1

Progress Report on A New Search for a Permanent Electric Dipole Moment of the Electron in a Solid State System

13th SUSY Conference, Durham UK, July 18-23, 2005

Chen-Yu Liu, S. K. LamoreauxG. Gomez, J. Boissevain, M. Espy, A. Matlachov

Los Alamos National Laboratory

2

Shapiro’s proposal -- using a solid state system to measure eEDM

Usp. Fiz. Nauk., 95 145 (1968)

B.V. Vasil’ev and E.V. Kolycheva, Sov. Phys. JETP, 47 [2] 243 (1978)

de=(0.81 1.16)10-22 e-cm

3

Features of solid state eEDM experiment

• High number density of bare electrons ~ 1022/cm3.PbO Cell Tl Beam:

N = nV ~ 1016 N = nV ~ 108

• Electrons are confined in solid No motional field effect.• Solid state sample:

– Large magnetic response.

• Solid state sample:– High dielectric strength.

• Concerns– Parasitic, hysteresis solid state effects might limit the sensitivity to the EDM

signals .€

Bmotional = v × E

Pros:

Cons:

4

Figure of Merit• Sensitive magnetometers

– Superconducting Quantum Interference Device (SQUID). – Atomic cell (non-linear Faraday effect).

• Measure induced magnetic flux:

€

ΔΦ=BA = χ mdE * μa( )A

Paramagnetic susceptibility m

Pick-up coil aread=de, enhancement factor Z3

Effective field, large dielectric constant K.

Large m

Large Z

Large E

Large A

A paramagnetic insulating sample

5

New experiment

Gadolinium Gallium Garnet(Gd3Ga5O12) polycryostal

•Gd3+ in GGG–4f75d06s0 ( 7 unpaired electrons).–Atomic enhancement factor = -4.91.6.

–Langevin paramagnet.–Dielectric constant ~ 12.–Low electrical conductivity and high dielectric strength

•Volume resistivity = 1016 -cm.•Dielectric strength = 10 MV/cm for amorphous sample.

–Cubic lattice.

Large Sample size: 100 cm3

Higher E field:10kV/cm

Better SQUID design

Lower Temperature:10mK

6

Comparison with the 1978 ExperimentB.V. Vasil’ev and E.V. Kolycheva, Sov. Phys. JETP, 47 [2] 243 (1978)• Sample: Nickel Zinc ferrite

–dielectric strength ~ 2kV/cm. –Fe3+: b = 4 B . (uncompensated moment) 2–Atomic enhancement factor = 0.52. 1–Magnetic permeability = 11 (at 4.2K). (m=0.8) –Electric permittivity =2.20.2. (=0K)–Cubic lattice.–No magnetoelectric effect.

• Sample size: 1cm in dia., 1mm in height. (0.08 c.c.) 500• E Field: 1KV/cm, 30Hz reversal rate 10 (field)• Temperature : 4.2K 100 (pending spin-glass)• rf-SQUID with a field sensitivity of 10-12 T. 1000-10000• dFe3+= (4.26.0) 10-23 e-cm de=(0.81 1.16)10-22 e-cm 10-30 e cm seems feasible!!!

7

Enhancement Factor of EDMof electrons in Gd3+ in garnet crystal

• Mukhamedjanov, Dzuba, Sushkov, Phys. Rev. A 68, 042103 (2003).

€

da = KatomKCFde

⇒ −2.2 × 9.5de = −20.9de

€

Δ =−20.9de E int =−20.9

30de E ext

⇒ 0.7de E ext

The enhancement factors has two contributions:Electrons in atom : Katom

Adjacent Oxygen electrons : KCF

8

EDM Sensitivity Estimate

• EDM signal: Φp = 17Φ0 per 10-27e-cm.– with 10kV/cm, T=10mK, A=100 cm2 around GGG

• SQUID noise: ΔΦsq = 0.2Φ0/√t (research quality)

• Coupling eff. = Φsq/Φp = √(LsqLi)/(Lp+Li)= 810-3.– Lsquid= 0.2 nH. – Lpick-up= 700 nH. (gradiometer)– Linput= 500 nH.

• de = ΔΦsq/Φsq=(0.2Φ0/√t)/(810-3 Φp)

– de = 1.4710-27 /√t e-cm

• In 10 days of averaging, de~ 10-30 e-cm.

S. K. Lamoreaux, Phys. Rev. A 66, 022109 (2002)

9

In 10 days of data accumulation,

de~ 10-30 e-cm.

J.M.Pendlebury and E.A. Hinds, NIMA 440 (2000) 471

10

Alumina Crucible

Single crystal GGG

Poly-crystalline GGG

Parallel platecapacitor

E.E. Hellstrom et al., J. Am. Ceram. Soc., 72 1376 (1989)

“ Solid State Reaction” to synthesize ceramics using oxide powders

11

Susceptibility m Measurements

• Paramagnetic susceptibility • Toroid inductor with GGG core • Resonant frequency:

€

m =C

T

€

C =Nμb

2

3kB

=1.29

€

NGd 3+

=1.03×1022 /cm3

€

1

2π LC

€

Ltoroid = μ0(1+ χ m )A

ln2

Traditional AC field method LC resonance circuit method

12

Magnetic flux pick-up coil: planar gradiometer • Common mode rejection ratio of residual external B fluctuations.

– measured ratio ~ 240 0.4% area mismatch.• Enhancement of sample flux pick-up.

5”2.5”

EDM Measurement Sequence:

• Reverse HV polarity

• monitor magnetization changes (AC flux change picked up by the SQUID)

A1

A2

A1=A2

13

Instrumentation• High Voltage Electrodes: Macor

coated with graphite.• Magnetic Shield (shielding factor

> 109) – Superconducting Pb foils (2

layers).– High Metglas alloy ribbons

in cryostat.– An additional cylinder of

“Conetic” sheet outside the cryostat.

• The whole assembly is immersed in L-He bath, which can be cooled by a high cooling power dilution refrigerator. (3.5mW at 120mK)

14

1.5 K L-He Cryostat

• Fluxgate– Shielding factor of the metglas shield ~

100– Shielding factor of the “Conetic” half

cylinder shields ~ 5• SQUID

– Learn to implement SQUIDs in our experiment

– Noise Measurement:– Measure the Shielding Factor of

• the metglas shield (did not help)• Pb shield (> 108)

– Sensitivity Calibration using current loop

15

SQUID Noise Spectrum

• One layer of Pb superconducting foil• Vibrational peaks• Background > Intrinsic SQUID noise

• Two layers of Pb superconducting foils• Vibrational peaks are gone• Background ~ Intrinsic SQUID noise• 1/f corner of SQUID noise < 1Hz

Baseline: 27.5 Φ0/rtHz Baseline: 5.8 Φ0/rtHz

Vibrational peaks

16

Learning about the SQUID

• Adding current bypass capacitors to the ground greatly reduce the high frequency spark signals into the SQUID.

• Stability of the SQUID feedback circuit.– A larger RC constant of the FB circuit makes the SQUID operation less

sucesptible to the constant HV polarity switches.• Normal vs. Superfluid Helium bath

17

WaveformsHV monitor

CurrentIn the ground plate

SQUIDsignal

ms

ms

ms

We have been turning on the HV and taking data using SQUID with GGG samples for 2 months.

18

eEDM signal

SQUID signal: (-2.68+-5.5)10-7 V (-0.66 +- 2.8)10-7 V (drift corrected)

Leakage Current: (-46 +- 1) 10 pA

4K, 2.8kVpp, 1.13Hz, 50 minutes

B.V. Vasil’ev and E.V. Kolycheva, Sov. Phys. JETP, 47 [2] 243 (1978)

de=(0.81 1.16)10-22 e-cm

de=(0.44 0.88) 10-23 e-cm

Preliminary

Preliminary Results:

19

Systematic Effects• Leakage current.

– <10-14A, should be feasible at low temp.

• Displacement current at field reversal.– Generate a large B field (helps to check SQUID functionality). – Residual magnetization due to solid state hysteresis effects???– Magnetize materials around the sample??? (put in another SQUID for field

monitor)

• Solid State effects:– Linear magneto-electric effect.– Magnetic impurities. (no problem, as long as they don’t move.)– Spin-lattice relaxation ???

20

Conclusions and Future Plans• The current setup is sensitive to eEDM signal ~ 10-23e-cm using a

hour of data.

• The prototype system cooled to 40 mK and 2 days of data averaging should have an eEDM sensitivity of 10-27e-cm. – Results from the prototype experiment expected in the end of 2005.

• Second generation experiment using – larger samples, (10 samples in parallel)

– and more sensitive magnetometers:• research grade SQUID (noise: 0.2Φ0/Hz)

• cryogenic atomic magnetometers (D. Budker’s group in Berkeley)

should further push the sensitivity of the experiment to 10-32 e-cm.

• Future: 10K (technically possible), eEDM sensitivity: 10-35 e-cm.

21

A new generation of electron EDM searches

Group System Advantages Projected gain

D. Weiss (Penn St.) Trapped Cs Long coherence ~100

D. Heinzen (Texas) Trapped Cs Long coherence ~100

H. Gould (LBL) Cs fountain Long coherence ?

L. Hunter (Amherst) GdIG Huge S/N 100?

S. Lamoreaux (LANL) GGG Huge S/N 100?-100,000?

E. Hinds (Imperial) YbF beam Internal E-field 2-?

D. DeMille (Yale) PbO* cell Internal E-field 100-10,000?

E. Cornell (JILA) trapped HBr+ Int. E + long T ??

N. Shafer-Ray (Okla.) trapped PbF Int. E + long T ??