Observation of momentum-dependent charge excitations in hole-doped cuprates using resonant inelastic x-ray scattering at the oxygen K edge

Abstract

We investigate electronic excitations in La2−x(Br,Sr)xCuO4 using resonant inelastic x-ray scattering (RIXS) at the oxygen K edge. RIXS spectra of the hole-doped cuprates show clear momentum dependence below 1 eV. The spectral weight exhibits positive dispersion and shifts to higher energy with increasing hole concentration. Theoretical calculation of the dynamical charge structure factor on oxygen orbitals in a three-band Hubbard model is consistent with the experimental observation of the momentum and doping dependence, and therefore the dispersive mode is ascribed to intraband charge excitations which have been observed in electron-doped cuprates.PACS numbers: 71.27.+a,74.25.Jb,74.72.Gh,78.70.Ck Strongly correlated transition-metal oxides display various interesting physical properties including metalinsulator transition, high-temperature superconductivity and colossal magnetoresistance, and some of the oxides are classified into doped Mott insulators where electron correlation significantly modifies their band structure which diverges from that of the noninteracting simple metal [1]. Among the doped Mott insulators, superconducting cuprates are most intensively studied [2]. This is mainly due to the superconductivity at high transition temperature and related phenomena such as pseudogap and a competing phase with charge order [3]. In addition to the interest of superconductivity, doped cuprates are important and suitable for the study of electronic structure of the doped Mott insulator because relatively simple theoretical models with a few orbitals are applicable to describe the electronic structure near the Fermi energy. They represent the benchmark of the doped Mott insulators and the clarification of the fundamental electronic structure is essential for understanding the mechanism of the physical phenomena in the doped cuprates.In the undoped cuprates, only the spin degree of freedom contributes to the low-energy electron dynamics. When carriers are doped, the charge degree of freedom becomes active and the electron dynamics is characterized by the motion of spin and charge. Therefore, we consider that both spin and charge excitations must be investigated on equal footing in order to understand the electron dynamics characterizing the physics of the cuprates. Inelastic neutron scattering (INS) has been widely used for studying the spin dynamics in the reciprocal lattice space, and high-resolution resonant inelastic x-ray scattering (RIXS) at the Cu L 3 -edge has recently become an alternative to measure momentum-resolved spin excitations up to several hundreds meV [4,5]. Charge excitations in the doped cuprates extend to higher energy than the spin excitations and the electron correlation affects the charge excitations of the order of a few eV. Optical studies [6,7] demonstrated that spectral weight of the intraband charge excitations emerges below the charge-transfer gap in the doped cuprates and the weight characterizes the charge excitations in the doped Mott insulators. The high-energy part of mome...

Detecting Crystallographic Lattice Chirality using Resonant Inelastic X-ray Scattering

“…Two-magnon RIXS is possible also at ligand K -edge in the soft x-ray regime. For copper oxides, two-magnon excitations and their dispersion have been observed at the O K -edge 35,60 , although the range of momentum transfer is somewhat restricted. Within the theoretical framework of this article, the two-magnon RIXS at ligand K -edges can be treated in a similar way as in the cases of transition-metal K -edges.…”

Polarization-resolved Cu L3 -edge resonant inelastic x-ray scattering of orbital and spin excitations in NdBa2Cu3O7−<

“…When performed at the Cu L 3 -edge (2p 3/2 → 3d transition) it enables momentumdependent studies of low-and medium-energy excitations of superconducting cuprates [5][6][7][9][10][11][12] . RIXS spectra contain a variety of excitations spanning over a wide range of energies, from phonons below 100 meV [13][14][15] , to magnetic excitations up to 500 meV in cuprates 5,6 , to orbital (dd, crystal field) 9,11,[16][17][18][19][20][21][22] and charge transfer [23][24][25][26] excitations in the eV range. Moreover, the elastic and quasi-elastic intensities collected in RIXS spectra carry information on charge density waves or charge orders and associated excitations 10,[27][28][29] .…”

Electron self-energy from quantum charge fluctuations in the layered t−J model with long-range Coulomb interaction

“…For hole-doped cuprates (h-cuprates), mainly low-energy charge fluctuations were reported [3][4][5] and their origin is under debate despite intensive theoretical studies [19][20][21][22][23][24][25][26]. The origin of high-energy charge excitations in h-cuprates [27] is also highly controversial. High-energy excitations can be (i) specific to e-cuprates [7,10], (ii) present as a broad peak of the particle-hole excitation spectrum [27], (iii) present as plasmons similar to the e-cuprates [11,12,17,28,29], and (iv) related to strange metal physics [30,31], not to plasmons.…”

“…The origin of high-energy charge excitations in h-cuprates [27] is also highly controversial. High-energy excitations can be (i) specific to e-cuprates [7,10], (ii) present as a broad peak of the particle-hole excitation spectrum [27], (iii) present as plasmons similar to the e-cuprates [11,12,17,28,29], and (iv) related to strange metal physics [30,31], not to plasmons.…”