arXiv subjects

Gloria Platero

Publications and source records attributed to Gloria Platero.

At least 73 records · Page 4Linked to original sources

arXiv2014

Photon assisted long-range tunneling

We analyze long-range transport through an ac driven triple quantum dot with one single electron. An effective model is proposed for the analysis of photoassisted cotunnel in order to account for the virtual processes which dominate the long-range transport, which takes place at n-photon resonances between the edge quantum dots. The AC field renormalizes the inter dot hopping, modifying the levels hybridization. It results in a non trivial behavior of the current with the frequency and intensity of the external ac field.

cond-mat.mes-hall↗

arXiv2014

Superexchange blockade in triple quantum dots

We propose the interaction of two electrons in a triple quantum dot as a minimal system to control long range superexchange transitions. These are probed by transport spectroscopy. Narrow resonances appear indicating the transfer of charge from one side of the sample to the other with the central one being occupied only virtually. We predict that two different intermediate states establish the two arms of a one dimensional interferometer. Configurations of destructive interference of the two superexchage trajectories totally block the current through the system. We emphasize the role of spin correlations giving rise to lifetime-enhanced resonances.

cond-mat.mes-hall↗

arXiv2014

Engineering Quantum Anomalous Hall Plateaus and Anti-Chiral States with AC Fields

We investigate the AC electric field induced quantum anomalous Hall effect in honeycomb lattices and derive the full phase diagram for arbitrary field amplitude and phase polarization. We show how to induce anti-chiral edge modes as well as topological phases characterized by a Chern number larger than $1$ by means of suitable drivings. In particular, we find that the Chern number develops plateaus as a function of the frequency, providing an time-dependent analogue to the ones in the quantum Hall effect.

cond-mat.mes-hall↗

arXiv2014

Merging of Dirac points and Floquet topological transitions in AC driven graphene

We investigate the effect of an in-plane AC electric field coupled to electrons in the honeycomb lattice and show that it can be used to manipulate the Dirac points of the electronic structure. We find that the position of the Dirac points can be controlled by the amplitude and the polarization of the field for high frequency drivings, providing a new platform to achieve their merging, a topological transition which has not been observed yet in electronic systems. Importantly, for lower frequencies we find that the multi-photon absorptions and emissions processes yield the creation of additional pairs of Dirac points. This provides an additional method to achieve the merging transition by just tuning the frequency of the driving. Our approach, based on Floquet formalism, is neither restricted to specific choice of amplitude or polarization of the field, nor to a low energy approximation for the Hamiltonian.

cond-mat.mes-hall↗

arXiv2014

Unidirectional direct current in coupled nanomechanical resonators by tunable symmetry breaking

We investigate theoretically the non-linear dynamics of a coupled nanomechanical oscillator. Under a weak radio frequency excitation, the resonators can be parametrically tuned into a self-sustained oscillatory regime. The transfer of electrons from one contact to the other is then mechanically assisted, generating a rectified current. The direction of the rectified current is, in most unstable regions, determined by the phase shift between the mechanical oscillations and the signal. However, we locate intriguing parametrical regions of uni-directional rectified current, suggesting a practical scheme for the realization of a self-powered device in the nanoscale. In these regions, a dynamical symmetry breaking is induced by the non-linear coupling of the mechanical and electrical degrees of freedom. When operating within the Coulomb blockade limit, we locate bands of instability of enhanced gain.

cond-mat.mes-hall↗

arXiv2013

Hyperfine interactions in two-dimensional HgTe topological insulators

We study the hyperfine interaction between the nuclear spins and the electrons in a HgTe quantum well, which is the prime experimentally realized example of a two-dimensional topological insulator. The hyperfine interaction is a naturally present, internal source of broken time-reversal symmetry from the point of view of the electrons. The HgTe quantum well is described by the so-called Bernevig-Hughes-Zhang (BHZ) model. The basis states of the BHZ model are combinations of both S- and P-like symmetry states, which means that three kinds of hyperfine interactions play a role: (i) The Fermi contact interaction, (ii) the dipole-dipole like coupling and (iii) the electron orbital to nuclear-spin coupling. We provide benchmark results for the forms and magnitudes of these hyperfine interactions within the BHZ model, which give a good starting point for evaluating hyperfine interactions in any HgTe nanostructure. We apply our results to the helical edge states of a HgTe two-dimensional topological insulator and show how their total hyperfine interaction becomes anisotropic and dependent on the orientation of the sample edge within the plane. Moreover, for the helical edge states the hyperfine interactions due to the P-like states can dominate over the S-like contribution in certain circumstances.

cond-mat.mes-hall↗

arXiv2013

Temperature-dependent dynamical nuclear polarization bistabilities in double quantum dots in the spin-blockade regime

The interplay of dynamical nuclear polarization (DNP) and leakage current through a double quantum dot in the spin-blockade regime is analyzed. A finite DNP is built up due to a competition between hyperfine (HF) spin-flip transitions and another inelastic escape mechanism from the triplets, which block transport. We focus on the temperature dependence of the DNP for zero energy-detuning (i.e. equal electrostatic energy of one electron in each dot and a singlet in the right dot). Our main result is the existence of a transition temperature, below which the DNP is bistable, so a hysteretic leakage current versus external magnetic field B appears. This is studied in two cases: (i) Close to the crossing of the three triplet energy levels near B=0, where spin-blockade is lifted due to the inhomogeneity of the effective magnetic field from the nuclei. (ii) At higher B-fields, where the two spin-polarized triplets simultaneously cross two different singlet energy levels. We develop simplified models leading to different transition temperatures T_TT and T_ST for the crossing of the triplet levels and the singlet-triplet level crossings, respectively. We find T_TT analytically to be given solely by the HF couplings, whereas T_ST depends on various parameters and T_ST>T_TT. The key idea behind the existence of the transition temperatures at zero energy-detuning is the suppression of energy absorption compared to emission in the inelastic HF transitions. Finally, by comparing the rate equation results with Monte Carlo simulations, we discuss the importance of having both HF interaction and another escape mechanism from the triplets to induce a finite DNP.

cond-mat.mes-hall↗

arXiv2013

Floquet-Bloch theory and topology in periodically driven lattices

We propose a general framework to solve tight binding models in D dimensional lattices driven by ac electric fields. Our method is valid for arbitrary driving regimes and allows to obtain effective Hamiltonians for different external fields configurations. We establish an equivalence with time independent lattices in D+1 dimensions, and analyze their topological properties. Further, we demonstrate that non-adiabaticity drives a transition from topological invariants defined in D+1 to D dimensions. Our approach provides a theoretical framework to analyze ac driven systems, with potential applications in topological states of matter, and non-adiabatic topological quantum computation, predicting novel outcomes for future experiments.

cond-mat.mes-hall↗

arXiv2013

Topological phases in adiabatic and nonadiabatic driven systems

In this work we study the geometrical and topological properties of non-equilibrium quantum systems driven by ac fields. We consider two tunnel coupled spin qubits driven by either spatially homogeneous or inhomogeneous ac fields. Our analysis is an extension of the classical model introduced by Berry with he addition of the spatial degree of freedom. We calculate the Berry and Aharonov-Anandan geometric phases, and demonstrate the influence of the different field parameters in the geometric properties. We also discuss the topological properties associated with the different driving regimes, and show that by tuning the different parameters one can induce topological phase transitions, even in the non-adiabatic regime.

quant-ph↗

arXiv2013

Dark Bell states in tunnel-coupled spin qubits

We investigate the dynamical purification of maximally entangled electron states by transport through coupled quantum dots. Under resonant ac driving and coherent tunneling, even-parity Bell states perform Rabi oscillations that decouple from the environment, leading to a dark state. The two electrons remain spatially separated, one in each quantum dot. We propose configurations where this effect will prove as antiresonances in transport spectroscopy experiments.

cond-mat.mes-hall↗

arXiv2012

Effect of a in-plane magnetic field on the microwave assisted magnetotransport in a two-dimensional electron system

In this work we present a theoretical approach to study the effect of an in-plane (parallel) magnetic field on the microwave-assisted transport properties of a two-dimensional electron system. Previous experimental evidences show that microwave-induced resistance oscillations and zero resistance states are differently affected depending on the experimental set-up: two magnetic fields (two-axis magnet) or one tilted magnetic field. In the first case, experiments report a clear quenching of resistance oscillations and zero resistance states. In a tilted field, one obtains oscillations displacement and quenching but the latter is unbalanced and less intense. In our theoretical proposal we explain these results in terms of the microwave-driven harmonic motion performed by the electronic orbits and how this motion is increasingly damped by the in-plane field.

cond-mat.mes-hall↗

arXiv2012

Dynamical detection of Majorana fermions in current-biased nanowires

We analyze the current-biased Shapiro experiment in a Josephson junction formed by two one-dimensional nanowires featuring Majorana fermions. Ideally, these junctions are predicted to have an unconventional $4π$-periodic Josephson effect and thus only Shapiro steps at even multiples of the driving frequency. Taking additionally into account overlap between the Majorana fermions, due to the finite length of the wire, renders the Josephson junction conventional for any dc-experiments. We show that probing the current-phase relation in a current biased setup dynamically decouples the Majorana fermions. We find that besides the even integer Shapiro steps there are additional steps at odd and fractional values. However, different from the voltage biased case, the even steps dominate for a wide range of parameters even in the case of multiple modes thus giving a clear experimental signature of the presence of Majorana fermions.

cond-mat.mes-hall↗

arXiv2012

Transport blocking and topological phases using ac magnetic fields

We analyze electron dynamics and topological properties of open double quantum dots (DQDs) driven by circularly polarized ac-magnetic fields. In particular we focus on the system symmetries which can be tuned by the ac-magnetic field. Remarkably, we show that in the electron spin resonance (ESR) configuration, where the magnetic fields in each dot oscillate with a phase difference of $π$, charge localization occurs giving rise to transport blocking at arbitrary intensities of the ac field. The conditions for charge localization are obtained by means of Floquet theory and related with quasienergies degeneracy. We also demonstrate that a topological phase transition can be induced in the adiabatic regime for a phase difference of $π$, either by tuning the coupling between dots or by modifying the intensity of the driving magnetic field.

cond-mat.mes-hall↗

arXiv2012

Effects of noise on hysteresis and resonance width in graphene and nanotubes resonators

We investigate the role that noise plays in the hysteretic dynamics of a suspended nanotube or a graphene sheet subject to an oscillating force. We find that not only the size but also the position of the hysteresis region in these systems can be controlled by noise. We also find that nano-resonators act as noise rectifiers: by increasing the noise in the setup, the resonance width of the characteristic peak in these systems is reduced and, as a result, the quality factor is increased.

cond-mat.mes-hall↗

arXiv2012

Microwave-induced off-resonance giant magnetoresistance in ultraclean two-dimensional electron systems

We report on theoretical studies of a recently discovered strong microwave-induced magnetoresistance peak obtained in ultra-clean two-dimensional electron systems at low temperatures. The most striking feature of such a peak is that it shows up on the second harmonic of the cyclotron resonance and with an amplitude that can reach an order of magnitude larger than the microwave-induced resistance oscillations. We apply the microwave-driven electron orbits model in the ultra-clean scenario. Accordingly, we calculate the elastic scattering rate (charged impurity) which will define the unexpected resonance peak position. We also obtain the inelastic scattering rate (phonon damping), that will be responsible of the large peak amplitude. Calculated results are in good agreement with experiments. These results would be of special interest in nanophotonics; they could lead to the design of novel ultrasensitive microwave detectors.

cond-mat.mes-hall↗

arXiv2012

Steady-State Coherent Transfer by Adiabatic Passage

We propose steady-state electron transport based on coherent transfer by adiabatic passage (CTAP) in a linearly arranged triple quantum dot with leads attached to the outer dots. Its main feature is repeated steering of single electrons from the first dot to the last dot without relevant occupation of the middle dot. The coupling to leads enables a steady-state current, whose shot noise is significantly suppressed provided that the CTAP protocol performs properly. This represents an indication for the direct transfer between spatially separated dots and, thus, may resolve the problem of finding experimental evidence for the non-occupation of the middle dot.

cond-mat.mes-hall↗

arXiv2012

Helical edge states coupled to a spin bath: Current-induced magnetization

We study current carrying helical edge states in a two-dimensional topological insulator coupled to an environment of localized spins, i.e. a spin bath. The localized spins mediate elastic spin-flip scattering between the helical edge states, and we show how this induces a spin-bath magnetization for a finite current through the edge states. The magnetization appears near the boundaries of the topological insulator, while the bulk remains unmagnetized, and it reaches its maximal value in the high bias regime. Furthermore, the helical edge states remain ballistic in steady state, if no additional spin-flip mechanisms for the localized spins are present. However, we demonstrate that if such mechanisms are allowed, then these will induce a finite current decrease from the ballistic value.

cond-mat.mes-hall↗

arXiv2012

Dynamical polarizability of graphene irradiated by circularly polarized ac electric fields

We examine the low-energy physics of graphene in the presence of a circularly polarized electric field in the terahertz regime. Specifically, we derive a general expression for the dynamical polarizability of graphene irradiated by an ac electric field. Several approximations are developed that allow one to develop a semianalytical theory for the weak field regime. The ac field changes qualitatively the single and many electron excitations of graphene: undoped samples may exhibit collective excitations (in contrast to the equilibrium situation), and the properties of the excitations in doped graphene are strongly influenced by the ac field. We also show that the intensity of the external field is the critical control parameter for the stability of these excitations.

cond-mat.mes-hall↗