RAPID COMMUNICATIONS PHYSICAL REVIEW B 87, 041303(R) (2013) Quantum Hall signatures of dipolar Mahan excitons G. J. Schinner, 1 J. Repp, 1 K. Kowalik-Seidl, 1 E. Schubert, 1 M. P. Stallhofer, 1 A. K. Rai, 2 D. Reuter, 2 A. D. Wieck, 2 A. O. Govorov, 1,3 A. W. Holleitner, 4 and J. P. Kotthaus 1 1 Center for NanoScience and Fakult¨ at f ¨ ur Physik, Ludwig-Maximilians-Universit¨ at, Geschwister-Scholl-Platz 1, 80539 M¨ unchen, Germany 2 Angewandte Festk¨ orperphysik, Ruhr-Universit¨ at Bochum, Universit¨ atsstraße 150, 44780 Bochum, Germany 3 Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA 4 Walter Schottky Institut and Physik-Department, Am Coulombwall 4a, Technische Universit¨ at M ¨ unchen, D-85748 Garching, Germany (Received 6 February 2012; revised manuscript received 10 September 2012; published 17 January 2013) We explore the photoluminescence of spatially indirect, dipolar Mahan excitons in a gated double quantum well diode containing a mesoscopic electrostatic trap for neutral dipolar excitons at low temperatures down to 250 mK and in quantizing magnetic fields. Mahan excitons in the surrounding of the trap, consisting of individual holes interacting with a degenerate two-dimensional electron system confined in one of the quantum wells, exhibit strong quantum Hall signatures at integer filling factors and related anomalies around filling factor ν = 2 3 , 3 5 , and 1 2 , reflecting the formation of composite fermions. Interactions across the trap perimeter are found to influence the energy of the confined neutral dipolar excitons by the presence of the quantum Hall effects in the two-dimensional electron system surrounding the trap. DOI: 10.1103/PhysRevB.87.041303 PACS number(s): 78.67.De, 71.35.Ji, 71.70.Di, 78.55.−m Interband optical excitations in solids containing degener- ate electron systems provide a probe for many-body interac- tions as reflected, for example, in the so-called Mahan exciton observed in degenerate semiconductors. 1 There, many-body interactions between an exciton and remaining free electrons in the Fermi sea cause a so-called Fermi edge singularity of the optical absorption or emission, similar to singularities observed in the x-ray photoemission spectra of metals. 2 Mahan excitons have been studied extensively in doped quantum wells containing a two-dimensional electron system 3 (2DES) and were found to also exhibit signatures in quantizing magnetic fields related to both the integer 4 and fractional 5 quantum Hall effects (QHE). 6–11 Coupled double quantum wells (CDQW), exhibiting long-living spatially indirect excitons, are of partic- ular interest for the study of many-body interactions between dipolar excitons, in part to explore potential Bose-Einstein condensation of excitons 12–14 predicted several decades ago, 15 but also to study the role of the strong dipolar interactions between excitons. 16–19 A related CDQW system, composed of two adjacent 2DES, is the bilayer quantum Hall system in which excitonic quasiparticles are formed in the ground state around half-filling of Landau levels (LLs) and investigated via magnetotransport experiments. 20,21 Here, we report on luminescence studies of excitons in a CDQW, consisting of an individual hole in one QW and a voltage-controlled 2DES in the other QW. Such types of dipolar quasiparticles we introduce as Mahan-type indirect excitons (MIX). In the presence of a quantizing magnetic field, we find such MIX to exhibit characteristic signatures at both integer and fractional Landau-level filling factors. Furthermore, at the perimeter of an electrostatically created circular excitonic trap, we find the QHE of the 2DES located outside the trap perimeter to influence the energies of neutral dipolar excitons confined within the trap, thus reflecting nonlocal interactions across the trap perimeter. Our studies enable new insights into complex many-body interactions in systems with restricted dimensionalities. Dipolar excitons are spatially indirect excitons (IX), 22 i. e., bound pairs consisting of an electron and a hole, spatially separated in two adjacent CDQW. 17,23–25 . In the absence of excess carriers, neutral dipolar IX in a magnetic field B , applied perpendicularly to the plane of the quantum wells, exhibit a diamagnetic energy shift of E dia ∼ r 2 e μ B 2 , with r e the effective Bohr radius and μ the reduced mass of the excitons. 26,27 A qualitatively different behavior is observed when the CDQW contains excess carriers 28 or an electron- hole plasma of density above the Mott transition. 24 In this case, discrete Landau-level features increasing in energy in proportion to the magnetic field are observed, reflecting free carrier behavior. The CDQW device studied here is a diode structure which can be voltage tuned via the quantum confined Stark effect (QCSE). It contains two 7-nm-thick In x Ga 1−x As QWs (x = 0.11) separated by a 10-nm-thick GaAs tunnel barrier. To achieve field-effect tunability, the CDQW is embedded between a degenerately n-doped GaAs back contact and 6-nm-thick semitransparent titanium top gates (for further details, see Ref. 19). The QCSE tunes the dipolar IX energy E IX =−p IX F where p IX = ed IX z is the IX dipole moment and d IX z the electron-hole separation. F = 1 l 0 (V FB − V ) is the electric field perpendicular to the QW plane where V is the applied gate voltage, V FB is the flat-band gate voltage at which the built-in electric field is compensated, and l 0 denotes the distance between the gate electrode and the back contact. The QCSE allows the tuning of the electron states in the CDQW relative to the pinned Fermi energy of the back contact. As can be seen in Fig. 1(a), in the high-field case, neutral direct excitons (DX) occupy only quantum well QW 1 , whereas indirect excitons (IX) extend across both quantum wells. In the low-field case, as illustrated in Fig. 1(b), excess electrons occupy one of the quantum wells (QW 1 ) and the CDQW is populated with Mahan-type direct (MDX) and indirect excitons (MIX). Employing a versatile confocal microscope with two objec- tives embedded in a 3 He refrigerator with a base temperature below 250 mK, we study the photoluminescence (PL) from the InGaAs CDQW in Faraday geometry. 18 With the focus 041303-1 1098-0121/2013/87(4)/041303(5) ©2013 American Physical Society