Terahertz cyclotron emission from two-dimensional Dirac fermions

Abstract

Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance an unfavorable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. A proven example of such gapped graphene-like materials are HgTe quantum wells close to the topological phase transition. In this work, we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by magnetic field and gate-voltage.

Tunable Terahertz Cyclotron Emission from Two-Dimensional Dirac Fermions

“…This evolution is driven by the cyclotron mass of the sample, determined by its electron carrier density, through the quasi-classical formula E = (ℏe/mc)B [5]. We measured samples with different electron densities and extracted the cyclotron mass [6]. The behavior of the latter with the electron density is in perfect agreement with a low energy model that we developed.…”

“…6,7 , N. N. Mikhailov 8,9 , S. A. Dvoretskii 8,10 & F. Teppe1 1 Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier, Montpellier, France, 2 Institut d'Electronique et des Systèmes (IES), UMR 5214 CNRS, Université de Montpellier, Montpellier, France 3. Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPSINSA-EMFL, Grenoble, France 4.…”

“…Institute of Physics, Charles University, Prague, Czech Republic 5. CEA, LETI, MINATEC Campus, DOPT, Grenoble, France 6. Institute for Physics of Microstructures of Russian Academy of Sciences, Nizhny Novgorod, Russia.…”

Giant THz Nonlinearity in Topological and Trivial HgTe-Based Heterostructures

“…Here, we report extremely strong THz nonlinearity in 2D TIs based on single HgTe/CdTe QW. 20 Epitaxial HgTe layers have been investigated using linear cw and time-domain THz spectroscopy, 21,22 including photogalvanic effect, 23 giant Faraday rotation, 24 and terahertz cyclotron emission, 25 but nonlinearity has not been reported so far. We find a nonlinear third-order susceptibility χ (3) ≈ 5 × 10 −9 m 2 V −2 , i.e., a factor of 5 higher than that in graphene, representing the record value for bare materials without any field-enhancement structures.…”

Topological interface states - A possible path towards a Landau-level laser in the THz regime

“…In such processes, an electron in the excited LL n + 1 can be promoted due to electron-electron interactions to the LL n + 2 while the required energy is provided by a simultaneous desexcitation of another electron from n+1 to n. Instead of using one excited electron to emit a photon of frequency ω c , two electrons in the LL n + 1 are thus lost without emission of any photon. Another obstacle equally related to equisitant LLs is reabsorption of cyclotron light due to the transition (n + 1) → (n + 2), which is resonant with the (n + 1) → n transition used in the emission of light [7][8][9].…”