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Abstract:We present a multi-band model for superconductivity at the metallic interface between insulating oxides LaAlO3 and SrTiO3 (001). Using a self-consistent Bogoliubov-de Gennes theory, formulated with the realistic bands at the interface, we investigate the spin-singlet and spin-triplet pairings in intra-band and inter-band channels. We find that the Rashba and atomic spin-orbit interactions at the interface induce singlet pairing in the inter-band channel and triplet pairing in both the intra-band and inter-band… Show more
“…The solutions due to this decoupling corresponds to a local swave pairing which is considered to be one of the most favored superconducting instability in the two-dimensional bulk. [45][46][47][48] To assess the stability of the superconducting states in the presence of an applied magnetic field, we solve the Bogoliubov-de Gennes equations in a selfconsistent way by an iterative scheme of computation until the desired accuracy is achieved. We point out that, apart from indications arising through the determination of the topological invariant, the quantum transition from trivial to topological superconducting states is also signaled by a rapid decrease of the order parameter as a function of the magnetic energy (M x or M y ).…”
We determine the optimal conditions to achieve topological superconducting phases having spinsinglet pairing for a planar nanowire with finite lateral width in the presence of an in-plane external magnetic field. We employ a microscopic description that is based on a three-band electronic model including both the atomic spin-orbit coupling and the inversion asymmetric potential at the interface between oxide band-gap insulators. We consider amplitudes of the pairing gap, spin-orbit interactions and electronic parameters that are directly applicable to nanowires of LaAlO3-SrTiO3. The lateral confinement introduces a splitting of the d-orbitals that alters the orbital energy hierarchy and significantly affects the electron filling dependence of the topological phase diagram. Due to the orbital directionality of the t2g-states, we find that in the regime of strong confinement the onset of topological phases is pinned at electron filling where the quasi flat heavy bands start to get populated. The increase of the nanowire thickness leads to a changeover from sparse-to-dense distribution of topologically non-trivial domains which occurs at the cross-over associated to the orbital population inversion. These findings are corroborated by a detailed analysis of the most favorable topological superconducting phases in the electron doping-magnetic field plane highlighting the role of orbital selective confinement.
“…The solutions due to this decoupling corresponds to a local swave pairing which is considered to be one of the most favored superconducting instability in the two-dimensional bulk. [45][46][47][48] To assess the stability of the superconducting states in the presence of an applied magnetic field, we solve the Bogoliubov-de Gennes equations in a selfconsistent way by an iterative scheme of computation until the desired accuracy is achieved. We point out that, apart from indications arising through the determination of the topological invariant, the quantum transition from trivial to topological superconducting states is also signaled by a rapid decrease of the order parameter as a function of the magnetic energy (M x or M y ).…”
We determine the optimal conditions to achieve topological superconducting phases having spinsinglet pairing for a planar nanowire with finite lateral width in the presence of an in-plane external magnetic field. We employ a microscopic description that is based on a three-band electronic model including both the atomic spin-orbit coupling and the inversion asymmetric potential at the interface between oxide band-gap insulators. We consider amplitudes of the pairing gap, spin-orbit interactions and electronic parameters that are directly applicable to nanowires of LaAlO3-SrTiO3. The lateral confinement introduces a splitting of the d-orbitals that alters the orbital energy hierarchy and significantly affects the electron filling dependence of the topological phase diagram. Due to the orbital directionality of the t2g-states, we find that in the regime of strong confinement the onset of topological phases is pinned at electron filling where the quasi flat heavy bands start to get populated. The increase of the nanowire thickness leads to a changeover from sparse-to-dense distribution of topologically non-trivial domains which occurs at the cross-over associated to the orbital population inversion. These findings are corroborated by a detailed analysis of the most favorable topological superconducting phases in the electron doping-magnetic field plane highlighting the role of orbital selective confinement.
Titanium oxides have many fascinating optical and electrical properties, such as the superconductivity at 2 K in cubic titanium monoxide (TiO) polycrystalline bulk. However, the lack of TiO single crystals or epitaxial films has prevented systematic investigations on its superconductivity. Here, we report the basic superconductivity characterizations of cubic TiO films epitaxially grown on (0001)-oriented α-Al 2 O 3 substrates. The magnetic and electronic transport measurements confirmed that TiO is a type-II superconductor and the recorded high T c is about 7.4 K. The lower critical field (H c1 ) at 1.9 K, the extrapolated upper critical field H c2 (0), and coherence length are about 18 Oe, 13.7 T, and 4.9 nm, respectively. With increasing pressure, the value of T c shifts to lower temperature while the normal state resistivity increases. Our results on the superconducting TiO films confirm the strategy to achieve higher T c in the epitaxial films, which may be helpful for finding more superconducting materials in various related systems.
“…Thus, carriers in a LAO/STO interface can be classified into two types: high-density electrons residing in the d xy state and low-density high-mobility electrons occupying a hybrid state, d xz / d yx , combined with d xz and d yz 45,48–50 . Carries in the d xz / d yx states are known to be engaged in superconductivity 4,51–53 . Under ordinary conditions, the d xz / d yz orbitals are rarely occupied; however, the system is ready to move to high-mobility states when electrons are supplied to occupy these states.Figure 4An illustration of electron transfer between the LAO/STO interface and a metal electrode.…”
We experimentally investigated the transport properties near metal electrodes installed on a conducting channel in a LaAlO3/SrTiO3 interface. The local region around the Ti and Al electrodes has a higher electrical conductance than that of other regions, where the upper limits of the temperature and magnetic field can be well defined. Beyond these limits, the conductance abruptly decreases, as in the case of a superconductor. The samples with the Ti- or Al-electrode have an upper-limit temperature of approximately 4 K, which is 10 times higher than the conventional superconducting critical temperature of LaAlO3/SrTiO3 interfaces and delta-doped SrTiO3. This phenomenon is explained by the mechanism of electron transfer between the metal electrodes and electronic d-orbitals in the LaAlO3/SrTiO3 interface. The transferred electrons trigger a phase transition to a superconductor-like state. Our results contribute to the deep understanding of the superconductivity in the LaAlO3/SrTiO3 interface and will be helpful for the development of high-temperature interface superconductors.
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