Person:
Díaz Fernández, Álvaro

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First Name
Álvaro
Last Name
Díaz Fernández
URI
https://hdl.handle.net/20.500.14352/86996
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
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2018 - 20192
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End date: 2019 × Subject: 538.9 ×

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Now showing 1 - 2 of 2
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    Robust midgap states in band-inverted junctions under electric and magnetic fields
    (Beilstein journal of nanotechnology, 2018) Díaz Fernández, Álvaro; del Valle, Natalia; Domínguez-Adame Acosta, Francisco
    Several IV-VI semiconductor compounds made of heavy atoms, such as Pb1-xSnxTc, may undergo band-inversion at the L point of the Brillouin zone upon variation of their chemical composition. This inversion gives rise to topologically distinct phases, characterized by a change in a topological invariant. In the framework of the k.p theory, band-inversion can be viewed as a change of sign of the fundamental gap. A two-band model within the envelope-function approximation predicts the appearance of midgap interface states with Dirac cone dispersions in band-inverted junctions, namely, when the gap changes sign along the growth direction. We present a thorough study of these interface electron states in the presence of crossed electric and magnetic fields, the electric field being applied along the growth direction of a band-inverted junction. We show that the Dirac cone is robust and persists even if the fields are strong. In addition, we point out that Landau levels of electron states lying in the semiconductor bands can be tailored by the electric field. Tunable devices are thus likely to be realizable, exploiting the properties studied herein.
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    Floquet engineering of Dirac cones on the surface of a topological insulator
    (Physical review B, 2019) Díaz Fernández, Álvaro; Díaz García, Elena; Gómez León, Álvaro; Platero, G.; Domínguez-Adame Acosta, Francisco
    We propose to Floquet engineer Dirac cones at the surface of a three-dimensional topological insulator. We show that a large tunability of the Fermi velocity can be achieved as a function of the polarization, direction, and amplitude of the driving field. Using this external control, the Dirac cones in the quasienergy spectrum may become elliptic or massive, in accordance with experimental evidence. These results help us to understand the interplay of surface states and external ac driving fields in topological insulators. In our work we use the full Hamiltonian for the three-dimensional system instead of effective surface Hamiltonians, which are usually considered in the literature. Our findings show that the Dirac cones in the quasienergy spectrum remain robust even in the presence of bulk states, and therefore, they validate the usage of effective surface Hamiltonians to explore the properties of Floquet-driven topological boundaries. Furthermore, our model allows us to introduce out-of-plane field configurations which cannot be accounted for by effective surface Hamiltonians.