Study of FeSe Superconductor as an example

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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

FeSe0.9  nanowire

500  nm

[100]

(2)

2

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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

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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 TH 235 K. In

particular, the dynamical parameters of water can be measured down to 180 K, approaching the suggested glass transition temperature Tg 165 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 NaxCoO2‧.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)

1st Fe-based SC Found in Japan

2nd Fe-based SC Found in

Germany 3rd Fe-based SC

Found in Taiwan

4th 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 e0.88  crys tal  

Resistance (102 Ω)

T  (K )

 

 Resistance(102Ω)

 

 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)

Ef 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

Astep

Temperature (K) 106 A fast , A step

Afast

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

Afast:

gap-like feature

τslow:

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 EF

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

 

F eS e0.88  crys tal  

Resistance (102 Ω)

T  (K )

 

 Resistance(102Ω)

 

 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

 

F eS e0.88  crys tal  

Resistance (102 Ω)

T  (K )

 

 Resistance(102 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

Tc ~ 33K

~ 48 K at 11 GPa K1-x Fe2-ySe2 (2011) Alkali intercalated FeSe

Tc ~ 9K

~ 36.7 K at 8.9GPa

Bulk FeSe (2008) FeSe monolayer (2012)

on SrTiO3 substrate

Tc > 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]

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 0.4n(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-Fe7Se8 (parallelogram: √8×√10) β-Fe9Se10 (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 e1.05S 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-Fe1-xSe from potassium removal of K1-xFe2-ySe2 bulk/crystal –  β-Fe1-xSe nanosheets via an aqueous chemical route

–  β-Fe1-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)

Figure

Updating...

References

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