Multiphoton processes in microwave photoresistance of two-dimensional electron systems

Abstract

We extend our studies of microwave photoresistance of ultra-high mobility two-dimensional electron system (2DES) into the high-intensity, non-linear regime employing both monochromatic and bichromatic radiation. Under high-intensity monochromatic radiation ω we observe new zeroresistance states (ZRS) which correspond to rational values of ε = ω/ωC (ωC is the cyclotron frequency) and can be associated with multiphoton processes. Under bichromatic radiation ω1, ω2 we discover new resistance minimum, possibly a precursor of bichromatic ZRS, which seems to originate from a frequency mixing process, ω1 + ω2. These findings indicate that multiphoton processes play important roles in the physics of non-equilibrium transport of microwave-driven 2DES, and suggest new directions for theoretical and experimental studies. Intense current interest to millimeterwave photoconductivity of two-dimensional electron systems (2DES) was triggered by the discovery of microwave-induced resistance oscillations (MIRO)1,2 and zero-resistance states (ZRS), 3,4 emerging in ultra-high mobility samples at weak magnetic fields and low temperatures. While a great deal of attention has been paid both experimentally, 5−19 and theoretically 7,20−49 In particular, some recent experimental results appear to challenge existing theories.17,18 To advance our understanding of the phenomena we explore new experimental regime of high-intensity microwave (MW) radiation.Phenomenologically, MIRO appear due to oscillatory microwave photoresistance (PR), ∆R ω = R ω −R 0 , which (i) is a periodic function in inverse magnetic field, 1/B with a period given by ε = ω/ω C , where ω = 2πf and ω C = eB/m * are microwave and cyclotron frequency, respectively, (ii) can take both positive (maxima) and negative (minima) values depending on ε, and (iii) can approach the background dark resistance by absolute value under certain experimental conditions. Although one could expect appearance of negative resistance at some of the MIRO minima, experiments (and theory 22 ) usually (see, however Ref. 10) show that 2DES instead exhibits ZRS, as the resistance saturates close to zero. Since the resistance maxima (+) and minima (−) appear in pairs 9 situated roughly symmetrically about cyclotron resonance harmonics, i.e., ε ± j ≈ j ∓ φ j , they are commonly associated with an integral j (ε ± j ≈ j). All ZRS reported to date were observed at ε j = j + φ j , j = 1, 2, 3, ...where φ j is experimentally found to be 0 < φ ≤ 1/4. The work reported here was provoked by peculiar photoresistance features far from integral ε, which were first noticed in experiments on moderate mobility samples. 1In particular, prominent resistance maximum and minimum were observed about ε ≈ 1/2 at f = 45 GHz. 1Later experiments confirmed this observation 7,10,16 and even reported features close to other rational values of ε ≈ j/m, e.g. 3/2, 5/2, and 2/3. 4,9 It was proposed, 9 that these features originate from two-(m = 2) and threephoton (m = 3) processes; here, an electron absorbs m photons to jump j Land...

Magnetoresistance oscillations induced by high-intensity terahertz radiation

“…These effects were extensively studied both experimentally [35][36][37][38][39] and theoretically 38,40,41 and generally require stronger magnetic field, ω c > τ…”

Microwave-induced resistance oscillations in tilted magnetic fields

“…Owing to both theoretical [14][15][16][17][18][19][20][21][22] and experimental [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] progress, our understanding of these phenomena has improved dramatically over the last decade. Theoretically, MIRO are usually discussed in terms of two distinct mechanisms, referred to as the displacement [15][16][17] and the inelastic.…”

Magnetotransport of electrons in quantum Hall systems

“…7.4 High-power effects, subleading mechanisms, fractional MIRO In addition to the peak-valley structure near integer ω/ω c (integer MIRO), several experiments [83,85,92,95,96,97,98] reported similar features near certain fractional values, ω/ω c = 1/2, 3/2, 5/2, 2/3.. ("fractional MIRO", or FMIRO), which at elevated microwave power also evolved into ZRS ("fractional ZRS") [97]. Initially, FMIRO were ascribed to multiphoton processes [95,99].…”