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Transport and Many-Body Studies at the LAO/STO Interface

Faridi, Azadeh | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51442 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Asgari, Reza; Langari, Abdollah
  7. Abstract:
  8. In this thesis, we investigate some transport and many body properties of the 2DEG at the interface of LaAlO3=SrTiO3. First, following Boltzmann approach,we calculate conductivity and mobility of the system. We find that the mobility varies inversely with the cubic power of the carrier density ( / n3 2D) in good agreement with the experimental results. Taking in to account the variations of the dielectric constant of SrTiO3 with carrier density together with the variable impurity density are remarkably important in order to explain the abrupt decrease of the mobility with increasing the density in this system. We find that although the multiband nature of the system and interband interactions are effecting in exploring the final result, but these assumptions are not enough to explain the reduction of the mobility. Then we investigate the transport properties of the system in presence of strong magnetic fields. We find a somehow anomalous beating pattern in density, longitudinal resistivilty(SdH) and also magnetization(dHvA) profiles specially at lower magnetic fields. We discuss the impact of electron density, Landau level broadening and Rashba spin-orbit constant on the appearance of the beatings at low magnetic fields and show that the observation of the beatings needs a system with rather higher carrier concentration so that we can minimize the Landau level broadening smoothing effect. The quantum Hall plateaus are evaluated and we can see that in large magnetic fields where Ziman splitting is the dominant spin splitting mechanism, both even and odd filling factors appear in Hall plateaus while at lower magnetic fields where the beating patterns are present, we can see alternatively transitions from both odd and even filling factors to the regions with only odd ones. As one of the most important many body features of an electronic system, we continue with investigating plasmon properties of the LaAlO3=SrTiO3 interface as well as graphene- aAlO3=SrTiO3 doublr layer. Calculating the density-density response matrix and also dielectric function of both systems, the plasmons are found both numerically and semi-analitically(in the long wavelength limit). One optical mode and two(three) acoustic modes are predicted for the LaAlO3=SrTiO3 (graphene-LaAlO3=SrTiO3) system. We show that along with the optical mode, only the uppermost acoustic mode of both systems can emerge above the electron-hole continuum depending on the characteristics of each system. In the case of the interface, the dielectric constant of SrTiO3 and also the spatial distance between orbitals play the crucial roles in appearance of the acoustic mode in the undamped region whereas in double layer case, this role is played by the distance between layers
  9. Keywords:
  10. Transport ; Hall Effect ; Perovskite ; Electron Gas ; LAO/STO Interface ; Magnetotransport ; Shubnikov–de Haas Oscillations ; Plasmon Modes

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