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
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The effective electric field in Eu0.5Ba0.5TiO3
E* 10 MV/cm
Eapplied = 0
[PRA 81, 022104 (2010)]
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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
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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
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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
