Many-body interaction and lasing in highly uniform quantum wires

Abstract

While the setup is still being optimized during daytime, first data has been collected during nights and week-ends over a period spanning 6 weeks. For each of 22 data blocks, one shown in Fig. 3 we remove a linear drift of -I H d h and fit to eq. (1). Analyzing the distribution ofthe fit results, we find an isotropy violation signal of (4.39 ? 0.58) Hz (Fig. 2). As preliminary r e d t ,we thur obtain IBI = ( 8 . 7 ? 1 3 ) . 1 0~1 0 .( 2)This limit has an uncertainty about three times smaller than the best previous test.' Future developments will include operation at an optimized rotation rate and a new setup using crossed (monolithic) COP& within a single block of crystalline material. This should ultimately lead to an improvement of another two orders of magnitude over the present setup.Since the first observation of ground-state lasing in quantum wire lasers,' many-body electron interactions and lasing mechanism in one-dimensional (1-0) wire lasers have been the central issues of our interest. Questions about existence of band-gap renormalization and contribution of excitons to gain in laring have been hotly argued but remains &olved for about a decade. Here, we study these problems by means of recently achieved highly-uniform T-shaped quantum wires (T-wires) of 14 nm x 6 nm cross-sectional size and lasers containing these T-wires. Highly uniform GaAs T-wires are fabricated by the cleaved-edge overgrowth method with molecular-beam epitaxy refined by a recently developed annealing technique' which dramatically improver (110) interface uniformity in T~wires.Interruption of the 4 9 0 T epitaxial GaAs overgrowth by a 10 minute anneal at 600'C under an As, overpressure produces an atomically-flat surface free of monolayer step edges over areas measuringseveral tensoipm.As a result,photoluminescence (PL) linewidth of present T-wires are typically I meV, which is about a factor of 1/10 sharper than that of previous T-wires. ' Then, we studied PL of modulation-doped single T-wire structures with tunable I-D electron density by electrical gating to study manybody electron interaction effects. It shows PL of I-D neutral excitons and charged excitons at low densities, which evolve^ as thedenrityinueases to band-to-band optical recombination of single holes and an electron plasma with significant band-gap renormalization?In undoped twenty-T-wire samples, we found clearsignaturesof I-Dfreeexcitonsand I-Dcantinuum States in PLE spectra, and biwitons and electron-hale plasma emission in stronglyWe then studiedlasingproperties oftwenty-Twire laser samples with 500 pm long cavity and uncoated mirrorsvia optical pumping. Threshold pumping power for lasing is about 5 mW at 5 K. Lasing by T-wires is observed up to about 100 K.Lasing energy is not at the free w i t o n energy, but at the low-energytail of biexcitons. Therefore, origin of gain for lasing is attributed not to free ex& tons, but most probably to biexcitons.Very recently, a single-T-wire laser has also been realized and its detailed study is in progress.Chemical synt...

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