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,

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

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).

“11”

“1111” “122”

“42622”

“111”

Superconductivity in Fe-Pnictides ― Family

Fe-pnictides

Tc ~ 55 K

The Second Generation Materials of High-Tc Superconductivity

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)

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”

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.

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

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

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)

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

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

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

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

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

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

Experiment 2: Single Crystalline Synchrotron XRD

BL02B1

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.

・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).

Data are omitted because they are unpublished.