C. Stephen Hellberg

LaAlO 3 stoichiometry is key to electron liquid formation at LaAlO 3 /SrTiO 3 interfaces

Emergent phenomena, including superconductivity and magnetism, found in the two-dimensional electron liquid (2-DEL) at the interface between the insulators lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) distinguish this rich system from conventional 2D electron gases at compound semiconductor interfaces. The origin of this 2-DEL, however, is highly debated, with focus on the role of defects in the SrTiO3, while the LaAlO3 has been assumed perfect. Here we demonstrate, through experiments and first-principle calculations, that the cation stoichiometry of the nominal LaAlO3 layer is key to 2-DEL formation: only Al-rich LaAlO3 results in a 2-DEL. Although extrinsic defects, including oxygen deficiency, are known to render LaAlO3/SrTiO3 samples conducting, our results show that in the absence of such extrinsic defects an interface 2-DEL can form. Its origin is consistent with an intrinsic electronic reconstruction occurring to counteract a polarization catastrophe. This work provides insight for identifying other interfaces where emergent behaviours await discovery.

What superconducts in sulfur hydrides under pressure and why

The recent discovery of superconductivity at 190~K in highly compressed H

Electron pairing without superconductivity

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Hamiltonian of the V15 spin system from first-principles density-functional calculations.

S is spectacular not only because it sets a record high critical temperature, but because it does so in a material that appears to be, and we argue here that it is, a conventional strong-coupling BCS superconductor. Intriguingly, superconductivity in the observed pressure and temperature range was predicted theoretically in a similar compound H

Quantum simulation of multiple-exciton generation in a nanocrystal by a single photon

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Phase Separation at all Interaction Strengths in the t-J Model

S. Several important questions about this remarkable result, however, are left unanswered: (1) Does the stoichiometry of the superconducting compound differ from the nominal composition, and could it be the predicted H

Efficiency of multiexciton generation in colloidal nanostructures.

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Stripes and the t-J Model

S compound? (2) Is the physical origin of the anomalously high critical temperature related only to the high H phonon frequencies, or does strong electron-ion coupling play a role? We show that at experimentally relevant pressures H

Properties of low-lying excited manifolds in Mn 12 acetate

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Green's-function Monte Carlo for lattice fermions: Application to the t-J model

S is unstable, decomposing into H