Observation of particle hole asymmetry and phonon excitations in non-Fermi-liquid systems: A high-resolution photoemission study of ruthenates

Abstract

PACS. 71.10.Hf -Non Fermi liquid ground states, electron phase diagrams and phase transitions in model systems. PACS. 63.20.Kr -Phonon -electron and phonon -phonon interactions. PACS. 71.45.Gm -Exchange, correlation, dielectric and magnetic response functions, plasmons.Abstract. -We investigate the temperature evolution of the electronic states in the vicinity of the Fermi level of a non-Fermi liquid (NFL) system, CaRuO3 using ultra high-resolution photoemission spectroscopy; isostructural SrRuO3 exhibiting Fermi liquid behavior despite similar electron interaction parameters as that of CaRuO3, is used as a reference. High-energy resolution in this study helps to reveal particle-hole asymmetry in the excitation spectra of CaRuO3 in contrast to that in SrRuO3. In addition, we observe signature of phonon excitations in the photoemission spectra of CaRuO3 at finite temperatures while these are weak in SrRuO3.Recent observations of various bulk properties in normal phase of high temperature superconductors [1], d and f electrons at quantum critical points [2], low dimensional systems [3] etc., exhibit deviations from Fermi-liquid (FL) behavior, the most fundamental paradigm in solid-state physics [4]. Such non-Fermi liquid (NFL) behavior has often been attributed to strong electron correlations and/or charge fractionalizations [5]. Interestingly, CaRuO 3 , a 3-dimensional orthorhombically distorted perovskite exhibits NFL behavior at low temperatures, while isostructural SrRuO 3 exhibits Fermi liquid (FL) behavior [6]. Magnetic measurements reveal ferromagnetic ground state in SrRuO 3 (Curie temperature, T C ∼ 165 K). However, CaRuO 3 does not exhibit long range order.The average Ru-O-Ru bond angle is slightly different in these two compounds (150 • in CaRuO 3 and 165• in SrRuO 3 ). It was believed that the decrease in the electron hopping interaction strength, t, due to smaller Ru-O-Ru angle in CaRuO 3 leads to an increase in effective electron correlation strength, U/W (U = electron-electron Coulomb repulsion strength, t ∝ W ∼ bandwidth), and hence the NFL behavior appears in CaRuO 3 [6]. However, a recent study based on band structure calculation and photoemission spectroscopy [7] shows that the width of various d-bands remains almost the same across the series and U/W is essentially ( * ) Corresponding author: kbmaiti@tifr.res.in c EDP Sciences

Complex temperature evolution of the electronic structure of CaFe2As2

“…Within this description, the spectral function of a correlated system in the intermediate coupling regime consists of three features; upper (unoccupied) and lower (occupied) Hubbard bands representing the correlation induced localized states and a central band at the Fermi level, termed as the coherent feature representing the itinerant carriers often captured well by the ab initio band structure calculations 21 . The decrease in temperature leads to an enhancement of the coherent feature intensity at the cost of the Hubbard band intensities 19,22 . The temperature induced changes in the valence band shown in Fig.…”

Manifestation of screening effects andA−Ocovalency in the core level spectra ofAsite elements in theABSingh1, Maiti2 2007Phys. Rev. B385240View full textAdd to dashboardCite

“…However, no long-range order is found in CaRuO 3 down to the lowest temperature studied. [2][3][4][5][6] These investigations predict a non-Fermi-liquid ground state in CaRuO 3 in contrast to the Fermi-liquid behavior observed in SrRuO 3 . [2][3][4] Both SrRuO 3 and CaRuO 3 form in an orthorhombic perovskite structure ͑ABO 3 type͒.…”

Evolution of the electronic structure of HoB4with temperature

“…Interestingly, the difference spectra (I(T )−I(300K)) exhibit larger change in spectral weight above ǫ F relative to that below ǫ F indicating a signature of particle-hole asymmetry. 20 Intensity at the Fermi level obtained by the symmetrization of the experimental spectra (I(ǫ − ǫ F ) + I(ǫ F − ǫ)) exhibits gradual decrease with the decrease in temperature. An additional sharp dip is observed in the 10 K data reflecting signature of the long range order in the ground state.…”