Breakdown of the topological protection by cavity vacuum fields in the integer quantum Hall effect

Appugliese, Felice; Enkner, Josefine; Paravicini-Bagliani, Gian Lorenzo; Beck, Mattias; Reichl, Christian; Wegscheider, Werner; Scalari, Giacomo; Ciuti, Cristiano; Faist, Jérôme

doi:10.48550/arxiv.2107.14145

Cited by 5 publications

(10 citation statements)

References 38 publications

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“…This is a very important result because it demonstrates that the long-range nature of the cavity photon-field circumvents the topological protection of the integer Hall effect and actually modifies this fundamental phenomenon of condensed matter physics. We believe that the modification of the Hall conductance can be measured for a 2DEG inside a cavity and could provide further insights on the recently observed modification of the integer Hall effect [53]. In conclusion, our findings provide new insights and pave the way for the exploration of quantum Hall physics, in the integer and the fractional regime, embedded in the field of cavity QED.…”

Section: Discussionsupporting

confidence: 56%

“…15), and to demonstrate that the cavity field modifies the plateaus of the Hall conductance in the integer regime. Such a cavity modification has also been measured recently experimentally [53].…”

Section: Cavity Modification Of the Integer Hall Conductancementioning

confidence: 65%

“…This opens the possibility of not only having a fractal/self-similar spectrum as a function of the relative flux, but also a fractal as a function of the lightmatter coupling constant η. The coupling constant η can be tuned experimentally either by varying the strength of the external magnetic field (i.e., changing the cyclotron frequency ω c ) or by varying the diamagnetic frequency ω p via the 2D electron density and the fundamental cavity frequency, or by shaping the cavity environment in order to achieve a smaller effective volume [51,53].…”

Section: Polaritonic Hofstadter Butterflymentioning

confidence: 99%

“…As a synthesis of QED and the quantum Hall setting, quantum Hall systems under cavity confinement have been studied both experimentally and theoretically, in the integer [44][45][46][47][48] and the correlated fractional [49,50] regime, and ultrastrong coupling to the photon field and modifications of their transport properties [51] have been demonstrated. Recently, a theoretical mechanism for a cavity-mediated hopping in the integer regime was also proposed [52] and the breakdown of the topological protection of the integer Hall effect due to cavity vacuum fields was demonstrated experimentally [53].…”

Section: Introductionmentioning

confidence: 99%

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Polaritonic Hofstadter Butterfly and Cavity-Control of the Quantized Hall Conductance

Rokaj,

Penz,

Sentef

et al. 2021

Preprint

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In a previous work [Phys. Rev. Lett. 123, 047202 (2019)] a translationally invariant framework called quantum-electrodynamical Bloch (QED-Bloch) theory was introduced for the description of periodic materials in homogeneous magnetic fields and strongly coupled to the quantized photon field. For such systems, we show that QED-Bloch theory predicts the existence of fractal polaritonic spectra as a function of the cavity coupling strength. In addition, for the energy spectrum as a function of the relative magnetic flux we find that a terahertz cavity can modify the standard Hofstadter butterfly. In the limit of no quantized photon field, QED-Bloch theory captures the well-known fractal spectrum of the Hofstadter butterfly and can be used for the description of 2D materials in strong magnetic fields, which are of great experimental interest. As a further application, we consider Landau levels under cavity confinement and show that the cavity alters the quantized Hall conductance and that the Hall plateaus are modified as σxy = e 2 ν/h(1 + η 2 ) by the light-matter coupling η. Most of the aforementioned phenomena should be experimentally accessible and corresponding implications are discussed.

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Section: Discussionsupporting

confidence: 56%

Section: Cavity Modification Of the Integer Hall Conductancementioning

confidence: 65%

Section: Polaritonic Hofstadter Butterflymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Polaritonic Hofstadter Butterfly and Cavity-Control of the Quantized Hall Conductance

Rokaj,

Penz,

Sentef

et al. 2021

Preprint

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“…Further, in the presence of a periodic potential, the Landau levels develop mini-gaps and for the energy spectrum a self-similar fractal pattern emerges, known as the Hofstadter butterfly, 6 which has become experimentally accessible via magnetotransprot measurements in Moiré materials. [7][8][9][10] The study of Landau levels and topological edge states is still very actively pursued and is currently even considered in quantum optics and cavity quantum electrodynamics (QED), where ultra-strong coupling of the Landau levels to the quantum vacuum fluctuations and the control of conduction properties have been achieved experimentally in a cavity, [11][12][13][14] with several theoretical studies and proposals accompanying these developments. [15][16][17][18][19] In parallel to the fundamental investigation of quantum systems exposed to magentic fields, the study of impurity models has a long lasting tradition in solid state physics.…”

Section: Introductionmentioning

confidence: 99%

New Class of Landau Levels and Hall Phases in a 2D Electron Gas Subject to an Inhomogeneous Magnetic Field: An Analytic Solution

Sidler¹,

Rokaj²,

Ruggenthaler³

et al. 2022

Preprint

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An analytic closed form solution is derived for the bound states of electrons subject to a static, inhomogeneous (1/rdecaying) magnetic field, including the Zeeman interaction. The solution provides access to many-body properties of a two-dimensional, non-interacting, electron gas in the thermodynamic limit. Radially distorted Landau levels can be identified as well as magnetic field induced density and current oscillations close to the magnetic impurity. These radially localised oscillations depend strongly on the coupling of the spin to the magnetic field, which give rise to non-trivial spin currents. Moreover, the Zeeman interaction introduces a lowest flat band for E F = 0 + assuming a spin g s -factor of two. Surprisingly, in this case the charge and current densities can be computed analytically in the thermodynamic limit. Numerical calculations show that the total magnetic response of the electron gas remains diamagnetic (similar to Landau levels) independent of the Fermi energy. However, the contribution of certain, infinitely degenerate energy levels may become paramagnetic. Furthermore, numerical computations of the Hall conductivity reveal asymptotic properties of the electron gas, which are driven by the anisotropy of the vector potential instead of the magnetic field, i.e. become independent of spin. Eventually, the distorted Landau levels give rise to different Hall conductivity phases, which are characterized by sharp sign flips at specific Fermi energies. Overall, our work merges "impurity" with Landau-level physics, which provides novel physical insights, not only locally, but also in the asymptotic limit. This paves the way for a large number of future theoretical as well as experimental investigations.

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Direct polariton-to-electron tunneling in quantum cascade detectors operating in the strong light-matter coupling regime

Lagrée¹,

Jeannin²,

Quinchard³

et al. 2021

Preprint

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We demonstrate mid-infrared quantum cascade detectors (QCD) operating in the strong light-matter coupling regime. They operate around λ = 10 µm with a minimum Rabi splitting of 9.3 meV. A simple model based on the usual description of transport in QCDs does not reproduce the polaritonic features in the photo-current spectra. On the contrary, a more refined approach, based on the semi-classical coupled modes theory, is capable to reproduce both optical and electrical spectra with excellent agreement. By correlating absorption/photo-response with the simulations, we demonstrate that -in this system -resonant tunneling from the polaritonic states is the main extraction mechanism. The dark intersubband states are not involved in the process, contrary to what happens in electrically injected polaritonic emitters.

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Breakdown of the topological protection by cavity vacuum fields in the integer quantum Hall effect

Cited by 5 publications

References 38 publications

Polaritonic Hofstadter Butterfly and Cavity-Control of the Quantized Hall Conductance

Polaritonic Hofstadter Butterfly and Cavity-Control of the Quantized Hall Conductance

New Class of Landau Levels and Hall Phases in a 2D Electron Gas Subject to an Inhomogeneous Magnetic Field: An Analytic Solution

Direct polariton-to-electron tunneling in quantum cascade detectors operating in the strong light-matter coupling regime

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