quantum fluctuations and criticality in pr based spin ice ...€¦ · quantum version of spin ice...
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Quantum Fluctuations and Criticality
in Pr based Spin Ice Systems
Satoru Nakatsuji
Institute for Solid State Physics, Univ. of Tokyo
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Collaborators
JHU/NIST, U.S.A.
Collin Broholm
Jiajia Wen
Chris Stock
Gottingen University
Y. Tokiwa
P. Gengenwart
National High Magnetic Field Lab.
Tallahassee
Luis Balicas
University of California, Riverside
Douglas MacLaughlin
Institute for Solid State Physics, University
of Tokyo
Kenta Kimura
Jun Ishikawa
Yo Machida (Tokyo IT)
Yasuo Ohta
Toshiro Sakakibara
Takashi Tayama
Yoshiya Uwatoko
RIKEN
S. Onoda
Nagoya Univ.
E. Nishibori
H. Sawa
Univ. of Ryukyus
Y. Karaki
Acknowledgement to Leon Balents, Yong Baek Kim
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Content Introduction
Spin Ice on Pyrochlore
Coulomb Phase and Monopoles
Quantum version of spin ice
Quantum Fluctuation Effects in Pr based Spin Ices
Quantum monopolar fluctuations in Pr2Zr2O7
Interplay between spin ice and conduction electron,
Chiral Spin Liquid Behavior and Quantum Criticality in Pr2Ir2O7
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Spin Ice : Pyrochlore Magnet
Classical Spins
Nearest-neighbor FM coupled <111> Ising Spins
No Magnetic Order
at T > 0
“Spin Ice”
M.J. Harris, S. Bramwell et al., (1997)
Disordered State w/
Residual Entropy
S0 ~ R/2ln(3/2)
A. Ramirez et al., (1997)
“2-in, 2-out”
4C2 = 6 fold
“H2O ice”
atom atom
atom
Low lying Defect
“3-in 1-out” state
Monopole
= 2Jff
Castelnovo et al. (2008).
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Coulomb Phase, Pinch point
In Spin Ice, 2-in 2-out can be considered as a divergence free condition:
It leads to power law spin-spin correlation~
Result in ‘pinch point’ singularity in scattering experiment.
Ice rule breaking states correspond to creation of magnetic monopole/ width.
0 M
'
1'
rrrr
Spin Ice Ho2Ti2O7 , Neutron Scattering Fennell, et al (2009)
Pinch Points
Experiment Monte Carlo
simulation
Coulomb Phase: quantum dimer system, Heisenberg AF on pyrochlore,…
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in in
out
out
out
out
in
in
FM
Novel quantum spin liquids and/or Coherent motion of monopoles?
“Classical” dipolar spin ice system
Dipolar spin ice on pyrochlore lattice1
Dipolar interaction, Classical FM coupling 1 K ex. Dy2Ti2O7 (Dy: large moment 10B) No quantum fluctuations in macroscopically degenerate spin ice manifold Monopole dynamics is only diffusive.
Effects of Quantum fluctuations?
[1] ex. Bramwell & Gingras, Science (2001).
ground state
monopole
2Jff
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O2-
O2-
Pr3+
Lee, Onoda, Balents
Quantum Spin Ice?
“2-in, 2-out” + quantum fluctuations = quantum spin liquid?
hybridization between Rare Earth(4f) and O(2p)
strong superexchange interaction with quantum transverse term (Jxy)
Non-kramers
Theory: M. Hermele et al., (2004), R. Moessner et al., (2003), A. Banerjee et al., (2008), S. Onoda et al., (2010).
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Content Introduction
Spin Ice on Pyrochlore
Coulomb Phase and Monopoles
Quantum version of spin ice
Quantum Fluctuation Effects in Pr based Spin Ices
Quantum monopolar fluctuations in Pr2Zr2O7
Interplay between spin ice and conduction electron,
Chiral Spin Liquid Behavior and Quantum Criticality in Pr2Ir2O7
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Pr2Zr2O7
Quantum monopolar fluctuations
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Specific heat estimate of energy scale ≈1 K
Magnetic specific heat Cm
0.5 1 5 100
1
2
Cm
(J/K
mo
le-P
r)
Pr2+xZr2-xO7+
#1 (x=-0.03) #2 (x=-0.01) #3 (x=-0.07) #4 (x=+0.06)
T (K)
0 5 10 15 20
2
3
4
5
Sm
(J/K
mo
le-P
r)
T (K)
Pr2Zr2O7
after subtract lattice contribution (La2Zr2O7)
peak ≈ 1.5 K
Pr3+
mJ = α|4+…
Schottky of 1st excited CEF level (~100 K)
Pr2Ir2O7 similar to Pr2Ir2O7 case
common feature in Pr-based pyrochlore
energy scale Jff: order of 1 K
exchange coupling dipolar (0.1 K)
Jff
peff = gJJz = 2.5B
CEF confirmed by Inelastic NS.
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Elastic neutron scattering for Pr2Zr2O7 (0
,0,l)
(h,h,0)
0
1
2
3
4
-1 0 1 2 3 -1 0 1 2 3
Monte Carlo Simulation
NN spin ice Dipolar spin ice
Pinch points at [200] , [111],… Coulomb Phase with NN FM coupling
Measurements were performed at MACS, NCNR, NIST, USA
Background was subtracted using the data taken at T = 15 K
-1 0 1 2 3
0 0.04 0.02 0.06
T = 0.1 K
Pr2Zr2O7
J. Wen, C. Broholm @ JHU S.T. Bramwell et al. PRL (2001).
Ñ×M » 0
Only 5 % of the total spectra weight is in the elastic channel: dynamic spin ice manifold
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Quantum Monopoles in Pr2Zr2O7
T = 0.1 K
Pinch points are filled in for the inelastic map. Quantum dynamics of monopoles
J. Wen,
C. Broholm
@ JHU Ñ×M » 0 Ñ×M ¹ 0
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Pr2Ir2O7
Spin Ice + Exotic Liquids =?
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Pr2Ir2O7 :
Geometrically Frustrated Kondo Lattice
S. Nakatsuji, Yo Machida, Y. Maeno, T. Tayama, T. Sakakibara et al. PRL 96 (2006).
Pr3+: 4f2 Localized Ising Moment
// <111> (CEF by Neutron Diffraction)
Ir4+ : 5d5 conduction electron,
Pauli Paramagnetism
Spin-Orbit Coupling Effect?
Strong Frustration:
No Long Range Order
Tf ~ 0.3 K<<qW 20 K No freezing at > 20 mK by μSR (D. MacLaughlin et al.)
1 mm
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T = 30 mK
<111> : Jump in resistance Metamagnetism
<100>, <110> : Smooth decrease
Magnetoresistance
SdH Oscillation seen for [111] fit to Lifshitz-Kosevich formula at B > Bc : Loss of scattering due to disordred Spin Ice State L ~ 500 – 800 Å : coherence due to uniform [1-in,3-out] state
L. Balicas, S. Nakatsuji, Y. Machida, and S. Onoda, Phys. Rev. Lett. 106, 217204 (2011).
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FM correlation below T ~ 2Jff ~ 1.5 K
FM correlation
between Ising moments
Broad peak at ~ 1.5 K
T < 1.5 K CM = AT1/2
SM = AT1/2
1.5 K
c3(q=0) : a steep negative
increase, and saturate to a
large negative value 1.5 K
Highly degenerate state
Quadrupoler Order
Monopole Creation
Δ = 2Jff
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qW 20 K 2Jff~1.4K T (K)
Kondo like
Behavior
Paramagnetic
Spin Liquid
Phase
Tf~0.3 K
Partial Spin
Freezing “2-in 2-out” configurations
Pr2Ir2O7 :
Geometrically Frustrated Kondo Lattice
Dipolar Spin Ice (eg. Dy2Ti2O7)
Spin freezing at T < Jff
Onset of Spontaneous HE
at TH ~ Jff
TRS broken Spin Liquid
Phase
-10
-5
0
-0.02
-0.01
00.1 1
H(B
= 0
) (
-1c
m-1
) M(B
= 0
) (B /P
r)
H
M
B = 0 T
T (K)
TH
Yo Machida, S. Nakatsuji, S. Onoda, T. Tayama, and S. Sakakibara, Nature 463, 210 (2010).
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Orbital currents in the Kagome plane
T = 0.5 K > Tf(~0.3 K)
<111> : Large hysteresis
<100>, <110> : Small hysteresis
T = 0.5 K
T = 0.5 K
T = 0.5 K H // <111>
H // <110>
H // <100>
H
S
S
AHE without Magnetic Order
L. Balicas, S. Nakatsuji, Y. Machida, and S. Onoda, Phys. Rev. Lett. 106, 217204 (2011).
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Summary:
Quantum effects in Pr based Spin Ice
Spin Liquid with Spin Ice Correlation
at T < 1.5 K ~ 2J: Monopole creation scale
Pr2Zr2O7
Quantum Monopolar Fluctuations
Pr2Ir2O7
Chiral Spin Liquid Behavior and Quantum Criticality
Role of Spin Orbit Coupling in the Ir Pyrochlore Network?
O2-
O2-
Pr3+