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Register a new userTunable magnetic interactions in LaAlO3/SrTiO3 heterostructures by ionic liquid gating
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The gating effect achieved by an ionic liquid and its electric double layer allows for charge transfer which can be an order of magnitude larger than with conventional dielectrics. However, the large charged ions also causes inevitable Coulomb scattering in the conducting channel formed at the interface, which can limit the carrier mobility enhancement. In this work, we study the effect of the LaAlO3 thickness on the transport properties in LaAlO3/SrTiO3 heterostructures by ionic liquid gating. We find that the transport properties of the LaAlO3/SrTiO3 interface are dominated by the intrinsic interactions rather than the LaAlO3 thickness and possible effects from the ions in the liquid. We observe a Kondo effect, which is enhanced while increasing the gate voltage. We also observe a gate-tunable and temperature-dependent anomalous Hall effect, which always emerges near the Kondo temperature. Our experiments pave the way to manipulate the various magnetic interactions in LaAlO3/SrTiO3 heterostructures.
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Electric gating can strongly modulate a wide variety of physical properties in semiconductors and insulators, such as significant changes of conductivity in silicon, appearance of superconductivity in SrTiO3, the paramagnet-ferromagnet transition in (In,Mn)As and so on. The key to such modulation is charge accumulation in solids. Thus, it has been believed that such modulation is out of reach for conventional metals where the number of carriers is too large. However, success in tuning the Curie temperature of ultrathin cobalt gave hope of finally achieving such degree of control even in metallic materials. Here, we show reversible modulation of up to two orders of magnitude of the inverse spin Hall effect - a phenomenon that governs interconversion between spin and charge currents - in ultrathin platinum. Spin-to-charge conversion enables the generation and use of electric and spin currents in the same device, which is crucial for the future of spintronics and electronics.
We formulate the effective Hamiltonian of Rashba spin-orbit coupling (RSOC) in $mathrm{LaAlO_3/SrTiO_3}$ (LAO/STO) heterostructures. We derive analytical expressions of properties, e.g., Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. While linear RSOC is dominant around the $Gamma$-point, cubic RSOC becomes significant at the higher-energy anti-crossing region. We find that linear RSOC stems from the structural inversion asymmetry (SIA), while the cubic term is induced by both SIA and bulk asymmetry. Furthermore, the SOC strength shows a striking dependence on the tunable heterostructure parameters such as STO thickness and the interfacial electric field which is ascribed to the quantum confinement effect near the LAO/STO interface. The calculated values of the linear and cubic RSOC are in agreement with previous experimental results.
We report the operation of a field-effect transistor based on a single InAs nanowire gated by an ionic liquid. Liquid gating yields very efficient carrier modulation with a transconductance value thirty time larger than standard back gating with the SiO2 /Si++ substrate. Thanks to this wide modulation we show the controlled evolution from semiconductor to metallic-like behavior in the nanowire. This work provides the first systematic study of ionic-liquid gating in electronic devices based on individual III-V semiconductor nanowires: we argue this architecture opens the way to a wide range of fundamental and applied studies from the phase-transitions to bioelectronics.
Resistance as a function of temperature down to 20mK and magnetic fields up to 18T for various carrier concentrations is measured for nanowires made from the SrTiO3/LaAlO3 interface using a hard mask shadow deposition technique. The narrow width of the wires (of the order of 50nm) allows us to separate out the magnetic effects from the dominant superconducting ones at low magnetic fields. At this regime hysteresis loops are observed along with the superconducting transition. From our data analysis we find that the magnetic order probed by the giant magnetoresistance (GMR) effect vanishes at TCurie = 954 mK. This order is not a simple ferromagnetic state but consists of domains with opposite magnetization having a preferred in-plane orientation.
The hysteretic piezoelectric response in LaAlO3/SrTiO3 heterostructures can provide important insights into the mechanism for interfacial conductance and its metastability under various conditions. We have performed a variety of nonlocal piezoelectric force microscopy experiments on 3 unit cell LaAlO3/SrTiO3 heterostructures. A hysteretic piezoresponse is observed under various environmental and driving conditions. The hysteresis is suppressed when either the sample is placed in vacuum or the interface is electrically grounded. We present a simple physical model which can account for the observed phenomena.
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