We provide an article-extract which points out that a microwave-induced modification in the resistance occurs at relatively "high" magnetic fields where the radiation is incapable of producing inter-Landau level excitations and, therefore, that the microwa

ARTICLEINPRESS

R.G.Mani/PhysicaE](]]]])]]]–]]]

3

illustratedbyFigs.3

and4.Atthelowestfrequency,f¼3:35GHz;seeFig.3(a),regularoscillationsdonotappearinRxx;andthemicrowaveradiationseemstoproducemostlynegativemagnetoresistance,suchthattheirra-diatedRxxfallsbelowthedarkRxxat eldswellaboveBf:At eldsaboveBf;theradiationseemsincapableofproducinginter-Landaulevelexcita-tions,andtherefore,anewmechanismappearsnecessarytodescribethislow-fbehavior.AstheradiationenergyattheappliedfinFig.3(a)seems

1.5

1.0)

( xxR0.5

0.0(a)

2.0

1.5

)

( xx1.0

R0.5

0.0Bf (15.6 GHz)

(b)

B (T)

Fig.3.This gureexhibitstheeffectofmicrowaveirradiationonthediagonalresistance,Rxx;atrelativelylowmicrowavefrequencies.(a)Atf¼3:35GHz;theradiationmostlypro-ducesnegativemagnetoresistanceatmagnetic eldswellaboveBf;wheretheradiationseemsincapableofproducinginter-Landaulevelexcitations.(b)Withincreasingf;theradiation-inducedreductioninRxxaboveBfbecomeslesspronouncedasaresistancemaximum,the‘‘ rstresistancemaximum,’’becomesperceptible.

tolieinthevicinityoftheexpectedzero- eldspinsplittingduetotheRashbaandDresselhaustermsinthisGaAs/AlGaAssystem[19],wesuggestthattheobservedlowfbehaviormightre ectradia-tion-inducedmixingbetweenspinlevelsofthesameLandauband,andthemodi cationofthismixing,duetothe eld-inducedZeemanterm.Theeffectofincreasingf;atrelativelylowf;isexhibitedinFig.3(b).Here,oneobservesthatasf