Multiple Bosonic Mode Coupling in the Electron Self-Energy of(La2−xSrx)CuO4

Abstract

High resolution angle-resolved photoemission spectroscopy data along the (0,0)-(π,π) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2−xSrx)CuO4 samples in the normal state. Fine structure at energies of (40∼46) meV and (58∼63)meV, and possible fine structure at energies of (23∼29)meV and (75∼85)meV, have been identified. These observations indicate that, in LSCO, more than one bosonic modes are involved in the coupling with electrons.PACS numbers: 74.25.Jb,71.18.+y,74.72.Dn, The recent observation of the electron self-energy renormalization effect in the form of a "kink" in the dispersion has generated considerable interest because it reveals a coupling of the electrons with a collective boson mode of the cuprate superconductors [1]. However, the nature of the bosons involved remains controversial mainly because the previous experiments can only be used to determine an approximate energy of the mode and this energy is close to both the optical phonon [2,3] and the spin resonance [4]. Determining the nature of the mode(s) that couple to the electrons is likely important in understanding the pairing mechanism of superconductivity.In conventional superconductors, identification of the fine structure for the phonon anomalies in the tunnelling spectra has played a decisive role in reaching a consensus on the nature of the bosons involved [5]. The fine structure provides fingerprints for much more stringent comparison with known boson spectra. So far, such fine structure has not been detected in the angleresolved photoemission spectroscopy (ARPES) data. In this Letter we present significantly improved high resolution ARPES data of (La 2−x Sr x )CuO 4 (LSCO) that, for the first time, reveal fine structure in the electron selfenergy, demonstrating the involvement of multiple boson modes in the coupling with electrons.The photoemission measurements were carried out on beamline 10.0.1 at the ALS, using Scienta 2002 and R4000 electron energy analyzers. As high energy resolution and high data statistics are crucial to identify fine structure in the electron self-energy, the experimental conditions were set to compromise between these two conflicting requirements. The measurement is particularly challenging for LSCO system because of the necessity to use a relatively high photon energy (55eV). Different energy resolution between 12 and 20 meV was used for various measurements on different samples, and the angular resolution is 0.3 degree. An example of the high quality of the raw data is shown in Figs. 1a and 1b. Due to space charge problem, the Fermi level calibration has a ±5 meV uncertainty. We mainly present our data on the heavily underdoped LSCO x=0.03 (nonsuperconducting), LSCO x=0.063 (T c =12 K) and LSCO x=0.07 (T c =14 K) samples. These heavily underdoped LSCO samples are best candidates because they exhibit a stronger band renormalization effect above T c [3]; a relatively large magnitude of the real self-energy makes the identification...

Pairing interactions and pairing mechanism in high-temperature copper oxide superconductors

“…On the other hand, there is overwhelming evidence that electron-phonon coupling is very strong in the cuprate superconductors [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . In particular, various unconventional oxygen-isotope effects Zhao and his coworkers have observed since 1994 clearly indicate that the electron-phonon interactions are so strong that polarons/bipolarons are formed in doped cuprates [5][6][7][8][9]11,12,[14][15][16][17]19 and manganites 21,22 , in agreement with a theory of high-temperature superconductivity 23 and the original motivation for the discovery of high-temperature superconductivity 1 .…”

Evidence for a charge collective mode associated with superconductivity in copper oxides from neutron and x-ray scattering measurements of La2−xSrxCuOPark1, Fukuda2, Hamann3 et al. 2014Phys. Rev. B450362View full textAdd to dashboardCite

“…x=0.20 showed a very strong phonon anomaly, which was dramatically reduced already at x=0.25. On the other hand, the magnitude of the kink in the electronic dispersions gradually decreases from x=0.05 to x=0.30 16,17 . The new data, combined with previously published data for other x, allowed us to correlate the doping dependence of the giant phonon anomaly with that of the the electronic dispersion kinks and of the superconducting transition temperature T c .…”

Electron-phonon coupling in a system with broken symmetry: Surface ofBe(0001)

“…, , is related to the lifetime of quasiparticles, resulting in rapid increase in the spectrum width as a function of binding energy, saturating at the highest phonon energy [18][19][20][21][22][23][34][35][36].…”

“…The ELF has been extracted from the measured , , using the Maximium Entrophy Method (MEM) to do the integral inversion [9,10,34,37].…”