Analysis of electron and phonon heat capacities of La2−xSrxCuO4 cuprate superconductor. (November 2019)

• Record Type: Journal Article
• Authors: Gupta, Anushri; Verma, Sanjeev K.; Kumari, Anita; Indu, B.D.
• Is Part Of: Journal of physics and chemistry of solids. Volume 134(2019)
• Page Start: 83
• Page End: 88
• Publication Date: 2019-11
• Subjects: Anharmonicities and defects -- Density of states -- Heat capacity -- High temperature superconductors; Solids -- Periodicals; Solides -- Périodiques; Solids; Periodicals; 530.41
• DOI: 10.1016/j.jpcs.2019.05.037
• Languages: English
• ISSNs: 0022-3697

Abstract

Abstract: Adopting the many body quantum dynamical Green's function (GF) theory via a versatile Hamiltonian that incorporates the contribution due to harmonic electron and phonon fields and their interactions, anharmonicities and point impurities; the expressions for phononic heat capacity (PHC) and electronic heat capacity (EHC) have been obtained using the method of density of states of phonons and electrons (PDOS and EDOS). The theory is applied to the high temperature superconductor (HTS) La 2 − x Sr x CuO 4 for successful numerical estimation. The expressions of PDOS and PHC can be separated into diagonal and non-diagonal components. The non-diagonal contribution emerges only in the impure crystals and becomes extinct in pure crystals. The presence of electron-phonon ( ep ) coupling constant in each term of EHC is an additional and unique feature of present formulation. The results are compared with the experimental data of heat capacity for La2− x Sr x CuO4 superconductor and results are found in good agreement. The electronic contribution is quite small in the comparison to the phononic contribution to total heat capacity. The doping concentration and ep coupling constant dependence of the PHC and EHC independently are investigated for La2− x Sr x CuO4 crystal and observed that orderly increases with doping concentration and ep coupling constant. Highlights: Adopting Green's function theory the expressions for phononic and electronic heat capacities (PHC & EHC) have been derived. The BMH potential to evaluate second, third and fourth order force constants for La2-xSrxCuO4 have been noticed suitable. The PHC is resolved into diagonal and non-diagonal parts, of which later is present chiefly due to presence of impurities. The EHC contribution is found quite small as compared to PHC contribution in conformity of present experimental results. EHC is less sensitive to effects of doping and electron-phonon coupling than PHC.