Julian Ingham | Columbia University (original) (raw)
Papers by Julian Ingham
arXiv: High Energy Physics - Phenomenology, 2015
the annihilation e + + e → µ + + µ . The probability of e e + collision is greatly enhanced due t... more the annihilation e + + e → µ + + µ . The probability of e e + collision is greatly enhanced due to a strong alignment of the electron and positron momenta with the electric field. The found muon creation rate exponentially exceeds the rate predicted by the direct Schwinger mechanism for muons, while the photon creation rate exponentially exceeds photon emission due to the fermion oscillation.
arXiv: High Energy Physics - Phenomenology, 2015
The collision of two intense, low-frequency laser beams is considered. The e−e+e^-e^+e−e+ pairs created... more The collision of two intense, low-frequency laser beams is considered. The e−e+e^-e^+e−e+ pairs created in this field are shown to exhibit recollisions, which take place at high energy accumulated due to the wiggling of fermions. The resulting e−e+e^-e^+e−e+ annihilation produces high energy photons, or heavy particles. The coherent nature of the laser field provides strong enhancement of the probability of these events. Analytical and numerical results are outlined.
Nature Communications
Recent experiments on kagome metals AV3Sb5 (A=K,Rb,Cs) identify twofold van Hove singularities (T... more Recent experiments on kagome metals AV3Sb5 (A=K,Rb,Cs) identify twofold van Hove singularities (TvHS) with opposite concavity near the Fermi energy, generating two approximately hexagonal Fermi surfaces – one electron-like and the other hole-like. Here we propose that a TvHS generates a novel time-reversal symmetry breaking excitonic order – arising due to bound pairs of electrons and holes located at opposite concavity van Hove singularities. We introduce a minimal model for the TvHS and investigate interaction induced many-body instabilities via the perturbative renormalisation group technique and a free energy analysis. Specialising to parameters appropriate for the kagome metals AV3Sb5, we construct a phase diagram comprising chiral excitons, charge density wave and a region of coexistence. We propose this as an explanation of a diverse range of experimental observations in AV3Sb5. Notably, the chiral excitonic state gives rise to a quantum anomalous Hall conductance, providing ...
Physical Review B, 2022
We demonstrate the existence of novel interaction effects in hole-doped semiconductor quantum wel... more We demonstrate the existence of novel interaction effects in hole-doped semiconductor quantum wells which are connected to dramatic changes in the Fermi surface geometry occurring upon variation of the doping. We present band structure calculations showing that quantum wells formed in p-type cubic semiconductors develop nested Fermi surfaces at a critical hole density set by the width d of the quantum well kF ∼ π/d. Nesting gives rise to competing superconducting and charge or spin density wave order, which we analyze using the perturbative renormalization group method. The correlated phases may be created or destroyed by tuning the hole density towards or away from the critical density. Our results establish p-type semiconductor quantum wells as a platform for novel correlated phases, which may be precisely controlled using electrostatic gating and external magnetic fields.
Physical Review Research, 2020
Artificial lattices have served as a platform to study the physics of unconventional superconduct... more 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.
2D Materials, 2021
We discuss a pairing mechanism in interacting two-dimensional multipartite lattices that intrinsi... more We discuss a pairing mechanism in interacting two-dimensional multipartite lattices that intrinsically leads to a second order topological superconducting state with a spatially modulated gap. When the chemical potential is close to Dirac points, oppositely moving electrons on the Fermi surface undergo an interference phenomenon in which the Berry phase converts a repulsive electron–electron interaction into an effective attraction. The topology of the superconducting phase manifests as gapped edge modes in the quasiparticle spectrum and Majorana Kramers pairs at the corners. We present symmetry arguments which constrain the possible form of the electron–electron interactions in these systems and classify the possible superconducting phases which result. Exact diagonalization of the Bogoliubov-de Gennes Hamiltonian confirms the existence of gapped edge states and Majorana corner states, which strongly depend on the spatial structure of the gap. Possible applications to vanadium-base...
arXiv: Superconductivity, 2019
Unconventional superconductivity featuring large pairing energies has attracted immense interest,... more Unconventional superconductivity featuring large pairing energies has attracted immense interest, yet tractable microscopic theories have proven elusive. A major breakthrough has been the advent of twisted bilayer graphene (TBG), which serves as a simple model system to 'look under the hood' of unconventional superconductivity. We propose a new model, within current experimental reach, to investigate the microscopics of strong-binding superconductivity. Our proposed device is semiconductor artificial graphene (AG), a two dimensional electron gas overlaid with a periodic potential (superlattice). We demonstrate a new mechanism for superconductivity that originates solely from the repulsive Coulomb interaction. The superlattice promotes certain interactions, which are antiscreened, cause attractive ppp-wave pairing and - in contrast to graphene - can be strongly enhanced through device engineering. The strength of the pairing energy is similar to TBG, and we find within the ac...
We explore higher-order topological superconductivity in an artificial Dirac material with intrin... more We explore higher-order topological superconductivity in an artificial Dirac material with intrinsic spin-orbit coupling. A mechanism for superconductivity due to repulsive interactions – pseudospin pairing – has recently been shown to result in higher-order topology in Dirac systems past a minimum chemical potential [1]. Here we apply this theory through microscopic modelling of a superlattice potential imposed on an inversion symmetric hole-doped semiconductor heterostructure, and extend previous work to include the effects of spin-orbit coupling. We find spin-orbit coupling enhances interaction effects, providing an experimental handle to increase the efficiency of the superconducting mechanism. We find that the phase diagram, as a function of chemical potential and interaction strength, contains three superconducting states – a first-order topological p + ip state, a second-order topological spatially modulated p + iτp state, and a second-order topological extended s-wave state,...
arXiv: High Energy Physics - Phenomenology, 2015
the annihilation e + + e → µ + + µ . The probability of e e + collision is greatly enhanced due t... more the annihilation e + + e → µ + + µ . The probability of e e + collision is greatly enhanced due to a strong alignment of the electron and positron momenta with the electric field. The found muon creation rate exponentially exceeds the rate predicted by the direct Schwinger mechanism for muons, while the photon creation rate exponentially exceeds photon emission due to the fermion oscillation.
arXiv: High Energy Physics - Phenomenology, 2015
The collision of two intense, low-frequency laser beams is considered. The e−e+e^-e^+e−e+ pairs created... more The collision of two intense, low-frequency laser beams is considered. The e−e+e^-e^+e−e+ pairs created in this field are shown to exhibit recollisions, which take place at high energy accumulated due to the wiggling of fermions. The resulting e−e+e^-e^+e−e+ annihilation produces high energy photons, or heavy particles. The coherent nature of the laser field provides strong enhancement of the probability of these events. Analytical and numerical results are outlined.
Nature Communications
Recent experiments on kagome metals AV3Sb5 (A=K,Rb,Cs) identify twofold van Hove singularities (T... more Recent experiments on kagome metals AV3Sb5 (A=K,Rb,Cs) identify twofold van Hove singularities (TvHS) with opposite concavity near the Fermi energy, generating two approximately hexagonal Fermi surfaces – one electron-like and the other hole-like. Here we propose that a TvHS generates a novel time-reversal symmetry breaking excitonic order – arising due to bound pairs of electrons and holes located at opposite concavity van Hove singularities. We introduce a minimal model for the TvHS and investigate interaction induced many-body instabilities via the perturbative renormalisation group technique and a free energy analysis. Specialising to parameters appropriate for the kagome metals AV3Sb5, we construct a phase diagram comprising chiral excitons, charge density wave and a region of coexistence. We propose this as an explanation of a diverse range of experimental observations in AV3Sb5. Notably, the chiral excitonic state gives rise to a quantum anomalous Hall conductance, providing ...
Physical Review B, 2022
We demonstrate the existence of novel interaction effects in hole-doped semiconductor quantum wel... more We demonstrate the existence of novel interaction effects in hole-doped semiconductor quantum wells which are connected to dramatic changes in the Fermi surface geometry occurring upon variation of the doping. We present band structure calculations showing that quantum wells formed in p-type cubic semiconductors develop nested Fermi surfaces at a critical hole density set by the width d of the quantum well kF ∼ π/d. Nesting gives rise to competing superconducting and charge or spin density wave order, which we analyze using the perturbative renormalization group method. The correlated phases may be created or destroyed by tuning the hole density towards or away from the critical density. Our results establish p-type semiconductor quantum wells as a platform for novel correlated phases, which may be precisely controlled using electrostatic gating and external magnetic fields.
Physical Review Research, 2020
Artificial lattices have served as a platform to study the physics of unconventional superconduct... more 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.
2D Materials, 2021
We discuss a pairing mechanism in interacting two-dimensional multipartite lattices that intrinsi... more We discuss a pairing mechanism in interacting two-dimensional multipartite lattices that intrinsically leads to a second order topological superconducting state with a spatially modulated gap. When the chemical potential is close to Dirac points, oppositely moving electrons on the Fermi surface undergo an interference phenomenon in which the Berry phase converts a repulsive electron–electron interaction into an effective attraction. The topology of the superconducting phase manifests as gapped edge modes in the quasiparticle spectrum and Majorana Kramers pairs at the corners. We present symmetry arguments which constrain the possible form of the electron–electron interactions in these systems and classify the possible superconducting phases which result. Exact diagonalization of the Bogoliubov-de Gennes Hamiltonian confirms the existence of gapped edge states and Majorana corner states, which strongly depend on the spatial structure of the gap. Possible applications to vanadium-base...
arXiv: Superconductivity, 2019
Unconventional superconductivity featuring large pairing energies has attracted immense interest,... more Unconventional superconductivity featuring large pairing energies has attracted immense interest, yet tractable microscopic theories have proven elusive. A major breakthrough has been the advent of twisted bilayer graphene (TBG), which serves as a simple model system to 'look under the hood' of unconventional superconductivity. We propose a new model, within current experimental reach, to investigate the microscopics of strong-binding superconductivity. Our proposed device is semiconductor artificial graphene (AG), a two dimensional electron gas overlaid with a periodic potential (superlattice). We demonstrate a new mechanism for superconductivity that originates solely from the repulsive Coulomb interaction. The superlattice promotes certain interactions, which are antiscreened, cause attractive ppp-wave pairing and - in contrast to graphene - can be strongly enhanced through device engineering. The strength of the pairing energy is similar to TBG, and we find within the ac...
We explore higher-order topological superconductivity in an artificial Dirac material with intrin... more We explore higher-order topological superconductivity in an artificial Dirac material with intrinsic spin-orbit coupling. A mechanism for superconductivity due to repulsive interactions – pseudospin pairing – has recently been shown to result in higher-order topology in Dirac systems past a minimum chemical potential [1]. Here we apply this theory through microscopic modelling of a superlattice potential imposed on an inversion symmetric hole-doped semiconductor heterostructure, and extend previous work to include the effects of spin-orbit coupling. We find spin-orbit coupling enhances interaction effects, providing an experimental handle to increase the efficiency of the superconducting mechanism. We find that the phase diagram, as a function of chemical potential and interaction strength, contains three superconducting states – a first-order topological p + ip state, a second-order topological spatially modulated p + iτp state, and a second-order topological extended s-wave state,...