High-energy fluctuation spectra in cuprates from infrared optical spectroscopy

Abstract

Coupling of the charge carriers in the high temperature superconducting oxides to bosonic modes has been widely reported using a variety of experimental probes. These include angular resolved photoemission (ARPES), scanning tunnelling spectroscopy (STS), Raman scattering (RS) and infrared optical spectroscopy (IRS). The energy scale investigated has been mostly limited to a relatively small range up to 300 meV or so. Although some ARPES experiments report boson structure up to 800 meV in the dressed electron dispersion curves the data are not analyzed to recover the spectral density of the fluctuation spectrum. We have extended to higher energies up to 2.2 eV the usual maximum entropy technique used to invert optical data so as to obtain an electron-boson spectral density. This has required that we include in our inversions, the calculated (LDA) particle-hole symmetrized energy dependent electronic density of states (DOS). Our analysis reveals that significant spectral weight remains in the fluctuation spectra up to 2.2 eV in the Bi-2212 family and to 1.2 eV in Bi-2201 for all doping levels considered.

Ultrafast optical spectroscopy of strongly correlated materials and high-temperature superconductors: a non-equilibrium approach

“…The results are in striking agreement with those obtained by ARPES and Raman spectroscopy, confirming the presence of a temperature dependent peak at ∼40 meV and a background with a cutoff at about ∼400 meV. More recent results [116], suggests the possibility that the spectrum of bosonic fluctuations may extend up to very high energies of the order of 1-2 eV.…”

“…The EDM has been widely employed to discuss the dynamics of the charge carriers in copper oxides and its relation with the onset of superconductivity [110,115,225,239,[244][245][246][247][248][249][250][251]. Recent results suggest that the fluctuation spectrum could extend up to several eV [116,252], hence of the order of the Hubbard energy U . The same formalism has been also applied to investigate the coupling in iron-based superconductors [253] and more conventional ferromagnetic systems [254].…”

Intrinsic temperature-dependent evolutions in the electron-boson spectral density obtained from optical data

“…The model-independent process does not impose any restrictions on the shape of I 2 χ ( ω ) except for one that the quantity is positive. Using this process a lot of important temperature and doping dependent properties of I 2 χ ( ω ) have been exposed from optical data12131415; in these studies the authors have used approximate Shulga et al 7 or Sharapov and Carbotte9 formulas. There also have been some other optical studies161718 which show less temperature and doping evolutions in the extracted glue (or I 2 χ ( ω )) functions; in these studies the authors have obtained a histogram representation of the glue function using a least-squares process and the full expression719 for the optical conductivity.…”

Effect of Pressure on the Pseudogap in Bi2223: Cuprates Are Not Strongly Coupled Superconductors

“…Таким образом, наблюдаемое увеличение отношения 2 0 /(kT c ) с давлением при убывании параметра kT c /(ħ 0 ) устраняет возможность решающего участия низкочастотных мод (с энергией ħ 0   40-50 мэВ) в механизме ВТСП. Поэтому купраты являются сверхпроводниками, в которых основную роль в куперовском спаривании могут играть высокочастотные электронные возбуждения [169][170][171][172]. Например, токовые петли [173,174] или парамагноны (магнитные возбуждения, подобные спиновым волнам с большим затуханием) [175][176][177][178][179][180][181], однако такая позиция уязвима для критики [182][183][184].…”

“…Например, токовые петли [173,174] или парамагноны (магнитные возбуждения, подобные спиновым волнам с большим затуханием) [175][176][177][178][179][180][181], однако такая позиция уязвима для критики [182][183][184]. Тем не менее, верхний предел для электронных возбуждений может превышать 1 эВ при константе связи   1 [169,170], что в модели БКШ позволяет достигать температур  200-300 К.…”