arXiv subjects

Adrian Del Maestro

Publications and source records attributed to Adrian Del Maestro.

68 records · Page 4Linked to original sources

arXiv2015

Quasi-one-dimensional electron gas bound to a helium-coated nanotube

A much-studied system is the quasi-2D electron gas in image-potential bound states at the surface of helium and hydrogen. In this paper, we report on an analogous quasi-1D system: electrons bound by image-like polarization forces to the surface of a helium-coated carbon nanotube. The potential is computed from an electron-helium pseudopotential, plus a dynamic image term evaluated from a semi-classical model of the nanotube's response function. Predictions are made for the bound states and potential many-body properties of this novel electron gas for a specific choice of tube radius and film thickness.

cond-mat.mes-hall↗

arXiv2015

A Simple Model for Long-Range Interacting Pendula

We show that the Hamiltonian mean field (HMF) model describes the equilibrium behavior of a system of long pendula with flat bobs that are coupled through long-range interactions (charged or self gravitating). We solve for the canonical partition function in the coordinate frame of the pendula angles. The Hamiltonian in the angles coordinate frame looks similar to the form of the HMF model but with the inclusion of an index dependent phase in the interaction term. We also show interesting non-equilibrium behavior of the pendula angles, namely that a quasistationary clustered state can exist when pendula angles are initially ordered by their index.

physics.class-ph↗

arXiv2012

Backscattering Between Helical Edge States via Dynamic Nuclear Polarization

We show that that the non-equilibrium spin polarization of one dimensional helical edge states at the boundary of a two dimensional topological insulator can dynamically induce a polarization of nuclei via the hyperfine interaction. When combined with a spatially inhomogeneous Rashba coupling, the steady state polarization of the nuclei produces backscattering between the topologically protected edge states leading to a reduction in the conductance which persists to zero temperature. We study these effects in both short and long edges, uncovering deviations from Ohmic transport at finite temperature and a current noise spectrum which may hold the fingerprints for experimental verification of the backscattering mechanism.

cond-mat.mes-hall↗

arXiv2012

Quantum Criticality for Extended Nodes on a Bethe Lattice in the Large Connectivity Limit

Theoretical description of anisotropic systems, such as layered superconductors and coupled spin chains, is often a challenge due to the different natures of interactions along different directions. As a model of such a system, we present an analytical study of d-dimensional "nodes" arranged as the vertices of a Bethe lattice, where each node has nonzero spatial dimension and is described by an O(N) quantum rotor model, and there is hopping between neighboring nodes. In the limit of large connectivity on the Bethe lattice, the hopping can be treated by constructing a self-consistent effective action for a single node. This procedure is akin to dynamical mean field theory, but generalized so that spatial as well as quantum fluctuations are taken into account on each node. The quantum phase transition is studied using this effective action for both infinite and finite N. The importance of the Perron-Frobenius uniform mode on the Bethe lattice is discussed, and its elimination via an "infinite range hopping" term shifts the transition, leading to nontrivial critical behavior. We calculate critical exponents and find that the internode hopping reduces the upper and lower critical dimensions each by one, indicating that--at least for the purposes of quantum criticality--the large number of internode couplings is similar to adding a single extra dimension to the theory describing a single node.

cond-mat.str-el↗

arXiv2012

A Luttinger Liquid Core Inside Helium-4 Filled Nanopores

As helium-4 is cooled below 2.17 K it undergoes a phase transition to a fundamentally new state of matter known as a superfluid which supports flow without viscosity. This type of dissipationless transport can be observed by forcing helium to travel through a narrow constriction that the normal liquid could not penetrate. Recent experiments have highlighted the feasibility of fabricating smooth pores with nanometer radii, that approach the truly one dimensional limit where it is believed that a system of bosons (like helium-4) may have startlingly different behavior than in three dimensions. The one dimensional system is predicted to have a linear hydrodynamic description known as Luttinger liquid theory, where no type of long range order can be sustained. In the limit where the pore radius is small, Luttinger liquid theory would predict that helium inside the channel behaves as a sort of quasi-supersolid with all correlations decaying as power-law functions of distance at zero temperature. We have performed large scale quantum Monte Carlo simulations of helium-4 inside nanopores of varying radii at low temperature with realistic helium-helium and helium-pore interactions. The results indicate that helium inside the nanopore forms concentric cylindrical shells surrounding a core that can be described via Luttinger liquid theory and provides insights into the exciting possibility of the experimental detection of this intriguing low dimensional state of matter.

cond-mat.mes-hall↗

arXiv2011

Helium-4 Luttinger liquids in nanopores

We study the low temperature properties of a helium-4 fluid confined in nanopores, using large-scale Quantum Monte Carlo simulations with realistic He-He and He-pore interactions. In the narrow-pore limit, the system can be described by the quantum hydrodynamic theory known as Luttinger liquid theory with a large Luttinger parameter, corresponding to the dominance of solid tendencies and strong susceptibility to pinning by a periodic or random potential from the pore walls. On the other hand, for wider pores, the central region appears to behave like a Luttinger liquid with a smaller Luttinger parameter, and may be protected from pinning by the wall potential, offering the possibility of experimental detection of a Luttinger liquid.

cond-mat.stat-mech↗

arXiv2010

Dynamical conductivity at the dirty superconductor-metal quantum phase transition

We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments.

cond-mat.dis-nn↗

arXiv2010

Interacting bosons in one dimension and Luttinger liquid theory

Harmonically trapped ultra-cold atoms and helium-4 in nanopores provide new experimental realizations of bosons in one dimension, motivating the search for a more complete theoretical understanding of their low energy properties. Worm algorithm path integral quantum Monte Carlo results for interacting bosons restricted to the one dimensional continuum are compared to the finite temperature and system size predictions of Luttinger liquid theory. For large system sizes at low temperature, excellent agreement is obtained after including the leading irrelevant interactions in the Hamiltonian which are determined explicitly.

cond-mat.stat-mech↗

arXiv2008

Theory of the pairbreaking superconductor-metal transition in nanowires

We present a detailed description of a zero temperature phase transition between superconducting and diffusive metallic states in very thin wires due to a Cooper pair breaking mechanism. The dissipative critical theory contains current reducing fluctuations in the guise of both quantum and thermally activated phase slips. A full cross-over phase diagram is computed via an expansion in the inverse number of complex components of the superconducting order parameter (one in the physical case). The fluctuation corrections to the direct current electrical and thermal conductivities are determined, and we find that the electrical conductivity has a non-monotonic temperature dependence in the metallic phase which may be consistent with recent experimental results on ultra-narrow wires. In the quantum critical regime, the ratio of the thermal to electrical conductivity displays a linear temperature dependence and thus the Wiedemann-Franz law is obeyed, with a new universal experimentally verifiable Lorenz number.

cond-mat.supr-con↗

arXiv2008

Infinite randomness fixed point of the superconductor-metal quantum phase transition

We examine the influence of quenched disorder on the superconductor-metal transition, as described by a theory of overdamped Cooper pairs which repel each other. The self-consistent pairing eigenmodes of a quasi-one dimensional wire are determined numerically. Our results support the recent proposal by Hoyos et al. (arXiv:0705.1865) that the transition is characterized by the same strong disorder fixed point describing the onset of ferromagnetism in the random quantum Ising chain in a transverse field.

cond-mat.dis-nn↗

arXiv2007

Low temperature specific heat and possible gap to magnetic excitations in the Heisenberg pyrochlore antiferromagnet Gd2Sn207

The Gd2Sn2O7 pyrochlore Heisenberg antiferromagnet displays a phase transition to a four sublattice Neel ordered state at a temperature near 1 K. Despite the seemingly conventional nature of the ordered state, the specific heat has been found to be described in the temperature range 350-800 mK by an anomalous T-squared power law. A similar temperature dependence has also been reported for Gd2Ti2O7, another pyrochlore Heisenberg material. Such anomalous T-squared behavior in Cv has been argued to be correlated to an unusual energy-dependence of the density of states which also seemingly manifests itself in low-temperature spin fluctuations found in muon spin relaxation experiments. In this paper, we report calculations of Cv that consider spin wave like excitations out of the Neel order observed in Gd2Sn2O7 and argue that the parametric T-squared behavior does not reflect the true low-energy excitations of Gd2Sn2O7. Rather, we find that the low-energy excitations of this material are antiferromagnetic magnons gapped by single-ion and dipolar anisotropy effects, and that the lowest temperature of 350 mK considered in previous specific heat measurements accidentally happens to coincide with a crossover temperature below which magnons become thermally activated and Cv takes an exponential form. We argue that further specific heat measurements that extend down to at least 100 mK are required in order to ascribe an unconventional description of magnetic excitations out of the ground state of Gd2Sn2O7 or to invalidate the standard picture of gapped excitations proposed herein.

cond-mat.mtrl-sci↗

arXiv2006

From stripe to checkerboard order on the square lattice in the presence of quenched disorder

We discuss the effects of quenched disorder on a model of charge density wave (CDW) ordering on the square lattice. Our model may be applicable to the cuprate superconductors, where a random electrostatic potential exists in the CuO2 planes as a result of the presence of charged dopants. We argue that the presence of a random potential can affect the unidirectionality of the CDW order, characterized by an Ising order parameter. Coupling to a unidirectional CDW, the random potential can lead to the formation of domains with 90 degree relative orientation, thus tending to restore the rotational symmetry of the underlying lattice. We find that the correlation length of the Ising order can be significantly larger than the CDW correlation length. For a checkerboard CDW on the other hand, disorder generates spatial anisotropies on short length scales and thus some degree of unidirectionality. We quantify these disorder effects and suggest new techniques for analyzing the local density of states (LDOS) data measured in scanning tunneling microscopy experiments.

cond-mat.str-el↗

arXiv2004

Thermal melting of density waves on the square lattice

We present the theory of the effect of thermal fluctuations on commensurate "p x p" density wave ordering on the square lattice (p >= 3, integer). For the case in which this order is lost by a second order transition, we argue that the adjacent state is generically an incommensurate striped state, with commensurate p-periodic long range order along one direction, and incommensurate quasi-long-range order along the orthogonal direction. We also present the routes by which the fully disordered high temperature state can be reached. For p=4, and at special commensurate densities, the "4 x 4" commensurate state can melt directly into the disordered state via a self-dual critical point with non-universal exponents.

cond-mat.str-el↗

arXiv2003

Understanding Paramagnetic Spin Correlations in the Spin-Liquid Pyrochlore Tb2Ti2O7

Recent elastic and inelastic neutron scattering studies of the highly frustrated pyrochlore antiferromagnet Tb2Ti2O7 have shown some very intriguing features that cannot be modeled by the local <111> classical Ising model, naively expected to describe this system at low temperatures. Using the random phase approximation to take into account fluctuations between the ground state doublet and the first excited doublet, we successfully describe the elastic neutron scattering pattern and dispersion relations in Tb2Ti2O7, semi-quantitatively consistent with experimental observations.

cond-mat.dis-nn↗