arXiv subjects

Chris A. Hooley

Publications and source records attributed to Chris A. Hooley.

At least 19 recordsLinked to original sources

arXiv2026

Particlelike solutions of the Einstein-Dirac-Higgs equations: ground, excited, and many-fermion states

We present an extended study of the gravitationally localized soliton-like solutions to the minimally-coupled Einstein-Dirac-Higgs equations, embedded in asymptotically Minkowski spacetimes. The equations of motion describing these Yukawa-coupled Dirac stars are generalized to any even number of constituent fermions. We first expand the discussion of two-fermion ground-state solutions initially analyzed in Leith et al. [Phys. Rev. D. 107, 106020 (2023)]. Upon extending our analysis to excited states and many-fermion states, we find that both exhibit different behaviors to their two-fermion ground-state counterparts. In these excited states and many-fermion states, the Higgs field may exhibit stepwise increases and at times decrease within the soliton, which has not been seen for the two-fermion ground states. We also propose the potential cause of a significant degree of ADM-to-fermion mass disparity, which is present in states with strong Yukawa-coupling.

gr-qc↗

arXiv2026

Engineering correlated phases through manipulation of Van Hove singularities

Controlling the ordered phases of correlated electron systems remains a central challenge in quantum materials design. Divergences in the electronic density of states, known as Van Hove singularities (VHSs), are one obvious route to such control. It is clear from recent work that the exact functional form of these divergences can profoundly affect which phases are realized; a full picture, however, remains elusive. In this work, we use both the hot-spot parquet renormalization group and the truncated-unity functional renormalization group to theoretically study the emergent correlated states of a two-dimensional square-lattice Hubbard model with VHSs at or near the Fermi level. By varying a single hopping parameter, $t_3$, we are able to change the strength of the VHS divergence in the density of states from logarithmic (for $t_3 < t_{3c}$) to power-law (for $t_3 = t_{3c}$). Further increase of $t_3$ ($t_3 > t_{3c}$) causes each original Van Hove point to split into two, both of the conventional logarithmic type. We show that which of these regimes we are in strongly influences the predicted ordered states. We also study the dependence on doping, and find that the ferromagnetic state that occurs at Van Hove filling in these models is unstable to very small shifts in the Fermi level, often giving way to distinct ordered states depending on whether the model is electron- or hole-doped. These results highlight the importance of tuning VHS properties to control ordered states in correlated materials, and offer design rules to engineer these phases in novel systems.

cond-mat.str-el↗

arXiv2025

'Stealth' singularities from self-gravitating fermions

We present a new analytic solution to the Einstein-Dirac equations formulated by Finster, Smoller, and Yau [Phys. Rev. D 59, 104020 (1999)] to describe the stationary states of a pair of gravitationally interacting neutral fermions. The fermions' wavefunction in our analytic solution, as in their numerical ones, is both exponentially localized and normalizable. However, our solution differs from theirs in two key respects: it features a naked spacetime singularity at the origin, and the gravitational (Arnowitt-Deser-Misner) mass of the localized object is zero, making it gravitationally undetectable to an external observer. This is despite the arbitrarily large mass of the constituent fermions. This unexpected result may have significant implications for astronomy and cosmology, as it gives a mechanism by which mass could become 'hidden' during the universe's evolution.

gr-qc↗

arXiv2024

Non-Fermi liquid induced by U(1) gauge field interactions: a functional renormalization group analysis

We study the non-Fermi-liquid state formed by an isotropic, degenerate Fermi gas in two spatial dimensions interacting with a U(1) gauge field. Our calculation uses the functional renormalization group (fRG) with a soft frequency cutoff for the fermions. The fRG scheme we employ takes account of the gauge symmetry, which imposes relations (modified Ward-Takahashi identities) between the couplings which constrain the RG flow. The critical exponents and couplings we find for the resulting non-Fermi liquid are mostly insensitive to whether or not we enforce the gauge symmetry constraints, which signifies either that the constraints are superfluous or that the frequency-cutoff scheme is particularly robust. The exception is the gauge-boson mass term, which is RG-relevant about the fixed point without the constraints, but is irrelevant when they are enforced. The latter is physically accurate, as a gauge symmetry cannot be spontaneously broken. In addition, we find $z=2$ and $Σ(ω,k_F)\simω^{1/2}$ for the boson dynamical exponent and scaling of the fermion self-energy, respectively. These results differ considerably from those of past works on the model, though we argue for their plausibility.

cond-mat.str-el↗

arXiv2023

Magnetic Order and Magnetic Excitations in FeTe: How Good is a Short-Range Heisenberg Model?

We revisit the fitting of the Fang-Bernevig-Hu model [Europhys. Lett. 86, 67005 (2009)] to inelastic neutron scattering data carried out by Lipscombe et al. [Phys. Rev. Lett. 106, 057004 (2011)]. We demonstrate that there are many quite different parameter choices within the experimentally observed phase (AFM3) that provide approximately equally good fits to the neutron data. We note that (a) all of these parameter sets lie very close to a point of transition between the AFM3 phase and one of its neighbors in the classical phase diagram, and (b) many of them involve rather large values of the third-neighbor coupling $J_3$. In light of these observations, we discuss whether the modeling of FeTe may need revision to allow for a slightly non-AFM3 ground state, orbital as well as spin physics on the Fe sites, the effects of electron itinerancy, or a combination of these.

cond-mat.str-el↗

arXiv2023

Gravitationally localized states of two neutral fermions interacting with a Higgs field

We present localized 'particle-like' states composed of a pair of neutral fermions interacting with a scalar Higgs field and the metric of spacetime, extending the Einstein-Dirac formalism introduced by Finster, Smoller, and Yau [Phys. Rev. D 59, 104020 (1999)]. We demonstrate that, when the coupling between the fermions and the Higgs field is strong, there is a class of states in which the total (ADM) mass no longer increases proportionally to the mass of the constituent fermions; indeed it decreases. This phenomenon enables fermionic particles with much larger masses than in the Higgs-free case to form localized states.

gr-qc↗

arXiv2023

Hierarchy of Lifshitz transitions in the surface electronic structure of Sr$_2$RuO$_4$ under uniaxial compression

We report the evolution of the electronic structure at the surface of the layered perovskite Sr$_2$RuO$_4$ under large in-plane uniaxial compression, leading to anisotropic $B_{1g}$ strains of ${\varepsilon_{xx}-\varepsilon_{yy}=-0.9\pm0.1\%}$. From angle-resolved photoemission, we show how this drives a sequence of Lifshitz transitions, reshaping the low-energy electronic structure and the rich spectrum of van Hove singularities that the surface layer of Sr$_2$RuO$_4$ hosts. From comparison to tight-binding modelling, we find that the strain is accommodated predominantly by bond-length changes rather than modifications of octahedral tilt and rotation angles. Our study sheds new light on the nature of structural distortions at oxide surfaces, and how targeted control of these can be used to tune density of states singularities to the Fermi level, in turn paving the way to the possible realisation of rich collective states at the Sr$_2$RuO$_4$ surface.

cond-mat.str-el↗

arXiv2021

Nonlinear effects in the excited states of many-fermion Einstein-Dirac solitons

We present an analysis of excited-state solutions for a gravitationally localized system consisting of a filled shell of high-angular-momentum fermions, using the Einstein-Dirac formalism introduced by Finster, Smoller, and Yau [Phys. Rev. D 59, 104020 (1999)]. We show that, even when the particle number is relatively low ($N_f\ge 6$), the increased nonlinearity in the system causes a significant deviation in behavior from the two-fermion case. Excited-state solutions can no longer be uniquely identified by the value of their central redshift, with this multiplicity producing distortions in the characteristic spiraling forms of the mass-radius relations. We discuss the connection between this effect and the internal structure of solutions in the relativistic regime.

gr-qc↗

arXiv2021

Fisher zeros and persistent temporal oscillations in non-unitary quantum circuits

We present a quantum circuit with measurements and post-selection that exhibits a panoply of space- and/or time-ordered phases, from ferromagnetic order to spin-density waves to time crystals. Unlike the time crystals that have been found in unitary models, those that occur here are \emph{incommensurate} with the drive frequency. The period of the incommensurate time-crystal phase may be tuned by adjusting the circuit parameters. We demonstrate that the phases of our quantum circuit, including the inherently non-equilibrium dynamical ones, correspond to complex-temperature equilibrium phases of the exactly solvable square-lattice anisotropic Ising model.

cond-mat.stat-mech↗

arXiv2021

Multi-fixed point numerical conformal bootstrap: a case study with structured global symmetry

In large part, the future utility of modern numerical conformal bootstrap depends on its ability to accurately predict the existence of hitherto unknown non-trivial conformal field theories (CFTs). Here we investigate the extent to which this is possible in the case where the global symmetry group has a product structure. We do this by testing for signatures of fixed points using a mixed-correlator bootstrap calculation with a minimal set of input assumptions. This 'semi-blind' approach contrasts with other approaches for probing more complicated groups, which 'target' known theories with additional spectral assumptions or use the saturation of the single-correlator bootstrap bound as a starting point. As a case study, we select the space of CFTs with product-group symmetry $O(15)\otimes{O}(3)$ in $d=3$ dimensions. On the assumption that there is only one relevant scalar ($\ell=0$) singlet operator in the theory, we find a single 'allowed' region in our chosen space of scaling dimensions. The scaling dimensions corresponding to two known large-$N$ critical theories, the Heisenberg and the chiral ones, lie on or very near the boundary of this region. The large-$N$ antichiral point lies well outside the 'allowed' region, which is consistent with the expectation that the antichiral theory is unstable, and thus has an additional relevant scalar singlet operator. We also find a sharp kink in the boundary of the 'allowed' region at values of the scaling dimensions that do not correspond to the $(N,M)=(15,3)$ instance of any large-$N$-predicted $O(N) \otimes O(M)$ critical theory.

hep-th↗

arXiv2020

Fidelity plateaus from correlated noise in isolated few-level quantum systems

We show that, in an isolated two-level quantum system described by a time-dependent Hamiltonian, correlated noise in the Hamiltonian's parameters can lead to an arbitrarily long plateau in the state-preparation fidelity as a function of elapsed time. We explain the formation of this plateau using the Bloch-sphere representation, deriving analytical expressions for its start and end times and its height. We also briefly discuss the extent to which this phenomenon is expected to be visible in more general quantum systems with $N>2$ levels.

cond-mat.quant-gas↗

arXiv2020

Infinite-redshift localized states of Dirac fermions under Einsteinian gravity

We present a set of localized states for an even number of Dirac fermions under Einsteinian gravity that have an infinite central redshift. Near the center of the localized state the components of the Dirac spinor and the spacetime metric all show simple power-law dependences on the radial distance; further out the fermionic wave function decays to zero and the spacetime becomes asymptotically flat. We show that this `central' solution of the equations of motion can be used to understand much of the structure observed by Finster, Smoller, and Yau [Phys. Rev. D 59, 104020 (1999)] in their numerical solutions of the same problem at finite central redshift.

gr-qc↗

arXiv2020

Dimensional crossover and the link between thermodynamics and dynamics: the case of Ising models at complex temperature

We study dimensional crossover in Ising systems at complex temperatures by comparing three types of system: the infinite isotropic 2D Ising model; the infinite anisotropic 2D Ising model; and Ising ladders with a finite number of legs. In particular we present evidence, from both tensor-network calculations and numerical evaluations based on the exact solution of the model, that the infinite anisotropic 2D Ising model exhibits long-range spatially modulated magnetization in certain regions of the complex-temperature plane. We discuss the physics of the special unitary points that exists in the complex-temperature plane, and their connections to the theory of quantum information processing.

cond-mat.stat-mech↗

arXiv2020

Can Fermi surface nesting alone drive the charge-density-wave transition in monolayer vanadium diselenide?

We demonstrate that charge-density-wave formation is possible via a purely electronic mechanism in monolayers of the transition metal dichalcogenide 1T-VSe$_2$. Via a renormalization group treatment of an extended Hubbard model we examine the competition of superconducting and density-wave fluctuations as sections of the Fermi surface are tuned to perfect nesting. We find regions of charge-density-wave order when the Heisenberg exchange interaction is comparable to the Coulomb repulsion, and $d$-wave superconductivity for purely repulsive interactions. We discuss the possible role of lattice vibrations in enhancing the effective Heisenberg exchange.

cond-mat.str-el↗

arXiv2020

Fermion self-trapping in the optical geometry of Einstein-Dirac solitons

We analyze gravitationally localized states of multiple fermions with high angular momenta, in the formalism introduced by Finster, Smoller, and Yau [Phys Rev. D 59, 104020 (1999)]. We show that the resulting soliton-like wave functions can be naturally interpreted in terms of a form of self-trapping, where the fermions become localized on shells the locations of which correspond to those of `bulges' in the optical geometry created by their own energy density.

gr-qc↗

arXiv2020

Mixed-parity superconductivity near Lifshitz transitions in strongly spin-orbit-coupled metals

We consider a strongly spin-orbit-coupled metal, one of whose Fermi surfaces is close to a Lifshitz (topological) transition. Via a renormalization group analysis of the square-lattice Hubbard model with strong Rashba spin-orbit coupling, we show that such a metal is generically unstable to the formation of mixed-parity superconductivity with a helical triplet component.

cond-mat.supr-con↗

arXiv2019

Resonant two-site tunnelling dynamics of bosons in a tilted optical superlattice

We study the non-equilibrium dynamics of a 1D Bose-Hubbard model in a gradient potential and a superlattice, beginning from a deep Mott insulator regime with an average filling of one particle per site. Studying a quench that is near resonance to tunnelling of the particles over two lattice sites, we show how a spin model emerges consisting of two coupled Ising chains that are coupled by interaction terms in a staggered geometry. We compare and contrast the behavior in this case with that in a previously studied case where the resonant tunnelling was over a single site. Using optimized tensor network techniques to calculate finite temperature behavior of the model, as well as finite size scaling for the ground state, we conclude that the universality class of the phase transition for the coupled chains is that of a tricritical Ising point. We also investigate the out-of-equilibrium dynamics after the quench in the vicinity of the resonance and compare dynamics with recent experiments realized without the superlattice geometry. This model is directly realizable in current experiments, and reflects a new general way to realize spin models with ultracold atoms in optical lattices.

cond-mat.quant-gas↗

arXiv2019

Spin-models, dynamics and criticality with atoms in tilted optical superlattices

We show that atoms in tilted optical superlattices provide a platform for exploring coupled spin chains of forms that are not present in other systems. In particular, using a period-2 superlattice in 1D, we show that coupled Ising spin chains with XZ and ZZ spin coupling terms can be engineered. We use optimized tensor network techniques to explore the criticality and non-equilibrium dynamics in these models, finding a tricritical Ising point in regimes that are accessible in current experiments. These setups are ideal for studying low-entropy physics, as initial entropy is "frozen-out" in realizing the spin models, and provide an example of the complex critical behaviour that can arise from interaction-projected models.

cond-mat.quant-gas↗