Laurent P. René de Cotret

McGill University | McGill · Department of Physics

Transition-metal dichalcogenide monolayers and heterostructures are highly tunable material systems that provide excellent models for physical phenomena at the two-dimensional (2D) limit. While most studies to date have focused on electrons and electron-hole pairs, phonons also play essential roles. Here, we apply ultrafast electron diffraction and...

Transition metal dichalcogenide monolayers and heterostructures are highly tunable material systems that provide excellent models for physical phenomena at the two-dimensional (2D) limit. While most studies to date have focused on electrons and electron-hole pairs, phonons also play essential roles. Here, we apply ultrafast electron diffraction and...

Significance Thermoelectrics can generate electrical power from waste heat and could make an important contribution to sustainable energy production if their efficiency is improved. Engineering efficient thermoelectrics, however, requires a sophisticated understanding of the fundamental interdependencies between electrical and thermal transport, fo...

The phonon dynamics and dielectrically screened electron-phonon coupling of atomically thin molybdenum disulfide are directly observed for the first time ever by UEDS diffuse intensity transients in excellent agreement with novel density functional theory calculations.

Using ultrafast electron scattering we directly observe the bimodal and anisotropic lattice distortions that drive carrier localization in SnSe. Large (18 . 7 Å), quasi-1D polarons form in 300 fs and smaller (4 . 2 Å) 3D polarons form in 4 ps.

SnSe is a layered material that currently holds the record for bulk thermoelectric efficiency. The primary determinant of this high efficiency is thought to be the anomalously low thermal conductivity resulting from strong anharmonic coupling within the phonon system. Here we show that the nature of the carrier system in SnSe is also determined by...

The complex coupling between charge carriers and phonons is responsible for diverse phenomena in condensed matter. We apply ultrafast electron diffuse scattering to unravel electron-phonon coupling phenomena in 1T-TiSe2 in both momentum and time. We are able to distinguish effects due to the real part of the many-body bare electronic susceptibility...

We report on subcycle terahertz light-field emission of electrons from tungsten nanotips under extreme conditions corresponding to a Keldysh parameter γK≈10−4. Local peak THz fields up to 40 GV/m are achieved at the apex of an illuminated nanotip, causing subcycle cold-field electron emission and acceleration in the quasistatic field. By simultaneo...

We report on sub-cycle terahertz light-field emission of electrons from tungsten nanotips under extreme conditions corresponding to a Keldysh parameter $\gamma_K\approx10^{-4}$. Local peak THz fields up to 40~GV/m are achieved at the apex of an illuminated nanotip, causing sub-cycle cold-field electron emission and acceleration in the quasi-static...

Interactions between the lattice and charge carriers can drive the formation of phases and ordering phenomena that give rise to conventional superconductivity, insulator-to-metal transitions, and charge-density waves. These couplings also play a determining role in properties that include electrical and thermal conductivity. Ultrafast electron diff...

The complex coupling between charge carriers and phonons is responsible for diverse phenomena in condensed matter. We apply ultrafast electron diffuse scattering to unravel these couplings in both momentum and time by following the response of semi-metallic 1T-TiSe$_2$ to selective photo-carrier doping. Wavevector-specific renormalization of a phon...

Interactions between the lattice and charge carriers can drive the formation of phases and ordering phenomena that give rise to conventional superconductivity, insulator-to-metal transitions, and charge-density waves. These couplings also play a determining role in properties that include electric and thermal conductivity. Ultrafast electron diffus...

We show that ultrafast electron diffuse (inelastic) scattering provides a detailed, momentum-resolved view of electron-phonon and phonon-phonon coupling across the entire Brillouin zone. Ultrafast time-resolution and scattering selection rules can distinguish between phonon branches without energy-resolution.

A novel laser-RF cavity synchronization scheme was developed for ultrafast electron diffraction instruments. The approach directly generates a synchronized microwave tone by retrieving a phase-locked high-harmonic by photodetection. The radio-frequency cavity which performs electron pulse compression is detuning compensated using an active phase st...

We combine ultrafast electron diffraction and time-resolved terahertz spectroscopy measurements to link structure and electronic transport properties during the photoinduced insulator–metal transitions in vanadium dioxide. We determine the structure of the metastable monoclinic metal phase, which exhibits antiferroelectric charge order arising from...

This paper details a software ecosystem comprising three free and open-source Python packages for processing raw ultrafast electron scattering (UES) data and interactively exploring the processed data. The first package, iris, is graphical user-interface program and library for interactive exploration of UES data. Under the hood, iris makes use of...

We combine ultrafast electron diffraction and time-resolved terahertz spectroscopy measurements to unravel the connection between structure and electronic transport properties during the photoinduced insulator-metal transitions in vanadium dioxide. We determine the structure of the metastable monoclinic metal phase, which exhibits anti-ferroelectri...

Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone (BZ) has proved difficult to obtain. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly prov...

The general problem of background subtraction in ultrafast electron powder diffraction (UEPD) is presented with a focus on the diffraction patterns obtained from materials of moderately complex structure which contain many overlapping peaks and effectively no scattering vector regions that can be considered exclusively background. We compare the pe...

We demonstrate the compression of electron pulses in a high-brightness ultrafast electron diffraction instrument using phase-locked microwave signals directly generated from a mode-locked femtosecond oscillator. Additionally, a continuous-wave phase stabilization system that accurately corrects for phase fluctuations arising in the compression cavi...