These authors contributed equally to this work.The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO 3 (LAO) and TiO 2 -terminated SrTiO 3 (STO) 1,2 . Transport and other measurements in this system display a plethora of diverse physical phenomena 3-14 . To better understand the interface conductivity, we used scanning superconducting quantum interference device (SQUID) microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in highly conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed upon thermal cycling above the STO cubic to tetragonal structural transition temperature, implying that local conductivity is strongly modified by STO tetragonal domain

In LaAlo 3 /srTio 3 heterointerfaces, charge carriers migrate from the LaAlo 3 to the interface in an electronic reconstruction. magnetism has been observed in LaAlo 3 /srTio 3 , but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlo 3 thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.

The interface between the insulating oxides LaAlO 3 and SrTiO 3 exhibits a superconducting two-dimensional electron system that can be modulated by a gate voltage. While the conductivity has been probed extensively and gating of the superconducting critical temperature has been demonstrated, the question as to whether, and if so how, the gate tunes the superfluid density and superconducting order parameter needs to be answered. We present local magnetic susceptibility, related to the superfluid density, as a function of temperature, gate voltage, and location. We show that the temperature dependence of the superfluid density at different gate voltages collapses to a single curve that is characteristic of a full superconducting gap. Further, we show that the dipole moments observed in this system are not modulated by the gate voltage.

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Manipulation of magnetism is a longstanding goal of research in exotic materials. In this work, we demonstrate that the small ferromagnetic patches in LaAlO(3)/SrTiO(3) heterostructures can be dramatically changed by in situ contact of a scanning probe. Our results provide a platform for manipulation of small magnets through either a strong magneto-elastic coupling or sensitivity to surface modification. The ability to locally control magnetism is particularly interesting due to the presence of superconductivity with strong spin-orbit coupling in LaAlO(3)/SrTiO(3).

We investigate the charge and lattice states in a quasi-one-dimensional organic ferroelectric material, TTF-QCl4, under pressures of up to 35 kbar by nuclear quadrupole resonance experiments. The results reveal a global pressure-temperature phase diagram, which spans the electronic and ionic regimes of ferroelectric transitions, which have so far been studied separately, in a single material. The revealed phase diagram clearly shows that the charge-transfer instability and the lattice symmetry breaking, which coincide in the electronic ferroelectric regime at low pressures, bifurcate at a certain pressure, leading to the conventional ferroelectric regime. The present results reveal that the crossover from electronic to ionic ferroelectricity occurs through the separation of charge and lattice instabilities.

We investigate the effect of LaTiO3 insertion at the interface between LaAlO3 and TiO2 terminated {100} SrTiO3, for a series of LaAlO3 and LaTiO3 thicknesses. A clear increase of the carrier density was observed while the Hall mobility was largely unchanged. In structures with LaAlO3 thickness ∼ 3 unit cells, close to the critical thickness for conductivity, as little as 0.25 unit cells of LaTiO3 drives an insulator-to-metal transition. These samples show a strong dependence of the conductivity on voltage with electrostatic back-gating, which can be understood in a two-carrier picture, and dominated by the change in carrier density at the interface.The LaAlO 3 /SrTiO 3 (LAO/STO) conducting interface is generating intense interest because of the highly mobile electrons present within a nanoscale thickness in the STO.[1] At the interface twodimensional (2D) superconductivity,[2] 2D Shubnikov-de Haas oscillations, [3,4] and magnetism, [5][6][7] have all been observed. Although the relative contributions of oxygen vacancies, [8][9][10] interdiffused dopants, [11] and the polar discontinuity (PD), [1,[12][13][14][15]] to these properties are still being debated, an intriguing aspect of the PD model is the possibility of modulation doping the STO, leading to relatively high Hall mobility due to the absence of scattering from ionized dopants.This system is particularly interesting since close to the critical thickness of LAO required for conductivity [∼ 3 unit cells (uc)], a back gate voltage applied on the STO can induce conductivity in an as-grown insulating sample at room temperature.[13] Back gating strategies have been used to tune the 2D superconductivity at low temperatures. [16] A disadvantage of gating is that the sheet carrier density n 2D is not modulated independently of the Hall mobility µ. [17] In order to fully explore the phase diagram of the LAO/STO system, other techniques to control n 2D are needed. Chemically doped STO layers, inserted between the LAO and undoped STO substrate, have been utilized to achieve this aim. [18][19][20] In the context of these open questions, the LAO/LaTiO 3 (LTO)/STO heterostructure is notable for several reasons. Given the stacking structure of ABO 3 in the {100} planes, two independent interfaces can be defined, corresponding to the positions at which the chemical make-up of the AO and BO 2 planes switch, as sketched in Fig. 1(a). The inserted LTO layer(s) spatially separates these A-site and B-site interfaces in a structurally clean manner, exploiting the close lattice match to STO. Simultaneously LTO can provide carrier modulation without placing dopant ions at the interface, since it contains a high density of electrons: for each layer of LTO, there exists a potential sheet carrier density of 6.5 × 10 14 cm −2 per lateral unit cell (uc). Usually these electrons are localized in a Mott insulating state, [21] however it has been shown that high µ conduction can be generated if these electrons are released into a STO host. [22][23][24][25] Here we investigate the use of...

Lattice polarization at the SrTiO 3 / LaAlO 3 interface was investigated by optical second harmonic generation. Superlattices with varying periodicity were employed to study the evolution of interface polarization, while separating substrate contributions. We observed large perpendicular optical nonlinearity, which abruptly increases when the sublattice thickness goes above 3 unit cells. The polarization is primarily in SrTiO 3 and develops up to 8 unit cells from the interface.