Observation of fractional elementary charges in an ultra-cold plasma of NO: A periodic many-body quantum system - Klaus Muller-Dethlefs

We report the experimental observation of a very striking periodicity in a many-body system--an ultra-cold plasma. A long life-time (>0.3 ms) quantum degenerate molecular Rydberg plasma is generated in the high-density region of a pulsed supersonic jet expansion by two-color resonant excitation of nitric oxide (10%) in neon (5bar) into the high-n Rydberg threshold region. Two synchronous UV laser pulses produce the plasma a few mm away from the jet nozzle. For plasma densities of > 10¹⁶ cm^-3 the electrons should become quantum degenerate, i.e. the electron de Broglie wavelength becomes larger than the Wigner-Seitz radius a.
A colinear time-of-flight (ToF) mass spectrometer is used to analyze the plasma. The observed positively charged objects of mass to charge ratio m/z in the ToF spectrum follow a strictly reproducible progression of (m/z) from 35 to 92.5. From the m/z numbers one obtains the corresponding ion to electron ratios of the 12 observed peaks from 7/1 to 37/25). The observed 12 many-body states have periodic ion/electron ratios of 28/4, 30/6; 40/16, 42/18, 44/20; 54/30, 56/32, 58/34; 68/44, 70/46, 72/48; 74/50 equivalent to Fractional Elementary Charges, FEC's (i.e. electron/ion ratios) of 1/7, 1/5; 2/5, 3/7, 5/11; 5/9, 4/7, 17/29; 11/17, 23/35, 2/3; 25/37. This progression looks very much like one observed for the Fractional Quantum Hall Effect.


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