Erratum: Fermi Surface Reconstruction and Electron Dynamics at the Charge-Density-Wave Transition in TiSe_{2} [Phys. Rev. Lett. 124, 167602 (2020)].

This corrects the article DOI: 10.1103/PhysRevLett.124.167602.

Fermi Surface Reconstruction and Electron Dynamics at the Charge-Density-Wave Transition in TiSe_{2}.

The evolution of the charge carrier concentrations and mobilities are examined across the charge-density-wave (CDW) transition in TiSe_{2}. Combined quantum oscillation and magnetotransport measurements show that a small electron pocket dominates the electronic properties at low temperatures while an electron and hole pocket contribute at room temperature. At the CDW transition, an abrupt Fermi surface reconstruction and a minimum in the electron and hole mobilities are extracted from two-band and Kohler analysis of magnetotransport measurements. The minimum in the mobilities is associated with the overseen role of scattering from the softening CDW mode. With the carrier concentrations and dynamics dominated by the CDW and the associated bosonic mode, our results highlight TiSe_{2} as a prototypical system to study the Fermi surface reconstruction at a density-wave transition.

Charge Order and Superconductivity in Underdoped YBa_{2}Cu_{3}O_{7-δ} under Pressure.

In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in T_{c} at the hole doping level where the CDW is strongest (n_{p}≃0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa_{2}Cu_{3}O_{7-δ} by measuring the temperature dependence of the Hall coefficient R_{H}(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases T_{c} by up to 10 K at 2.6 GPa, it has very little effect on R_{H}(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in T_{c} with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in T_{c} at n_{p}≃0.12 at ambient pressure is probably not caused by the CDW formation.

Lifshitz transition enabling superconducting dome around a charge-order critical point.

Superconductivity often emerges as a dome around a quantum critical point (QCP) where long-range order is suppressed to zero temperature, mostly in magnetically ordered materials. However, the emergence of superconductivity at charge-order QCPs remains shrouded in mystery, despite its relevance to high-temperature superconductors and other exotic phases of matter. Here, we present resistance measurements proving that a dome of superconductivity surrounds the putative charge-density-wave QCP in pristine samples of titanium diselenide tuned with hydrostatic pressure. In addition, our quantum oscillation measurements combined with electronic structure calculations show that superconductivity sets in precisely when large electron and hole pockets suddenly appear through an abrupt change of the Fermi surface topology, also known as a Lifshitz transition. Combined with the known repulsive interaction, this suggests that unconventional s± superconductivity is mediated by charge-density-wave fluctuations in titanium diselenide. These results highlight the importance of the electronic ground state and charge fluctuations in enabling unconventional superconductivity.

Pressure-Induced Metallization of BaH2 and the Effect of Hydrogenation.

Using optical spectroscopy, X-ray diffraction, and electrical transport measurements, we have studied the pressure-induced metallization in BaH2 and Ba8H46. Our combined measurements suggest a structural phase transition from BaH2-II to BaH2-III accompanied by band gap closure and transformation to a metallic state at 57 GPa. The metallization is confirmed by resistance measurements as a function of the pressure and temperature. We also confirm that, with further hydrogenation, BaH2 forms the previously observed Weaire-Phelan Ba8H46, synthesized at 45 GPa and 1200 K. In this compound, metallization pressure is shifted to 85 GPa. Through a comparison of the properties of these two compounds, a question is raised about the importance of the hydrogen content in the electronic properties of hydride systems.

Fröhlich interaction dominated by a single phonon mode in CsPbBr3.

The excellent optoelectronic performance of lead halide perovskites has generated great interest in their fundamental properties. The polar nature of the perovskite lattice means that electron-lattice coupling is governed by the Fröhlich interaction. Still, considerable ambiguity exists regarding the phonon modes that participate in this crucial mechanism. Here, we use multiphonon Raman scattering and THz time-domain spectroscopy to investigate Fröhlich coupling in CsPbBr3. We identify a longitudinal optical phonon mode that dominates the interaction, and surmise that this mode effectively defines exciton-phonon scattering in CsPbBr3, and possibly similar materials. It is additionally revealed that the observed strength of the Fröhlich interaction is significantly higher than the expected intrinsic value for CsPbBr3, and is likely enhanced by carrier localization in the colloidal perovskite nanocrystals. Our experiments also unearthed a dipole-related dielectric relaxation mechanism which may impact transport properties.

Fine Structure of Nearly Isotropic Bright Excitons in InP/ZnSe Colloidal Quantum Dots.

The fine structure of exciton states in colloidal quantum dots (QDs) results from the compound effect of anisotropy and electron-hole exchange. By means of single-dot photoluminescence spectroscopy, we show that the emission of photoexcited InP/ZnSe QDs originates from radiative recombination of such fine structure exciton states. Depending on the excitation power, we identify a bright exciton doublet, a trion singlet, and a biexciton doublet line that all show pronounced polarization. Fluorescence line narrowing spectra of an ensemble of InP/ZnSe QDs in magnetic fields demonstrate that the bright exciton effectively consists of three states. The Zeeman splitting of these states is well described by an isotropic exciton model, where the fine structure is dominated by electron-hole exchange and shape anisotropy leads to only a minor splitting of the F = 1 triplet. We argue that excitons in InP-based QDs are nearly isotropic because the particular ratio of light and heavy hole masses in InP makes the exciton fine structure insensitive to shape anisotropy.

Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots.

Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size-tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = ±2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = ±1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.