Temperature-dependent Photoemission Spectroscopy Research Articles

Origin of the temperature dependence of the energy gap in Cr-doped Bi2Se3.

Recent progress in impurity-doped topological insulators has shown that the gap at the Dirac point shrinks with reducing temperature. This is an obstacle for experimental realization of the quantum anomalous Hall effect at higher temperature due to the requirement of a larger energy gap. In order to solve this puzzle, we study the gap at the Dirac point by performing temperature-dependent photoemission spectroscopy and X-ray diffraction experiments in Cr-doped Bi2Se3. Our valence band photoemission study revealed that the gap alters with temperature due to residual gas condensation on the sample surface with cooling. Residual gas on the sample surface creates an electron doping effect that modifies the chemical potential of the system resulting in the change of the gap size with variable temperature. Furthermore, such electron doping can weaken the ferromagnetism and lead to a bulk band contribution in the transport measurements. Therefore, such effects can hinder the existence of the quantum anomalous Hall state at higher temperatures. Hence, this work can pave the way for future studies towards a high-temperature quantum anomalous Hall effect.

Photoemission spectroscopy and the unusually robust one-dimensional physics of lithium purple bronze

Temperature-dependent photoemission spectroscopy in Li0.9Mo6O17 contributes to evidence for one-dimensional (1D) physics that is unusually robust. Three generic characteristics of the Luttinger liquid are observed: power law behavior of the k-integrated spectral function down to temperatures just above the superconducting transition, k-resolved lineshapes that show holon and spinon features, and quantum critical (QC) scaling in the lineshapes. Departures of the lineshapes and the scaling from expectations in the Tomonaga–Luttinger model can be partially described by a phenomenological momentum broadening that is presented and discussed. The possibility that some form of 1D physics obtains even down to the superconducting transition temperature is assessed.

Temperature-dependent photoemission spectroscopy study of RExC60 (RE=Yb and Sm) films

Temperature-dependent electronic structures of RExC60 (where RE denotes Yb and Sm) films have been studied by high-resolution photoemission spectroscopy (PES). Our results indicate that Yb5C60 is the only metallic phase among all the phases in Yb doped C60 films. For the Sm fullerides, PES results show that there is no Sm valence transition during the negative thermal expansion in Sm2.75C60 below 32K. The Sm valence state in Sm2.75C60 films is nearly +2 at room temperature and remains stable in the films down to 16K. In addition, the negative thermal expansion effect does not result any distinct change in valence-band electronic structures of Sm2.75C60.

Photoemission study of the temperature-dependent energy-gap formation in the Kondo semiconductor CeRhAs

The temperature dependence of the Ce 4f state of a Kondo semiconductor CeRhAs has been examined by means of high-resolution temperature-dependent photoemission spectroscopy. The Ce 4f spectral intensity near the Fermi level ( E F) is gradually decreased on cooling indicating temperature-dependent metal-to-insulator transition. The magnitudes of the energy-gap for the f, d, and p states are the same, indicating that these states are strongly hybridized near E F and form the energy-gap.

Pseudogap formation in Kondo insulators CeRhSb and CeRhAs studied by ultrahigh-resolution photoemission spectroscopy

We report an ultrahigh-resolution (Δ E∼8 meV) temperature-dependent photoemission spectroscopy on the Kondo insulators CeRhAs and CeRhSb. We have observed a pseudogap at the Fermi level at low temperature for both compounds, which is gradually filled-in with increasing temperature. We found that the size of pseudogap is well scaled with the Kondo temperature ( T K) while the temperature evolution is dominated by another characteristic temperature much lower than T K.

Electron–phonon interaction of quantum-well states on Ag nanofilms studied by temperature-dependent photoemission spectroscopy

We have carried out a temperature-dependent angle-resolved photoemission study for Ag(111) nanofilms grown on Cu(111) substrates. The valence band photoemission spectra of Ag nanofilms exhibit the features associated with the quantum-well (QW) states. It is found that the linewidth of the QW state broadens systematically with increasing temperature from 40 to 350 K and it depends linearly on the temperature. The observed temperature dependence is explained as the phonon contribution to the inverse hole lifetime. It is indicated that these results allow the discussion of the electron–phonon interaction through the electron–phonon mass enhancement parameter λ , which enters the linewidth as 2π λk B T. The experimental electron–phonon mass enhancement parameters for the QW states have been compared to that for surface state on the Ag(111) surface and that reported as an average over the bulk Fermi surface.