Photofield emission spectroscopy and surface density of states

A novel procedure for the investigation of optical excitations on the metal surface by the photofield emission method is reviewed. A separation procedure of thermocurrent, accompanying the measured photocurrent, induced by the chopped light beam, is described. A differentiation of the true photocurrent curve allows one to obtain an energy distribution of photoelectrons. For the (0 0 0 1) face of Ti, it exhibits very small and densely spaced maxima, confirmed by theory as surface resonances. The dependence of the density on the thickness of the Ti crystal, grown by evaporation of Ti on the W field emitter surface, was verified experimentally. The possibility of observing surface resonances on a microcrystal of a homogeneous field emitter is discussed.     

Photo field emission spectroscopy of Γ-P AND Γ-〈013〉 bands of tungsten

Photo field emission currents from clean (013) and clean and barium covered (111) regions of a tungsten tip have been measured in a field emission microscope using two wavelengths of laser radiation and phase-sensitive detection. The photo field emission current-voltage characteristics show various slopes and shoulders. These shoulders are considered as correlated with optical transitions between energy bands of tungsten. The final and initial energies are evaluated from the excitation energy and the known lowering of the barrier maximum. The obtained results are in fairly good agreement with the band structure of tungsten calculated by Christensen and Feuerbacher [1]. Except direct transitions which are prevailing also some indirect transitions were found. The slopes of the photocurrent characteristics are discussed.     

Photo field-emission spectroscopy of optical transitions in the band structure of tungsten

Photo field-emission currents of clean and barium-covered tungsten tips in a sligthly modified FEM-configuration have been measured under UHV-conditions by modulating monochromatic mercury arc radiation and phase-sensitive detection. From Fowler-Nordheim plots of the field-emission currents field strength and work function were determined as usual. The photo field-emission current—voltage characteristics show various slopes and shoulders which are dependent on excitation energy, work function, and applied field. The shoulders are interpreted to indicate optical transitions, whose final and initial energies are evaluated from the excitation energy and the Schottky lowering of the barrier maximum. A comparison with the band structure of tungsten as calculated by Mattheiss or Christensen and Feuerbacher demonstrates that apart from single nondirect transitions from or to band extrema direct (k-conserving) transitions are prevailing. Some properties of this new method for the investigation of band structure details are given.     

Correlation between Quantum Entanglement and Quantum Coherence in the Case of XY Spin Chains with the Dzyaloshinskii–Moriya Interaction

Journal of Experimental and Theoretical Physics - Recently, there has been an increased interest in studying quantum entanglement and quantum coherence. Since both of these properties are...