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Optimally doped cuprate are characterized by the presence of superconducting fluctuations in a relatively large temperature region above the critical transition temperature. We reveal here that the effect of thermal disorder, which decreases the condensate phase coherence at equilibrium, can be dynamically contrasted by photoexcitation with ultrashort midinfrared pulses. In particular, our findings reveal that light pulses with photon energy comparable to the amplitude of the superconducting gap and polarized in plane along the copper-copper direction can dynamically enhance the optical response associated with the onset of superconductivity. We propose that this effect can be rationalized by an effective d-wave BCS model, which reveals that midinfrared pulses result in a transient increase of the phase coherence.

The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role in the superconducting mechanisms is still controversial. Here we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c-axis phonon modes and the in-plane electronic charge excitations in optimally doped YBa2Cu3O7. The nonequilibrium Raman tensor is measured by means of the broadband "coherent-phonon" response in pump-probe experiments and is qualitatively described by our model using density functional theory in the frozen-phonon approximation plus single-band dynamical mean-field theory to account for the electronic correlations. The major outcome of our experimental and theoretical study is to establish the link between out-of-plane copper ion displacements and the in-plane electronic correlations, and to estimate at a few unit cells the correlation length of the associated phonon mode. The approach introduced here could help in revealing the complex interplay between fluctuations of different nature and spatial correlation in several strongly correlated materials.

The transient optical conductivity of photoexcited 1T-TaS2 is determined over a three-order-of-magnitude frequency range. Prompt collapse and recovery of the Mott gap is observed. However, we find important differences between this transient metallic state and that seen across the thermally-driven insulator-metal transition. Suppressed low-frequency conductivity, Fano phonon lineshapes, and a mid-infrared absorption band point to polaronic transport. This is explained by noting that the photo-induced metallic state of 1T-TaS2 is one in which the Mott gap is melted but the lattice retains its low-temperature symmetry, a regime only accessible by photo-doping.

We have studied the magnetodielectric and magnetoelastic coupling in TbFe3(BO3)(4) single crystals by means of capacitance, magnetostriction, and Raman spectroscopy measurements. The data reveal strong magnetic field effects on the dielectric constant and on the macroscopic sample length which are associated to long-range magnetic ordering and a field-driven metamagnetic transition. We discuss the coupling of the dielectric, structural, and magnetic order parameters and attribute the origin of the magnetodielectric coupling to phonon mode shifts according to the Lyddane-Sachs-Teller relation.

Time-resolved dynamics in charge-density-wave materials have revealed interesting out-of-equilibrium electronic responses. However, these are typically only performed in a single material possessing a CDW. As such, it is challenging to separate subtle effects originating from the CDW. Here, we report on the ultrafast dynamics of the GdSbxTe2–x–δ series of materials where EF can be tuned, resulting in a change from an undistorted tetraganal phase to a CDW with a wavevector that depends on x. Using mid-infrared, near-infrared, and visible excitation, we find the dynamics are sensitive to both EF and the presence of the CDW. Specifically, as the Sb content of the compounds increases, transient spectral features shift to higher probe energies. In addition, we observe an enhanced lifetime and change in the sign of the transient signal upon removing the CDW with high Sb concentrations. Finally, we reveal fluence- and temperature-dependent photoinduced responses of the differential reflectivity, which provide evidence of transient charge density wave suppression in related telluride materials. Taken together our results provide a blueprint for future ultrafast studies of CDW systems.

We present a novel approach to transient Raman spectroscopy, which combines stochastic probe pulses and a covariance-based detection to measure stimulated Raman signals in alpha-quartz. A coherent broadband pump is used to simultaneously impulsively excite a range of different phonon modes, and the phase, amplitude, and energy of each mode are independently recovered as a function of the pump–probe delay by a noisy-probe and covariance-based analysis. Our experimental results and the associated theoretical description demonstrate the feasibility of 2D-Raman experiments based on the stochastic-probe schemes, with new capabilities not available in equivalent mean-value-based 2D-Raman techniques. This work unlocks the gate for nonlinear spectroscopies to capitalize on the information hidden within the noise and overlooked by a mean-value analysis.

Superconductivity in the cuprates is characterized by an anisotropic electronic gap of $d$-wave symmetry. The aim of this work is to understand how this anisotropy affects the nonequilibrium electronic response of high-${T}_{c}$ superconductors. Here we use a polarization selective time domain experiment to address the dynamics of electronic excitation of different symmetry in optimally doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Y}}_{0.08}{\mathrm{Ca}}_{0.92}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ and measure the nodal and antinodal nonequilibrium response resulting from photoexcitations with ultrashort pulses with photon energy comparable to the superconducting gap. The response to long wavelength photoexcitation with pump polarization along the Cu-Cu axis of the sample is discussed with the support of an effective $d$-wave BCS model which suggests that such transient response could be ascribed to an increase of pair coherence in the antinodal region.

Unveiling and controlling the time evolution of the momentum and position of low energy excitations such as phonons, magnons, and electronic excitation is the key to attain coherently driven new functionalities of materials. Here we report the implementation of femtosecond time- and frequency-resolved multimode heterodyne detection and show that it allows for independent measurement of the time evolution of the position and momentum of the atoms in coherent vibrational states in α -quartz. The time dependence of the probe field quadratures reveals that their amplitude is maximally changed when the atoms have maximum momentum, while their phase encodes a different information and evolves proportionally to the instantaneous atomic positon. We stress that this methodology, providing the mean to map both momentum and position in one optical observable, may be of relevance for both quantum information technologies and time-domain studies on complex materials.

Strong light-matter coupling is emerging as a fascinating way to tune optical properties and modify the photophysics of molecular systems. In this work, we studied a molecular chromophore under strong coupling with the optical mode of a Fabry-Perot cavity resonant to the first electronic absorption band. Using femtosecond pump-probe spectroscopy, we investigated the transient response of the cavity-coupled molecules upon photoexcitation resonant to the upper and lower polaritons. We identified an excited state absorption from upper and lower polaritons to a state at the energy of the second cavity mode. Quantum mechanical calculations of the many-molecule energy structure of cavity polaritons suggest assignment of this state as a two-particle polaritonic state with optically allowed transitions from the upper and lower polaritons. We provide new physical insight into the role of two-particle polaritonic states in explaining transient signatures in hybrid light-matter coupling systems consistent with analogous many-body systems.