Direct Measurement of Itinerant Electron Magnetization in non-degenerate GaAs using time-varying Magnetic Fields

In semiconductors, the electron chemical potential, also known as the Fermi level, is known to depend on temperature, carrier concentration, and electric field. Theoretical calculations show that it depends on magnetic field as well, and experiments have been designed, since the 1960s, to practically demonstrate this effect. Although successful in two dimensional electron systems at cryogenic temperatures, such measurements have been notoriously difficult to perform in bulk (3D) solids. The sample signal is too small, and is largely overshadowed by effects arising from several other physics [1]. In this talk I will highlight a recent successful attempt made at measuring this signal in GaAs at room temperature [2]. I will discuss, in details, the step by step experimental protocol following which the signal was obtained. Such a measurement, in semiconductors, directly yields the itinerant electron magnetization even at low carrier concentrations, making this technique useful in knowing what fraction of a specimen’s magnetization originates from its itinerant carriers. This is particularly relevant for some diluted magnetic semiconductors [3] and hexaborides [4] in which such a debate exists at present. In summary, this talk will describe how clear signals from the itinerant electrons of non-degenerate GaAs was obtained in the presence of a thousand-times-greater contribution stemming from bound electrons in the lattice, thus making this experimental technique gain a measurement sensitivity ten times that of the SQUID magnetometer [2].
     
Reference:
[1] 	Faraday’s law of electromagnetic induction; M. Peter … D. Shoenberg, Physics Letters, vol. 33A, p. 357, 1970.
[2] 	Aditya N. Roy Choudhury and V. Venkataraman, Physical Review B, vol. 93, p. 045208, 2016.     
[3] 	A. H. Macdonald … N. Samarth, Nature Materials, vol. 4, p. 195, 2005; J. Philip … J. S. Moodera, Nature Materials, vol. 5, p. 298, 2006.
[4] 	D. P. Young ... R. Zysler, Nature, vol. 397, p. 412, 1999; Y. Zhang and S. D. Sarma, Physical Review B, vol. 72, p. 115317, 2005.