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