Vortex Degrees Of Freedom Research Articles

Sound waves and vortices in a polarized relativistic fluid

We extend the effective theory approach to the ideal fluid limit where the polarization of the fluid is non-zero. After describing and motivating the equations of motion, we expand them around the hydrostatic limit, obtaining the sound wave and vortex degrees of freedom. We discuss how the presence of polarization affects the stability and causality of the ideal fluid limit.

Emergence of order from turbulence in an isolated planar superfluid.

We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation the remaining vortices self-organize into two macroscopic coherent "Onsager vortex" clusters that are stable indefinitely--despite the absence of driving or external dissipation in the dynamics. We demonstrate that this occurs due to a novel physical mechanism--the evaporative heating of the vortices--that results in a negative-temperature phase transition in the vortex degrees of freedom. At the end of our simulations the system is trapped in a nonthermal state. Our computational results provide a pathway to observing Onsager vortex states in a superfluid Bose gas.

Characterizing symmetry breaking patterns in a lattice by dual degrees of freedom

A duality transformation in quantum field theory is usually established first through partition functions. It is always important to explore the dual relations between various correlation functions in the transformation. Here, we explore such a dual relation to study quantum phases and phase transitions in an extended boson Hubbard model at 1/3 (2/3) filling on a triangular lattice. We develop systematically a simple and effective way to use the vortex degrees of freedom on dual lattices to characterize both the density wave and valence bond symmetry breaking patterns of the boson insulating states in the direct lattices. In addition to a checkerboard charge density wave (X-CDW) and a stripe CDW, we find a novel CDW-VBS phase which has both local CDW and local valence bond solid (VBS) orders. Implications for Quantum Monte Carlo simulations are addressed. The possible experimental realizations of cold atoms loaded on optical lattices are discussed.

The quantum mechanics of perfect fluids

We consider the canonical quantization of an ordinary fluid. The resulting long-distance effective field theory is derivatively coupled, and therefore strongly coupled in the UV. The system however exhibits a number of peculiarities, associated with the vortex degrees of freedom. On the one hand, these have formally a vanishing strong-coupling energy scale, thus suggesting that the effective theory's regime of validity is vanishingly narrow. On the other hand, we prove an analog of Coleman's theorem, whereby the semiclassical vacuum has no quantum counterpart, thus suggesting that the vortex premature strong-coupling phenomenon stems from a bad identification of the ground state and of the perturbative degrees of freedom. Finally, vortices break the usual connection between short distances and high energies, thus potentially impairing the unitarity of the effective theory.

Global string and vortex superfluids in a supersymmetric scenario

The main goal of this work is to investigate the possibility of finding the supersymmetric version of the U(1)-global string model which behaves as a vortex-superfluid. To describe the superfluid phase, we introduce a Lorentz-symmetry breaking background that, in an approach based on supersymmetry, leads to a discussion on the relation between the violation of Lorentz symmetry and explicit soft supersymmetry breakings. We also study the relation between the string configuration and the vortex-superfluid phase. In the framework we settle down in terms of superspace and superfields, we actually establish a duality between the vortex degrees of freedom and the component fields of the Kalb-Ramond superfield. We make also considerations about the fermionic excitations that may appear in connection with the vortex formation.

Magnetotransport properties near the superconductor-insulator transition in two dimensions

We analyze here the behavior near the two-dimensional insulator-superconductor quantum critical point in the presence of a perpendicular magnetic field. We show that with increasing field H, the quantum disordered and quantum critical regimes, in which vortex degrees of freedom are suppressed, crossover to a new magnetically activated (MA) regime, where the correlation length $\ensuremath{\xi}\ensuremath{\sim}1/\sqrt{H}.$ In this regime, we show that the conductivity decreases monotonically as opposed to the anticipated saturation predicted from hyperuniversality arguments. This discrepancy arises from the lack of commutativity of the frequency and temperature tending to zero limits of the conductivity. In the low-field regime such that $\sqrt{H}\ensuremath{\ll}\ensuremath{\Delta},$ and in the absence of Ohmic dissipation, where $\ensuremath{\Delta}$ is a measure of the distance from the quantum critical point, the resistivity saturates to the Bose metal value found previously for Cooper pairs lacking phase coherence.

Disorder Driven Destruction of a Phase Transition in the Vortex System of a Superconductor

We investigate the effects of point disorder on the magnetically induced vortex system of a layered superconductor. The clean system is known to have a first order phase transition which is clearly identified by a sharp peak in the specific heat. The peak is lost abruptly as the strength of the disorder is increased. Hence, for strong disorder there is no phase transition (in the vortex degrees of freedom) as a function of temperature but merely a crossover which is still detectable in the I-V characteristic.

Current-induced vortex dynamics in Josephson-junction arrays: Imaging experiments and model simulations

We study the dynamics of current-biased Josephson-junction arrays with a magnetic penetration depth ${\ensuremath{\lambda}}_{\ensuremath{\perp}}$ smaller than the lattice spacing. We compare the dynamics imaged by low-temperature scanning electron microscopy to the vortex dynamics obtained from model calculations based on the resistively shunted junction model, in combination with Maxwell's equations. We find three bias current regions with fundamentally different array dynamics. The first region is the subcritical region, i.e., below the array critical current ${I}_{c}.$ The second, for currents $I$ above ${I}_{c},$ is a ``vortex region,'' in which the response is determined by the vortex degrees of freedom. In this region, the dynamics is characterized by spatial domains where vortices and antivortices move across the array in opposite directions in adjacent rows and by transverse voltage fluctuations. In the third, for still higher currents, the dynamics is dominated by coherent-phase motion, and the current-voltage characteristics are linear.