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Doped IrTe2 is considered a platform for topological superconductivity and therefore receives currently a lot of interest. In addition, the superconductivity in these materials exists in close vicinity to electronic order and the formation of molecular orbital crystals, which we explore here by means of high-pressure single crystal x-ray diffraction in combination with density functional theory. Our crystallographic refinements provide detailed information about the structural evolution as a function of applied pressure up to 42 GPa. Using this structural information for density functional theory calculations, we show that the local multicenter bonding in IrTe2 is driven by changes in the Ir-Te-Ir bond angle. When the electronic order sets in, this bond angle decreases drastically, leading to a stabilization of a multicenter molecular orbital bond. This unusual local mechanism of bond formation in an itinerant material provides a natural explanation for the different electronic orders in IrTe2. It further illustrates the strong coupling of the electrons with the lattice and is most likely relevant for the superconductivity in this material. The transition metal dichalcogenide IrTe2 is a candidate system to realise topological superconductivity, a sought-after state which could host Majorana fermions, and hence is of interest to the field of quantum computing. Here, the authors combine high-pressure X-ray diffraction and DFT calculations to investigate the evolution in the crystal- and electronic structure of IrTe2 as a function of pressure, highlighting the role of the Te-Ir-Te bond angle. [ABSTRACT FROM AUTHOR]

Spin-momentum locking in topological insulators and materials with Rashba-type interactions is an extremely attractive feature for novel spintronic devices and is therefore under intense investigation. Significant efforts are underway to identify new material systems with spin-momentum locking, but also to create heterostructures with new spintronic functionalities. In the present study we address both subjects and investigate a van der Waals-type heterostructure consisting of the topological insulator Bi2Se3 and a single Se-Ta-Se triple-layer (TL) of H-type TaSe2 grown by a method which exploits an interface reaction between the adsorbed metal and selenium. We then show, using surface x-ray diffraction, that the symmetry of the TaSe2-like TL is reduced from D3h to C3v resulting from a vertical atomic shift of the tantalum atom. Spin- and momentum-resolved photoemission indicates that, owing to the symmetry lowering, the states at the Fermi surface acquire an in-plane spin component forming a surface contour with a helical Rashba-like spin texture, which is coupled to the Dirac cone of the substrate. Our approach provides a route to realize chiral two-dimensional electron systems via interface engineering in van der Waals epitaxy that do not exist in the corresponding bulk materials. Current limitations of spintronics devices based on bulk topological materials stimulate the search for new materials and structures with interesting spin properties. Here the authors report a chiral spin texture around the Fermi level related to structural symmetry breaking in a TaSe2 layer grown on a Bi2Se3 surface. [ABSTRACT FROM AUTHOR]

Photo-induced switching between collective quantum states of matter is a fascinating rising field with exciting opportunities for novel technologies. Presently, very intensively studied examples in this regard are nanometer-thick single crystals of the layered material 1T-TaS2, where picosecond laser pulses can trigger a fully reversible insulator-to-metal transition (IMT). This IMT is believed to be connected to the switching between metastable collective quantum states, but the microscopic nature of this so-called hidden quantum state remained largely elusive up to now. Here, we characterize the hidden quantum state of 1T-TaS2 by means of state-of-the-art x-ray diffraction and show that the laser-driven IMT involves a marked rearrangement of the charge and orbital order in the direction perpendicular to the TaS2-layers. More specifically, we identify the collapse of interlayer molecular orbital dimers as a key mechanism for this non-thermal collective transition between two truly long-range ordered electronic crystals. The microscopic understanding of photo-induced insulator-to-metal transition (IMT) in 1T-TaS2 remains elusive. Here, Stahl et al. identify the collapse of interlayer molecular orbital dimers during a collective electronic phase transition as a key mechanism for the IMT in 1T-TaS2. [ABSTRACT FROM AUTHOR]

Doped IrTe2 is considered a platform for topological superconductivity and therefore receives currently a lot of interest. In addition, the superconductivity in these materials exists in close vicinity to electronic order and the formation of molecular orbital crystals, which we explore here by means of high-pressure single crystal x-ray diffraction in combination with density functional theory. Our crystallographic refinements provide detailed information about the structural evolution as a function of applied pressure up to 42 GPa. Using this structural information for density functional theory calculations, we show that the local multicenter bonding in IrTe2 is driven by changes in the Ir-Te-Ir bond angle. When the electronic order sets in, this bond angle decreases drastically, leading to a stabilization of a multicenter molecular orbital bond. This unusual local mechanism of bond formation in an itinerant material provides a natural explanation for the different electronic orders in IrTe2. It further illustrates the strong coupling of the electrons with the lattice and is most likely relevant for the superconductivity in this material. The transition metal dichalcogenide IrTe2 is a candidate system to realise topological superconductivity, a sought-after state which could host Majorana fermions, and hence is of interest to the field of quantum computing. Here, the authors combine high-pressure X-ray diffraction and DFT calculations to investigate the evolution in the crystal- and electronic structure of IrTe2 as a function of pressure, highlighting the role of the Te-Ir-Te bond angle. [ABSTRACT FROM AUTHOR]