Search results for "conductivity"
showing 10 items of 1988 documents
Vortex rings in two-dimensional harmonic traps
2006
We use the configuration interaction technique to study vortex formation in rotating systems of interacting spinless fermions and bosons trapped in a two-dimensional harmonic potential. In the fermionic case, the vortices appear as holes in the Fermi sea and localize in rings. The yrast spectrum is dominated by rigid rotation of the vortex ring, showing periodic oscillations. The Bose system shows a similar yrast spectrum and vortex formation. This can be explained by a one-to-one correspondence of the fermion and boson many-particle configurations. A simple mean-field model can reproduce the oscillations in the yrast spectrum, but fails to explain the localization of vortices.
Phase sticking in one-dimensional Josephson junction chains
2013
Published version of an article in the journal: Physical Review B - Condensed Matter and Materials Physics. Also available from the publisher at: http://dx.doi.org/10.1103/PhysRevB.88.104501 We studied current-voltage characteristics of long one-dimensional Josephson junction chains with Josephson energy much larger than charging energy, EJ EC. In this regime, typical I-V curves of the samples consist of a supercurrent-like branch at low-bias voltages followed by a voltage-independent chain current branch, Ichain at high bias. Our experiments showed that Ichain is not only voltage-independent but it is also practically temperature-independent up to T=0.7TC. We have successfully model the tr…
Laser-induced collective excitations in a two-component Fermi gas
2002
We consider the linear density response of a two-component (superfluid) Fermi gas of atoms when the perturbation is caused by laser light. We show that various types of laser excitation schemes can be transformed into linear density perturbations, however, a Bragg spectroscopy scheme is needed for transferring energy and momentum into a collective mode. This makes other types of laser probing schemes insensitive for collective excitations and therefore well suited for the detection of the superfluid order parameter. We show that for the special case when laser light is coupled between the two components of the Fermi gas, density response is always absent in a homogeneous system.
Hartree-Fock-Bogoliubov theory of polarized Fermi systems
2008
Condensed Fermi systems with an odd number of particles can be described by means of polarizing external fields having a time-odd character. We illustrate how this works for Fermi gases and atomic nuclei treated by density functional theory or Hartree-Fock-Bogoliubov (HFB) theory. We discuss the method based on introducing two chemical potentials for different superfluid components, whereby one may change the particle-number parity of the underlying quasiparticle vacuum. Formally, this method is a variant of non-collective cranking, and the procedure is equivalent to the so-called blocking. We present and exemplify relations between the two-chemical-potential method and the cranking approxi…
Quasiparticles and quantum phase transition in universal low-temperature properties of heavy-fermion metals
2006
We demonstrate, that the main universal features of the low temperature experimental $H-T$ phase diagram of CeCoIn5 and other heavy-fermion metals can be well explained using Landau paradigm of quasiparticles. The main point of our theory is that above quasiparticles form so-called fermion-condensate state, achieved by a fermion condensation quantum phase transition (FCQPT). When a heavy fermion liquid undergoes FCQPT, the fluctuations accompanying above quantum critical point are strongly suppressed and cannot destroy the quasiparticles. The comparison of our theoretical results with experimental data on CeCoIn5 have shown that the electronic system of above substance provides a unique opp…
Asymmetric Tunneling Conductance and the non-Fermi Liquid Behavior of Strongly Correlated Fermi Systems
2018
Tunneling differential conductivity (or resistivity) is a sensitive tool to experimentally test the nonFermi liquid behavior of strongly correlated Fermi systems. In the case of common metals the Landau– Fermi liquid theory demonstrates that the differential conductivity is a symmetric function of bias voltage V . This is because the particle-hole symmetry is conserved in the Landau–Fermi liquid state. When a strongly correlated Fermi system turns out to be near the topological fermion condensation quantum phase transition, its Landau–Fermi liquid properties disappear so that the particle-hole symmetry breaks making the differential tunneling conductivity to be asymmetric function of V . Th…
Low energy properties of color-flavor locked superconductors
2005
We discuss some low energy properties of color-flavor locked (CFL) superconductors. First, we study how an external magnetic field affects their Goldstone physics in the chiral limit, stressing that there is a long-range component of the field that penetrates the superconductor. We note that the most remarkable effect of the applied field is giving a mass to the charged pions and kaons. By estimating this effect, we see that for values $e B \sim 2 f_\pi \Delta$, where $\Delta$ is the quark gap, and $f_\pi$ the pion decay constant, the charged Goldstone bosons become so heavy, that they turn out to be unstable. The symmetry breaking pattern is then changed, agreeing with that of the magnetic…
Universal vortex formation in rotating traps with bosons and fermions.
2004
When a system consisting of many interacting particles is set rotating, it may form vortices. This is familiar to us from every-day life: you can observe vortices while stirring your coffee or watching a hurricane. In the world of quantum mechanics, famous examples of vortices are superconducting films and rotating bosonic $^4$He or fermionic $^3$He liquids. Vortices are also observed in rotating Bose-Einstein condensates in atomic traps and are predicted to exist for paired fermionic atoms. Here we show that the rotation of trapped particles with a repulsive interaction leads to a similar vortex formation, regardless of whether the particles are bosons or (unpaired) fermions. The exact, qu…
Momentum-dependent pseudogaps in the half-filled two-dimensional Hubbard model
2012
We compute unbiased spectral functions of the two-dimensional Hubbard model by extrapolating Green functions, obtained from determinantal quantum Monte Carlo simulations, to the thermodynamic and continuous time limits. Our results clearly resolve the pseudogap at weak to intermediate coupling, originating from a momentum selective opening of the charge gap. A characteristic pseudogap temperature T*, determined consistently from the spectra and from the momentum dependence of the imaginary-time Green functions, is found to match the dynamical mean-field critical temperature, below which antiferromagnetic fluctuations become dominant. Our results identify a regime where pseudogap physics is …
Quantum engineering of Majorana quasiparticles in one-dimensional optical lattices
2017
We propose a feasible way of engineering Majorana-type quasiparticles in ultracold fermionic gases on a one-dimensional (1D) optical lattice. For this purpose, imbalanced ultracold atoms interacting by the spin-orbit coupling should be hybridized with a three-dimensional Bose-Einstein condensate (BEC) molecular cloud. By constraining the profile of an internal defect potential we show that the Majorana-type excitations can be created or annihilated. This process is modelled within the Bogoliubov-de Gennes approach. This study is relevant also to nanoscopic 1D superconductors where modification of the internal defect potential can be obtained by electrostatic means.