Phase transition and field effect topological quantum transistor made of monolayer MoS2.

We study topological phase transitions and topological quantum field effect transistor in monolayer molybdenum disulfide (MoS2) using a two-band Hamiltonian model. Without considering the quadratic (q 2) diagonal term in the Hamiltonian, we show that the phase diagram includes quantum anomalous Hall effect, quantum spin Hall effect, and spin quantum anomalous Hall effect regions such that the topological Kirchhoff law is satisfied in the plane. By considering the q 2 diagonal term and including one valley, it is shown that MoS2 has a non-trivial topology, and the valley Chern number is non-zero for each spin. We show that the wave function is (is not) localized at the edges when the q 2 diagonal term is added (deleted) to (from) the spin-valley Dirac mass equation. We calculate the quantum conductance of zigzag MoS2 nanoribbons by using the nonequilibrium Green function method and show how this device works as a field effect topological quantum transistor.

Analytic Thermal Modeling for dc-to-Midrange Modulation Frequency Responses of Thin-Film High- T c Superconductive Edge-Transition Bolometers.

Thin-film superconductive edge-transition bolometers are modeled with a one-dimensional analytic thermal model with joule heating, film and substrate materials, and the physical interface effects taken into consideration. The results from the model agree well with the experimental results of samples made of large-meander-line Yba(2)Cu(3)O(7-x) films on crystalline SrTiO(3), LaAlO(3), and MgO substrates up to 100 kHz, the limits of the experimental setup. Compared with the results of the SrTiO(3) substrate samples, the results from the model of the LaAlO(3) and the MgO substrate samples deviate slightly from the measured values at very low modulation frequencies (below ~10 Hz). The deviation increases for higher thermal-conductive substrate materials. When the model was used, the substrate absorption and the thermal parameters of the devices could also be investigated.

Control of the Responsivity and the detectivity of superconductive edge-transition YBa2Cu3O7-x bolometers through substrate properties.

The detectivity D* limits of YBa(2)Cu(3)O(7-x) bolometers on 0.05-cm-thick crystalline substrates are investigated, and a method to increase D* to greater than 10(9) (cm Hz(1/2))/W at a 20-microm wavelength is proposed. Because the response increases proportionally with the bias current I(b), whereas the noise near T(c) (the transition or critical temperature) of our MgO and SrTiO(3) substrate samples does not, an increase in D* of these samples is obtained by an increase in I(b). Another limiting factor is the dc thermal conductance G(0) of the device, which, although controlled by the substrate-holder thermal boundary resistance for our samples, can be changed by means of thinning the substrate to increase D*. The optimal amount of thinning depends on the substrate's thermal parameters and the radiation modulation frequency. D* in our samples is also found to follow the spectral-radiation absorption of the substrate material.