Optical excitations inSr2CuO3

Abstract

We investigated excitation spectra of the one-dimensional chain compound Sr2CuO3. The small peak at 2.3 eV in the loss function turned out to correspond to the strong charge transfer transition at 1.8 eV in conductivity. It has the excitonic character expected in one dimensional extended Hubbard model of the transition from the lower Hubbard band to the Zhang-Rice singlet state. The strongest peak at 2.7 eV in the loss function is attributed to the continuum excitation of the excitonic charge transfer transition. The spectral weight sum rule is satisfied within these transitions.PACS numbers: 71.27.+a, 71.35.-y, 78.20.-e, 78.67.-n Superconducting cuprates have a CuO 2 plane in common which is composed of a two dimensional (2D) cornersharing network of CuO 4 plaquettes. The electronic property of an undoped CuO 2 plane should be metallic without strong onsite Coulomb repulsion at Cu sites, which divides the Cu d x 2 −y 2 state into two Hubbard bands of upper Hubbard band (UHB) and lower Hubbard band (LHB) opening a charge transfer gap between LHB (from a hole point of a view) and O 2p states. Charge doping changes the electronic structure of the CuO 2 plane finally giving rise to the high temperature superconductivity. It is important to understand the properties of insulating cuprates to solve the mystery of the high temperature superconductivity.Optical spectroscopy is one of fundamental tools to investigate electronic structure, which can directly measure the charge transfer gap. By absorbing light, holes in LHB can be excited to O 2p states. When a hole is introduced into the CuO 2 plane, the ground state becomes a well known Zhang-Rice singlet (ZRS) state evenly residing at surrounding O 2p orbitals. 1 Because an optical excitation is a charge conserving process, to be involved in optical excitations for the ZRS state, one CuO 4 plaquette should give a hole to a neighboring CuO 4 plaquette, which is possible in corner-sharing CuO 4 plaquette structures. Therefore, the first optical excitation crossing the charge transfer gap should be from LHB to the ZRS state in the CuO 2 plane as depicted in fig. 1. The second excitation is expected to be from LHB to nonbonding (NB) O 2p states in the CuO 2 plane, which is localized within one plaquette. Energies of these two excitations are essential to model the electronic structure of the CuO 2 plane.However, the electronic structure of insulating cuprates remains still unclear. Optical spectra of insulating cuprates of 1D and 2D corner-sharing structure show similar spectral feature of two peaks around 2 eV like the peaks A and B in fig. 2. It is clear that the lowest energy peak, which is rather sharp and has a large spectral weight in common, should be the charge transfer transition α from LHB to ZRS. But the origin of the other peak, which comes at about 0.5 eV higher, is still unclear. This peak is relatively broad and the strength varies depending on materials. It is rather small and appear as a hump-like shape in RE 2 CuO 4 (RE: rare earth ions) and Sr 2 CuO 3...

l1 -norm coherence of assistance

“…where the maximization is taken over all pure state decompositions of ρ = i p i |ψ i ψ i | [12]. Similarly, we shall show the l 1 norm of coherence of assistance corresponds to the entanglement called the convex-roof extended negativity of assistance [22], which is defined as N a (ρ) = max i p i N(|ψ i ), where the maximization is taken over all pure state decompositions of ρ = i p i |ψ i ψ i |, N(ρ) is the negativity of ρ which is a well known entanglement measure defined as the sum of all absolute values of negative eigenvalues of ρ P T where the superscript P T denotes the partial transposition [23]. Theorem 3.…”

Non-Hermitian approach for quantum plasmonics

“…The lower panel of Fig. 5(b) shows the associated concurrence [19] of the two quantum dots, calculated by tracing out the plasmon quantum numbers to obtain a reduced two quantum dot density matrix and then performing the required computations [6,7]. The concurrence is a measure of the degree of entanglement between the quantum dots, taking on a value of unity for maximal entanglement and 0 if the system is completely unentangled.…”

“…It is also clear that this can easily be extended to studying the dynamics of many more quantum dots interacting with a plasmon mode. As an example, we consider fifty quantum dots in resonance with a single plasmonic mode with (i) homogeneous couplings (all dot/plasmon couplings equal to the value given in the lower parameter set of Table I ( Figure 6 displays the average bipartite concurrence [19] for both cases with the initial condition being one quantum dot excited. The magnitudes of these concurrences are much smaller than the two quantum dot case.…”

Polygamy of multiparty q -expected quantum entanglement

“…One property that makes quantum entanglement fundamentally different from other classical correlations is the restricted shareability and distribution of entanglement in multi-party quantum systems, namely, monogamy and polygamy relations of quantum entanglement [4,5]. Mathematically, the monogamy of quantum entanglement has been characterized as monogamy inequalities using various entanglement measures [6][7][8][9][10][11]. These monogamy inequalities of entanglement show the mutually exclusive structures of entanglement shareability in multi-party quantum systems.…”