Out-of-equilibrium electrons and the Hall conductance of a Floquet topological insulator

Hossein Dehghani, Takashi Oka, Aditi Mitra

    Research output: Contribution to journalArticle

    Abstract

    Graphene irradiated by a circularly polarized laser has been predicted to be a Floquet topological insulator showing a laser-induced quantum Hall effect. A circularly polarized laser also drives the system out of equilibrium, resulting in nonthermal electron distribution functions that strongly affect transport properties. Results are presented for the Hall conductance for two different cases. One is for a closed system, such as a cold-atomic gas, where transverse drift due to nonzero Berry curvature can be measured in time-of-flight measurements. For this case the effect of a circularly polarized laser that has been suddenly switched on is studied. The second is for an open system coupled to an external reservoir of phonons. While for the former the Hall conductance is far from the quantized limit, for the latter, coupling to a sufficiently low temperature reservoir of phonons is found to produce effective cooling, and thus an approach to the quantum limit, provided the frequency of the laser is large as compared to the bandwidth. For laser frequencies comparable to the bandwidth, strong deviations from the quantum limit of conductance are found even for a very low temperature reservoir, with the precise value of the Hall conductance determined by a competition between reservoir-induced cooling and the excitation of photocarriers by the laser. For the closed system, the electron distribution function is determined by the overlap between the initial wave function and the Floquet states, which can result in a Hall conductance which is opposite in sign to that of the open system.

    Original languageEnglish (US)
    Article number155422
    JournalPhysical Review B - Condensed Matter and Materials Physics
    Volume91
    Issue number15
    DOIs
    StatePublished - Apr 20 2015

    Fingerprint

    insulators
    Electrons
    Lasers
    lasers
    electrons
    Open systems
    Phonons
    electron distribution
    Distribution functions
    phonons
    distribution functions
    Cooling
    Quantum Hall effect
    bandwidth
    Electron transport properties
    Bandwidth
    cooling
    Graphite
    cold gas
    monatomic gases

    ASJC Scopus subject areas

    • Condensed Matter Physics
    • Electronic, Optical and Magnetic Materials

    Cite this

    Out-of-equilibrium electrons and the Hall conductance of a Floquet topological insulator. / Dehghani, Hossein; Oka, Takashi; Mitra, Aditi.

    In: Physical Review B - Condensed Matter and Materials Physics, Vol. 91, No. 15, 155422, 20.04.2015.

    Research output: Contribution to journalArticle

    @article{618b22c867c34c4e8dccba30a57019d4,
    title = "Out-of-equilibrium electrons and the Hall conductance of a Floquet topological insulator",
    abstract = "Graphene irradiated by a circularly polarized laser has been predicted to be a Floquet topological insulator showing a laser-induced quantum Hall effect. A circularly polarized laser also drives the system out of equilibrium, resulting in nonthermal electron distribution functions that strongly affect transport properties. Results are presented for the Hall conductance for two different cases. One is for a closed system, such as a cold-atomic gas, where transverse drift due to nonzero Berry curvature can be measured in time-of-flight measurements. For this case the effect of a circularly polarized laser that has been suddenly switched on is studied. The second is for an open system coupled to an external reservoir of phonons. While for the former the Hall conductance is far from the quantized limit, for the latter, coupling to a sufficiently low temperature reservoir of phonons is found to produce effective cooling, and thus an approach to the quantum limit, provided the frequency of the laser is large as compared to the bandwidth. For laser frequencies comparable to the bandwidth, strong deviations from the quantum limit of conductance are found even for a very low temperature reservoir, with the precise value of the Hall conductance determined by a competition between reservoir-induced cooling and the excitation of photocarriers by the laser. For the closed system, the electron distribution function is determined by the overlap between the initial wave function and the Floquet states, which can result in a Hall conductance which is opposite in sign to that of the open system.",
    author = "Hossein Dehghani and Takashi Oka and Aditi Mitra",
    year = "2015",
    month = "4",
    day = "20",
    doi = "10.1103/PhysRevB.91.155422",
    language = "English (US)",
    volume = "91",
    journal = "Physical Review B-Condensed Matter",
    issn = "1098-0121",
    publisher = "American Physical Society",
    number = "15",

    }

    TY - JOUR

    T1 - Out-of-equilibrium electrons and the Hall conductance of a Floquet topological insulator

    AU - Dehghani, Hossein

    AU - Oka, Takashi

    AU - Mitra, Aditi

    PY - 2015/4/20

    Y1 - 2015/4/20

    N2 - Graphene irradiated by a circularly polarized laser has been predicted to be a Floquet topological insulator showing a laser-induced quantum Hall effect. A circularly polarized laser also drives the system out of equilibrium, resulting in nonthermal electron distribution functions that strongly affect transport properties. Results are presented for the Hall conductance for two different cases. One is for a closed system, such as a cold-atomic gas, where transverse drift due to nonzero Berry curvature can be measured in time-of-flight measurements. For this case the effect of a circularly polarized laser that has been suddenly switched on is studied. The second is for an open system coupled to an external reservoir of phonons. While for the former the Hall conductance is far from the quantized limit, for the latter, coupling to a sufficiently low temperature reservoir of phonons is found to produce effective cooling, and thus an approach to the quantum limit, provided the frequency of the laser is large as compared to the bandwidth. For laser frequencies comparable to the bandwidth, strong deviations from the quantum limit of conductance are found even for a very low temperature reservoir, with the precise value of the Hall conductance determined by a competition between reservoir-induced cooling and the excitation of photocarriers by the laser. For the closed system, the electron distribution function is determined by the overlap between the initial wave function and the Floquet states, which can result in a Hall conductance which is opposite in sign to that of the open system.

    AB - Graphene irradiated by a circularly polarized laser has been predicted to be a Floquet topological insulator showing a laser-induced quantum Hall effect. A circularly polarized laser also drives the system out of equilibrium, resulting in nonthermal electron distribution functions that strongly affect transport properties. Results are presented for the Hall conductance for two different cases. One is for a closed system, such as a cold-atomic gas, where transverse drift due to nonzero Berry curvature can be measured in time-of-flight measurements. For this case the effect of a circularly polarized laser that has been suddenly switched on is studied. The second is for an open system coupled to an external reservoir of phonons. While for the former the Hall conductance is far from the quantized limit, for the latter, coupling to a sufficiently low temperature reservoir of phonons is found to produce effective cooling, and thus an approach to the quantum limit, provided the frequency of the laser is large as compared to the bandwidth. For laser frequencies comparable to the bandwidth, strong deviations from the quantum limit of conductance are found even for a very low temperature reservoir, with the precise value of the Hall conductance determined by a competition between reservoir-induced cooling and the excitation of photocarriers by the laser. For the closed system, the electron distribution function is determined by the overlap between the initial wave function and the Floquet states, which can result in a Hall conductance which is opposite in sign to that of the open system.

    UR - http://www.scopus.com/inward/record.url?scp=84929120924&partnerID=8YFLogxK

    UR - http://www.scopus.com/inward/citedby.url?scp=84929120924&partnerID=8YFLogxK

    U2 - 10.1103/PhysRevB.91.155422

    DO - 10.1103/PhysRevB.91.155422

    M3 - Article

    AN - SCOPUS:84929120924

    VL - 91

    JO - Physical Review B-Condensed Matter

    JF - Physical Review B-Condensed Matter

    SN - 1098-0121

    IS - 15

    M1 - 155422

    ER -