Berlin 2024 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 52: Nickelates II

TT 52.2: Talk

Wednesday, March 20, 2024, 15:30–15:45, H 3010

Tuning of the carrier localization, magnetic and thermoelectric properties in ultrathin (LaNiO_3−δ)₁/(LaAlO₃)₁(001) superlattices by oxygen vacancies — •Manish Verma and Rossitza Pentcheva — Department of Physics, Universität Duisburg-Essen

Understanding the role of defects on the complex behavior of transition metal oxides in bulk and the ultrathin limit is at the forefront of condensed matter physics. Using a combination of density functional theory calculations with an on-site Coulomb repulsion term (DFT+U) and Boltzmann transport theory within the constant relaxation time approximation, we explore the effect of oxygen vacancies on the electronic, magnetic, and thermoelectric properties in ultrathin (LaNiO_3−δ)₁/(LaAlO₃)₁(001) superlattices (SLs). For the pristine SL, an antiferromagnetic charge-disproportionated (AFM-CD) (d⁸L²)_S=0(d⁸)_S=1 phase is stabilized, irrespective of strain. At δ = 0.125 and 0.25, the localization of electrons released from the oxygen defects in the NiO₂ plane triggers a charge-disproportionation, leading to a ferrimagnetic insulator both at a_STO (tensile strain) and a_LSAO (compressive strain). At δ = 0.5, an insulating phase emerges with alternating stripes of Ni²⁺ (high-spin) and Ni²⁺ (low-spin) and oxygen vacancies ordered along the [110] direction (S-AFM), irrespective of strain. This results in a robust n-type in-plane power factor of 24 µW/K² cm at a_STO and 14 µW/K² cm at a_LSAO at 300 K (assuming relaxation time τ = 4 fs). Additionally, the pristine and δ = 0.5 SLs are shown to be dynamically stable.

Keywords: Strongly correlated electrons; magnetism; superlattices