Friday, November 09, 2012

Measurement of Electron Electric Dipole Using Solid State Experiment

Another example where the so-called "applied" physics field can make as fundamental of a contribution to physics knowledge as any other "pure" field.

A while back, a new and improved measurement of the electron dipole moment using beams of electrons reveals that there is still no internal structure to the electron. A new experiment has significantly improved the ability of a solid state experiment to measure the electron dipole moment.

The electron’s EDM must be collinear with its spin. Solid-state EDM searches, therefore, typically apply an electric field to a sample and try to measure the induced magnetic signal. Stephen Eckel and colleagues at Yale University in Connecticut perform such an experiment with Eu0.5Ba0.5TiO3, a ceramic with a high density of unpaired, unordered spins, and a sizable ferroelectric response. This means that an external electric field creates an even larger internal electric field for the spins. The authors place a sensitive magnetic pickup loop between two 12-mm-diameter, 1.7-mm-thick disks of Eu0.5Ba0.5TiO3 and apply a series of short electric field pulses to modulate the signal from the EDM and cancel out stray fields.

Eckel et al. conclude that if the EDM is nonzero, it cannot be greater than 6.05 x 1025ecm. Compared with the best limit of 1.05 x 1027ecm from atomic beam measurements, it may seem like a losing battle to continue with a solid-state approach, but the prospect of new materials and lower noise measurements motivates continued research.
With the discovery of the same physics for a magnetic monopole in the spin-glass system, possible discovery of skyrmions, and the recent discovery of Majorana fermions, condensed matter experiments are producing a lot of fundamental results that used to be the sole realm of particle physics. The myth that condensed matter physics does not produce "fundamental knowledge" should be thoroughly destroyed by now.


No comments: