7 research outputs found
Study of effective coupling between charge degrees of freedom in low dimensional hole-doped quantum antiferromagnets
Expressions for generalized charge stiffness constant at zero temperature are
derived corresponding to low dimensional hole doped quantum antiferromagnets,
describable by the t-J-like models, with a view to understanding fermionic
pairing possibilities and charge couplings in the itinerant antiferromagnetic
systems. A detailed comparison between spin and charge correlations and
couplings are presented in both strong and weak coupling limits. The result
highlights that the charge and spin couplings show very similar behaviour in
the over-doped region in both the dimensions, whereas they show a completely
different trend in the lower doping regimes. A qualitative equivalence of
generalized charge stiffness constant with the effective Drude weight and
Coulomb interaction is established based on the comparison with other
theoretical and experimental results. The fall in charge stiffness with
increase in doping then implies reduction in the magnitude of effective Coulomb
repulsion between the mobile carriers. This leads to an enhanced possibility of
fermionic pairing with increase in doping in the possible presence of some
other attraction producing mechanism from a source outside the t-J-like models.
Moreover, under certain conditions in the weakly correlated phase, the t-J-like
models themselves are able to produce attractive interaction for pairing.Comment: 19 pages, 6 figure
Effect of magnetic field on the long-time dynamics of two charged coupled harmonic oscillators in the presence of a common heat bath
In this paper, the moderately long-time behaviours of the position
autocorrelation, position velocity correlation and velocity autocorrelation
functions for two charged coupled harmonic oscillators connected to a heat bath
are derived in the presence of a magnetic field via the Quantum Langevin
equation. It is seen that at long times the correlation functions at T->0
exhibit a power law decay with the coefficients of the power laws being
completely different for the two masses that affect the overall trends of the
decays of the correlation functions. The effect of the bath-induced force on
mass m1 mediated by the interaction of m2 with the common heat bath is studied
and the results are highlighted in the presence of an external magnetic field.
This brings out the distinctness of the coupled oscillator scenario from the
independent single oscillator model studied earlier in the literature. The
results in the absence of a magnetic field are also presented, which are
extremely important for analyzing the dynamics of atoms in protein molecules at
low temperatures.Comment: 12 pages; 7 figure
Decoherence and the ultraviolet cutoff: non-Markovian dynamics of a charged particle in a magnetic field
We derive a non-Markovian master equation for a charged particle in a
magnetic field coupled to a bath and study decoherence by analysing the
temporal decay of the off-diagonal elements of the reduced density matrix in
the position basis. The coherent oscillations characterised by the cyclotron
frequency get suppressed as a result of decoherence due to coupling with the
environment. We consider an Ohmic bath with three distinct models for the
high-frequency cutoff for the spectral density of the bath and compare the
three cases. As expected, the three cutoff models converge in the limit of the
uppermost frequency of the bath tending to infinity. We notice a dramatic
slowing down of loss of coherence in the low-temperature limit dominated by
zero point quantum fluctuations compared to the high-temperature classical
limit dominated by thermal fluctuations. We also go beyond the Ohmic model and
study super-Ohmic and sub-Ohmic baths with the spectral densities deviating
from a linear dependence on the frequency. Our results are testable in a state
of the art cold atom laboratory.Comment: 21 pages, 4 figure