Study of FeSe Superconductor as an example

(1)

1

M. K. Wu

Na$onal Dong-‐Hwa University

Institute of Physics, Academia Sinica

Lecture at the Center for Condensed Ma4er Sciences NTU, 15 October 2013

What have we learned from Nanosciences—

Study of FeSe Superconductor as an example

FeSe_0.9 nanowire

500 nm

[100]

(2)

2

(3)

3

What we have advanced in

Sciences, and how?

(4)

Establishment of Core Facili$es

p 

Academic centers are located at the Academia Sinica, Na,onal Taiwan University, Na,onal Tsing Hua University, Na,onal Chiao Tung University, Na,onal Chung Cheng University, Na,onal Cheng Kung University, Na,onal Sun Yet-‐Sen University, and Na,onal Dung Hua University.

p 

A biomedical nano-‐imaging center was also set up in 2007.

p 

These core-‐facility centers provide professional

services that signiﬁcantly enhance eﬀorts to sa$sfy

needs of academic and industrial R&D.

(5)

NTHU

Core Facilities for Southern Taiwan Nanotechnology Research Center, NCKU

Center for Microscopy and Nano-analysis, NTU

Core Facility for Nano Lithography and Nano Biotechnology, NTHU

Nano-laboratory for Kaohsiung and Ping-Tung Area , NSYSU

NDHU Nano-science and Technology

Center in Central Taiwan, NCCU /NCHU

Core Facility for Nano Fabrication and Nano Characterization, NCTU

Nano Common Laboratories, ITRI

Interdisciplinary Bio-medical Imaging Research Center, NSRRC

Core Facilities Center for Nanoscience and

Nanotechnology, AS

NSRRC

Nano-science and Technology

Research Center in Eastern Formosa, NDHU

ITRI

Core Facili$es Progrm

NTHU

Core Facilities for Southern Taiwan Nanotechnology Research Center, NCKU

Center for Microscopy and Nano-analysis, NTU

Core Facility for Nano Lithography and Nano Biotechnology, NTHU

Nano-laboratory for Kaohsiung and Ping-Tung Area , NSYSU

NDHU Nano-science and Technology

Center in Central Taiwan, NCCU /NCHU

Core Facility for Nano Fabrication and Nano Characterization, NCTU

Nano Common Laboratories, ITRI

Interdisciplinary Bio-medical Imaging Research Center, NSRRC

Core Facilities Center for Nanoscience and

Nanotechnology, AS

NSRRC

Nano-science and Technology

Research Center in Eastern Formosa, NDHU

ITRI

(6)

6 Core-shell

Nanotip Wire/Rod

Tube

Belt

Peapod

Adv. Mater. 14, 1847 (2002) Nature Mater. 5, 102 (2006) Appl. Phys. Lett. 81, 22 (2002)

JACS 123, 2791 (2001) JACS 127, 2820 (2005)

APL .79, 3179 (2001)

Adv. Func. Mate. 12, 687, (2002) APL 81, 4189 (2002)

APL 86, 203119 (2005) JACS 128, 8368 (2006)

APL. 81, 1312 (2002) Nano. Lett. 3, 537 (2003)

Z.L. Wang Ed., Chapter 9, pp.259-309, Kluwer

(2004)

Adv. Fun. Mat. 16, 537 (2006)

APL. 83, 1420 (2003) Nano. Lett. 4, 471 (2004) Chem. Mater. 17, 553 (2005) Adv. Func. Mat. 15, 783 (2005) APL 86, 203119 (2005)

US Patent 6,960,528,B2 APL (2006)

Brush

Adv. Func. Mater. 14, 233 (2004) Other Thin Films:

DRM 14, 1010 (2005) APL 86, 21911 (2005) APL 86, 83104 (2005) APL 86, 161901 (2005) APL 87, 261915 (2005) JVST B 24, 87 (2006) APL 88, 73515 (2006)

1-D Functionalized Integrated Systems

(7)

The violation of the Stokes–Einstein relation in supercooled water

B

y confining water in nanopores, so narrow that the liquid cannot freeze, it is possible to explore its properties well below its homogeneous nucleation temperature T_H 235 K. In

particular, the dynamical parameters of water can be measured down to 180 K, approaching the suggested glass transition temperature T_g165 K. Here we present experimental evidence, obtained from Nuclear Magnetic Resonance and Quasi-Elastic Neutron Scattering

spectroscopies, of a well defined decoupling of transport properties (the self-diffusion

coefficient and the average translational relaxation time), which implies the breakdown of the Stokes–Einstein relation.

Abstract

Sow-Hsin Chen, Francesco Mallamace, Chung-Yuan Mou, Matteo Broccio, Carmelo Corsaro, Antonio Faraone, and Li Liu

I

n 2005, PNAS established an annual award that recognizes recently published

PNAS papers of outstanding scientific excellence and originality. The lab motto of Nick Cozzarelli, our late Editor-in-Chief, was “Blast ahead,” as he encouraged researchers to push the envelope of discovery. This year the award is renamed the Cozzarelli Prize, and the Editorial Board has reorganized the above article, “The violation of the Stokes-Einstein Relation in supercooled water”, as an excellent example of these same qualities.

(8)

Mesoporous silica as Nanocarriers

S.H. Wu, Y. Hung, C.Y. Mou, Chem Comm (Feature Article, 2011, In Press)

8.5m m 7mm

Photodynamic therapy Magnetic Resonance Angiography Oral drug delivery

(9)

GaN Nanorod Array for White-‐light LED

•  Good quality of GaN nanorod arrays have been demonstrated.

– Strain free, defect suppression, low refrac,ve index

•  Nanorods-‐on-‐

Si growth templates can serve as a good system for InGaN-‐

nanodisk-‐based full-‐color light-‐emiXng devices.

•  A new approach is shown for genera$ng high-‐

quality white light LED with high color rendering capability and high eﬃciency.

Appl. Phys. LeH. 97, 073101 (2010)

(10)

Creating Monodispersed Ordered Arrays of Surface-Magic- Clusters and Anodic Alumia Nanochannels by Constrained

Self-organization

Prof. Yuh-Lin Wang 王玉麟 IAMS Academia Sinica, Taiwan

(11)

Cover Story

Appl. Phys. LeH., 92, 063101 (2008)

Electrical and thermal transport in single nickel nanowire Ins,tute of Physics, Academia Sinica

Cover Story

Appl. Phys. LeH., 94, 062105 (2009)

Self-‐assembled GaN hexagonal micropyramid and microdisk Department of Physics, Na,onal Sun Yat-‐Sen University

Cover Story

Proteomics 7, 3038-‐3050 (2007)

Targeted protein quan,ta,on and proﬁling using PVDF aﬃnity probe and MALDI-‐TOF MS

Ins,tute of Chemistry, Academia Sinica

NanoCore Research Highlights

(12)

NanoCore Research Highlights (cont’d)

Invited Review Ar$cle

Materials Today, 14(12), 526 (2011) Developments in nanocrystal memory

Department of Physics, Na,onal Sun Yat-‐Sen University

Cover Story

Dalton Transac,ons, 41, 723 (2012)

A 3D α-‐Fe₂O₃ nanoﬂake urchin-‐like structure for electro-‐magne,c wave absorp,on

Department of Chemical Engineering, Na,onal Chung Cheng University

Science ,334, 629 (2011)

Porphyrin-‐Sensi,zed Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Eﬃciency

Department of Chemistry and Center of Nanoscience and Nanotechnology, Na,onal Chung Hsing University

Department of Applied Chemistry and Ins,tute of Molecular Scinece, Na,onal Chiao Tung University

(13)

u  What has Nanotechnology done for Sciences and Society ?

Ø  For Sciences

²  New Insights into: Quantum phenomena;

Atomic assembly; Interactions among biology and physical sciences; New

tools—Atomic manipulation, bioimaging...

Ø  For Society

²  New Technology for: Biomedical

applications; Daily life applications;

Agriculture; Energy; Water;

Environment; New industries….

(14)

14

An Example: Development in High Temperature

Superconductivity—My

Personal Journey

(15)

15/45

75 yrs

(16)

16

Discovery of Tc > 77K SC

(17)

Schematic phase diagram of high-Tc superconductors showing hole doping right side and electron doping left side. From

Damascelli et al., 2003.

(18)

The Best Accomplishments

"   Triumph of Physicists, Chemists and Material Scien,sts

MgB₂

Rb Dopded C₆₀ Na_xCoO₂‧．yH₂O

(19)

FeSe system

•  Structure type: B10, anti-PbO

•  Pearson symbol: tP4

•  Space group: P4/nmm, No. 129

•  a= 3.783, C= 5.534

•  Fe 2a x=0 y=0 z=0

•  Se 2c x=0 y=1/2 z=0.26

(20)

1^st Fe-based SC Found in Japan

2^nd Fe-based SC Found in

Germany 3^rd Fe-based SC

Found in Taiwan

4^th Fe-based SC Found in China

Fe-based superconductors all discovered in 2008

The common Features in Fe-based superconductors

(21)

0 50 100 150 200 250 300 0

2 4 6 8 10 12

2 4 6 8 10 12 14 16

0.0 0.4 0.8 1.2 1.6 2.0

F eS e_0.88 crys tal

Resistance (10−2 Ω)

T (K )

Resistance(10−2Ω)

T(K )

0T 1T 3T 5T 7T 9T

!;"

"

A':F"B"

"

" "

(CaPr)FeAs 122

From B. Lv et al.

The common Features in Fe-based superconductors?

(22)

0 50 100 150 200 250 300 350 -40

-30 -20 -10 0 10 20

S ee be ck Co ef ficie nt ( µ V /K )

Temperature (K)

Thermopower of FeSe

The common Features in Fe-based superconductors

(23)

Thermopower of PnicIdes

F-‐ doped 1111 , LaFeAsO1-‐xFx, x=0, 0.1

From Prof. Z.A.

Xu

!f"

"

A':F";"

"

" "

From Prof. C.W. Chu

Electron‐Doped CaFe2As2

(24)

Thermoepower of K _1-x Fe _2-y Se ₂ in three regimes

From Prof. X. H. Chen

(25)

0 50 100 150 200 250 300 0.0

0.3 0.6 0.9 1.2 1.5

1.8 FeSe

_0.82

ρ (m Ω− cm)

T(K)

3 6 9 12

0.0 0.1 0.2

ρ(mΩ−cm)

T(K)

H=0,1, 3, 5, 7, 9T

0.4 0.6 0.8 1.0 0

4 8 12

Hc2(0)~17.9T ξ₀(0)~43 ang.

Hc2(T)

[T/Tc(H=0)]²

0 20 40 60 80 100 120 140

90.0 90.1 90.2 90.3

3.766 3.768 3.770 3.772 3.774 3.776 3.778

5.506 5.508 5.510 5.512 5.514 5.516

γ (degree)

T (K )

a c

M.K. Wu et al., Physica C., 2009 RT

6K Simulation

(26)

McQueen et al., PRL 2009

The Structural Phase Transition in Fe

_1+x

Se

(27)

(001) (221) 70.4170

LT HT

No LT Distortion,

No Superconductivity!

(28)

Femtosecond optical pump-probe spectroscopy

Optical pump

Optical probe

Optical Reflectivity Change ΔR/R (t)

Photon

E(k)

E_f Free carrier

absorption Interband

transition

FeSe Substrate Pump/probe = 400/800 nm

(corresponding to probe of Fe 3-d orbital) Pump fluence = 5.3 µJ/cm

²

(measurement was done under the perturbation regime)

(29)

0 100 200 300 4

6 8 10 12 14 16

Temperature (K) τ slow(ps)

10 100

1 2 3 4 5

A_step

Temperature (K) 106 A fast , A step

A_fast

300

0 50 100 150 200

0.8 1.0 1.2 1.4 0.0 0.5 1.0

fnorm

Temperature (K) Ap, norm

Correlation between different dynamics at T = 80~130 K

80 K 130 K

Indication of spin fluctuation Indication of optical absorption

A_fast:

gap-like feature

τ_slow:

carrier-phonon thermalization

130 K

130 K 80 K

0 20 40 60 80 100 120 140

90.0 90.1 90.2 90.3

3.766 3.768 3.770 3.772 3.774 3.776 3.778

5.506 5.508 5.510 5.512 5.514 5.516

Gamma value (degree)

Temperature (K) a c

Wen, et al., PRL 108, 267002 (2012)

(30)

Relation between all clues obtained by optical pump-probe

Change of shear stiffness

Nematic

spin fluctuation

Reduction of

Optical absorption

Reduction of DOS near E_F

Prolongation of ps c-p thermalization

Emersion of sub-ps quasiparticle relaxation

Gap opening near E

_F

T ~(80)-130 K T ~80-130 K T ~80 K, T ~130 K T ~130 K

Spin fluctuation and modification of electronic band structure develop at/near the temperature of structural phase transition.

Wen, et al., PRL 108, 267002 (2012)

(31)

31

-2 0 2 4 6 8 10 12 14 16

5 10 15 20 25 30 35 40

T C (K)

Pressure (GPa)

Present Tonset) Tanaka

Cava(Tonset) Guidline Guidline Guidline

Mizuguchi Y et al., APL, 2008; Medvedev, S et al., NAT. MATER., 2009

Pressure Effect on FeSe

C.Q. Jin et al., unpublished

0 50 100 150 200 250 300

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

R(om)

T (K )

0.3G P a 0.5G P a 1.3G P a 2.3G P a 3.4G P a 3.9G P a 4.4G P a

in ab plane

(32)

0 50 100 150 200 250 300 0

2 4 6 8 10 12

2 4 6 8 10 12 14 16

0.0 0.4 0.8 1.2 1.6 2.0

T (K )

Resistance(10−2Ω)

T(K )

0T 1T 3T 5T 7T 9T

!;"

"

A':F"B"

"

" "

(CaPr)FeAs 122

From B. Lv et al.

Resistivity of FeSe & (CaPr)FeAs

(33)

Electrical Resistivity of FeSe—Suggest the existence of higher Tc phase?

Tm

0 50 100 150 200 250 300

0 2 4 6 8 10 12

2 4 6 8 10 12 14 16

0.0 0.4 0.8 1.2 1.6 2.0

T (K )

Resistance(10−2 Ω)

T(K )

0T 1T 3T 5T 7T 9T

(34)

McQueen et al., PRL 2009

What is the Exact Stoichiometry of Fe

_1+x

Se ?

(35)

35

Y. Mizuguchi and Y. Takano, A Review, 2013

What is the Phase Diagram of Fe

_1+x

Se ?

(36)

Three kinds of Fe selenide superconductors

T_c ~ 33K

~ 48 K at 11 GPa K_1-x Fe_2-ySe₂ (2011) Alkali intercalated FeSe

T_c ~ 9K

~ 36.7 K at 8.9GPa

Bulk FeSe (2008) FeSe monolayer (2012)

on SrTiO₃ substrate

T_c > 30K ~ 65K ? decreasing dimensionality

(37)

Fe vacancy order in K

_1-x

Fe

_2-y

Se

₂

Yan, et al., PRL 106, 087005 (2011)

KFe

_1.5

Se

₂

rhombus-order

K

_0.8

Fe

_1.6

Se

₂

√5 × √5 order

Fe Fe vacancy

(38)

Study of FeSe Nano-‐Structure

•   The unanswered ques$ons led us to speculate that the presence of defects in FeSe is cri$cal to its superconduc$vity

•   Nanostructures provide important insight into the beaer understanding of defects in

materials of interest

•   Techniques to fabricate FeSe nanostructure are well-‐developed and simple

38

(39)

39

Fe was mixed with Se/(SeTe) powder and introduced into a 2 ml stainless steel Swagelok union reactor at room temperature in a N₂-filled glove box.

The filled reactor was closed tightly with another plug and placed at the center of the tube’s furnace.

The temperature of the furnace was raised to 700℃ at a rate of 20℃/min, and the temperature was keep at 700 ℃ for 30 min.

The reactor, heated to 700 ℃ , was gradually cooled (5h) to room temperature and open.

(40)

40

!

(41)

0 50 100 150 200 250 300 1.9x10^-4

2.0x10^-4 2.1x10^-4 2.2x10^-4 2.3x10^-4 2.4x10^-4 2.5x10^-4 2.6x10^-4

ZFC 30 Oe FC 30 Oe

FeTe 0.8 ^S 0.2 - Nanoparticle

T (K)

χ (emu/g*Oe)

Fe-Te-S Nanoparticle

C.C. Chang et al., unpublished

(42)

42

!

21-1 20-1 020

ZA=[102]

growth direction [010]

FeSe-tetragonal a = 3.729 Å

c =5.730 Å ^21-1 _20-1

020 ZA=[102]

21-1 20-1 020

ZA=[102]

growth direction [010]

FeSe-tetragonal a = 3.729 Å c =5.730 Å

Fe-Se-(Te) (tetragonal) Nanowire

(43)

Nanowires, Fe(Te-S/Se)

after electrode patterning

(44)

44

!

Electrical Resistance of Fe-Se-(Te) Nanowires

H.H. Chang et al., submitted

4 6 8 10 12 14 16 18 20 22 24 0

100 200 300 400

500 na nowires

F eT e0.8S 0.2-‐20111115

Resistance (ohm)

T empera ture (K )

(45)

FeSe

_0.9

nanowire

500 nm

200

020

⊗[001]

[100]

1 nm

(100)

3.77Å

FeSe _0.9 nanowire

For all nanowires

the average Se/Fe

ratio is about 1.26

(~ 4/5)

(46)

(a) (b)

(c)

FeSe FeSeTe

FeTeS

⁰ ^0.2 ^0.4_n(1,3,0)^0.6 ^0.8 ¹

(d)

^FeSe_FeSeTe

FeTeS 1(1,3,0)

q = 5

(47)

200 020

000

FeSe Nanowire_20120827-8F_no.2

(48)

FeTeS Nanowire_20120202_no.3

200 020

000

130

(49)

FeSeTe Nanowire_20120207_no.3

200 020

000

130

(50)

200 020

Refs: Nature Physics 8(2012)709.

Electron diffraction of FeSe NPS

⊗[001]

Superlattice structure

(51)

Yan, Gao, Lu, Xiang, PRL 106, 087005 (2011) KFe

_1.5

Se

₂

rhombus-order

K

_0.8

Fe

_1.6

Se

₂

√5 × √5 order Fe Fe vacancy

Fe vacancy order in K _1-x Fe _2-y Se ₂

K is not necessary!!

(52)

Wire 97nm Wire 125nm

20130626_FeSe_Nanowires

(53)

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 0

50000 100000 150000 200000 250000 300000

Resistance (Ω)

Temperatur (K)

20130626_Fe0.8Se_2-probes_125nm_2nA

(54)

20130626_FeSe NW_125nm

d-‐spacing

(Å) degree to

spot#1 (h k l) d-‐spacing (Å)

Refs. degree to spot#1 refs.

1 1.988 0.00 (2, 0, 0) 1.885 0

2 2.773 45.43 (1, 1, 0) 2.666 45

3 1.955 89.34 (0, 2, 0) 1.885 90

4 2.791 134.47 (-‐1, 1, 0) 2.666 135

1 2

3 4

⊗[001]

_tet.

(Ref: J. Phys. Chem. Solids 71(2010)495)

Fe

₄

Se

₅

(55)

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 1800

1900 2000 2100 2200 2300 2400 2500

Resistance (Ω)

Temperature (K)

20130626_Fe0.8Se_2-probes_97nm_2nA

(56)

20130626_FeSe NW_97nm

d-‐spacing

(Å) degree to

spot#1 (h k l) d-‐spacing (Å)

Refs. degree to spot#1 refs.

1 1.265 0.00 (0, -‐3, 1) 1.225 0

2 1.054 33.31 (2, -‐3, 1) 1.027 33.02

3 1.946 88.83 (2, 0, 0) 1.885 90

4 1.066 146.60 (2, 3, -‐1) 1.027 146.98

5 1.200 18.12 (1, -‐3, 1) 1.165 18

1

2

3

4

⊗[013]

_tet.

5

(Ref: J. Phys. Chem. Solids 71(2010)495)

~Fe

₂₄

Se

₂₅

(57)

20130321_Fe

_1.05

Se_700 ℃-50 h-quenching

Se

Amprphous Iron oxide nanoparticle

Se Se

Fe Fe

Se

0 5 10 15

keV

Full Scale 627 cts Cursor: 4.779 (8 cts) Spectrum 1

Fe:Se : 52:48

(58)

MT of FeSe nano-particle

S2, H perpendicular to c

T

_m

~ 50 - 100 K

S1, H along c

0 50 100 150 200 250 300 20

30 40 50

ZFC FC

Moment (10-5 emu/g.Oe)

Temperature (K)

~ 55K

FeSe nanosheet

H // C

0 50 100 150 200 250 300 0

20 40 60 80

ZFC FC

Moment (10-5 emu/g.Oe)

Temperature (K)

~ 105 K

FeSe nanosheet

H ⊥ C

The stoichiometry is Fe ₄ Se ₅

(59)

Resistivity of FeSe nanosheet

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0

2 4 6 8 10 12

Sample 1 Sample 2 Sample 3

Ln Resistance (a.u.)

Temperature (T^-1/3) FeSe nanosheet

~ 80 K

0 50 100 150 200 250 300 0

10000 20000 30000 40000

Sample 1 Sample 2 Sample 3

Resistance (Ω)

Temperature (K) FeSe nanosheet

10 Ω

T

_σ

~ T

_m

!

Structure/magnetic transition around 80 K?

Fe vacancy scattering induced VRH?

(60)

β-Fe₄Se₅(square: √5×√5) Fe

Se

with twinned superstructure with forbidden reflections at h00, 0k0, h odd, k odd.

?

β-Fe

₄

Se

₅

→ √5×√5

ZA = [001] ZA = [001] ZA = [001]

q₁ = (1/5, 3/5, 0) q₂= (3/5, 1/5, 0)

(61)

β-Fe

₃

Se

₄

→ √2×√2 with d

₁₀₀

shift every other plane

ZA = [-131] ZA = [-121] ZA = [-111] ZA = [010]

simulated kinematical electron diffraction patterns

q

₃

= (1/2, 1/2, 1/2)

(62)

β-Fe₉Se₁₀ → √10×√10 with twin and with ½d₃₁₀ shift every other plane

ZA = [-101] ZA = [-212] ZA = [-111] ZA = [-121]

simulated kinematical electron diffraction patterns

q₄= (2/5, 1/5, 0) q₅= (1/5, 2/5, 0)

(63)

Fe-vacancy I-cell

β-Fe

₉

Se

₁₀

→ √10×√10 with twin and with

½d

₃₁₀

shift every other plane

Fe Se

β-Fe₉Se₁₀ with twinned superstructure d₃₁₀

a b c

(64)

β-Fe

_1-x

Se

₄

(x = ?) unknown superstructure ZA=[1-13]

ZA=[1-12] ZA=[001]

(65)

β-Fe₁Se₂ β-Fe₂Se₃ β-Fe₃Se₄ (stripe)

β-Fe✔ ₃Se₄ (rhombus: √2×2√2) β-Fe✔ ₃Se₄ (square: √2×√2) β-Fe✔ ₄Se₅(square: √5×√5) Fe Fe vacancy ✔ have been observed experimentally

(66)

β-Fe₅Se₆ β-Fe₅Se₆ β-Fe₆Se₇

β-Fe₇Se₈ (square: 2×2) ^β-Fe₇✔ ^Se₈ (parallelogram: √8×√10) β-Fe✔ ₉Se₁₀ (square: √10×√10)

Fe Fe vacancy ✔ have been observed experimentally

(67)

0 50 100 150 200 250 300 -‐2

-‐1 0 1 2 3 4 5 6

20130415_F e_1.05S e_5.1mg _700ºC

Z F C @ 20O e F C @ 20O e

χ(10-‐4 emu/g*Oe)

T empera ture (K )

0 10 20

0.0000 0.0002 0.0004

χ(10-‐4 emu/g*Oe)

T emperature (K )

700 ℃-7 h-quenching

SC. Ratio: 3.5%

(68)

0 50 100 150 200 250 300 0.0

0.5 1.0 1.5 2.0 2.5

20130226_#-22-1_K2Fe4.1Se5_7.5mg

χ (10-4 emu/g*Oe)

T (K)

ZFC@30 Oe FC@30 Oe

T

_c

~ 30K

0 50 100 150 200 250 300

3 4 5 6

7 #22-5_K2Fe4.1Se5-400oC quench_15mg

χ (10-4 emu/g*Oe)

T (K)

ZFC@30 Oe FC@30 Oe

400

^o

C quench 750

^o

C quench

0 50 100 150 200 250 300

-6 -4 -2 0

20130307_#22-8_K2Fe4.1Se5_7mg

χ (10-4 emu/g*Oe)

T (K)

ZFC@30 Oe FC@30 Oe

750

^o

C quench

14 16 18 20 22

2.8 3.0 3.2

Intensity (a.u.)

2θ (degree)

#22-1 #14-2

14 16 18 20 22 24

2.6 2.8 3.0 3.2

Intensity (a.u.)

2θ (degree)

#22-5 #14-2

14 16 18 20 22

2.6 2.8 3.0 3.2

Intensity (a.u.)

2θ (degree)

#22-8 #14-2

* * FeSe(t) *

K-Fe-Se

(69)

•  Possible types of Fe-vacancy order

•  Samples:

–  β-Fe_1-xSe from potassium removal of K_1-xFe_2-ySe₂ bulk/crystal –  β-Fe_1-xSe nanosheets via an aqueous chemical route

–  β-Fe_1-xSe small crystal from a high-pressure route

•  β-Fe

₃

Se

₄

(x = 0.25) → √2×√2

•  β-Fe

₄

Se

₅

(x = 0.2) → √5×√5

•  β-Fe

₉

Se

₁₀

(x = 0.1) → √10×√10

Summary of Fe-vacancy

(70)

70

Fe-vacancy order

AFM regime Tetragonal Fe-Se

Orthorhombic Fe-Se

Superconducting Fe

_a’

Se

_b’

t-Fe

_a

Se

_b

Proposed Phase Diagram of Fe-Se

(71)

Schematic phase diagram of high-Tc superconductors showing hole doping right side and electron doping left side. From

Damascelli et al., 2003.

(72)

Summary

•  A new phase diagram for Fe-chalcogenides is proposed—Needs further confirmation

—detailed studies by annealing nanowires (or nanoparticles) of different compositions

•  All observed anomalies from transport, magnetic, and optical measurements can

possibly associate with orbital modification and gap opening—needs theoretical support

72

(73)

73

(74)

Study of FeSe Superconductor as an example

M. K. Wu

Na$onal Dong-­‐Hwa University

Institute of Physics, Academia Sinica

What have we learned from Nanosciences—

Study of FeSe Superconductor as an example

What we have advanced in

Sciences, and how?

Establishment of Core Facili$es

Academic centers are located at the Academia Sinica, Na,onal Taiwan University, Na,onal Tsing Hua University, Na,onal Chiao Tung University, Na,onal Chung Cheng University, Na,onal Cheng Kung University, Na,onal Sun Yet-­‐Sen University, and Na,onal Dung Hua University.

A biomedical nano-­‐imaging center was also set up in 2007.

These core-­‐facility centers provide professional

services that signiﬁcantly enhance eﬀorts to sa$sfy

needs of academic and industrial R&D.

Core Facili$es Progrm

1-D Functionalized Integrated Systems

The violation of the Stokes–Einstein relation in supercooled water

B

Abstract

I

Mesoporous silica as Nanocarriers

GaN Nanorod Array for White-­‐light LED

Appl. Phys. LeH. 97, 073101 (2010)

Creating Monodispersed Ordered Arrays of Surface-Magic- Clusters and Anodic Alumia Nanochannels by Constrained

Self-organization

NanoCore Research Highlights

NanoCore Research Highlights (cont’d)

u What has Nanotechnology done for Sciences and Society ?

Ø For Sciences

² New Insights into: Quantum phenomena;

Atomic assembly; Interactions among biology and physical sciences; New

tools—Atomic manipulation, bioimaging...

Ø For Society

² New Technology for: Biomedical

applications; Daily life applications;

Agriculture; Energy; Water;

Environment; New industries….

An Example: Development in High Temperature

Superconductivity—My

Personal Journey

75 yrs

Discovery of Tc > 77K SC

The Best Accomplishments

" Triumph of Physicists, Chemists and Material Scien,sts

FeSe system

Fe-based superconductors all discovered in 2008

The common Features in Fe-based superconductors

The common Features in Fe-based superconductors?

S ee be ck Co ef ficie nt ( µ V /K )

Temperature (K)

Thermopower of FeSe

The common Features in Fe-based superconductors

Thermopower of PnicIdes

From Prof. Z.A.

Xu

From Prof. C.W. Chu

Thermoepower of K 1-x Fe 2-y Se 2 in three regimes

From Prof. X. H. Chen

0 50 100 150 200 250 300 0.0

0.3 0.6 0.9 1.2 1.5

1.8 FeSe

ρ (m Ω− cm)

T(K)

a c

The Structural Phase Transition in Fe

Se

LT HT

No LT Distortion,

No Superconductivity!

Femtosecond optical pump-probe spectroscopy

FeSe Substrate Pump/probe = 400/800 nm

(corresponding to probe of Fe 3-d orbital) Pump fluence = 5.3 µJ/cm

(measurement was done under the perturbation regime)

Correlation between different dynamics at T = 80~130 K

Relation between all clues obtained by optical pump-probe

Gap opening near E

Pressure Effect on FeSe

Resistivity of FeSe & (CaPr)FeAs

Electrical Resistivity of FeSe—Suggest the existence of higher Tc phase?

What is the Exact Stoichiometry of Fe

Na$onal Dong-‐Hwa University

Academic centers are located at the Academia Sinica, Na,onal Taiwan University, Na,onal Tsing Hua University, Na,onal Chiao Tung University, Na,onal Chung Cheng University, Na,onal Cheng Kung University, Na,onal Sun Yet-‐Sen University, and Na,onal Dung Hua University.

A biomedical nano-‐imaging center was also set up in 2007.

These core-‐facility centers provide professional

GaN Nanorod Array for White-‐light LED

u  What has Nanotechnology done for Sciences and Society ?

Ø  For Sciences

²  New Insights into: Quantum phenomena;

Ø  For Society

²  New Technology for: Biomedical

"   Triumph of Physicists, Chemists and Material Scien,sts

Thermoepower of K _1-x Fe _2-y Se ₂ in three regimes

Study of FeSe Nano-‐Structure

•   The unanswered ques$ons led us to speculate that the presence of defects in FeSe is cri$cal to its superconduc$vity

•   Nanostructures provide important insight into the beaer understanding of defects in

•   Techniques to fabricate FeSe nanostructure are well-‐developed and simple

FeTe 0.8 ^S 0.2 - Nanoparticle

FeSe _0.9 nanowire

Fe vacancy order in K _1-x Fe _2-y Se ₂