Emergent Nematic State in Iron-based Superconductors...Emergent Nematic State in Iron-based...
Transcript of Emergent Nematic State in Iron-based Superconductors...Emergent Nematic State in Iron-based...
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Emergent Nematic State in Iron-based Superconductors
H.J. Shi2, K. Hashimoto2, S. Tonegawa2, Y. Mizukami2,
K. Sugimoto3, T. Fukuda4,
A. Nevidomskyy5,
T. Terashima1, T. Shibauchi2, Y. Matsuda2
1) Research Center for Low Temperature & Materials Sciences, Kyoto University
2) Department of Physics, Kyoto University
3) Japan Synchrotron Radiation Research Institute, SPring-8
4) Quantum Beam Science Directorate, JAEA SPring-8
5) Department of Physics and Astronomy, Rice University,
S. Kasahara1,2,
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Outline
*Experimental
Magnetic Torque Measurements
Single Crystalline Synchrotron XRD
*Introduction:
High Temperature Superconductivity in Fe-pnictides
& Possible Nematic State in This Class of Materials
*Results & Discussion
Evidence for the Electronic Nematic State
*Summary
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Fe-pnictides
The Second Generation Materials of High-Tc Superconductivity
Y. Kamihara, et al.,
JACS, 130, 3296 (2008).
LaFeAs(O,F) (“1111”)
Tc ~ 55 K
Superconductivity in Fe-Pnictides ― Discovery
H. Takahashi et al.,
Nature 453, 376 (2008).
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“11”
“1111” “122”
“42622”
“111”
Superconductivity in Fe-Pnictides ― Family
Fe-pnictides
Tc ~ 55 K
The Second Generation Materials of High-Tc Superconductivity
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2D square lattice of Fe-atoms
From c-axis
Fe
Pnictogen
(Chalcogen)
From a-axis
Fe
“11”
“1111” “122”
“42622”
“111”
Superconductivity in Fe-Pnictides ― Family
Pnictogen
(Chalcogen)
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Parent compounds
The magneto-structural transition is suppressed by doping or applying pressure.
Superconductivity in a close proximity to magneto-structural order.
S. Nandi et al., PRL 104, 057006 (2010). H. Luetkens et al., Nature Materials 8, 305 (2009).
“1111”
Phase Diagram
Structural transition (Ts) & AFM transition (TN) “122”
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Parent compounds
The magneto-structural transition is suppressed by doping or pressure.
Superconductivity in a close proximity to magneto-structural order.
S. Nandi et al., PRL 104, 057006 (2010). H. Luetkens et al., Nature Materials 8, 305 (2009).
“1111”
Phase Diagram
Structural transition (Ts) & AFM transition (TN) “122”
Understanding the underlying physics of spin/orbital
&
its connection to the superconductivity is particularly important.
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Parent compounds
Structural transition (Ts) & AFM transition (TN)
Phase Diagram
Ba Ba
S. Nandi et al., PRL 104, 057006 (2010).
Tetragonal
Paramagnetic
Orthorhombic.
Antiferromagnetic
“122”
Fe
Stripe type AFM
Symmetry Breaking
High-T Low-T
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K. Kuroki et al., New J. Phys. 11, 025017 (2009).
Original BZ
Unfolded BZ
D.J. Singh and M.H. Du,
Phys. Rev. Lett. 100, 237003 (2008).
Q ~ (π,π)
hole
electron
Original BZ
Multiband electronic structure with
well-separated hole and electron sheets
Five-fold degenerate Fe 3d orbitals participate: XZ/YZ, XY, 3Z2-R2, X2-Y2
Fermi Surface
Theoretical approach: Itinerant Picture
Good nesting between
hole and electron sheets
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Frustration between J1 and J2 and its
removal by orbital ordering
J1a=J1b J1aJ1b
Lv et al., PRB 80, 224506 (2009).
PRB 82, 045125 (2010).
Chen et al., PRB 80, 180418(R) (2009).
Theoretical approach: Localized Picture
E. Fradkin et al., Science 327, 155 (2010).
Electronic Nematic State
Broken Rotational Symmetry
Nematic & Smectic in Liquid Crystals
(Wikipedia)
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Finite in-plane anisotropy above Ts
in detwinned crystals.
Experiments Suggesting the Nematic State
J. Chu et al. Science (2010). Resistivity ARPES M. Yi et al., PNAS (2011).
BaFe2As2 Ba(Fe0.975Co0.025)As2
Experiments Suggesting the Electronic Nematic State
rb > ra above Ts
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1. Intrinsic?
Questions on the Electronic Nematic State
2. Thermodynamic phase?
Ultra-Precise Torque Magnetometry
&
Single Crystalline Synchrotron XRD
3. Connections to the Magneto-Structural transition
and Superconductivity? Electronic Nematic
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Micro-piezoresistive cantilever
Very high sensitivity
Experiment 1: Magnetic torque measurements
(at m0H=4T)
5x10-12 e.m.u. SQUID 10-8 e.m.u. torque
t : magnetic torque V: sample volume
M: magnetization
H: applied Field
Thermodynamic Quantity
Change in the piezoresistance
Magnetic Torque
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a b
c
t
q scan
b c
a
H H
Experiment 1: Magnetic torque measurements
f scan
Field Rotation within the ab-plane Field Rotation within the ac-plane
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Direct probe of the In-plane Anisotropy without detwining
Experiment 1: Magnetic torque measurements
t2f ≠ 0
caa = cbb, cab = 0
Broken rotational symmetry
caa ≠ cbb, or cab ≠ 0
t2f = 0 Preserved tetragonal symmetry
t
t
Preserved C4 Symmetry
Broken C4 Symmetry
f
f
p
p/2
b c
a
H
f scan
Field Rotation within the ab-plane
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Vector magnet and mechanical rotator system
We can rotate H continuously within the ab plane
with a misalignment less than 0.02 deg.
Experiment 1: Magnetic torque measurements
t : magnetic torque V: sample volume
M: magnetization
H: applied Field
Thermodynamic Quantity
b c
a
H
Single crystal
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Experiment 2: Single Crystalline Synchrotron XRD
BL02B1
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Experiment 2: Single Crystalline Synchrotron XRD
BL02B1
Equipped with a large cylindrical image-plate camera (350 mm x 683 mm)
(h h 0)T
2q values: -60 deg < 2q < 145 deg Higher order peaks (7 7 0)T or (8 8 0)T
Sensitive experiments to the orthorhombic distortions.
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・Clear Anomalies at Ts & TSDW
Quantum oscillations are observed
in a wide range (0.38 < x < 1.0)
・Pure crystals are available
SK et al., PRB 81, 184519 (2010).
An ideal system to study Iron-pnictides
0 100 200 3000
200
400
600
T (K)
rxx
( m
c
m)
T0
TSDW
Tcon
x = 0 0.07 0.14 0.20
0.23 0.27 0.33 0.41
0.56 0.64 0.71
BaFe2(As1-xPx)2 Paramagnetic -Tetragonal
Superconducting
Antiferromagnetic
-Orthorhombic
0 0.2 0.4 0.60
100
200
x
T (
K)
System: BaFe2(As1-xPx)2
H. Shishido et al., PRL 104, 057008 (2010).
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Data are omitted because they are unpublished.