Evolution of the gaps through the cuprate phase-diagram

The actual physical origin of the gap at the antinodes, and a clear identification of the superconducting gap are fundamental open issues in the physics of high-$T_c$ superconductors. Here, we present a systematic electronic Raman scattering study of a mercury-based single layer cuprate, as a function of both doping level and temperature. On the deeply overdoped side, we show that the antinodal gap is a true superconducting gap. In contrast, on the underdoped side, our results reveal the existence of a break point close to optimal doping below which the antinodal gap is gradually disconnected from superconductivity. The nature of both the superconducting and normal state is distinctly different on each side of this breakpoint

Coupling between quasiparticles and a bosonic mode in the normal state of HgBa2_2CuO4+δ_{4+\delta}

We report a doping dependent study of the quasiparticles dynamics in HgBa$_2$CuO$_{4+\delta}$ via Electronic Raman Scattering. A well-defined energy scale is found in the normal state dynamics of the quasiparticles over a broad doping range. It is interpreted as evidence for coupling between the quasiparticles and a collective bosonic mode whose energy scale depend only weakly with doping. We contrast this behavior with that of the superconducting gap whose amplitude near the node continuously decreases towards the underdoped regime. We discuss the implications of our findings on the nature of the collective mode and argue that electron-phonon coupling is the most natural explanation.Comment: 5 pages, 4 figure

The nodal gap component as a good candidate for the superconducting order parameter in cuprates

Although more than twenty years have passed since the discovery of high temperature cuprate superconductivity, the identification of the superconducting order parameter is still under debate. Here, we show that the nodal gap component is the best candidate for the superconducting order parameter. It scales with the critical temperature $T_c$ over a wide doping range and displays a significant temperature dependence below $T_c$ in both the underdoped and the overdoped regimes of the phase diagram. In contrast, the antinodal gap component does not scale with $T_c$ in the underdoped side and appears to be controlled by the pseudogap amplitude. Our experiments establish the existence of two distinct gaps in the underdoped cuprates

Incommensurate phonon anomaly and the nature of charge density waves in cuprates

While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wavevectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here we investigate the temperature dependence of the low energy phonons in the canonical CDW ordered cuprate La$_{1.875}$Ba$_{0.125}$CuO$_{4}$. We discover that the phonon softening wavevector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wavevector of 0.238 reciprocal space units (r.l.u.) below the ordering transition temperature up to 0.3~r.l.u. at 300~K. This high-temperature behavior shows that "214"-type cuprates can host CDW correlations at a similar wavevector to previously reported CDW correlations in non-"214"-type cuprates such as YBa$_{2}$Cu$_{3}$O$_{6+\delta}$. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low temperature ordering wavevectors.Comment: Accepted in Phys. Rev. X; 9 pages; 5 figures; 3 pages of supplementary materia

Two Distinct Electronic Contributions in the Fully Symmetric Raman Response of High TcT_{c} Cuprates

We show by non resonant effect in HgBa$_2$CuO$_{4+\delta}$ (Hg-1201)and by Zn substitutions in YBa$_2$Cu$_3$O$_{7-\delta}$ (Y-123) compounds that the fully symmetric Raman spectrum has two distinct electronic contributions. The A$_{1g}$ response consists in the superconducting pair breaking peak at the 2$\Delta$ energy and a collective mode close to the magnetic resonance energy. These experimental results reconcile the \textit{d-wave} model to the A$_{1g}$ Raman response function in so far as a collective mode that is distinct from the pair breaking peak is present in the A$_{1g}$ channel.Comment: 4 pages, 2 figure

Magnetotransport of SrIrO 3 -based heterostructures

Transition-metal oxide (TMO) based heterostructures provide fertile playground to explore or functionalize novel quantum materials. In this regard, the combination of 3d and 5d TMOs have gained special interest because of the simultaneous appearance of strong spin-orbit coupling and electron correlation at the interface of those heterostructures. Artificial breaking of the inversion symmetry in heterostructures may also result in a distinct interfacial Dzyaloshinskii- Moriya interaction (DMI) and the formation of non-collinear magnetic spin structures in case of magnetic TMOs. Among the 5d TMOs, SrIrO3 (SIO) has gained significant attention because of its large spin-orbit coupling and the semi-metallic ground state, which are highly susceptible to structural distortions. Here, we report on the preparation and the characterisation of structural, electronic and magnetic properties of epitaxial heterostructures consisting of the 5d TMO SIO and the 3d antiferromagnetic insulator LaFeO3

Patterning of two-dimensional electron systems in SrTiO₃ based heterostructures using a CeO₂ template

Two-dimensional electron systems found at the interface of SrTiO3-based oxide heterostructures often display anisotropic electric transport whose origin is currently under debate. To characterize transport along specific crystallographic directions, we developed a hard-mask patterning routine based on an amorphous CeO2 template layer. The technique allows preparing well-defined microbridges by conventional ultraviolet photolithography which, in comparison to standard techniques such as ion- or wet-chemical etching, does not induce any degradation of interfacial conductance. The patterning scheme is described in detail and the successful production of microbridges based on amorphous Al2O3-SrTiO3 heterostructures is demonstrated. Significant anisotropic transport is observed for T < 30 K which is mainly related to impurity/defect scattering of charge carriers in these heterostructures

In-between Bragg reflections: Thermal diffuse scattering and vibrational spectroscopy with x-rays

In the last decade diffuse scattering studies re-gained their place in the domain of lattice dynamics studies. The use of thermal diffuse scattering becomes particularly efficient when coupled with vibrational spectroscopy, where inelastic x-ray scattering can be advantageous compared to inelastic neutron scattering, and state-of-the-art ab initio calculations. We present a brief summary of the experimental and theoretical background, give an overview of the principal experimental implementations, and discuss a representative set of examples of such a combined approach