The
dark and bright solitons in different systems are already known. If the
intrinsic field is only considered, then the modal dynamics for small
oscillations could be characterized by the bound state in a limited range of
frequency, revealed via associated Legendre polynomial. The pairing and
interplay between the dark and bright solitons occur. The disappearance of the bound
state after a critical frequency gives rise to dark solitons in the unbound
states that propagate through the domains. In a two-part partition function based on our Hamiltonian, a frequency-temperature relation is worked out. Above the upper boundary of the bound
states, the estimated frequencies of dark solitons at 300K and 319K match with those experimentally
found for ‘acoustical memory’. In 2002 in PRL (89 (2002) 115506), the experimental evidence was shown by McPherson, Ostrovskii and Breazeale at University of Mississippi (USA).
In a nonlinear system (e.g. LN),
solitons are basically considered as phonons that have both optical and
acoustic branches in the dispersion curve, as nonlinearity arises from the
anharmonicity of the inter-atomic forces including the quantized vibrations,
i.e. phonons. While both bright and dark solitons are sensitive to optical
excitations, dark solitons manly respond to acoustic stimulation or pulses that
is a subject matter of this paper. Hence, the same material (LN) may respond to
optical pulses in one frequency range and then in another frequency range, it
could also remember sound and respond to an acoustic pulse, as has been
demonstrated in PRL in 2002. For soliton dynamics, in the low frequency
range, the bound state will predominate and in the higher range, the phonon
mode takes over in the unbound state, and here these are the main issues for
dark soliton that guides not only optical experiments but also plays a role in
acoustic emission. In another paper in PRB (64 (2001)
064302), an experiment with picosecond ultrasonic pulse technique was done on
different crystalline solids and the usefulness of solitons via KdV equation
was shown. In the present work, different soliton solutions and their
respective responses to ultrasonic waves are not discussed.
A I P-Advances 4, 087101 (2014).
Keywords: Dark and Bright Solitons,
Bound and Unbound States, Acoustic Memory.
