The interplay between intra-band motion and inter-band transitions in photoexcited germanium is investigated by attosecond transient reflection spectroscopy. Advanced theoretical simulations interpret the sub-femtosecond optical response as charge carrier dynamics in the band structure.

In a molecular junction (MJ) which connects two electrical leads, electron-phonon coupling has significant effects on the transport properties. However, the MJ is not thermally isolated and the phonons can be coupled to another thermal bath. For strong enough couplings, the bath thermalizes phonons on the MJ so that their number would be bias independent. However, in medium and weak coupling regimes, the number of phonons created in MJ depends on the bias voltage. Obtaining the master equation (ME) for this system and comparing the results with the case where we have no such thermal bath, we show that if the bath temperature is greater than the leads, at low bias voltages (where in the absence of the thermal bath the probability of phonon excitation is low), the thermal bath heats up our MJ and decreases electronic current. On the other hand, at high bias voltages the bath cools down MJ and increases the current. However, if the bath temperature is less than the leads, it always increases the current and the heat flows from the junction to the leads.

In this work we consider a current carrying molecular junction with both electronphonon and electron-electron interactions taken into account. After performing Lang-Firsov transformation and considering Markov approximations in accordance to weak coupling to the electronic leads, we obtain the master equation governing the time evolution of the reduced density matrix of the junction. The steady state of the density matrix can be used to obtain I-V characteristic of the junction in several regimes of strengths of the interactions. Our results indicate that the system can show negative differential conductance (that is, the current decreases by increasing the applied bias voltage) in some regimes as an interplay between the electron-phonon and Coulomb interactions.

a b s t r a c tWe consider a single impurity Anderson model (SIAM) in which the quantum dot(QD) is strongly coupled to a phonon bath in polaron regime. This coupling results in an effective e-e attraction. By computing the self energies using a current conserving approximation which is up to second order in this effective attraction, we show that if the interaction is strong enough, in non particle-hole (PH) symmetric case, the system would be bi-stable and we have hysteresis loop in the I-V characteristic. Moreover, the system shows negative differential conductance in some bias voltage intervals.

In this paper we use a simple discrete model for Slinky to explore some of its static properties. We derive some relations for vertically and U-shaped suspended Slinkies, based on which, some demonstrations are proposed that can be simply done in freshmen physics classes. *