NATIONAL HIGH MAGNETIC FIELD LABORATORY 2004 RESEARCH REPORT MAGNETO-PLASMONIC PHOTOLUMINESCENCE IN STRONG MAGNETIC FIELDS: EVIDENCE FOR STIMULATED EMISSION PROCESSES Y.D. Jho, X. Wang, D. H. Reitze, G. D. Sanders, C. J. Stanton, (University of Florida, Physics); J. Kono (Rice University, ECE), X. Wei (NHMFL), G. Solomon (Stanford, Physics) Introduction Investigations of the interactions of strong laser fields with semiconductor systems in strong magnetic fields are now possible owing to the availability of ultrafast laser sources available at the NHMFL. Here, we report on the observation of anomalous photoluminescence from inter-Landau level transitions in dense magneto-plasmas [1]. Previous studies on electron-hole magneto-plasmas have been limited to relatively low ac electric fields and/or low magnetic fields [2,3]. Our experiments encompass an unexplored regime in which intense short pulse laser fields and strong magnetic fields are simultaneously employed to create extremely high carrier densities in quantum well heterostructures and observe their emission processes. Experimental Using a 150 fs, 775 nm Ti:sapphire chirped pulse amplifier and optical parametric amplifier, we study magneto- photoluminescence (MPL) at 4.2 K on the heavy hole (HH) exciton in In 0.2 Ga 0.8 As as a function of laser power up to 25 GW/cm 2 (corresponding to a carrier density ~ 2.4x10 12 cm -2 ) and magnetic field up to 25 T using a 50 mm bore resistive magnet. . Results and Discussion Fig. 1, we plot the MPL as a function of excitation intensity for a pump wavelength of 1.3 mm. Each peak is assigned, from the low energy side, to the (00), (11), and (22) HH transitions, respectively. Above a critical threshold of 10 GW/cm 2 , the (11) and higher peaks have a significantly different character than the (00) peak. At low excitation, broad and weak (11) and (22) peaks appear above the (00) peak. Above a threshold intensity, narrow peaks appear on the high-energy side of these peaks, and become dominant at high excitation power. A threshold magnetic field of > 13 T is also necessary to observe the high energy sharp features. To determine how the MPL peak scales with pump power, we plot the integrated peak intensity of (00), (11) low energy tail, and (11) high-energy peak (shown in the inset). The high energy peak shows no emission until the threshold pump intensity and then increases super-linearly. Both the intensity dependence and the magnetic field dependence of the MPL, particularly the evidence of a threshold in both carrier density and field, strongly suggest that the emission process has a coherent character, either arising from purely inter- LL stimulated emission or from a more exotic emission such as superradiance [4]. More systematic studies including time- resolved spectroscopy are currently underway to determine the exact nature of the emission process. Acknowledgements This work is supported by the NHMFL In-House Research Program, and the NSF ITR (DMR-0325499) and IMR programs (DMR-0216838). References [1] Y. D. Jho, et al., International Journal of Modern Physics B, to appear. [2] L. V. Butov et al., Phys. Rev. B 46, 12765 (1992). [3] G.E.W. Bauer, Phys. Rev. Lett. 64, 60 (1990). [4] A.A. Belyanin et al., Quantum Semiclass. Opt. 9, 73683 (1997) 1.30 1.35 1.40 1.45 10 100 1000 10000 100000 3 GW/cm 2 25 GW/cm 2 0 5 10 15 20 25 10X 10X Intregrated PL Intensity Excitation Power (GW/cm 2 ) 00 11tail 11peak 11 00 PL Intensity (arb) Energy (eV)