The fine balancing of the lateral intermolecular interactions and the bonding to the substrate enables the self‐assembly of supramolecular nanostructures at surfaces to be achieved. The scanning tunneling microscopy image shows the formation of a twin chain of 4‐[trans‐2‐(pyrid‐4‐yl)vinyl]benzoic acid deposited on an Ag(111) surface in ultra‐high vacuum.

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We report on a novel approach to measure the phase relaxation length and femtosecond lifetime of hot quasiparticles on metal surfaces. A 4 K scanning tunneling microscope has been used to study the spatial decay of interference patterns in the local density of states for surface state electrons on Ag(111) and Cu(111). This decay is governed by inelastic electron-electron scattering. We find a ͑E 2 E F ͒ 22 energy dependence of the lifetimes for both Ag and Cu, and our values are comparable to the corresponding bulk electron lifetimes. This indicates that electron-electron interaction of hot surface state electrons with the Fermi sea is dominated by the underlying bulk electrons.[S0031-9007 (99)09260-1] PACS numbers: 73.20.At, 61.16.Ch, 72.10.Fk, 72.15.LhThe phase relaxation length L f , i.e., the distance a quasiparticle can propagate without losing its phase memory, is a key quantity in solid state physics. Quantum mechanical interference phenomena can prevail only if L f is larger than any other relevant length scale [1]. Examples include Aharonov-Bohm oscillations, quantum Hall effect, Friedel oscillations, and localization. With respect to surface physics, L f -or equivalently the lifetime t f of the quasiparticle-is of particular interest, since it governs the dynamics of charge transfer and electronic excitations in surface chemistry [2].Elegant experiments have been performed to determine

The temperature-dependent damping of quantum-mechanical interference patterns from surface-state electrons scattering off steps on Ag͑111͒ and Cu͑111͒ has been studied using scanning tunneling microscopy ͑STM͒ and spectroscopy in the temperature range 3.5-178 K. The thermal damping of the electron standing waves is described quantitatively within a simple plane-wave model accounting for thermal broadening due to the broadening of the Fermi-Dirac distributions of sample and tip, for beating effects between electrons with different k ͉͉ vectors, and for inelastic collisions of the electrons, e.g., with phonons. Our measurements reveal that Fermi-Dirac broadening fully explains the observed damping for Ag and Cu. From the analysis of our data, lower limits of the phase-relaxation lengths at the Fermi energy E F of the two-dimensional electron gas of L (E F )տ600 Å at 3.5 K and տ250 Å at 77 K for Ag͑111͒, and of L (E F )տ660 Å at 77 K and տ160 Å at 178 K for Cu͑111͒ are deduced. In contrast to integral measurements such as photoemission we measure L close to E F and also locally. The latter eliminates residual line widths due to surface defect scattering found in the integrating techniques. Our STM results, therefore, currently provide a very good absolute estimate of L and the inelastic lifetime ϭL /v F , respectively. Our values can be combined with photoemission results on dL /dT to derive the inelastic lifetime of surface state electrons at any T. ͓S0163-1829͑99͒02524-2͔

The specific heat C p (T,H) and the magnetization M (T,H) of a large twinned single crystal of YBa 2 Cu 3 O 7 have been measured using a high-resolution differential-thermal-analysis calorimeter and superconducting quantum interference device magnetometry, in magnetic fields up to 7 T. An apparently reasonable scaling of the data may be obtained using either the three-dimensional ͑3D͒ XY model or the lowest-Landaulevel approximation. The high relative accuracy of the data allows a direct evaluation of the critical temperature T c and the critical exponent of the 3D XY model. This analysis indicates that the data do not obey 3D