Phonon-induced backscattering in helical edge states

A single pair of helical edge states as realized at the boundary of a quantum spin Hall insulator is known to be robust against elastic single particle backscattering as long as time reversal symmetry is preserved. However, there is no symmetry preventing inelastic backscattering as brought about by phonons in the presence of Rashba spin orbit coupling. In this Letter, we show that the quantized conductivity of a single channel of helical Dirac electrons is protected even against this inelastic mechanism to leading order. We further demonstrate that this result remains valid when Coulomb interaction is included in the framework of a helical Tomonaga Luttinger liquid.     

Hubbard regime for the mixed-valence systems

We consider the hybridization of atomic and nearly free states in the mixed-valence systems within the procedure which allows to separate in special cases the Hubbard and Fermi branches of elementary excitations. We discuss the physical consequences of this separation and propose a mechanism of phase transition with the valence change where the localized moments of the f-states disappear in the low-temperature phase due to the Mott-Hubbard transition.     

Phonon-induced polariton superlattices

We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.     

Spatial correlations of rare-earth ions in mixed-valence systems

An effective interaction between 4?-occupied rare-earth ions arises from the scattering of the conduction electrons with the localized 4?-electrons. Due to the space dependence of this interaction the ground state energy depends on the distribution of the localized 4?-electrons. We discuss the possibility of clustering and ordering in simple cases.     

Phonon-induced exciton dephasing in quantum dot molecules

A new microscopic approach to the optical transitions in quantum dots and quantum dot molecules, which accounts for both diagonal and nondiagonal exciton-phonon interaction, is developed. The cumulant expansion of the linear polarization is generalized to a multilevel system and is applied to calculation of the full time dependence of the polarization and the absorption spectrum. In particular, the broadening of zero-phonon lines is evaluated directly and discussed in terms of real and virtual phonon-assisted transitions. The influence of Coulomb interaction, tunneling, and structural asymmetry on the exciton dephasing in quantum dot molecules is analyzed.     

Phonon-induced charge transfer in ZnO

Using the high-resolution 93.3 keV Mössbauer transition in ⁶⁷Zn we studied the temperature dependence of the center shift in ZnO single crystals between 4.2 and 77.3 K. Already at low temperature dependent isomer shift is present. The latter originates from phonon-induced electron transfer from zinc to oxygen     

Phonon-induced optical superlattice

We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments.     

Effects of counter anion on mixed-valence states of binuclear ferrocene derivatives

The mixed-valence states of iron atoms in 1, 1-dialkylbiferrocenium cations were found to be affected by the kind of their counter anions. The TCNQ salts showed only an averaged-valence state from 78 K to room temperature, while the triiodide salts showed only a trapped-valence state or a temperature dependent trapped-to-averaged valence state depending on the kind of alkyl group.     

Phonon-induced Quantum Entanglement in Diamond Nanostructures

We consider the quantum entanglement such as spin squeezing and the reciprocal of the mean quantum Fisher information per particle(RMQFIP) resulted from the phonon-induced spin-spin interactions in diamond nanoresonator. The entangled state can be generated by adjusting the near-resonant coupling and the single phonon coupling strength and the better entanglement and a longer entangled time interval can be achieved by increasing the number of charged nitrogen-vacancy (NV) centers.     

Phonon-induced resistivity of electron liquids in quantum wires

We study the resistivity of a quantum wire caused by backscattering of electrons by acoustic phonons. In the presence of Coulomb interactions, backscattering is strongly enhanced at low temperatures due to Luttinger liquid effects. Information about the strength of the interactions can be obtained from a measurement of the temperature dependence of the resistivity.     

Off-perturbative states in disordered systems

The systematic approach for the off-perturbative calculations in disordered systems is developed. The proposed scheme is applied for the random temperature and the random field ferromagnetic Ising models. It is shown that away from the critical point, in the paramagnetic phase of the random temperature model, and in the ferromagnetic phase of the random field one, the free energy contains non-analytic contributions which have the form of essential singularities. It is demonstrated that these contributions appear due to localized in space instanton-like excitations.     

Bound and virtual bound states in semiconductor quantum wells

The bound and virtual bound (resonant) levels of GaAs-Ga(Al)As double quantum wells are calculated within the framework of the envelope function approach. The theoretical work, taken together with the results of excitation spectroscopy measurements, indicates the participation of a light hole virtual bound state in an optical transition.     

Low-lying states of trinuclear mixed-valence cluster: [Fe3S4]0

Low-lying energy states of the [Fe₃S₄]⁰ cluster have been calculated by taking into account the double exchange, superexchange and vibronic interaction. It was found that the adiabatic potential of the excited state withS=0 corresponds to the full delocalization of the “excess” charge. From the analysis of experimental data of Mössbauer spectroscopy and the temperature dependence of the magnetic susceptibility the double exchange parametert≥4000 cm^?1 and the vibronic interaction parameter λ₂/2k cm^?1 have been estimated.     

Phonon-induced decoherence and dissipation in donor-based charge qubits

We investigate the phonon-induced decoherence and dissipation in a donor-based charge quantum bit realized by the orbital states of an electron shared by two dopant ions which are implanted in a silicon host crystal. The dopant ions are taken from the group-V elements Bi, As, P, Sb. The excess electron is coupled to deformation potential acoustic phonons which dominate in the Si host. The particular geometry tailors a non-monotonous frequency distribution of the phonon modes. We determine the exact qubit dynamics under the influence of the phonons by employing the numerically exact quasi-adiabatic propagator path integral scheme thereby taking into account all bath-induced correlations. In particular, we have improved the scheme by completely eliminating the Trotter discretization error by a Hirsch-Fye extrapolation. By comparing the exact results to those of a Born-Markov approximation we find that the latter yields appropriate estimates for the decoherence and relaxation rates. However, noticeable quantitative corrections due to non-Markovian contributions appear.     

Vertical hopping conduction via virtual states in intentionally disordered superlattices

A new mechanism of vertical conduction in intentionally disordered superlattices is examined. It is shown that low-temperature conduction due to phonon-assisted tunneling between distant quantum wells of a superlattice is determined mainly by hopping processes via virtual intermediate states. Under standard conditions a weak temperature dependence of vertical conduction is obtained for this mechanism. The characteristic behavior of the conductivity as a function of disorder amplitude is found for this mechanism. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 879–884 (25 June 1999)     

Multiple decoherence-free states in multi-spin systems

A numerical procedure is presented for mapping the vicinity of the null-space of the spin relaxation superoperator. The states populating this space, i.e. those with near-zero eigenvalues, of which the two-spin singlet is a well-studied example, are long-lived compared to the conventional T(1) and T(2) spin-relaxation times. The analysis of larger spin systems described herein reveals the presence of a significant number of other slowly relaxing states. A study of coupling topologies for n-spin systems (4≤n≤8) suggests the symmetry requirements for maximising the number of long-lived states.