Josephson Flux Flow Oscillator: the Microscopic Tunneling Approach

We elaborate a theoretical description of large Josephson junctions which is based on the Werthamer's microscopic tunneling theory. The model naturally incorporates coupling of electromagnetic radiation to the tunnel currents and, therefore, is particularly suitable for description of the self-coupling effect in Josephson junction. In our numerical calculations we treat the arising integro-differential equation, which describes temporal evolution of the superconducting phase difference coupled to the electromagnetic field, by the Odintsov-Semenov-Zorin algorithm. This allows us to avoid evaluation of the time integrals at each time step while taking into account all the memory effects. To validate the obtained microscopic model of large Josephson junction we focus our attention on the Josephson flux flow oscillator. The proposed microscopic model of flux flow oscillator does not involve the phenomenological damping parameter, rather, the damping is taken into account naturally in the tunnel current amplitudes calculated at a given temperature. The theoretically calculated current-voltage characteristics is compared to our experimental results obtained for a set of fabricated flux flow oscillators of different lengths. Our theoretical calculation agrees well with the obtained experimental results, and, to our knowledge, is the first where theoretical description of Josephson flux flow oscillator is brought beyond the perturbed sine-Gordon equation.Comment: 13 pages, 2 figure

Excitonic effects in time-dependent density functional theory from zeros of the density response

We show that the analytic structure of the dynamical xc kernels of semiconductors and insulators can be sensed in terms of its poles which mark physically relevant frequencies of the system where the counter-phase motion of discrete collective excitations occurs: if excited, the collective modes counterbalance each other, making the system to exhibit none at all or extremely weak density response. This property can be employed to construct simple and practically relevant approximations of the dynamical xc kernel for time-dependent density functional theory (TDDFT). Such kernels have simple analytic structure, are able to reproduce dominant excitonic features of the absorption spectra of monolayer semiconductors and bulk solids, and promise high potential for future uses in efficient real-time calculations with TDDFT.Comment: 10 pages, 4 figure

Травма как привыкание к новой катастрофической реальности в романе «Брисбен» Е. Водолазкина

The study is devoted to the motif of trauma in the novel “Brisbane” by E. Vodolazkin. The article provides an analysis of the realization of the trauma motif as a creative crisis in which the protagonist is gradually immersed. The novel represents the hero’s habituation to his new traumatic condition. Two temporal layers – past and present – run simultaneously in the novel. Soon the gap between them becomes hardly recognizable, eventually merging into the unity of the existence experienced in the present and colored by the past. Balancing on the edge of past and present, where the echoes of each period resonate in the hero’s soul, constitutes the polyphony of the novel “Brisbane”. It is realized at two levels: temporal-spatial and narrative-musical setting of the work.The study is devoted to the motif of trauma in the novel “Brisbane” by E. Vodolazkin. The article provides an analysis of the realization of the trauma motif as a creative crisis in which the protagonist is gradually immersed. The novel represents the hero’s habituation to his new traumatic condition. Two temporal layers – past and present – run simultaneously in the novel. Soon the gap between them becomes hardly recognizable, eventually merging into the unity of the existence experienced in the present and colored by the past. Balancing on the edge of past and present, where the echoes of each period resonate in the hero’s soul, constitutes the polyphony of the novel “Brisbane”. It is realized at two levels: temporal-spatial and narrative-musical setting of the work.Данное исследование посвящено мотиву травмы в романе «Брисбен» Е. Водолазкина. В работе предложен анализ реализации мотива травмы как творческого кризиса, в который постепенно погружается главный герой. Роман представляет собой привыкание героя к новому травматическому состоянию. Два временных пласта – прошлое и настоящее – протекают одновременно. Постепенно разрыв между ними становится все меньше, в итоге сливаясь в единство переживаемой в настоящем реальности, окрашенной прошлым. Балансирование на грани прошлого и настоящего, где отзвуки каждого периода резонируют в душе героя, составляет полифонизм романа «Брисбен», который реализуется на двух уровнях: временно-пространственной и повествовательно-музыкальной организации произведения

Three-particle states and brightening of intervalley excitons in a doped MoS2_2 monolayer

Optical spectra of two-dimensional transition-metal dichalcogenides (TMDC) are influenced by complex multi-particle excitonic states. Their theoretical analysis requires solving the many-body problem, which in most cases, is prohibitively complicated. In this work, we calculate the optical spectra by exact diagonalization of the three-particle Hamiltonian within the Tamm-Dancoff approximation where the doping effects are accounted for via the Pauli blocking mechanism, modelled by a discretized mesh in the momentum space. The single-particle basis is extracted from the {\it ab initio} calculations. Obtained three-particle eigenstates and the corresponding transition dipole matrix elements are used to calculate the linear absorption spectra as a function of the doping level. Results for negatively doped MoS$_2$ monolayer (ML) are in an excellent quantitative agreement with the available experimental data, validating our approach. The results predict additional spectral features due to the intervalley exciton that is optically dark in an undoped ML but is brightened by the doping. Our approach can be applied to a plethora of other atomically thin semiconductors, where the doping induced brightening of the many-particle states is also anticipated