996 research outputs found
FFLO correlation and free fluids in the one-dimensional attractive Hubbard model
In this Rapid Communication we show that low energy macroscopic properties of
the one-dimensional (1D) attractive Hubbard model exhibit two fluids of bound
pairs and of unpaired fermions. Using the thermodynamic Bethe ansatz equations
of the model, we first determine the low temperature phase diagram and
analytically calculate the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing
correlation function for the partially-polarized phase. We then show that for
such a FFLO-like state in the low density regime the effective chemical
potentials of bound pairs and unpaired fermions behave like two free fluids.
Consequently, the susceptibility, compressibility and specific heat obey simple
additivity rules, indicating the `free' particle nature of interacting fermions
on a 1D lattice. In contrast to the continuum Fermi gases, the correlation
critical exponents and thermodynamics of the attractive Hubbard model
essentially depend on two lattice interacting parameters. Finally, we study
scaling functions, the Wilson ratio and susceptibility which provide universal
macroscopic properties/dimensionless constants of interacting fermions at low
energy.Comment: In this Letter we analytically study FFLO pairing correlation and the
universal nature of the FFLO-like state. More detailed studies of this model
will be presented in arXiv:1710.08742 and arXiv:1708.0778
Analysis of two stroke marine diesel engine operation including turbocharger cut-out by using a zero-dimensional model
In this article, the operation of a large two-stroke marine diesel engine including various cases with turbocharger cut-out was thoroughly investigated by using a modular zero-dimensional engine model built in MATLAB/Simulink environment. The model was developed by using as a basis an in-house modular mean value engine model, in which the existing cylinder block was replaced by a more detailed one that is capable of representing the scavenging ports-cylinder-exhaust valve processes. Simulation of the engine operation at steady state conditions was performed and the derived engine performance parameters were compared with the respective values obtained by the engine shop trials. The investigation of engine operation under turbocharger cut-out conditions in the region from 10% to 50% load was carried out and the influence of turbocharger cut-out on engine performance including the in-cylinder parameters was comprehensively studied. The recommended schedule for the combination of the turbocharger cut-out and blower activation was discussed for the engine operation under part load conditions. Finally, the influence of engine operating strategies on the annual fuel savings, CO2 emissions reduction and blower operating hours for a Panamax container ship operating at slow steaming conditions is presented and discussed
Asymptotic correlation functions and FFLO signature for the one-dimensional attractive Hubbard model
We study the long-distance asymptotic behavior of various correlation
functions for the one-dimensional (1D) attractive Hubbard model in a partially
polarized phase through the Bethe ansatz and conformal field theory approaches.
We particularly find the oscillating behavior of these correlation functions
with spatial power-law decay, of which the pair (spin) correlation function
oscillates with a frequency (). Here is the mismatch in the Fermi surfaces of
spin-up and spin-down particles. Consequently, the pair correlation function in
momentum space has peaks at the mismatch , which has been
observed in recent numerical work on this model. These singular peaks in
momentum space together with the spatial oscillation suggest an analog of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in the 1D Hubbard model. The
parameter representing the lattice effect becomes prominent in critical
exponents which determine the power-law decay of all correlation functions. We
point out that the backscattering of unpaired fermions and bound pairs within
their own Fermi points gives a microscopic origin of the FFLO pairing in 1D.Comment: 26 pages, 4 figures, published version, a series of study on the 1D
attractive Hubbard model, few typos were corrected, references were added,
also see arXiv:1708.07784 and arXiv:1708.0777
Dimensionless ratios: characteristics of quantum liquids and their phase transitions
Dimensionless ratios of physical properties can characterize low-temperature
phases in a wide variety of materials. As such, the Wilson ratio (WR), the
Kadowaki-Woods ratio and the Wiedemann\--Franz law capture essential features
of Fermi liquids in metals, heavy fermions, etc. Here we prove that the phases
of many-body interacting multi-component quantum liquids in one dimension (1D)
can be described by WRs based on the compressibility, susceptibility and
specific heat associated with each component. These WRs arise due to additivity
rules within subsystems reminiscent of the rules for multi-resistor networks in
series and parallel --- a novel and useful characteristic of multi-component
Tomonaga-Luttinger liquids (TLL) independent of microscopic details of the
systems. Using experimentally realised multi-species cold atomic gases as
examples, we prove that the Wilson ratios uniquely identify phases of TLL,
while providing universal scaling relations at the boundaries between phases.
Their values within a phase are solely determined by the stiffnesses and sound
velocities of subsystems and identify the internal degrees of freedom of said
phase such as its spin-degeneracy. This finding can be directly applied to a
wide range of 1D many-body systems and reveals deep physical insights into
recent experimental measurements of the universal thermodynamics in ultracold
atoms and spins.Comment: 12 pages (main paper), (6 figures
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