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Register a new userInhomogeneous superconductivity and quasilinear magnetoresistance at amorphous LaTiO3/SrTiO3 interfaces
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We have studied the transport properties of LaTiO3/SrTiO3 (LTO/STO) heterostructures. In spite of 2D growth observed in reflection high energy electron diffraction, Transmission Electron Microscopy images revealed that the samples tend to amorphize. Still, we observe that the structures are conducting, and some of them exhibit high conductance and/or superconductivity. We established that conductivity arises mainly on the STO side of the interface, and shows all the signs of the 2-dimensional electron gas usually observed at interfaces between SrTiO3 and LaTiO3 or LaAlO3, including the presence of two electron bands and tunability with a gate voltage. Analysis of magnetoresistance (MR) and superconductivity indicates presence of a spatial fluctuations of the electronic properties in our samples. That can explain the observed quasilinear out-of-plane MR, as well as various features of the in-plane MR and the observed superconductivity.
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Several experiments reveal the inhomogeneous character of the superconducting state that occurs when the carrier density of the two-dimensional electron gas formed at the LaXO3/SrTiO3 (X=Al or Ti) interface is tuned above a threshold value by means of gating. Re-analyzing previous measurements, that highlight the presence of two kinds of carriers, with low and high mobility, we shall provide a description of multi-carrier magneto-transport in an inhomogeneous two-dimensional electron gas, gaining insight into the properties of the physics of the systems under investigation. We shall then show that the measured resistance, superfluid density, and tunneling spectra result from the percolative connection of superconducting puddles with randomly distributed critical temperatures, embedded in a weakly localizing metallic matrix. We shall also show that this scenario is consistent with the characteristics of the superconductor-to-metal transition driven by a magnetic field. A multi-carrier description of the superconducting state, within a weak-coupling BCS-like model, will be finally discussed.
We have measured photoemission spectra of SrTiO3/LaTiO3 superlattices with a topmost SrTiO3 layer of variable thickness. Finite coherent spectral weight with a clear Fermi cut-off was observed at chemically abrupt SrTiO3/LaTiO3 interfaces, indicating that an ``electronic reconstruction occurs at the interface between the Mott insulator LaTiO3 and the band insulator SrTiO3. For SrTiO3/LaTiO3 interfaces annealed at high temperatures (~ 1000 C), which leads to Sr/La atomic interdiffusion and hence to the formation of La1-xSrxTiO3-like material, the intensity of the incoherent part was found to be dramatically reduced whereas the coherent part with a sharp Fermi cut-off is enhanced due to the spread of charge. These important experimental features are well reproduced by layer dynamical-mean-field-theory calculation.
We study the magnetic field driven Quantum Phase Transition (QPT) in electrostatically gated superconducting LaTiO3/SrTiO3 interfaces. Through finite size scaling analysis, we show that it belongs to the (2+1)D XY model universality class. The system can be described as a disordered array of superconducting islands coupled by a two dimensional electron gas (2DEG). Depending on the 2DEG conductance tuned by the gate voltage, the QPT is single (corresponding to the long range phase coherence in the whole array) or double (one related to local phase coherence, the other one to the array). By retrieving the coherence length critical exponent u, we show that the QPT can be clean or dirty according to the Harris criteria, depending on whether the phase coherence length is smaller or larger than the island size. The overall behaviour is well described by a theoretical approach of Spivak et al., in the framework of the fermionic scenario of 2D superconducting QPT.
We analyze the evidence of Majorana zero modes in nanowires that came from tunneling spectroscopy and other experiments, and scout the path to topologically protected states that are of interest for quantum computing. We illustrate the importance of the superconductor-semiconductor interface quality and sketch out where further progress in materials science of these interfaces can take us. Finally, we discuss the prospects of observing more exotic non-Abelian anyons based on the same materials platform, and how to make connections to high energy physics.
We report a systematic study on Edelstein magnetoresistance (Edelstein MR) in Co25Fe75/Cu/Bi2O3 heterostructures with a strong spin-orbit interaction at the Cu/Bi2O3 interface. We succeed in observing a significant dependence of the Edelstein MR on both Cu layer thickness and temperature, and also develop a general analytical model considering distinct bulk and interface contributions on spin relaxation. Our analysis, based on the above model, quantitatively illustrates a unique property of the spin transport near the Rashba interface, revealing a prominent role of the spin relaxation process by determining the ratios of the spin relaxation inside and outside the interface. We further find the characteristic spin transport is unaffected by temperature. Our results provide an essential tool for exploring the transport in a system with spin-momentum-locked two-dimensional states.
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