Collin Broholm
Johns Hopkins Institute for Quantum Matter
Superconductivity & spin fluctuations
CeCoIn5
― Spin resonance
―ZEEMAN effect
― Condensation energy
 FeSexTe1-x
― Spin resonance
― Competition for momentum space
Conclusions

CeCoIn5 (PRL 100, 087001 (2008))
―
―
―
―

ISIS
IQM-JHU
NIST
BNL
FeSe0.4Te0.6 (PRL 103, 067008 (2009))
―
―
―
―
―
―
―
―
―
―

C. Stock,
Y. Zhao,
H. J. Khang,
C. Petrovic,
Funding:
Y. Qiu,
W. Bao,
Y. Zhao,
V. Stanev,
Y. C. Gasparovic,
S. Chang,
J. Hu,
B. Qian,
M. Fang,
Z. Mao,
NIST
Remnin Univ.
IQM-JHU
IQM-JHU
NIST
NIST
Tulane U.
Tulane U.
Tulane U.
Tulane U.
FeSe0.4Te0.6 (Unpublished)
―
―
―
―
W. Bao,
V. Thampy
J. Wen
J. Rodriguez
Remnin U.
IQM-JHU
IQM-JHU
NIST
Neutrons:
Fisk, Thompson, Petrovic,…
CeCoIn5 : HF superconductor Tc=2.3 K
CeIrIn5 : HF superconductor Tc=0.38 K
CeRhIn5 : HF Antiferromagnet TN=3.8 K
Nicklas etetal.al(2007)
Kenzelmann
(2008)
CaFe2As2



CeCoIn5
CeCoIn5

~300×10 mm2 x-tals
Fixed by Fomblin H-free
pump oil
Edge aligned
3o FWHM mosaic
Qc   12 12 12 
c  7 1 Ǻ
ab  10 1 Ǻ
Normal State: relaxation
  0.30  0.15 meV
Superconductor: Resonance
0  0.60  0.03 meV
  0.1 meV
TT(Kelvin)
(Kelvin)
4/14/2008
Resonance
energy is
less
T-dependent
Increased
Damping
largest
effect
expected
for9TD(T)
ofthan
heating
through
c
Bulut & Scalapino (1993)
 12 12 12 
Resonance in CeCoIn5
D p  Qc   D p 
D  p   px2  py2
Zero-moment sum-rule (Scalapino & White, Demler & Zhang ):
S R  S R

3
d 3q

d 
   q  cos q  R  R
2 
4  g B  0  q
q
First-moment sum-rule (Hohenberg & Brinkman):

2
 S
0

 q  d 
1
2
 S q ,H , S  q 



To use it we must know the form of the spin Hamiltonian
H 4f  H K  H RKKY  H CF
Kondo:
1
2
 S q ,H K , S q    H K



Crystal field
1
2
H CF  nm BnmOnm
 S z q ,H CF , S z q    12 H CF



RKKY Exchange
1
2
H K  K  R s  R   SR
H RKKY  RR J RRSR  SR
 S q ,H RKKY , S q   2  J RRSR  SR 1  cos q   R  R 

RR


S  q 
Changes in near neighbor
RKKY exchange dominate
through TC
Compare:
D H RKKY 

2
4  g B
To net condensation energy
c
 DTr    q ,  d


0
2
0
T
Tref
0
0
DE T    C T  dT 
 C T  dT
T
10 K
0
0
DE T    C T   dT  
H RKKY 

2
4  g B
 C T  dT 
c
Tr    q  d


2
0

Appearance of qdependent resonance
indicates energy
reduction through RKKY

The correlation length
however does not
change substantially
~20 mm
Hsu F et al. PNAS 2008;105:14262-14264
Z. Mao et al. (2009)
Qiu et al. PRL (2009)
FeSe0.4Te0.6

Superconducting CeCoIn5 and FeSeTe both have spin resonance
excitations at similar reduced energies

Heavy Fermion CeCoIn5:
― First moment sum-rule indicates d-wave superconductivity is
stabilized by a reduction of RKKY exchange energy
― ZEEMAN splitting indicates a spin-doublet resonance

Iron superconductor FeSe0.4Te0.6:
― Complex Wave vector dependence in indicates competing nesting
instabilities
― Frozen short range spin correlations coexist in the optimally doped
sample but are unaffected by superconductivity.

Detailed characterization of the field and wave vector
dependence of the spin resonance in a range of magnetic
superconductors is needed to elucidate its significance