Title: Role of orbital filling on nonlinear ionic Raman scattering in perovskite titanates

Abstract

The linear and nonlinear phononic interactions between an optically excited infrared (IR) or hyper-Raman mode and a driven Raman mode are computed for the d⁰ (CaTiO₃) and d¹ (LaTiO₃) titanates within a first-principles density functional framework. We calculate the potential energy surface expanded in terms of the Ag or B_1g mode amplitudes coupled to the A_u or the B_3u mode and determine the coupling coefficients for these multimode interactions. We find that the linear-quadratic coupling dominates the anharmonicities over the quadratic-quadratic interaction in the perovskite titanates. The IR and Raman modes both modify the electronic structure with the former being more significant but occurring on a different time scale; furthermore, the coupled-mode interactions lead to sizable perturbations to the valence bandwidth (~100 meV) and band gap (~ 50 meV). By comparing the coupling coefficients of undoped CaTiO₃ and LaTiO₃ to those for electron-doped (CaTiO₃) and hole-doped (LaTiO₃) titanates, we isolate the role of orbital filling in the nonlinear coupling process. We find that with increasing occupancy of the d manifold, the linear-quadratic interaction decreases by approximately 30% with minor changes induced by the cation chemistry (that mainly affect the phonon mode frequencies) or by electron correlation. We identify the importancemore » of the Ti-O bond stiffness, which depends on the orbital filling, in governing the lattice anharmonicitiy. This microscopic understanding can be used to increase the nonlinear coupling coefficient to facilitate more facile access of nonequilibrium structures and properties through ionic Raman scattering processes.« less

Authors:

Gu, Mingqiang ^[1]; Rondinelli, James M. ^[1]

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+ Show Author Affiliations

1. Northwestern Univ., Evanston, IL (United States)

Publication Date:

Wed Jan 11 00:00:00 EST 2017

Research Org.:

Pennsylvania State Univ., University Park, PA (United States); Argonne National Laboratory (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1535821

Alternate Identifier(s):

OSTI ID: 1339007

Grant/Contract Number:  

SC0012375; AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review. B

Additional Journal Information:

Journal Volume: 95; Journal Issue: 2; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Materials Science; Physics; Optical phonons; Stimulated Raman scattering; Oxides; Density functional theory