(3×1)-Br/Pt(110) structure and the charge-density-wave-assistedc(2×2)to

Abstract

After our recent report on the formation of a (3ϫ1) charge-density-wave phase in the quasi-onedimensional system Br/Pt͑110͒ we present a detailed investigation of the c(2ϫ2)⇒(3ϫ1) transition in the Br/Pt͑110͒ adsorption system. This includes the atomic structure of the (3ϫ1) phase as determined by quantitative low-energy electron diffraction ͑LEED͒ and density functional theory calculations. While in the parent c(2ϫ2) phase with coverage ⌰ϭ1/2 ML the Br atoms occupy every second short-bridge site on the unreconstructed (1ϫ1)-Pt͑110͒ surface, the adatoms in the (3ϫ1) phase at coverage ⌰ϭ2/3 ML reside in every third short-bridge and long-bridge sites. Charge densities and vertical relaxations of the Pt atoms forming the short-and long-bridge sites are different, thus yielding a modulation of both, the charge and the position of the outermost Pt atoms with a period of three nearest-neighbor spacings. For 1/2 MLϽ⌰р0.58 ML LEED intensity and scanning tunneling microscope ͑STM͒ measurements reveal the nucleation of (3ϫ1) islands surrounded by areas with a local coverage of 1/2 ML. Within the latter areas the STM measurements indicate dynamical fluctuations of the Br positions at room temperature. In the time average every short-bridge site is sampled by the mobile Br atoms, but in the neighborhood of (3ϫ1) islands every third short-bridge site seems to be preferentially occupied.

The surface electronic structure of Br/Pt(110) phases

“…Br was dosed onto the sample from a solid state electrolysis cell [13]. Desired coverages were prepared by a Br exposure corresponding to more than 1 ML and subsequent annealing to calibrated temperatures yielding the optimum LEED patterns for either the cð2 Â 2Þ or the (3 · 1) structure [14,15]. ARUPS spectra were recorded by means of an OMICRON AR 65 analyzer mounted on a two-axis goniometer.…”

Fluctuating Charge Order: A Universal Phenomenon in Unconventional Superconductivity?

“…However, in the space between the pinned domains, only a (1ˆ1) contrast is visible. This is due to the fluctuation driven mobility of the Br atoms, which, in the time averaged STM image, visit every adsorption site with equal probability [25]. Analogously, one could envision that defect pinning of the charge fluctuations in superconductors does not necessarily lead to a global static charge ordering.…”

“…Pt exhibits a strong Kohn anomaly in its phonon dispersion, signaling a coupling of the phonons to electronic excitations with finite wave vector q at E F . On the strongly anisotropic (110) surface, this results in a tendency to develop a surface CDW [25]. Saddle-points in the surface electronic structure [26][27][28] at E F favor a CDW phase by providing a large joint density of states.…”

“…(110)) recorded at T = 50 K [29]. Imaging of the time-dependent domains is possible, since the fluctuations are slow at 50 K; (b) STM image of (3ˆ1) domains (0.55 ML Br/Pt(110)) recorded at room temperature [25]. Here, imaging of the domains is possible, because they are pinned at defects.…”

“…In other words, the adsorbate elicits the CDW order in a kind of bootstrap mechanism. [25]. Here, imaging of the domains is possible, because they are pinned at defects.…”