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Quantum Derivation of Ginzburg-Landau Equation. New Formula for Penetration Depth
Authors:Shigeji Fujita  Salvador Godoy
Affiliation:1. Department of Physics, State University of New York at Buffalo, Buffalo, New York, 14260, USA
2. Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, México, 04510, D. F., México
Abstract:The Cooper pair (pairon) field operator ψ(r,t) changes in time, following Heisenberg’ s equation of motion. If the system Hamiltonian $mathcal{H}The Cooper pair (pairon) field operator ?(r,t) changes in time, following Heisenberg's equationof motion. If the system Hamiltonian contains the pairon kineticenergies h0, the condensation energy per paironagr(< 0) and the repulsive point-like potentialbetagamma(r1r2), beta > 0, the evolution equation for ?is non-linear, from which we obtain the Ginzburg-Landau equation: 
$$h_0 (r, - ibar hnabla )Psi _sigma (r) + alpha Psi _sigma (r) + beta |Psi _sigma (r)|^2 Psi _sigma (r) = 0$$
for the complex order parameter 
$$Psi _sigma (r): = < r|n^{1/2} |sigma >$$
, where sgr denotes thestate of the condensed pairons, and n the pairon densityoperator. The total kinetic energy h0 forldquoelectronrdquo (1) and ldquoholerdquo(2) pairons is 
$$h_0 Psi _sigma (r) = left{ {frac{1}{2}v_F^{(1)} | - ibar hnabla + 2eA(r)| + frac{1}{2}v_F^{(2)} | - ibar hnabla - 2eA(r)|} right}Psi _sigma (r)$$
where 
$$v_F^{(j)} equiv (2varepsilon _F /m_j )^{1/2}$$
are Fermi velocities, and A thevector potential. A new expression for the penetration depth lambda isobtained: 
$$lambda = frac{c}{e}left[ {frac{p}{{4pi n_0 (v_F^{(2)} + v_F^{(1)} )}}} right]^{1/2}$$
where p and n0 are respectively themomentum and density of condensed pairons.
Keywords:Ginzburg-Landau equations  penetration depth  microscopic derivation of G-L equations  validity of G-L equations
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