Abstract
Artificial lattices have served as a platform to study the physics of unconventional superconductivity. We study semiconductor artificial graphene -- a honeycomb superlattice imposed on a semiconductor heterostructure -- which hosts the Dirac physics of graphene but with a tunable periodic potential strength and lattice spacing, allowing control of the strength of the electron-electron interactions. We demonstrate a new mechanism for superconductivity due to repulsive interactions which requires a strong lattice potential and a minimum doping away from the Dirac points. The mechanism relies on the Berry phase of the emergent Dirac fermions, which causes oppositely moving electron pairs near the Dirac points to interfere destructively, reducing the Coulomb repulsion and thereby giving rise to an effective attraction. The attractive component of the interaction is enhanced by a novel antiscreening effect which, in turn, increases with doping; as a result there is a minimum doping beyond which superconducting order generically ensues. The dominant superconducting state exhibits a spatially modulated gap with chiral $p$-wave symmetry. Microscopic calculations suggest that the possible critical temperatures are large relative to the low carrier densities, for a range of experimentally realistic parameters.
Highlights
Two dimensional semiconductor systems have provided striking manifestations of both the quantum behavior of single electrons and a variety of paradigmatic interacting states of matter [1]
Experimental technology has advanced to allow remarkable control and tunability over these systems, and access to a variety of fundamental physical effects. Designer superlattices such as artificial graphene (AG)—a semiconductor heterostructure patterned with a honeycomb lattice potential—seek to combine the novel physics of materials like graphene with the high degree of control in semiconductor devices [2,3,4,5,6,7,8,9,10,11,12]
The periodic potential in AG gives rise to a pair of band crossings near which the single–electron dynamics may be described by a 2 + 1 dimensional Dirac fermionic theory with emergent relativistic invariance
Summary
Two dimensional semiconductor systems have provided striking manifestations of both the quantum behavior of single electrons and a variety of paradigmatic interacting states of matter [1]. Experimental technology has advanced to allow remarkable control and tunability over these systems, and access to a variety of fundamental physical effects Designer superlattices such as artificial graphene (AG)—a semiconductor heterostructure patterned with a honeycomb lattice potential—seek to combine the novel physics of materials like graphene with the high degree of control in semiconductor devices [2,3,4,5,6,7,8,9,10,11,12]. Provides the attraction between electrons via a novel interference effect, that promotes Cooper pairing as a way to lower the energy cost of Coulomb repulsion We find that this mechanism is effective when the atomic orbitals of the superlattice become localized, unlike in graphene, a regime which can be reached by narrowing or deepening the minima of the superlattice potential.
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