Giant Friedel Oscillations on the Beryllium(0001) Surface

Abstract

Large-amplitude electron density oscillations were observed on a Be(0001) surface by means of variable-temperature scanning tunneling microscopy. Fourier transforms of the images showed a ring of radius 2kF, where kF is the Fermi wave vector of the Be(0001) surface state. This wavelength was expected from Friedel oscillations caused by electronic screening of surface defects, but the amplitude of the waves for energies near the Fermi energy was anomalously large and inconsistent with the Friedel concept of screening. The enhanced amplitude of the waves must be a many-body effect, either in the electron gas (possibly an incipient charge density wave) or in the response of the lattice (electron-phonon coupling).

Single impurity in ultracold Fermi superfluids

“…However, under many circumstances, impurities, rather than representing a nuisance, serve useful purposes such as the detection of quantum effects [1,2]. Single impurities have been employed in the detection of superconducting pairing symmetry within unconventional superconductors [3] and to demonstrate Friedel oscillations [4]. In strongly correlated systems, they may be used to pin one of the competing orders [5].…”

Scanning Tunneling Spectroscopy of Ag Films: The Effect of Periodic versus Quasiperiodic Modulation

“…For each energy level, the Fourier transformation of E; y is calculated as E; q y R E; y e iq y y dy. As discussed earlier [13,14], the spatial modulation of the LDOS with a wave vector of q is a consequence of the scattering between two degenerate states jE 1 ; k 1 i and jE 2 ; k 2 i with q k 1 -k 2 and E 1 E 2 . For a 1D case, this corresponds to the scattering between jki and j ÿ ki, where k q=2.…”

“…In addition, as the electronic structures are probed locally using scanning tunneling spectroscopy (STS), the spatial averaging effect masking fine electronic structures is completely avoided. The k-resolved electronic structures are obtained through a Fourier analysis, following the so-called Fourier-transformed STS [13,14].…”

Quasiparticle echoes in scanning tunneling microscopy

“…In the case of a superconductor, the method can potentially distinguish the nature of the scattering by a particular impurity. PACS numbers: 74.55.+v,72.10.Fk,73.20.At,74.72.ah Scanning Tunneling Microscopy (STM), which measures the "local density of states" (LDOS) as a function of position and energy set by the bias voltage, has opened the door to imaging the sub-nanoscale topography and electronic structure of materials, including normal metals [1] and especially cuprate superconductors [2,3,4,5,6,7,8,9].The dispersion relations of (Landau or Bogoliubov) quasiparticles may be extracted from STM data on normal metals [10,11] and superconductors [13], via the inverse method called Fourier transform scanning tunneling spectroscopy (FT-STS) [10,13], or directly in real space [11]. This technique is based on the fact that impurities produce spatial modulations of the LDOS in their vicinity -standing waves in the electronic structure that generalize the Friedel oscillations found in metals at the Fermi energy.…”

“…The dispersion relations of (Landau or Bogoliubov) quasiparticles may be extracted from STM data on normal metals [10,11] and superconductors [13], via the inverse method called Fourier transform scanning tunneling spectroscopy (FT-STS) [10,13], or directly in real space [11]. This technique is based on the fact that impurities produce spatial modulations of the LDOS in their vicinity -standing waves in the electronic structure that generalize the Friedel oscillations found in metals at the Fermi energy.…”