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A quantum critical point (QCP) describes a phase change independent of thermal fluctuations and instead can be driven by chemical or hydrostatic pressure. Here, the authors investigate by X-ray diffraction the evolution of the charge density wave in 2H-TaSe₂ as a function of pressure and demonstrate how it is intertwined with a QCP and the superconducting phase of the system.

Insulators can be classified according to the kind of electronic interactions they are dominated by. Hellmannet al. used time- and angle-resolved photoelectron spectroscopy to determine the dominant interactions in a series of transition metal dichalcogenides.

Weyl semimetals exhibit Berry flux monopoles in momentum-space, but direct experimental evidence has remained elusive. Here, the authors reveal topologically non-trivial winding of the orbital-angular-momentum at the Weyl nodes and a chirality-dependent spin-angular-momentum of the Weyl bands, as a direct signature of the Berry flux monopoles in TaAs.

The nature of the charge density wave transition in VSe₂ is still debated. Here, the authors demonstrate that the transition is mainly driven by electron-phonon interactions, despite the presence of the Fermi-surface nesting, and that Wan-der-Waals forces are responsible for melting of the charge density wave order.

The electronic and structural components of charge density waves occurring in layered transition metal dichalcogenides are known to be interdependent, yet have only been probed in separate measurements. Now, a broadband terahertz spectroscopy approach that monitors the evolution of these two order parameters simultaneously is demonstrated.

The non-equilibrium dynamics of correlated electron materials are still poorly understood. Here, the authors use time- and angle-resolved photoemission spectroscopy to show that carrier multiplication is important in initial non-equilibrium dynamics of 1T-TiSe₂and depends on the size of the energy gap.

A tracing of the phase-ordering kinetics of a charge density wave system demonstrates the potential of ultrafast low-energy electron diffraction for studying phase transitions and ordering phenomena at surfaces and in low-dimensional systems.

A theoretical and experimental study reveals the relation between charge density waves and orbital textures for different stackings in a two-dimensional layered material.

Matrix element effects in ARPES are important for addressing properties of the initial state wave functions, but the results can strongly vary with experimental configuration or final state. The authors show that an observable called time-reversal dichroism can filter out such effects, providing a direct link to orbital angular momentum and pseudospin.

The study of electronic structure of new materials has benefited from more widely available angle-resolved photoelectron spectroscopy (ARPES) at synchrotron sources, but hard X-ray ARPES, capable of mapping at a depth of some tens nanometres is still of limited access. The authors report on a method to obtain bulk electronic structure using hard X-rays ARPES combined with an effective data processing background removal strategy capable of revealing the valence band electronic dispersion of metal and semiconductor surfaces.

Local inversion symmetry breaking in centrosymmetric materials can lead to large spin polarization of the electronic band structure in separate sectors of the unit cell. Here, the authors reveal such hidden spin polarisation in ZrSiTe using spin and angle resolved photoemission spectroscopy in combination with ab initio band structure calculations and investigate the resultant spin polarised bulk and surface properties

Angle resolved photoelectron spectroscopy can reveal the band and spin structures of a system but the contribution of different types of photoelectron diffraction is challenging to interpret. Here, the authors develop an analysis method to reveal the contribution of Laue- and Kikuchi-type diffraction to the valence band spectra when using photoemission techniques.