New experimental limit on the electric dipole moment of the electron in a paramagnetic insulator

We report results of an experimental search for the intrinsic electric dipole moment of the electron (eEDM) using a solid-state technique. The experiment employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a large magnetic response at low temperatures. The presence of the eEDM would lead to a small but nonzero magnetization as the GGG sample is subjected to a strong electric field. We search for the resulting Stark-induced magnetization with a sensitive magnetometer. Recent progress on the suppression of several sources of background allows the experiment to run free of spurious signals at the level of the statistical uncertainties. We report our first limit on the eEDM of $(-5.57\pm 7.98\pm 0.12)\times {10}^{-25}\mathrm{e}\mathrm{cm}$ with 5 days of data averaging.

Figure 1

Volume magnetic susceptibility of the GGG sample as a function of temperature, measured at a maximum applied magnetic field of 400 Oe. The solid curve shows the Curie-Weiss fit.

Figure 2

Schematic of the experimental setup for the GGG-based solid-state eEDM experiment.

Figure 3

The magnetic flux pickup coil in the form of a planar gradiometer. It is placed between the ground electrodes. The inner diameter matches the diameter of the GGG sample. For the best CMMR, the inner area $\pi R_1^2$ is matched to the outer area $\pi R_3^2-\pi R_2^2$.

Figure 4

Magnetic noise spectra of the DC SQUID detector operated at 4.2 K, showing nominal noise spectrum (dashed curve), and measured spectrum with an external magnetic field of 10 gauss at 2 Hz, applied outside the magnetic shield.

Figure 5

Time traces of averaged signals on one HV monitor, one leakage current monitor, and the SQUID readout (over three hours of sampling) presented as two cycles of field reversal. Data were taken using the 24-bit DAQ system, with a sampling rate of 715 Hz.

Figure 6

Distribution of the eEDM observable (processed with the drift-correction algorithm). Data points were collected over one uninterrupted run (3 hours).

Figure 7

SQUID readout (averaged over one uninterrupted run) folded modulo one cycle of field reversal. This data set illustrates the worst case of DC voltage drift.

Figure 8

Results of eEDM measurements, processed using the fitting algorithm. Each data point is the averaged result of one run. The final data point is the final average result over 40 experimental runs.

Figure 9

Measured eEDM as a function of the applied HV. The data point at $9.4{\mathrm{kV}}_{pp}$ contains the highest statistics.