Broadband transient absorption is a widely used tool in the domain of ultrafast spectroscopy. However, standard chemometrie methods for decomposing spectra into components associated to the involved species like global and target analysis or singular value decomposition cannot be used when the spectral shapes of these components exhibit temporal changes, for instance due to internal...
Generation of entangled photons in semiconductor microcavities through lower and upper polariton scattering via biexciton state was theoretically predicted. However, the ideal condition for its implementation has not yet been experimentally established. A groundbreaking demonstration of a polaritonic Feshbach resonance was realized when the energy of two lower polaritons with anti-parallel...
Electronic spins in solid-state media have recently attracted large interest in quantum information science. Their large magnetic moments offers fast operations in computation and communication applications and high sensitivity for sensors. However, this implies also high sensitivity to magnetic noise, thus reducing coherence times. In our work, we demonstrate strong suppression of decoherence...
We present an angle-resolved photoemission spectroscopy study of low-temperature adsorption of potassium on the 1T-TiSe2 charge density wave (CDW) compound. Combined with simulations of one-electron spectral functions, our measurements allow for discussing the impact of K on the CDW order parameter, chemical potential and spin-orbit coupling. Our study reveals a coverage-dependent...
The origin of the four pre-edge peaks (1s-3d) in the Ti K-edge XAS spectrum of anatase TiO$_2$ is still actively debated. By combining X-ray Absorption Linear Dichroism with ab-initio finite difference method calculations, we provide an unambiguous assignment of these peaks. These forbidden transitions arise from a strong mixing of the 3d orbitals with 4p$_z$ and 4p$_{x,y}$ orbitals, with an...
Anatase TiO2 is a superior material for converting light into other forms of energies. Despite the extensive studies of its photophysics, only recently the importance of e-h interactions in TiO2 was understood [1]. Here, we apply a novel ultrafast broadband deep-UV spectroscopy setup to access for the first time the nonequilibrium dynamics of TiO2 at the band edge. By monitoring the evolution...
By performing Resonant Inelastic X-ray Scattering (RIXS) experiments at the O K and Ir L-edge on thin films of Sr$_2$IrO$_4$ grown on different substrates we observe the evolution of the spin, orbital and charge elementary excitations upon strain. We find the local lattice distortions to control the magnetic correlations, with the spin-wave dispersion showing an anisotropic softening affecting...
Transition Metal Oxides (TMO) represent an ideal platform to exploit exotic phenomena in solid state physics. Conductivity and superconductivity in the Two Dimensional Electron System (2DES) at the LAO3/STO3 (LAO/STO) interface is one of them.
The 2DES sits on the STO part of the interface, in a potential well created by band bending. Reducing the thickness of the hosting STO material can be a...
Three-dimensional magnetic systems promise significant opportunities for applications as well as new functionalities. Two main challenges concerning their experimental investigation have been addressed, namely the fabrication of three-dimensional magnetic architectures, and the characterisation of three-dimensional magnetisation configurations. In particular, an artificial magnetic buckyball...
Solar cells based on lead halide perovskites have recently emerged. Within few years their power-conversion efficiency (now 22%) has approached values of established photovoltaic technologies. In this contribution, light is shed on some peculiar properties of perovskites. These are their defect tolerance, which allows for high photovoltages and luminescence yields; Furthermore, the mixed...
Thermodynamics provides a powerful description of energy flow in macroscopic systems. We study its validity upon reducing the number of particles comprising the system down to a single electron. We perform work on an electron residing in a quantum dot coupled to a reservoir and extract the heat it produces when equilibrating with the reservoir. Due to the small system size, the values for heat...
Hybrid perovskite solar cells have been capturing an enormous research interest in photovoltaics due to their extraordinary performances and ease of fabrication [1]. However, low device lifetime, mainly due to device degradation upon water exposure, challenges their near-future commercialization. Diverse technological approaches have been proposed, but still not sufficient, requesting a...
Magnetic systems with competing interactions often adopt exotic ground states, which can be relevant to study new physics in quantum matter. The quantum spin ice ground state is expected in certain types of pyrochlore magnets, and theory predicts its low-energy physics to be a lattice analogue of quantum electrodynamics. In Pr$_2$Hf$_2$O$_7$, a ground state with indications of spin ice...
Different from the situation in conventional paramagnets, spins in the frustrated magnets can fluctuate or dance collectively, leaving a trace in reciprocal space that can be detected using neutron scattering. Here we present our neutron scattering results for two typical spinel compounds: MnSc2S4 and CdEr2X4, where the magnetic ions form the diamond...
Quasi one-dimensional (1D) spin ladders host exotic low-energy excitations. Recently, susceptibility measurements suggested that Co doping alters the magnetism in the spin ladder of Sr14Cu24O41. We studied the Co impurity effects of Sr14Cu24O41 using Resonant Inelastic X-Ray Scattering (RIXS) at Cu L3- and O K-edges. Cu L3 RIXS has been shown to be a powerful probe of magnetic excitations in...
Superconductivity is achieved in T'-Nd2CuO4 by means of oxygen annealing which injects electrons via controlled defect engineering. Here, we use Resonant Inelastic X-Ray Scattering (RIXS) to study the evolution of magnetic and charge excitations in parent and superconducting compounds. Our RIXS study reveals a hardening of the spin waves and the enhancement of charge excitations in the...
Superconducting fluctuations above the critical temperature provide valuable insight in the pairing mechanisms of superconductivity. The recent discovery of a pseudogap phase in NbN has opened many new questions. In this study we measure the paraconductivity and the Hall effect response in NbN originating from superconducting fluctuations. These experimental results are compared to a recent...
Unconventional superconductivity often emerges from an insulating/bad metallic parent compound phase, such as anti-ferromagnetic, charge density wave or spin density wave. However, the existence and influence of the parent compound correlation on superconductor state are poorly understood. Here we investigate this matter in the bismuthate high-temperature superconductor using angle-resolved...
The structural coherence across the ferroelectric transition in improper ferroelectric YMnO3 and other related multiferroic hexagonal manganites is not well understood. Here we reveal the evolution of the local structure in YMnO3 using neutron total scattering and first-principles calculations. We show that, at room temperature, the local and average structures are...
