Strong-coupling charge density wave in a one-dimensional topological metal

Abstract

Scanning tunnelling microscopy and low energy electron diffraction show a dimerization-like reconstruction in the one-dimensional atomic chains on Bi(114) at low temperatures. While onedimensional systems are generally unstable against such a distortion, its observation is not expected for this particular surface, since there are several factors that should prevent it: One is the particular spin texture of the Fermi surface, which resembles a one-dimensional topological state, and spin protection should hence prevent the formation of the reconstruction. The second is the very short nesting vector 2kF , which is inconsistent with the observed lattice distortion. A nesting-driven mechanism of the reconstruction is indeed excluded by the absence of any changes in the electronic structure near the Fermi surface, as observed by angle-resolved photoemission spectroscopy. However, distinct changes in the electronic structure at higher binding energies are found to accompany the structural phase transition. This, as well as the observed short correlation length of the pairing distortion, suggest that the transition is of the strong coupling type and driven by phonon entropy rather than electronic entropy.

Statics and dynamics of multivalley charge density waves in Sb(111)

“…The high sensitivity of HAS to CDWs as compared to other surface probes allowing for a precise determination of the transition temperatures and critical exponents was demonstrated long ago for layered chalcogenides 15,16 as well as recently for the 1D topological metal Bi(114). 17 The observation of phason dispersion curves with HAS was previously reported for the long-period reconstruction of the Au(111) 23 ffiffi ffi 3 p surface 18 and another hint comes from the non-adiabatic Kohn-anomalies observed for Mo(110):H and W(110):H [19][20][21][22] which are associated with electron-hole pair excitations. However, a signature of collective surface electronic excitations in elastic atom-surface scattering spectra has remained missing up to date.…”

Atom-surface van der Waals potentials of topological insulators and semimetals from scattering measurements

“…One of the most fascinating aspects when studying surfaces is that their physical and chemical properties can be radically different from those of the corresponding bulk material. The semimetals Bi and Sb are striking examples for these differences with the surfaces being much better metals than the bulk due to the existence of electronic surface states [66][67][68] . There are even more peculiar surface dominated effects when it comes to topological insulators: The material class of topological insulators (TIs) has recently attracted high interest [69][70][71][72][73][74] , due to their unique electronic structure which exhibits protected conducting surface as well as insulating bulk states 75,76 .…”

Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials

“…9,147 In this way, periodicity is measured at highest precision, see also Section 3.5, which allows for example an exact determination of surface phase transitions. Hofmann et al 148 recently showed (111) provides a sensitive probe to determine the surface phonon dispersion and energy dissipation processes in terms of the electron-phonon coupling constant l. The inset on the left illustrates the surface electronic structure of Bi 2 Se 3 (111) with the Dirac cone in green and a spin-split electron gas.…”

“…Since HAS or HeSE excite phonons via phonon-induced surface charge density oscillations, another consequence is that these probes may in principle excite also low-energy collective electronic excitations like surface phasons, 147 surface acoustic plasmons in the THz and sub THz domains, 9,158 charge density waves 147,148 as well as electron-hole excitations. 9,147 The observation of collective electronic excitations such as phasons and surface acoustic plasmons in interesting 2D conducting materials like topological insulators and graphene, 147,164 makes HAS a tool for the investigation of THz plasmonics, with great relevance for sensors and other nano-technologies.…”