thermal conductivity within the Kubo formalism. We find a low temperature power law dependence of the thermal conductivity asT^α, with 1 <α< 2, (lower thanT³behavior) due to optical phonons near the quantum critical point. This result is in accord with the experimental findings and indicates the importance of quantum fluctuations in the thermal conduction in these materials.

Polaronic States and Superconductivity in WO3-x

Superconducting domain boundaries were found in WO3-x and doped WO3. The charge carriers in WO3-type materials were identified by Schirmer and Salje as bipolarons. Several previous attempts to determine the electronic properties of polarons in WO3 failed until Bousque et al. (2020) reported a full first principle calculation of free polarons in WO3. They confirmed the model of Schirmer and Salje that each single polaron is centred around one tungsten position with surplus charges smeared over the adjacent eight tungsten positions. Small additional charges are distributed further apart. Further calculations to clarify the coupling mechanism between polaron to form bipolarons are not yet available. These calculations would help to identify the carrier distribution in Magneli clusters, which were shown recently to contain high carrier concentrations and may indicate totally localized superconductivity in non-percolating clusters.