Observation of extreme field-induced mass deviations in double quantum wells

Abstract

Large deviations are measured in the c 1 t e cyc o ron effective mass m near the r energy gap arising in strongly cou led G A e recently observed partial coup e a s double quantum wells ( W's Bll' The energy gap results f s) subject to in-plane magnetic esu s rom an anticrossing of the two W dis 1 ' h b B T" repressed by more than a factor of 3 near the u er y II. The severely distorted dis ersion p sion near the gap yields an I, gap e ge. The data show excellent agreement ' h a ed e. a ac or o near the upper gap edge, and enhanced b -50 ce y -% near the lower n agreement with recent theoretical calculations. because the Double-quantum-well (DQW) syst sys ems are of interest ecause they constitute a system in which an additional electronic degree of freedom in th h d e growt direction can be controllably introduced int t -d' g tron as. Most 'n o a wo-imensional elecmagnetotransport measurements on DQW's have been for high magnetic fields er end' grow h plane B~, where the electron's kinetic enerina e. ' Recent work has investigated th ff e e ects of pure y in-p ane fields BII, in which case sin le-r 1 tun nelin case sing e-particle the two el e ing ynamics dominate the intera t' 1 ac ions etween e wo electron layers. The primary effect of B is a linear transverse shif 'ft in the canonical momentum Ak of e ectrons in one quantum well (QW) 1 re ative to the other. is produces a strong modulation of the tunnelin conductance 6 (B ) due ce~I I ue to the conservation of energ o e tunneling and in-plane k. ergy Very recently, in our previous work " an" or and in work y urobe et a . , it was demonstrated that h h a w ent eincouphng is sufficiently strong, a hi h B stron 1 m g) a ig II also tunneling causes the shifted dispersion curves of the icross, opening a partial energ W's to ant' gy gap, or minie minigap, the elecgap, of width EG. At the edges of th tron group velocities are strongly distorted, and the density of states D(E form swee in B t c orms van Hove singularities. B p g II, the minigap is made to pass through the chemical potential p, with the singularities in D(s) producing two sharp features in R =G II ' a mi imum and a maximum as shown in Fig. 1(a), correspondin h wer gap edges, respectively. The data exhibited excellent agreement with th 1 eoretical predictions, and cG could be extracted from th d t Th e a a. is system is unusual in that its Fermi surface (FS) has several com-A similarl sha ' ar y s aped FS, although not tunable b B and II' arisin from g a different mechanism, was studied man years ago in vicinal planes of Si. ' Here we report measurements of th 1 e cyc otron mass m, o e ectrons near the edges of the field-ind d DQW uce 'gap. 'he masses are measured by addin a sma11 ing a sma o~~, and examining the temperature ( T) dependence of the resulting Shubnikov -de Haas (SdH) oscillations. In th n the upper-energy branch of the dispersion C) II l-CCI CL" C) C) II CD CC 0.065 ( 0.045 C) II 0.025 CC &I 0.005 Bii (T) FIG. 1. Normalized RII vs BII for 0=0 0' showin the anticrossing features. (b) Plo...

In-plane magnetophotoluminescence studies of modulation-doped GaAs/AlGaAs coupled double quantum wells

“…The anticrossing of the two dispersion curves in the presence of in-plane magnetic fields can produce a partial energy gap. [7][8][9] This yields large in-plane B-field tunable distortions in the Fermi surface and the density of states (DOS). Large maxima and minima are observed in the in-plane conductance.…”

“…1-5 Modulation-doping of a CDQW creates two parallel two-dimensional electron gas (2DEG) layers. [6][7][8][9][10] This additional electronic degree of freedom in the growth (z) direction can be controlled by varying the barrier thickness, external gate voltages, and magnetic fields. For a strong tunneling structure, wherein two quantum wells are separated by a very thin barrier (typically < 40Å), a tunnel split bandgap (∆ SAS ) is formed such that the symmetric and antisymmetric states are nearly degenerate in energy.…”

“…The primary effect is to produce a partial energy gap and a strong modulation of the in-plane conductance due to an anti-crossing of the k-dispersion curves as demonstrated by Simmons et. al.. 7,9 In a recent theoretical investigation, Huang and Lyo 12 describe many different phenomena related to the inplane magnetic field dependence of the photoluminescence (PL) spectra. Their calculations show that, as the magnetic field increases, transition energy between the antisymmetric and symmetric states displays an Ntype kink, namely a maximum followed by a minimum.…”

Analysis of the scattering of electrons by special vibrational modes in a GaAs quantum well with a thin AlAs middle barrier: Mobility modulated by a transversal electric field

“…The possibility of measuring the properties of that structure made it a very popular one in recent literature. [21][22][23][24][25][26] The scattering rates for both the inter-and intrasubband transitions in that double well are determined by the structure parameters, i.e., the middle barrier and the well widths. There is, however, a way to study the effect of the middle barrier in the mobility based on the analysis of a single sample.…”

Photoluminescence transitions of GaAs/AlGaAs asymmetric double-well structures

“…Coupled double quantum well (CDQW) structures, where the two wells are separated by a thin barrier, are of interest due to an enhanced quantum Stark effect and provide an ideal system for studying tunneling dynamics [1][2][3][4][5]. Modulation-doping of a CDQW creates two parallel twodimensional electron gas (2DEG) layers [6][7][8][9][10]. This additional electronic degree of freedom in the growth (z) direction can be controlled by varying the barrier thickness, external gate voltages, and magnetic fields.…”