The electron EDM search in solid ferroelectric Eu0.5Ba0.5TiO3

Alex SushkovSteve Eckel Steve Lamoreaux

2

The Yale experiment

Steve Eckel

vacuum pumps

electronics

EDM experiment enclosed in magnetic shielding

liquid helium cryostat

3

The idea for a solid-state search

EdBH aa

0B

4

The idea for a solid-state search

ad E

atomic EDM

EdH a

5

The idea for a solid-state search

ad E

a

B

d Enk T

atomic EDM

temperature

polarization

EdH a

6

The idea for a solid-state search

ad E

a

B

d Enk T

aa

B

d EM nk T

atomic EDM

temperature

polarization

magneticdipolemomentof one atomatom density

magnetizationd as EDM vector

has to point along the spin

EdH a

7

The idea for a solid-state search

aa

B

d EM nk T

8

Europium

Eu2+

ground state: 8S7/2 (L=0, S=7/2, J=7/2), configuration: [Xe] 4f7

The electrons

with unpaired

spins

9

Ferroelectric Eu0.5Ba0.5TiO3:the perovskite crystal structure

O2-

Ti4+

Eu2+ or Ba2+

T > Tc(e): dielectric

cubic symmetry, effective electric field E* = 0

10

Ferroelectric Eu0.5Ba0.5TiO3:the perovskite crystal structure

O2-

Ti4+

Eu2+ or Ba2+

T < Tc(e): ferroelectric

symmetry broken, effective electric field E* 10 MV/cm

11

The effective electric field in Eu0.5Ba0.5TiO3

E* 10 MV/cm

Eapplied = 0

[PRA 81, 022104 (2010)]

12

Making Eu0.5Ba0.5TiO3 ceramics

OH41TiOBaEu H

41TiO

21BaTiO

21OEu

41

230.50.522332

Solid-state reaction at 1200 C in hydrogen/argon atmosphere

First time this material

has been synthesized and studied

[Nature Materials,July 2010]

13

Crystal structure of Eu0.5Ba0.5TiO3

OH41TiOBaEu H

41TiO

21BaTiO

21OEu

41

230.50.522332

X-ray diffraction spectra

Cubic (perovskite)

structure

14

Multiferroic properties of Eu0.5Ba0.5TiO3

cB

B

TTn

k

3

)8( 2

:Fit

magnetic moment of

Eu2+ ion

density of Eu2+ ions

magnetic ordering

temperature

K cm -3

)1.07.1(106 21

cTn

Magnetic susceptibility measurement

Multiferroic The EDM experiment is in the paramagnetic phase

15

EDM experiment schematic

2 samples

ground plane(graphite-painted)

superconducting Pb foil with a slit

for improving magnetic field homogeneity

2 layers of superconducting

magnetic shielding (Pb foil)

3 SQUID pickup loops

2 high-voltage electrodes

(graphite-painted)

superconducting solenoid

16

Some very recent EDM data

Time (s)

SQU

ID si

gnal

(0)

E EM M

EDM signature

17

Some very recent EDM data

Time (s)

SQU

ID si

gnal

(0)

E EM M

displacement-current spikes during

polarization switching

18

A few minutes of EDM data

Systematics

• Sample heating + magnetic field

• Magnetoelectric effect: P2M2

• No leakage currents

• No Berry’s phase

• No interference from external magnetic fields

Eapplied = 0

superconducting magnetic shielding

Beam/cell systematics we don’t have to deal with:

Systematics we have to deal with:

Need absolute magnetic field control at 100 nG

level to suppress these to 10-28 ecm

Sample heating + magnetic field

H

Reverse sample polarization sample heats up! sample permeability drops

sample magnetization dropsH flux through the pickup loop drops

SQUID signal correlated with polarization reversal

The good news: no systematic at H=0

The magnetoelectric effect

22222

)(2828

MPMPMMHHPPEE

thermodynamic free energy

polarization magnetization

appliedelectric field

appliedmagnetic field

the EDM term:violates P- andT-symmetries

the magnetoelectric term: obeys P- and T-

symmetries

gives rise to magnetization: zzz HPM 2

external magnetic field

quadratic inwhile EDM is linear in

zPBUT if the polarization reversal is imperfect, then we get a signal

that mimics EDM

zP

Magnetoelectric effect

Magnetoelectric magnetization: zzz HPM 2

external magnetic field

mG 10zH

The good news:no systematic at H=0

23

The sensitivity of electron EDM search

magnetic field sensitivity:

effective electric field:

3 fT/ HzB

* 10 MV/cmE

Electric dipole moment sensitivity

temperature:Boltzmann’s constant

Eu2+ number density:Eu2+ magnetic moment:

Bottom line:

After 1 hour of averaging: After 10 days of averaging:

current best limit

*8)(3EB

nTTkd

B

cBe

K 2.4T K 1.7cT

Ba 8 -321 cm 106n

cme 102 27 ed cme 28103ed

[PRA 81, 022104 (2010)]

Summary

• First data run 10-24 ecm after a few minutes of

data taking

• Modifications in progress:

sapphire ground plane

magnetic shielding

to conduct heat away from the sample

to reduce background magnetic field