Doctoral thesis (Dissertations and theses)
Origin and properties of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface: a first-principles hybrid functional study.
Fontaine, Denis
2014
 

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Keywords :
electronic gas; 2DEG; oxide; LAO; STO; interface
Abstract :
[en] Complex oxides exhibit a wide range of physical properties making them very attractive for future electronic and device applications. Although more and more studied, additional scientific investigations are required, especially in oxide interfaces, where new and amazing phenomena can arise. A prototypical example is the LaAlO3-SrTiO3 interface that appear to be conducting, magnetic or even supra-conducting while these properties are not present in the LaAlO3 and SrTiO3 bulk insulator compounds. The conductivity arises from the formation of a highly localized electron gas at the interface which exhibits a different behavior than the one at semiconductor interfaces. Even nowadays, its exact origin, intrinsic versus extrinsic, is still intensively debated. The existence of an electric field in LaAlO3 used as a key feature of models based on an intrinsic origin is highly controversial. In these models, the closing of the band gap with increasing LaAlO3 film thicknesses finally results to a Zener breakdown and to the metal/insulator transition. In this Ph.D. thesis we aim to investigate the various consequences of the presence of an electric field in LaAlO3 through first-principles calculations in pristine LaAlO3-SrTiO3 interfaces. First, using both experimental and theoretical structural distortions in LaAlO3, we predicted a lattice expansion via an electrostrictive effect, supporting the existence of an electric field in LaAlO3. Second, the metal/insulator transition was tuned with regards to the intensity of the electric field in the film, which was controlled by the composition of a solid solution between LaAlO3 and SrTiO3. The theoretical results match the experimental one where, nevertheless, extrinsic origin mechanisms are allowed and defects are present. These two works are in favors of an intrinsic origin of the electronic gas observed in LaAlO3-SrTiO3 heterostructures. In addition, a relationship between the sheet carrier density and spatial extension of the gas was established and thus setting an intrinsic threshold to the sheet carrier concentration. At lower density the electrons are strictly localized close to the interface while above this value the carriers start to spill into the SrTiO3 substrate.
Disciplines :
Physics
Author, co-author :
Fontaine, Denis ;  Université de Liège - ULiège > Département de physique > Physique théorique des matériaux
Language :
English
Title :
Origin and properties of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface: a first-principles hybrid functional study.
Defense date :
11 September 2014
Institution :
ULiège - Université de Liège
Degree :
Docteur en sciences
Promotor :
Ghosez, Philippe  ;  Université de Liège - ULiège > Complex and Entangled Systems from Atoms to Materials (CESAM)
President :
Verstraete, Matthieu  ;  Université de Liège - ULiège > Complex and Entangled Systems from Atoms to Materials (CESAM)
Jury member :
Bousquet, Eric  ;  Université de Liège - ULiège > Complex and Entangled Systems from Atoms to Materials (CESAM)
Bilc, Daniel ;  Université de Liège - ULiège > Département de physique > Physique théorique des matériaux
Triscone, Jean-marc
Filippetti, Alessio
Available on ORBi :
since 21 November 2014

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