Quantum electrical transport in LAO/STO heterostructures

Applied Physics Letters, 2014

Advanced Materials Interfaces, 2013

Physical Review B

2011

We describe magnetotransport experiments performed on Hall crosses made from quantum wires at LaAlO 3 /SrTiO 3 interfaces. Shubnikov-de Haas oscillations measured in a 14nm wide structure exhibit modulations that are consistent with spin-orbit coupling or valley degeneracies. Hall measurements performed on the 6 nm-wide Hall cross reveal dissipative coupling to magnetic phases. Hall plateaus are observed that deviate significantly from twodimensional quantum Hall counterparts. Non-monotonic dips in the Hall resistance are attributed to one-dimensional confinement and spin-orbit coupling.

Physical Review B, 2018

Multiband transport in superconductors is interesting both from an academic as well as an application point of view. It has been postulated that interband scattering can significantly affect the carrier dynamics in these materials. In this article we present a detailed study of the electrical transport properties of the high-mobility two-dimensional electron gas residing at the interface of LaAlO3/SrTiO3, a prototypical multi-band superconductor. We show, through careful measurements of the gate dependence of the magnetoresistance and resistance fluctuations at ultra-low temperatures, that transport in the superconducting regime of this system has contributions from two bands which host carriers of very different characters. We identify a gate-voltage tunable Lifshitz transition in the system and show that the resistance fluctuations have strikingly different features on either side of it. At low carrier densities, resistance noise is dominated by number-density fluctuations arising from trapping-detrapping of charge carriers from defects in the underlying SrTiO3 substrate, characteristic of a single-band semiconductor. Above the Lifshitz transition, the noise presumably originates from inter-band scattering. Our work highlights the importance of inter-band scattering processes in determining the transport properties of low-dimensional systems and projects resistance fluctuation spectroscopy as a viable technique for probing the charge carrier dynamics across a Lifshitz transition.

Journal of the Korean Physical Society, 2013

We report the fabrication of nanopatterned conduction channels and electrical transport of a two-dimensional electron gas formed at a LaAlO3/SrTiO3 heterointerface. The nanoscale channels are formed by electron beam lithography and Ar-ion etching. The negative magnetoconductance data observed at low temperature are attributed to the weak antilocalization effect due to the strong spin-orbit interaction inherent in the electron gas at the heterointerface whereas the conductance fluctuations are caused by quantum interference between the electron wavefunctions. The gatedependent characteristic parameters, obtained using the Maekawa-Fukuyama model, reveal that the spin-orbit interaction in the nanopatterned metal-oxide heterostructure is gate-tunable, which will be useful for building spintronic devices.

Physical Review B, 2012

Anisotropic magnetoresistance and negative magnetoresistance for in-plane fields are compared for the LaAlO3/SrTiO3 interface and the symmetric Nb-doped SrTiO3 heterostructure. Both effects are exceptionally strong in LaAlO3/SrTiO3. We analyze their temperature, magnetic field and gate voltage dependencies and find them to arise from a Rashba type spin-orbit coupling with magnetic scatterers that have two contributions to their potential: spin exchange and Coulomb interaction. Atomic spin-orbit coupling is sufficient to explain the small effects observed in Nb-doped SrTiO3. These results clarify contradicting transport interpretations in SrTiO3-based heterostructures.

Physical Review Letters, 2007

We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High mobility conduction is observed at low deposition oxygen pressures (PO2 < 10 −5 mbar) and has a three-dimensional character. However, at higher PO2 the conduction is dramatically suppressed and nonmetallic behavior appears. Experimental data strongly support an interpretation of these properties based on the creation of oxygen vacancies in the SrTiO3 substrates during the growth of the LaAlO3 layer. When grown on SrTiO3 substrates at low PO2, other oxides generate the same high mobility as LaAlO3 films. This opens interesting prospects for all-oxide electronics. PACS numbers: 73.40.-c, 73.50.Fq, 66.30.Jt

Applied Physics Letters, 2013

Quantum magnetotransport properties of ultrathin topological insulator films J. Appl. Phys. 113, 043720 (2013) Electrical properties and thermal stability of Pd-doped copper nitride films J. Appl. Phys. 113, 043705 Photocarrier generation in CuxO thin films deposited by radio frequency sputtering Appl. Phys. Lett. 102, 032101 Controlling interfacial states in amorphous/crystalline LaAlO3/SrTiO3 heterostructures by electric fields Appl. Phys. Lett. 102, 021602 (2013) A comparative study of transport properties in polycrystalline and epitaxial chromium nitride films

2012

ACS applied materials & interfaces, 2016

Clarification of the role of magnetic ordering and scattering in two-dimensional electron gas has become increasingly important to understand the transport and magnetic behavior in the LaAlO3 (LAO)/SrTiO3 (STO) heterostructures. In this work, we report the sheet resistance of the LAO/STO heterostructures as functions of temperature, magnetic field, and field orientation. An unexpected resistance minimum was discovered at ∼10 K under a sufficiently high in-plane magnetic field. An anisotropic magnetoresistance (MR) is clearly identified, indicating the presence of magnetic scattering which may be related to the interaction between itinerant electrons and localized magnetic moments in the LaAlO3/SrTiO3 heterostructures. It is believed that the high concentration of oxygen vacancies induced by the ultralow oxygen partial pressure during the deposition process plays a predominant role in the occurrence of the anisotropic MR.

APL Materials, 2015

Transistor operation and mobility enhancement in top-gated LaAlO 3 /SrTiO 3 heterostructures

Journal of Physics Communications

Using x-ray magnetic circular dichroism and ab-initio calculations, we explore the La 1−x Sr x MnO 3 /LaAlO 3 /SrTiO 3 (001) heterostructure as a mean to induce transfer of spin polarized carriers from ferromagnetic La 1−x Sr x MnO 3 layer into the 2DEG (two-dimensional electron gas) at the LaAlO 3 /SrTiO 3 interface. By out-of-plane transport measurements, the tunneling across the LaAlO 3 barrier is also analyzed. Our results suggest small or vanishing spin-polarization for the 2DEG: magnetic dichroism does not reveal a neat signal on Ti atoms, while calculations predict, for the pristine stoichiometric interface, a small spin-resolved mobile charge of 2.5×10 13 cm −2 corresponding to a magnetic moment of 0.038 μ B per Ti atom, tightly confined within the single SrTiO 3 layer adjacent to LaAlO 3. Such a small magnetization is hard to be detected experimentally and perhaps not robust enough to survive to structural disorder, native doping, or La 1−x Sr x MnO 3 dead-layer effects. Our analysis suggests that, while some spin-diffusion cannot be completely ruled out, the use of ferromagnetic La 1−x Sr x MnO 3 epilayers grown on-top of LaAlO 3 /SrTiO 3 is not effective enough to induce robust spin-transport properties in the 2DEG. The examined heterostructure is nevertheless an excellent test-case to understand some fundamental aspects of the spin-polarized charge transfer in 2D wells.

arXiv (Cornell University), 2022

Strongly correlated electronic systems exhibit a wealth of unconventional behavior stemming from strong electron-electron interactions. The LaAlO3/SrTiO3 (LAO/STO) heterostructure supports rich and varied low-temperature transport characteristics including low-density superconductivity, and electron pairing without superconductivity for which the microscopic origins is still not understood. LAO/STO also exhibits inexplicable signatures of electronic nematicity via nonlinear and anomalous Hall effects. Nanoscale control over the conductivity of the LAO/STO interface enables mesoscopic experiments that can probe these effects and address their microscopic origins. Here we report a direct correlation between electron pairing without superconductivity, anomalous Hall effect and electronic nematicity in quasi-1D ballistic nanoscale LAO/STO Hall crosses. The characteristic magnetic field at which the Hall coefficient changes directly coincides with the depairing of non-superconducting pairs showing a strong correlation between the two distinct phenomena. Angle-dependent Hall measurements further reveal an onset of electronic nematicity that again coincides with the electron pairing transition, unveiling a rotational symmetry breaking due to the transition from paired to unpaired phases at the interface. The results presented here highlights the influence of preformed electron pairs on the transport properties of LAO/STO and provide evidence of the elusive pairing "glue" that gives rise to electron pairing in SrTiO3based systems.

Journal of Physics: Condensed Matter, 2021

We have investigated the illumination effect on the magnetotransport properties of a two-dimensional electron system at the LaAlO3/SrTiO3 interface. The illumination significantly reduces the zero-field sheet resistance, eliminates the Kondo effect at low-temperature, and switches the negative magnetoresistance into the positive one. A large increase in the density of high-mobility carriers after illumination leads to quantum oscillations in the magnetoresistance originating from the Landau quantization. The carrier density (∼2 × 1012 cm−2) and effective mass (∼1.7m e) estimated from the oscillations suggest that the high-mobility electrons occupy the d xz/yz subbands of Ti:t2g orbital extending deep within the conducting sheet of SrTiO3. Our results demonstrate that the illumination which induces additional carriers at the interface can pave the way to control the Kondo-like scattering and study the quantum transport in the complex oxide heterostructures.