We consider the quantum transport in a tight-binding chain with a locally applied potential which is oscillating in time. The steady state for such a driven impurity can be calculated exactly for any energy and applied potential using the Floquet formalism. The resulting transmission has a non-trivial, non-monotonic behavior depending on incoming momentum, driving frequency, and the strength of the applied periodic potential. Hence there is an abundance of tuning possibilities, which allows to find resonances of total reflection for any choice of incoming momentum and periodic potential. Remarkably, this implies that even for an arbitrarily small infinitesimal impurity potential it is always possible to find a resonance frequency at which there is a catastrophic breakdown of the transmission T = 0. The points of zero transmission are closely related to the phenomenon of Fano resonances at dynamically created bound states in the continuum. The results are relevant for a variety of one-dimensional systems where local AC driving is possible, such as quantum nanodot arrays, ultracold gases in optical lattices, photonic crystals, or molecular electronics. PACS numbers: 72.10.Fk 73.63.-b 05.60.GgDriven quantum systems appear in many different contexts in physics and chemistry [1][2][3][4][5][6][7][8][9][10]. At the same time there has been remarkable progress in the controlled design of nanoscale quantum systems with a high degree of coherence and tunability. Systems containing just a few molecules are promising candidates for the realization of electronic components on the sub-silicon scale (molecular electronics) [11][12][13][14][15][16]. The quantum transfer of particles between such localized structures can be well described by the tight-binding model in order to gain understanding of the transport mechanisms involved [17][18][19][20]. Another versatile realization of near-perfect tightbinding models are ultracold gases in optical lattices with a great variety of possible geometries [21], where tunable local impurities [22], periodic driving [6-10], and dimensional crossover [23] have also been realized. Tightbinding models are also applicable when investigating other driven systems such as quantum dot arrays [3]. Finally, photonic cavities and photonic crystals have been used as quantum simulators to fabricate interesting quantum tight-binding systems [24][25][26]. In practical applications time-dependent effects such as electromagnetic radiation or gate voltages can be used to manipulate the transport properties of nanodevices [3]. Driven tunneling between two quantum wells has been well studied [3][4][5][6]. A natural further development is the transport through a driven impurity in an extended structure of coupled wells with a finite bandwidth.In the present Letter we consider the steady state of a generic model system, consisting of a one-dimensional tight-binding chain for bosons or fermions with a periodically varying potential µ at one impurity site (i = 0)where we have used standard notation and the hoppin...

Using the Floquet formalism we study transport through an AC-driven impurity in a tight binding chain. The results obtained are exact and valid for all frequencies and barrier amplitudes. At frequencies comparable to the bulk bandwidth we observe a breakdown of the transmission T=0 which is related to the phenomenon of Fano resonances associated to AC-driven bound states in the continuum. We also demonstrate that the location and width of these resonances can be modified by tuning the frequency and amplitude of the driving field. At high frequencies there is a close relation between the resonances and the phenomenon of coherent destruction of tunneling. As the frequency is lowered no more resonances are possible below a critical value and the results approach a simple time average of the static transmission. J n j J J n New J. Phys. 19 (2017) 043029 S A Reyes et al 4.3. Inhomogeneous coupling to the impurity site ¢ ¹ J J Let us now go back to the tight binding model in order to explore what happens when we consider a different coupling to the impurity site ( ¢ ¹ J J ) corresponding to physical realizations where the coupling to the driven impurity may also differ from the ones along the chain.In figure 5 we show results for the transmission for a weaker hopping amplitude ¢ = J J 0.9 . While there are similarities to the homogeneous case discussed above, the resonances now start at a finite value of m > 0 according to equation (17). As can clearly be seen in the bottom part of figure 5 for w = J 3 accordingly there is a dip but no resonance for m = J , while the resonance at m = J 3 is relatively sharp. As shown in figure 6 (top) for larger hopping amplitude ¢ = J J 2 we observe a general increase in transmission across the parameter space and the resonances move to higher frequencies for a given energy of the incoming wave following equation (16). Correspondingly, the resonances are also displaced in energy at fixed frequency w = J 3 as shown in figure 6 (bottom). These features can be interpreted nicely by using the Fano resonances due to the 'side-attached' systems explained above and depicted in figure 2. It turns out that the two resonances we observe in figures 5 and 6 are Figure 4. Transmission coefficient in the limit of vanishing lattice spacing for  ¢ = 1 in units of 1/2m, i.e. for a quadratic dispersion relation with a local driving in form of a delta-function. 6 New J. Phys. 19 (2017) 043029 S A Reyes et alFigure 5. Transmission coefficient for modified coupling ¢ = J J 0.9 . Top: for a fixed energy  = -J 0.5 as a function of μ and ω. The dashed lines depict the analytic approximations for the location of the resonances at high frequencies (green), and close to where they emerge (red) from equation (15). Bottom: for fixed frequency w = J 3 .Figure 6. Transmission coefficient for modified coupling ¢ = J J 2 . Top: for a fixed energy  = -J 0.5 as a function of μ and ω. The red dashed lines depict the analytic approximations for the location of the resonances close to where they emerge from equation ...

We consider the problem of particle tunneling through a periodically driven ferromagnetic quantum barrier connected to two leads. The barrier is modeled by an impurity site representing a ferromagnetic layer or a quantum dot in a tight-binding Hamiltonian with a local magnetic field and an ac-driven potential, which is solved using the Floquet formalism. The repulsive interactions in the quantum barrier are also taken into account. Our results show that the time-periodic potential causes sharp resonances of perfect transmission and reflection, which can be tuned by the frequency, the driving strength, and the magnetic field. We demonstrate that a device based on this configuration could act as a highly tunable spin valve for spintronic applications.