arXiv subjects

C. Hooley

Publications and source records attributed to C. Hooley.

13 recordsLinked to original sources

arXiv2024

The Weyl-Mott point: topological and non-Fermi liquid behavior from an isolated Green's function zero

We present a model in which a Hatsugai-Kohmoto interaction is added to a system of fermions with a Weyl point in their non-interacting dispersion relation, and analyze its behavior as a function of the chemical potential. We show that the model exhibits a Weyl-Mott point -- a single isolated Green's function zero -- and that this implies an emergent non-Fermi-liquid state at the border of the metallic regime and a gapped topological state for the insulating one. The Weyl-Mott point inherits the topological charge from the original Green's function pole, and is therefore naturally associated with a strongly correlated chiral anomaly.

cond-mat.str-el↗

arXiv2019

Kondo exhaustion and conductive surface states in antiferromagnetic YbIr$_3$Si$_7$

The interplay of Kondo screening and magnetic ordering in strongly correlated materials containing local moments is a subtle problem.[1] Usually the number of conduction electrons matches or exceeds the number of moments, and a Kondo-screened heavy Fermi liquid develops at low temperatures.[2] Changing the pressure, magnetic field, or chemical doping can displace this heavy Fermi liquid in favor of a magnetically ordered state.[3,4] Here we report the discovery of a version of such a `Kondo lattice' material, YbIr$_3$Si$_7$, in which the number of free charge carriers is much less than the number of local moments. This leads to `Kondo exhaustion':[5] the electrical conductivity tends to zero at low temperatures as all the free carriers are consumed in the formation of Kondo singlets. This effect coexists with antiferromagnetic long-range order, with a Néel temperature $T\rm_N = 4.1\,{\rm K}$. Furthermore, the material shows conductive surface states with potential topological nature, and thus presents an exciting topic for future investigations.

cond-mat.str-el↗

arXiv2012

Thermal versus Quantum Fluctuations of Optical Lattice Fermions

We show that, for fermionic atoms in a one-dimensional optical lattice, the fraction of atoms in doubly occupied sites is a highly non-monotonic function of temperature. We demonstrate that this property persists even in the presence of realistic harmonic confinement, and that it leads to a suppression of entropy at intermediate temperatures that offers a route to adiabatic cooling. Our interpretation of the suppression is that such intermediate temperatures are simultaneously too high for quantum coherence and too low for significant thermal excitation of double occupancy thus offering a clear indicator of the onset of quantum fluctuations.

cond-mat.quant-gas↗

arXiv2008

Critical behavior driven by the confining potential in optical lattices with ultra-cold fermions?

A recent paper [V. L. Campo et. al., Phys. Rev. Lett. 99, 240403 (2007) has proposed a two-parameter scaling method to determine the phase diagram of the fermionic Hubbard model from optical lattice experiments. Motivated by this proposal, we investigate in more detail, the behavior of the ground-state energy per site as a function of trap size(L) and confining potential (V(x) = t(x/L)^alpha) in the one-dimensional case. Using the BALDA-DFT method, we find signatures of critical behavior as alpha goes to infinity.

cond-mat.str-el↗

arXiv2008

Pomeranchuk instability: symmetry breaking and experimental signatures

We discuss the emergence of symmetry-breaking {\it via} the Pomeranchuk instability from interactions that respect the underlying point-group symmetry. We use a variational mean-field theory to consider a 2D continuum and a square lattice. We describe two experimental signatures: a symmetry-breaking pattern of Friedel oscillations around an impurity; and a structural transition.

cond-mat.str-el↗

arXiv2005

Finite-curvature scaling in optical lattice systems

We address the problem posed by the inhomogeneous trapping fields when using ultracold fermions to simulate strongly correlated electrons. As a starting point, we calculate the density of states for a single atom. Using semiclassical arguments, we show that this can be made to evolve smoothly towards the desired limit by varying the curvature of the field profile. Implications for mutually interacting atoms in such potentials are briefly discussed.

cond-mat.stat-mech↗

arXiv2004

Single-atom density of states of an optical lattice

We consider a single atom in an optical lattice, subject to a harmonic trapping potential. The problem is treated in the tight-binding approximation, with an extra parameter κdenoting the strength of the harmonic trap. It is shown that the κ\to 0 limit of this problem is singular, in the sense that the density of states for a very shallow trap (κ\to 0) is {\it qualitatively different} from that of a translationally invariant lattice (κ= 0). The physics of this difference is discussed, and densities of states and wave functions are exhibited and explained.

cond-mat.stat-mech↗

arXiv2003

Spin dynamics from Majorana fermions

Using the Majorana fermion representation of spin-1/2 local moments, we show how it is possible to directly read off the dynamic spin correlation and susceptibility from the one-particle propagator of the Majorana fermion. We illustrate our method by applying it to the spin dynamics of a non-equilibrium quantum dot, computing the voltage-dependent spin relaxation rate and showing that, at weak coupling, the fluctuation-dissipation relation for the spin of a quantum dot is voltage-dependent. We confirm the voltage-dependent Curie susceptibility recently found by Parcollet and Hooley [Phys. Rev. B {\bf 66}, 085315 (2002)].

cond-mat.str-el↗

arXiv2002

On the perturbative expansion of the magnetization in the out-of-equilibrium Kondo model

This paper is concerned with the out-of-equilibrium two-lead Kondo model, considered as a model of a quantum dot in the Kondo regime. We revisit the perturbative expansion of the dot's magnetization, and conclude that, even at order 0 in the Kondo interactions, the magnetization is not given by the usual equilibrium result. We use the Schwinger-Keldysh method to derive a Dyson equation describing the steady state induced by the voltage between the two leads, and thus present the correct procedure for calculating perturbative expansions of steady-state properties of the system.

cond-mat.str-el↗

arXiv2001

Oscillatory instabilities in d.c. biased quantum dots

We consider a `quantum dot' in the Coulomb blockade regime, subject to an arbitrarily large source-drain voltage V. When V is small, quantum dots with odd electron occupation display the Kondo effect, giving rise to enhanced conductance. Here we investigate the regime where V is increased beyond the Kondo temperature and the Kondo resonance splits into two components. It is shown that interference between them results in spontaneous oscillations of the current through the dot. The theory predicts the appearance of ``Shapiro steps'' in the current-voltage characteristics of an irradiated quantum dot; these would constitute an experimental signature of the predicted effect.

cond-mat.mes-hall↗

arXiv2001

Is the quantum dot at large bias a weak-coupling problem?

We examine the two-lead Kondo model for a d.c. biased quantum dot in the Coulomb blockade regime. From perturbative calculations of the magnetic susceptibility, we show that the problem retains its strong-coupling nature, even at bias voltages larger than the equilibrium Kondo temperature. We give a speculative discussion of the nature of the renormalization group flows and the strong-coupling state that emerges at large voltage bias.

cond-mat.mes-hall↗

arXiv1999

Spin-gap physics, ground state degeneracy, and bound states on the depleted kagome lattice

We analyse the antiferromagnetic spin-1/2 Heisenberg model on a depleted kagome lattice, where some bonds have been reduced to exchange integral J_2 << J_1. The fully depleted system consists of 1D chains, each with a doubly degenerate singlet-pair ground state and a spectral gap (like the Majumdar-Ghosh model). There are localised and itinerant low-energy excitations. The modes from the lowest branch of excitations are incapable of lifting the 2D system's ground state degeneracy at finite J_2/J_1 << 1. Low-energy excitations of the 2D system are dominated by coherently propagating bound states of the 1D excitations.

cond-mat.str-el↗

arXiv1998

Kagom{é} Lattice Antiferromagnet Stripped to Its Basics

We study a model of a spin S = 1/2 Heisenberg antiferromagnet on a one dimensional lattice with the local symmetry of the two dimensional kagom{é} lattice. Using three complementary approaches, it is shown that the low energy spectrum can be described by two critical Ising models with different velocities. One of these velocities is small, leading to a strongly localized Majorana fermion. These excitations are singlet ones whereas the triplet sector has a spectral gap.

cond-mat.str-el↗