1 Progress Report on A New Search for a Permanent Electric Dipole Moment of the Electron in a Solid State System 13 th SUSY Conference, Durham UK, July 18-23, 2005 Chen-Yu Liu, S. K. Lamoreaux G. 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., (1968) B.V. Vasil’ev and E.V. Kolycheva, Sov. Phys. JETP, 47 [2] 243 (1978) d e =(0.81  1.16)  e-cm

3 Features of solid state eEDM experiment High number density of bare electrons ~ /cm 3. PbO Cell Tl Beam: N = nV ~ N = nV ~ 10 8 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. Pros: Cons:

4 Figure of Merit Sensitive magnetometers –Superconducting Quantum Interference Device (SQUID). –Atomic cell (non-linear Faraday effect). Measure induced magnetic flux: Paramagnetic susceptibility  m Pick-up coil area d=  d e, enhancement factor   Z 3 Effective field, large dielectric constant K. Large  m Large Z Large E Large A A paramagnetic insulating sample

5 New experiment Gadolinium Gallium Garnet (Gd 3 Ga 5 O 12 ) polycryostal Gd 3+ in GGG –4f 7 5d 0 6s 0 ( 7 unpaired electrons). –Atomic enhancement factor =  1.6. –Langevin paramagnet. –Dielectric constant ~ 12. –Low electrical conductivity and high dielectric strength Volume resistivity =  -cm. Dielectric strength = 10 MV/cm for amorphous sample. –Cubic lattice. Large Sample size: 100 cm 3 Higher E field: 10kV/cm Better SQUID design Lower Temperature: 10mK

6 Comparison with the 1978 Experiment B.V. Vasil’ev and E.V. Kolycheva, Sov. Phys. JETP, 47 [2] 243 (1978) Sample: Nickel Zinc ferrite –dielectric strength ~ 2kV/cm. –Fe 3+ :  b = 4  B. (uncompensated moment)  2 –Atomic enhancement factor =  1 –Magnetic permeability = 11 (at 4.2K). (  m =0.8) –Electric permittivity  =2.2  0.2. (  =  0 K) –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 T.  d Fe3+ = (4.2  6.0)  e-cm  d e =(0.81  1.16)  e-cm e cm seems feasible!!!

7 Enhancement Factor of EDM of electrons in Gd 3+ in garnet crystal Mukhamedjanov, Dzuba, Sushkov, Phys. Rev. A 68, (2003). The enhancement factors has two contributions: Electrons in atom : K atom Adjacent Oxygen electrons : K CF

8 EDM Sensitivity Estimate EDM signal:  p = 17  0 per e-cm. –with 10kV/cm, T=10mK, A=100 cm 2 around GGG SQUID noise:  sq = 0.2  0 /√t (research quality) Coupling eff. =  sq /  p = √(L sq L i )/(L p +L i )= 8  –L squid = 0.2 nH. –L pick-up = 700 nH. (gradiometer) –L input = 500 nH. d e =  sq /  sq =(0.2  0 /√t)/(8    p ) –d e = 1.47  /√t e-cm In 10 days of averaging, d e ~ e-cm. S. K. Lamoreaux, Phys. Rev. A 66, (2002)

9 In 10 days of data accumulation, d e ~ e-cm. J.M.Pendlebury and E.A. Hinds, NIMA 440 (2000) 471

10 Alumina Crucible Single crystal GGG Poly-crystalline GGG Parallel plate capacitor E.E. Hellstrom et al., J. Am. Ceram. Soc., (1989) “ Solid State Reaction” to synthesize ceramics using oxide powders

11 Susceptibility  m Measurements Paramagnetic susceptibility Toroid inductor with GGG core Resonant frequency: 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) A1A1 A2A2 A 1 =A 2

13 Instrumentation High Voltage Electrodes: Macor coated with graphite. Magnetic Shield (shielding factor > 10 9 ) –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)

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 (> 10 8 ) –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  0 /rtHz Baseline: 5.8  0 /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 Waveforms HV monitor Current In the ground plate SQUID signal ms We have been turning on the HV and taking data using SQUID with GGG samples for 2 months.

18 eEDM signal SQUID signal: ( )  V ( )  V (drift corrected) Leakage Current: ( )  10 pA 4K, 2.8kVpp, 1.13Hz, 50 minutes B.V. Vasil’ev and E.V. Kolycheva, Sov. Phys. JETP, 47 [2] 243 (1978) d e =(0.81  1.16)  e-cm d e =(0.44  0.88)  e-cm Preliminary Preliminary Results:

19 Systematic Effects Leakage current. –< A, 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 ~ e-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 e-cm. –Results from the prototype experiment expected in the end of Second generation experiment using –larger samples, (10 samples in parallel) –and more sensitive magnetometers: research grade SQUID (noise: 0.2  0 /  Hz) cryogenic atomic magnetometers (D. Budker’s group in Berkeley) should further push the sensitivity of the experiment to e-cm. Future: 10  K (technically possible), eEDM sensitivity: e-cm.

21 A new generation of electron EDM searches GroupSystemAdvantagesProjected gain D. Weiss (Penn St.)Trapped CsLong coherence~100 D. Heinzen (Texas)Trapped CsLong coherence~100 H. Gould (LBL)Cs fountainLong coherence? L. Hunter (Amherst)GdIGHuge S/N100? S. Lamoreaux (LANL)GGGHuge S/N100?-100,000? E. Hinds (Imperial)YbF beamInternal E-field2-? D. DeMille (Yale)PbO* cellInternal E-field100-10,000? E. Cornell (JILA)trapped HBr + Int. E + long T?? N. Shafer-Ray (Okla.)trapped PbFInt. E + long T??