Effects of the Fermi-surface shrinking on the optical sum rule in pnictides

Benfatto, Lara; Cappelluti, E.

doi:10.1103/physrevb.83.104516

Cited by 32 publications

(47 citation statements)

References 37 publications

(77 reference statements)

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“…If related to spin fluctuations, one could expect interband interactions to weaken at high T, as the strength of spin fluctuations decreases [11]. In Fig.…”

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confidence: 89%

“…These simulations allow to account for about half the experimental shift. Part of the expansion of the electron pockets could also be due to the weakening of the k-shift, as proposed in [11] for the model of interband interactions, or to an evolution of correlation effects.Single crystals of Ba(Fe 1−x Co x ) 2 As 2 were grown using a FeAs self-flux method and studied in detail by transport measurements [12]. ARPES experiments were carried out at the CASSIOPEE beamline at the SOLEIL synchrotron, with a Scienta R4000 analyzer, an angular resolution of 0.2…”

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confidence: 96%

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Large Temperature Dependence of the Number of Carriers in Co-DopedBaFe2As2

et al. 2013

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Using angle-resolved photoemission spectroscopy, we study the evolution of the number of carriers in Ba(Fe1−xCox)2As2 as a function of Co content and temperature. We show that there is a kdependent energy shift compared to density functional calculations, which is large at low Co contents and low temperatures and reduces the volume of hole and electron pockets by a factor 2. This k-shift becomes negligible at high Co content and could be due to interband charge or spin fluctuations. We further reveal that the bands shift with temperature, changing significantly the number of carriers they contain (up to 50%). We explain this evolution by thermal excitations of carriers among the narrow bands, possibly combined with a temperature evolution of the k-dependent fluctuations.PACS numbers: 79.60.-i, 71.18.-y, 71.30.-h Since the discovery of iron based superconductors, angle resolved photoelectron spectroscopy (ARPES) has given valuable information about their electronic structure [1,2]. In most cases, the measured spectra are in broad agreement with Density Functional Theory (DFT) calculations, after renormalization by a factor 2 to 3. This range of values is in good agreement with mass enhancements predicted by Dynamical Mean Field Theory (DMFT) [3,4]. More unusual is a shrinking of the hole and electron pocket sizes compared to DFT calculations, observed both by ARPES and de Haas-Van Alphen experiments [5]. In a Fermi liquid (FL) picture, this corresponds to a down shift of the hole bands compensated by an up shift of the electron ones, as sketched in Fig. 1(a). As it depends on k, we refer to this effect as kshift in the following. Its origin is so far unclear, but it seems associated with the strength of correlations. In P-substituted BaFe 2 As 2 , dHvA measurements reported that the maximum k-shift corresponds to the largest effective masses [6]. In Ru-substituted BaFe 2 As 2 , both the k-shift and the renormalization weaken at large doping content [7,8]. Ortenzi et al. showed that interband interactions mediated by low energy bosons, such as spin fluctuations, can lead to such a k-shift [9]. If this is indeed the case in pnictides, it contains important information about the interactions in these compounds and deserves a detailed study.We show here with ARPES in Co-doped BaFe 2 As 2 that the k-shift is suppressed for high Co content, when the hole pockets fill up. We reveal in addition a very strong temperature (T) dependence of the electronic structure. Up to 10% Co, the electron pockets are expanding with increasing T by an amount as large as 50%.A similar T dependence was reported recently for Rudoped BaFe 2 As 2 [10]. At higher Co content (30%), the electron pockets on the contrary shrink at high T. We show that this can be largely explained by thermal excitations in these narrow multiband systems. We present both simple models and calculations using the density of states (DOS) obtained by DFT within the Local Density Approximation (LDA) and by DMFT in order to simulate the effect of temperature within a...

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“…If related to spin fluctuations, one could expect interband interactions to weaken at high T, as the strength of spin fluctuations decreases [11]. In Fig.…”

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confidence: 89%

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confidence: 96%

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Large Temperature Dependence of the Number of Carriers in Co-DopedBaFe2As2

et al. 2013

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“…It is well known that the cuprates are single-band system where x 2 -y 2 band solely contributes to the electrodynamics. 7 Whereas the Fe-SCs are multiband systems, 60 spectral weight analyses of the Ba122 systems showed that the contribution of itinerant carriers extends to mid-infrared region in the form of featureless, incoherent conductivity. 16,37,61 The spectral weight associated with the itinerant carrier response can be used to quantify the impact of many-body effects.…”

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confidence: 99%

Infrared pseudogap in cuprate and pnictide high-temperature superconductors

et al. 2014

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Japan 2We investigate infrared manifestations of the pseudogap in the prototypical cuprate and pnictide superconductors: YBa 2 Cu 3 O y and BaFe 2 As 2 (Ba122) systems. We find remarkable similarities between the spectroscopic features attributable to the pseudogap in these two classes of superconductors. The hallmarks of the pseudogap state in both systems include a weak absorption feature at about 500 cm -1 followed by a featureless continuum between 500 and 1500 cm -1 in the conductivity data and a significant suppression in the scattering rate below 700 -900 cm -1 . The latter result allows us to identify the energy scale associated with the pseudogap  PG . We find that in the Ba122-based materials the superconductivity-induced changes of the infrared spectra occur in the frequency region below 100 -200 cm -1 , which is much lower than the energy scale of the pseudogap. We performed theoretical analysis of the scattering rate data of the two compounds using the same model which accounts for the effects of the pseudogap and electron-boson coupling. We find that the scattering rate suppression in Ba122-based compounds below  PG is solely due to the pseudogap formation whereas the impact of the electron-boson coupling effects is limited to lower frequencies. The magnetic resonance modes used as inputs in our modeling are found to evolve with the development of the pseudogap, suggesting an intimate correlation between the pseudogap and magnetism.

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“…(8)] (see Refs. [23,27] and the Supplemental Material [28]). As one can see, this is irrelevant on the Hall transport, while it contributes in part to the temperature dependence of the longitudinal conductivity, as discussed in Ref.…”

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Unconventional Hall Effect in Pnictides from Interband Interactions

et al. 2012

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We calculate the Hall transport in a multiband system with a dominant interband interaction between carriers having electron and hole character. We show that this situation gives rise to an unconventional scenario, beyond the Boltzmann theory, where the quasiparticle currents dressed by vertex corrections acquire the character of the majority carriers. This leads to a larger (positive or negative) Hall coefficient than what may be expected on the basis of the carrier balance, with a marked temperature dependence. Our results explain the puzzling measurements in pnictides and provide a more general framework for transport properties in multiband materials.

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Effects of the Fermi-surface shrinking on the optical sum rule in pnictides

Cited by 32 publications

References 37 publications

Large Temperature Dependence of the Number of Carriers in Co-DopedBaFe2As2

Large Temperature Dependence of the Number of Carriers in Co-DopedBaFe2As2

Infrared pseudogap in cuprate and pnictide high-temperature superconductors

Unconventional Hall Effect in Pnictides from Interband Interactions

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