Magneto-optical probing of weak disorder in a two-dimensional hole gas (original) (raw)
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Physical Review B, 2004
A theory of shake-up processes in photoabsorption of an interacting low-density two-dimensional electron gas (2DEG) in strong magnetic fields is presented. In these processes, an incident photon creates an electron-hole pair and, because of Coulomb interactions, simultaneously excites one particle to higher Landau levels (LL's). In this work, the spectra of correlated charged spin-singlet and spin-triplet electron-hole states in the first hole LL and optical transitions to these states (i.e., shake-ups to the first hole LL) are studied. Our results indicate, in particular, the presence of optically-active three-particle quasi-discrete states in the exciton continuum that may give rise to surprisingly sharp Fano resonances in strong magnetic fields. The relation between shake-ups in photoabsorption of the 2DEG and in the 2D hole gas (2DHG), and shake-ups of isolated negative X − and positive X + trions are discussed. I.
Magneto-optical evidence of many-body effects in a spin-polarized two-dimensional electron gas
Physical Review B, 2000
Modulation-doped Cd x Mn 1Ϫx Te/Cd y Mg 1Ϫy Te quantum wells are studied at 1.7 K by magnetoabsorption experiments performed near the fundamental heavy-hole-electron (HH 1-E 1) transition. In the investigated range of Mn content (xϷ0.02) and electron concentration ͓n e Ϸ(2-3)ϫ10 11 cm Ϫ2 ], the two-dimensional electron gas is fully spin-polarized at magnetic fields as low as Hϭ1.5 T. The interband optical spectra exhibit unusual magnetic field dependence resulting from electron-hole interactions and phase-space-filling effects. An additional enhancement of the spin splitting of Landau levels found in this study is attributed to the electronexchange interaction. A simplified theoretical model including the exchange energy and the electron-hole interaction provides a coherent quantitative description of the overall experimental features.
Optical probing of composite fermions in a two-dimensional electron gas
Nature Physics, 2006
I n a high magnetic field, electrons confined to two dimensions form highly correlated states driven entirely by electron-electron interactions 1-3 . Transport and cyclotron-resonance experiments 4-12 on these fractional quantum Hall effect states, and the associated fractionally charged excitations, suggest the existence of composite fermions-electrons with two flux quanta attached 4-12 . Using optical spectroscopy 13-19 , we show that the two flux quanta in a composite fermion interacting with an exciton (a bound state of an electron and a hole) lead to filling-factor-dependent features in the optical emission spectrum, which are symmetric around filling factor ν = 1/2, and fractionally charged excitations lead to fractionally charged excitons. In the vicinity of the incompressible ν = 1/3 state we observe a doublet structure in the emission line, corresponding to excitations of the incompressible fluid. At filling factors ν > 1/3, corresponding to the transition to a compressible metallic state 20 , a new emission line appears, which we attribute to the fractionally charged quasi-exciton. shows the emission spectra from a high-mobility two-dimensional electronic system (2DES) in high magnetic fields B = 8-28 T, corresponding to filling factors ν < 1, at a temperature T = 30 mK. To better visualize the features observed, the linear magnetic field dependence has been subtracted from the photon energy. The spectra are measured on a two-dimensional electron gas (2DEG) in a modulation-doped GaAs/GaAlAs quantum well with a width of 20 nm, carrier density n = 2.2 × 10 11 cm −2 , and mobility μ = 3 × 10 6 cm −2 V −1 s −1 . The most striking features are the oscillations in the energy of the emission line, which correlate with the fractional filling factors, and which are symmetric around filling factor ν = 1/2. In particular, jumps in energy and line splittings are observed in the vicinity of filling factors ν = 1, 2 3 , 3 5 , 3 7 , 2 5 and 1 3 . For example, shows blue-shifts of the emission energy at a magnetic field corresponding to the filling factor ν = 1/3 and, symmetrically, at the filling factor ν = 1. The two fillings correspond to the formation of a closed shell of composite fermions (CFs), the CF filling factor ν CF = 1 state.
Charged Excitons in the Fractional Quantum Hall Regime
Physical Review Letters, 2001
We study the photoluminescence spectrum of a low density (ν < 1) twodimensional electron gas at high magnetic fields and low temperatures. We find that the spectrum in the fractional quantum Hall regime can be understood in terms of singlet and triplet charged-excitons. We show that these spectral lines are sensitive probes for the electrons compressibility. We identify the dark triplet charged-exciton and show that it is visible at the spectrum at T < 2 K. We find that its binding energy scales like e 2 /l, where l is the magnetic length, and it crosses the singlet slightly above 15 T.
Tunneling spectroscopy of disordered two-dimensional electron gas in the quantum Hall regime
Physical Review B, 2011
Recently, Dial et al. presented measurements of the tunneling density of states into the bulk of a two dimensional electron gas under strong magnetic fields. Several high energy features appear in the measured spectrum showing a distinct dependence on filling factor and a unique response to temperature. We present a quantitative account of the observed structure, and argue it results from the repulsive Coulomb interactions between the tunneling electron and states localized at disorder potential wells. The quenching of the kinetic energy by the applied magnetic field leads to an electron addition spectrum that is primarily determined by the external magnetic field and is nearly independent of the disorder potential. Using a Hartree-Fock model we reproduce the salient features of the observed structure.
Non-Fermi-liquid behavior of two-dimensional electron gas with disorder
Solid State Commun, 1995
The problem of strongly correlated disordered two-dimensional electron gas on a lattice is studied by computer modeling. The long-range Coulomb interaction is assumed. It is proved that for zero hopping amplitude J the lowest residue of the one-particle Green function is zero. It is shown by quantum Monte-Carlo computations that the Coulomb gap in the one-particle density of states exists and the lowest residues remain small for J > 0 and independent of J at the same range of J where, according to other criteria, many-particle wave functions become delocalized.
Many-body effects in a quasi-one-dimensional electron gas
Physical Review B, 2014
We have investigated electron transport in a quasi-one dimensional (quasi-1D) electron gas as a function of the confinement potential. At a particular potential configuration, and electron concentration, the ground state of a 1D quantum wire splits into two rows to form an incipient Wigner lattice. It was found that application of a transverse magnetic field can transform a double-row electron configuration into a single-row due to magnetic enhancement of the confinement potential.
Excitons, spin-waves and Skyrmions in the optical spectra of a two dimensional electron gas
Solid-State Electronics, 1998
ÐWe present a comprehensive study of photoluminescence (PL) mechanisms in high-quality GaAs/AlGaAs two dimensional electron gases (2DEGs) close to the integer quantum Hall state, n=1. At this ®lling factor the lowest-energy spin-split electron Landau level (eQ) is fully occupied and the higher spin-state (eq) empty. We demonstrate the Coulomb interaction between the 2DEG electrons and valence band (vb) hole has a crucial in¯uence on the PL. This is elucidated by PL experiments on two dierent types of sample where we can vary the electron±hole separation. In single quantum well (QW) structures with front and back depleting gates we are able to apply an electric ®eld normal to the well, in order to polarise the hole wavefunction toward the opposite face of the well from the 2DEG. In double QWs, we study even larger separations where the 2DEG and hole are con®ned in neighbouring wells. Our results prove the existence of excitons formed between the hole and the charge excitations of the 2DEG, i.e. quasi-particles or Skyrmions. For small electron±hole separations the Coulomb interaction is suciently strong to cause the spin reversal of a single 2DEG electron for n<1 to form an exciton. Increasing the electron±hole separation results in the n<1 ground state changing nature to be non-excitonic. For the very large electron±hole separations found in the double QW, our results suggest extra spin-reversals take place to form a n>1 ground state consisting of a Skyrmion bound to the hole. The spectra also show shake-up structure due to the formation of spin-waves after recombination of an electron in the full spin-state.