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Ortolani, Michele; Calvani, P.; Lupi, S.

doi:10.1103/physrevlett.94.067002

Cited by 66 publications

(106 citation statements)

References 21 publications

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“…This means that the incoherent carrier is not localized in a unit cell but is extended over several lattice constants. The coherence of charge carriers can also be monitored by the spectral weight around ω = 0 or Drude weight in optical conductivity [27,28,29,30]. Depression of the Drude weight with temperature has been observed as expected theoretically [31].…”

Section: Fig 3: (Color Online) Characteristic Temperatures For Lscomentioning

confidence: 61%

Crossover from coherent quasiparticles to incoherent hole carriers in underdoped cuprates

et al. 2009

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In underdoped cuprates, only a portion of the Fermi surface survives as Fermi arcs due to pseudogap opening. In hole-doped La2CuO4, we have deduced the "coherence temperature" T coh of quasi-particles on the Fermi arc above which the broadened leading edge position in angle-integrated photoemission spectra is shifted away from the Fermi level and the quasi-particle concept starts to lose its meaning. T coh is found to rapidly increase with hole doping, an opposite behavior to the pseudogap temperature T * . The superconducting dome is thus located below both T * and T coh , indicating that the superconductivity emerges out of the coherent Fermionic quasi-particles on the Fermi arc. T coh remains small in the underdoped region, indicating that incoherent charge carriers originating from the Fermi arc are responsible for the apparently metallic transport at high temperatures.

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Section: Fig 3: (Color Online) Characteristic Temperatures For Lscomentioning

confidence: 61%

Crossover from coherent quasiparticles to incoherent hole carriers in underdoped cuprates

et al. 2009

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“…A further model-independent method to determine ω p and then n from the IR data is provided by the oscillator strength sum rules 43 , which can be applied only once the optical constants are calculated in the entire IR range by the Kramers-Kronig (KK) transformations, as done in Ref. 46 and below in this work.…”

Section: A Infrared Estimate Of the Free Carrier Densitymentioning

confidence: 99%

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

et al. 2016

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Heavily-doped semiconductor films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on different substrates, in-situ doped in the 10 17 to 10 19 cm −3 range, by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and dc transport measurements to determine the relation between plasma edge and carrier density and to quantify mid-infrared plasmon losses. We demonstrate that the unscreened plasma frequency can be tuned in the 400 -4800 cm −1 range and that the average electron scattering rate, dominated by scattering with optical phonons and charged impurities, increases almost linearly with frequency. We also found weak dependence of losses and tunability on the crystal defect density, on the inactivated dopant density and on the temperature down to 10 K. In films where the plasma was optically activated by pumping in the near-infrared, we found weak but significant dependence of relaxation times on the static doping level of the film. Our results suggest that plasmon decay times in the several-picosecond range can be obtained in ntype germanium thin films grown on silicon substrates hence allowing for underdamped mid-infrared plasma oscillations at room temperature.The recent push towards applications of spectroscopy for chemical and biological sensing in the mid-infrared (mid-IR)1-8 has prompted the need for conducting thin films displaying values of the complex dielectric functionǫ(ω) = ǫ ′ (ω) + iǫ ′′ (ω) that can be tailored to meet the needs of novel electromagnetic designs exploiting the concepts of metamaterials, transformation optics and plasmonics 9 . In the design of metamaterials, where subwavelength sized conducting elements are embedded in dielectric matrices, if the values of ǫ ′ of the metal and the dielectric are of the same order, but have opposite sign, the geometric filling fractions of the metal and dielectric can be readily tuned to achieve subwavelengthresolution focusing of radiation 10 . Such requirement is met by silver for wavelengths λ around 400 nm. The same condition cannot be achieved in the IR range by using elemental metals, however, because metals possess an extremely high negative value of ǫ ′ not equaled, in

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“…The issue of sum rule attracted substantial interest in the studies of high T c cuprates [5][6][7][8][9][10][11][12][13][14][15][16][17][18][21][22][23][24][25][26] in which pairing is without doubts a strong coupling phenomenon. From a theoretical perspective, the interest in this issue was originally triggered by a similarity between W K and the kinetic energy K = 2 ε k n k .…”

Section: Introductionmentioning

confidence: 99%

“…A good amount of experimental effort has been put into addressing the issue of the optical sum rule in the c−axis 7 and in-plane conductivities [8][9][10][11][12][13][14][15][16] in overdoped, optimally doped, and underdoped cuprates. The experimental results demonstrated, above all, outstanding achievements of experimental abilities as these groups managed to detect the value of the optical integral with the accuracy of a fraction of a percent.…”

Section: Introductionmentioning

confidence: 99%

Optical integral and sum-rule violation in high-Tcsuperconductors

Maiti

Chubukov

2010

Phys. Rev. B

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The purpose of this work is to investigate the role of the lattice in the optical Kubo sum rule in the cuprates. We compute conductivities, optical integrals W , and ∆W between superconducting and normal states for 2-D systems with lattice dispersion typical of the cuprates for four different models -a dirty BCS model, a single Einstein boson model, a marginal Fermi liquid model, and a collective boson model with a feedback from superconductivity on a collective boson. The goal of the paper is two-fold. First, we analyze the dependence of W on the upper cut-off (ωc) placed on the optical integral because in experiments W is measured up to frequencies of order bandwidth. For a BCS model, the Kubo sum rule is almost fully reproduced at ωc equal to the bandwidth. But for other models only 70%-80% of Kubo sum rule is obtained up to this scale and even less so for ∆W , implying that the Kubo sum rule has to be applied with caution. Second, we analyze the sign of ∆W . In all models we studied ∆W is positive at small ωc, then crosses zero and approaches a negative value at large ωc, i.e. the optical integral in a superconductor is smaller than in a normal state. The point of zero crossing, however, increases with the interaction strength and in a collective boson model becomes comparable to the bandwidth at strong coupling. We argue that this model exhibits the behavior consistent with that in the cuprates.

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Frequency-Dependent Thermal Response of the Charge System and the Restricted Sum Rules ofLa2−xSrx

Cited by 66 publications

References 21 publications

Crossover from coherent quasiparticles to incoherent hole carriers in underdoped cuprates

Crossover from coherent quasiparticles to incoherent hole carriers in underdoped cuprates

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

Optical integral and sum-rule violation in high-Tcsuperconductors

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