|
|
|
- Transients in disordered solids Electron transients
induced by femtosecond laser pulses in semiconductors, in particular
semiconductor alloys, were studied in the self-consistent Born approximation.
The tool was an analytical and direct numerical solution of the Dyson
equations for non-equilibrium Green's functions. The particle correlation
function carrying the statistical information about the transient response
was found to consist of a coherent transient and an incoherent back-scattered
component. The particle number was conserved only if the field induced coherence
was fully incorporated. The statistical correlation of disorder in the
valence and conduction bands givers rise to kinematical correlation of
electrons and holes manifested in effects similar to true excitons and well
known for linear response. The onset and the ripe stage of the
pulse excitation clearly demonstrated that the effective kinematic
correlation in non-linear transients can be charaterized as a "final
state interaction", an e-h interaction in the outgoing channel. A. Kalvová and B. Velický: Photoexcited
Transients in Disordered Semiconductors: Quantum Coherence at Very Short to
Intermediate Times, Phys. Rev. B 65 155329 (2002) A.
Kalvová and B. Velický: Photoexcited
Transients in Disordered Semiconductors: Kinematically Induced Electron-Hole
Correlation: in book Progress in Nonequilibrium Green’s
Function II, eds. M. Bonitz, D. Semkat, World Scientific, London,
(2003), p. 322-329 A.
Kalvová and B. Velický: Disorder
Induced e-h Correlation in Photoexcited Transients in Semiconductors:
in book Nonequilibrium Physics at Short Time Scales, Formation of
Correlations, ed. K. Morawetz, Springer, Berlin, (2004), p. 273-293 22nd
General Conference of the CMD EPS, 25-28 August 2008 „La
Sapienza“ University, Roma, Italy poster: A NGF
solver for fast transients in semiconductors PosterRoma.pdf - Fast transients in mesoscopic systems A transient
response of electrons in a mesoscopic system depends on the joint effect of
the initial state with correlations and of the driving external disturbances
abruptly setting on at the initial time. If the initial state results from
the previous history of the system, its role can be transformed onto the
coherence effects between the transient and its antecedent, as given by the
blocks of the self-energy off-diagonal in time. The early period of the
transient requires the full NGF for its description. After the disturbances
cease acting and the initial correlations evanesce, the process enters the
non-equilibrium quasi-particle mode permitting a reduced description by a
generalized master equation. As an example, we consider a molecular bridge
between two leads. The transient is induced by rapid changes in the coupling
between the leads and the bridge. Without interactions the model is soluble
to the end. B. Velický, A.
Kalvová and V. Špička: Single
molecule bridge as a testing ground for using NGF outside of steady current
regime, Physica E 42, 539 (2010) doi:10.1016/j.physe.2009.08.006 B. Velický, A.
Kalvová and V. Špička: Correlated Initial
Condition for an Embedded Process by Time Partitioning , Phys. Rev. B 81,
235116 (2010) doi: 10.1103/PhysRevB.81.235116 A. Kalvová, V. Špička and B. Velický: Fast Transients
in Mesoscopic Systems , Non-equilibrium Statistical Physics Today, AIP Conf. Proc. 1332,
223-225 (2011) workshop:
Progress in Nonequilibrium Green’s Functions IV, Glasgow 17 – 21
August, 2009 11th Granada
Seminar on Computational and Statistical Physics (Foundations of Nonequilibrium
Statistical Physics), La Herradura 13-17, 2010, Spain seminář
MFF UK, katedra elektronových struktur, 17.2. 2012 - Time dynamics of many-electron systems These studies were extended
to a general investigation of time dynamics of many-electron systems with
correlations on the time scale from the fast initial transients up to the
kinetic stage of evolution. Several results were established developing the
general Non-Equilibrium Green's Function (NGF) theory without the need for
resorting to specific models. A Reconstruction Theorem was proved answering
to the Bogolyubov Postulate concerning the possibility of inverse
recovery of the non-equilibrium correlation functions from the one-particle
quantum distribution function. The NGF theory was in this way paralleled to
the Time Dependent Density Functional Theory. The corresponding
reconstruction equations represent a renormalized version of the approximate
factorizations known as the family of causal ansatzes generalizing the
Kadanoff-Baym ansatz for NGF. A new Time Partitioning Method was
developed and applied to the Dyson equation for the particle
correlation function to take account of the weak time non-locality of the
action of the correlated initial conditions and their decay. V.
Špička, B. Velický and A. Kalvová: Long and
Short Time Quantum Dynamics: I. Between Green’s Functions and Transport
Equations : Physica E 29, (2005) p. 154-174 V.
Špička, B. Velický and A. Kalvová: Long and
Short Time Quantum Dynamics: II Kinetic Regime . Physica E 29,
(2005) p. 175-195 V.
Špička, B. Velický and A. Kalvová: Long and Short Time Quantum Dynamics: III Transients
Physica E 29, (2005) p.196-212 - Non-equilibrium quasiparticles The
approximate factorization of propagators known as the Semi-Group Rule also
permits a renormalization, which serves to guarantee validity of the
non-equilibrium generalization of the Ward Identity leading to the particle
number conservation. The quasi-particle form of the semi-group rule leads to
an operational definition of non-equilibrium quasi-particles: the
quasi-particle regime is achieved, if the propagator possesses a time-local
optical potential. This can be determined from a non-linear integral
Phase Equation obtained as a condition for self-consistent cancellation
of the vertex in the renormalized semi-group rule.
B. Velický, A. Kalvová and V. Špička: Between
Green’s Functions and Transport Equations: Reconstruction Theorems and
the Role of Initial Conditions, Journal of Physics: Conference Series
Progress in Nonequilibrium Green’s Functions III, Vol. 35, (2006), p.
1-16 B.
Velický, A. Kalvová and V. Špička: Quasiparticle
States of Electron Systems out of Equilibrium , Phys. Rev. B 75,
195125 (2007) B.
Velický, A. Kalvová and V. Špička: Ward identity
for nonequilibrium Fermi systems, Phys. Rev. B 77, 041201 (2008) ======================================================================================== LECTURES (in pdf format): December 2004, Seminar at
the Theor. Dpt., Prague: Disorder induced e-h correlations in
photo-transients in semiconductors May 2005, Interdisciplinary
Seminar, University Plzeň: Slow and stop light after five years LectureStopLight.pdf (in Czech language) ZpomalenéSvětlo.doc (sborník z
XII semináře o filosofických otázkách matematiky a fyziky) November 2005, Topical Problems in Theor. Stat. Phys., December 2007, Topical Problems in Theor. Stat. Phys., December 01-06, 2008, Workshop on Nonequilibrium
Nanostructures NONNA08: Non-equilibrium
Ward Identity
UNIVERSITY
COURSES Faculty of Science, Palacký University, Olomouc
Introduction into the Physics of the Condensed
Systems |
