Effect of multiband transport on charge carrier density fluctuations at the LaAlO3_3/SrTiO3_3 interface

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 LaAlO$_3$/SrTiO$_3$, 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 SrTiO$_3$ 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.Comment: 6 pages, 5 figure

Chemical potential shift and gap-state formation in SrTiO3−δ_{3-\delta} revealed by photoemission spectroscopy

In this study, we report on investigations of the electronic structure of SrTiO$_3$ annealed at temperature ranging between 550 and 840$^\circ$C in an ultrahigh vacuum. Annealing induced oxygen vacancies (O$_{vac}$) impart considerable changes in the electronic structure of SrTiO$_3$. Using core-level photoemission spectroscopy, we have studied the chemical potential shift ($\Delta\mu$) as a function of annealing temperature. The result shows that the chemical potential monotonously increases with electron doping in SrTiO$_{3-\delta}$. The monotonous increase of the chemical potential rules out the existence of electronic phase separation in the sample. Using valence band photoemission, we have demonstrated the formation of a low density of states at the near Fermi level electronic spectrum of SrTiO$_{3-\delta}$. The gap-states were observed by spectral weight transfer over a large energy scale of the stoichiometric band gap of SrTiO$_3$ system leading finally to an insulator - metal transition. We have interpreted our results from the point of structural distortions induced by oxygen vacancies.Comment: 7 pages, 6 figures, 1 tabl

LaScO3/SrTiO3: A conducting polar heterointerface of two 3d band insulating perovskites

This work reports a quasi-two-dimensional electron gas (q-2DEG) system at the interface of two wideband-gap insulators, (TiO2-terminated) SrTiO3 and LaScO3, with a minimum thickness of 4-unit cell (uc). The highly crystalline and abrupt heterointerface is confirmed with high-resolution electron microscopy. The mixed Ti4+ and Ti3+ valence states (for 4 uc of LaScO3) obtained from the x-ray photoelectron spectroscopy study suggest an intrinsic electronic reconstruction at the interface, leading to a metallic nature. This origin is well supported by density functional theory calculations that reveal an emergence of 3.3 states/eV/spin at the Fermi level for 4 uc in accordance with the polar catastrophe model. The study offers one more perovskite heterostructure, like LaAlO3/SrTiO3, for unraveling the q-2DEG phenomena toward a clear mechanism and futuristic applications

Influence of Al doping in LaCoO3 on structural, electrical and magnetic properties

We report investigations on polycrystalline LaCo1-xAlxO3 (x = 0-0.9) bulk samples. The solid state synthesized samples showed a coexistence of rhombohedral and monoclinic phases in the intermediate concentrations (0.2 <= x <= 0.5) and pure rhombohedral phase otherwise. The observed effect of Al doping on dc transport has been analysed on the basis of small polaron hopping mechanism. The magnetisation results presented give evidence of weak ferromagnetism and anomalous temperature dependence of coercivity which we associate to the canting of the localised high-spin Co(III) and anti-symmetric exchange interactions at low temperatures

Observation of transient superconductivity at the LaAlO3_3/SrTiO3_3 interface

We report the observation of a magnetic field assisted transient superconducting state in the two dimensional electron gas existing at the interface of LaAlO$_3$/SrTiO$_3$ heterostructures. This metastable state depends critically on the density of charge carriers in the system. It appears concomitantly with a Lifshitz transition as a consequence of the interplay between ferromagnetism and superconductivity and the finite relaxation time of the in-plane magnetization. Our results clearly demonstrate the inherently metastable nature of the superconducting state competing with a magnetic order in these systems. The co-existence of superconductivity and ferromagnetism in the conducting electronic layer formed at the interface of insulating oxides has thrown up several intriguing and as yet unanswered questions. An open question in this field is the energetics of the interplay between these two competing orders and the present observation goes a long way in understanding the underlying mechanism.Comment: 11 pages, 14 figure

Note: Fiber optic transport probe for Hall measurements under light and magnetic field at low temperatures: Case study of a two dimensional electron gas

A fiber optic based probe is designed and developed for electrical transport measurements in presence of quasi-monochromatic (360-800 nm) light, varying temperature (T = 1.8-300 K), and magnetic field (B = 0-7 T). The probe is tested for the resistivity and Hall measurements performed on a LaAlO3-SrTiO3 heterointerface system with a conducting two dimensional electron gas

Note: Fiber optic transport probe for Hall measurements under light and magnetic field at low temperatures: Case study of a two dimensional electron gas

A fiber optic based probe is designed and developed for electrical transport measurements in presence of quasi-monochromatic (360-800 nm) light, varying temperature (T = 1.8-300 K), and magnetic field (B = 0-7 T). The probe is tested for the resistivity and Hall measurements performed on a LaAlO3-SrTiO3 heterointerface system with a conducting two dimensional electron gas

Structural, Optical, and Magnetic Properties Of FeVO3

We report the structural, optical, and magneticproperties ofpolycrystalline FeVO(3)synthesized by solid state reaction technique.While FeVO3 has rhombohedral crystal structure With space group R-3c (167)identical to the parent alpha-Fe2O3, the lattice volume reduces due to the replacement of Fe3+ with V3+ having smaller ionic radii. The most remarkable outcome of doping is reduction in band gap from 2.1 (alpha-Fe2O3) to 1.5 eV (FeVO3), which is favorable for photo electrochemical applications. Although the canted ferromagnetism persists in FeVO3, an enhancement in magnetic moment is observed as compared to the parent compound

Structural and Transport Studies on LaAl1-xCoxO3

We report the structural and dc transport studies on LaAl1-xCoxO3 (x = 0.2, 0.5, 0.8, 1.0). LaAl1-xCoxO3 samples have been prepared by solid state reaction synthesis. P-XRD patterns refined using FullProf to get the unit cell dimensions and the Co-O bond lengths. The intermediate samples exhibited mixture of rhombohedral and monoclinic phase indicating the distorted nature. The low temperature DC transport reveals small polaron hopping conduction with increasing activation energies with decrease in Co concentration