Radiation damaged MgBRadiation damaged MgB22: a : a comparison with A15 comparison with A15 superconductorssuperconductors
Marina Putti
CNR-INFM LAMIA and University of Genoa, Italy
ASC, NHMF, Florida State University, Tallahasse
Ruggero Vaglio CNR-INFM and University of Naples, Italy
John Rowell School of Materials, Arizona State UniversitySupercond. Sci. Technol. 21 (2008) 043001
FermiLab, April 30, 2009
MotivationMotivation
Tc0 (K) N(0) (states/eV cell)
V3Si 17 15 1.1Nb3Sn 18 12 1.44Nb3Ge 22 8 1.8Nb3Al 18.6 15 1.6MgB2 39 0.71 0.7
MgB2 vs A15 High Tc superconductors with conventional e-ph coupling
Radiation experimentsTo investigate superconducting mechanisms To increase of superconducting properties
bandsbands 2D , hole-like
strongly coupled with ph: ~~11
Large energy gap: 7 meV 7 meV
bandsbands 3D, one electron, one hole-like
weakly coupled with ph: ~~0.30.3
Large energy gap: 2 meV 2 meV
Brief Remarks on MgB2
M. Iavarone et al. PRL 89, 187002 (2002)
The existence of more parameters (Ni , ijij) allows a larger Tc in respect to the isotropic system
In a two-band s/c interband scattering In a two-band s/c interband scattering mixes strong mixes strong --pairspairs with weak with weak -pairs -pairs andand causes pair breaking.causes pair breaking. A.A.Golubov and I.I.Mazin, PRB 55 (1977)
Role of disorderRole of disorder
In the strong scattering limitThe critical temperature is expected to decrease down to a saturation value 19-25 K19-25 KThe energy gaps should merge to the BCS value 3.563.56
O.V. Dolgov et al. PRB 72, 024504 (2005)
Interband scattering affects Interband scattering affects TTcc and and two-gap naturetwo-gap nature of of
superconductivitysuperconductivity
andandbandsbandshave have different parity different parity Interband Interband scattering is suppressedscattering is suppressed
OutlineOutline1.1. Irradiation Experiments Irradiation Experiments 2.2. Tc vs residual resistivity behaviourTc vs residual resistivity behaviour3.3. Upper critical fieldUpper critical field4.4. Specific heatSpecific heat5.5. Temperature dependence of resistivity Temperature dependence of resistivity 6.6. Energy Gap Energy Gap 7.7. Theoretical model for the degradation of Theoretical model for the degradation of
superconducting propertiessuperconducting properties8.8. ConclusionsConclusions9.9. AcknowledgmentsAcknowledgments
All the results are systematically compared with similar experiments performed in the past on A15 superconductors.
1. Irradiation 1. Irradiation ExperimentsExperiments
2 MeV 4He irradiation experiments:Gandikota R et al 2005 Appl. Phys. Lett. 86 012508 Gandikota R et al 2005 Appl. Phys. Lett. 87 072507
Neutron irradiation experiments: Kar’kin et al 2001 JETP Lett. 73 570 Eisterer et al 2002 Supercond. Sci. Technol. 15 L9 Wang et al 2003 J. Phys. Condens. Matter 15 883 Zehetmayer et al 2004 Phys. Rev. B 69 054510 Putti et al 2005 Appl. Phys. Lett. 86 112503 Tarantini et al 2006 Phys. Rev. B 73 134518 Wilke et al 2006 Phys. Rev. B 73 134512 Ferrando et al 2007 J. Appl. Phys. 101, 043903
Sweedler et al 1974 Phys. Rev. Lett. 33 168 Sweedler et al 1978 J. Nucl. Mater. 72 50 Poate et al 1976 Phys. Rev. Lett. 37 168 Ghosh A K and Myron Strongin 1980 Superconductivity in d- and f-Band Metals 305Wiesman et al 1978 J. Low Temp. Phys. 30 513Rowell J M and Dynes R C “Bad metals, good Superconductors”Alterovitz et al 1981 Phys. Rev. B 24 90Noolandi J and Testardi L R 1977 Phys. Rev. B 15 5462Sweedler A R and Cox D E 1975 Phys. Rev. B 12 147 Cox D E and Tarvin J A 1978 Phys. Rev. B 18 22 Burbank R D, Dynes R C and Poate J M 1979 J. Low Temp. Phys. 36 573Testardi et al 1977 Phys. Rev. Lett. 39 716Flukiger R 17th International Conference on Low Temperature Physics-LT-17, Ref. 4, 609Nolscher C and Saemann-Ischenko G 1985 Phys. Rev. B 32 1519Bett R 1974 Cryogenics 14 361Vonzovski S V, Izyumov Yu A and Kurmaev E K 1982 Superconductivity of Transition Metals (Berlin: Springer)Alterovitz S A, et al., 1981 Phys. Rev. B 24 90Karkin A E, Mirmelshtein A V, Arkhipov V E andGoshchitskii B N 1980 Phys. Status Solidi a 61 K117Cort B, Stewart G R, Snead C L Jr, Sweedler A R andMoechlecke S 1981 Phys. Rev. B 24 3794Phys. Rev. Lett. 37 168Ghosh A K, Gurvitch M, Wiesmann H and Strongin M 1978 Phys. Rev. B 18 6116…………
Comparison with Comparison with A15sA15s
3. T3. Tcc vs residual resistivity behaviour vs residual resistivity behaviour
cm
KKK
g
gcor
5.7
)40()300()40(
,0
Rowell criterion
A15sA15s
MgBMgB22
20 K
TTcc/T/Tc0 c0 vs vs
0 25 50 75 100 125 1500.0
0.2
0.4
0.6
0.8
1.0 Nb3Sn
Nb3Ge
V3Si
MgB2
T c/Tc0
0 (cm)
0.0 0.1 0.2 0.3 0.4 0.50.0
0.2
0.4
0.6
0.8
1.0 Nb3Sn
Nb3Ge
V3Si
MgB2
(eV) T
c/Tc0
TTcc/T/Tc0 c0 vs vs
20 p
Comparison with A15sComparison with A15s
0 5 10 15 20 25 30 35 400
10
20
30
40
50
H
c2(0
) (T)
Tc (K)
4He irradiated film4He irradiated film
Gandikota et al n irradiated polycrystals
Tarantini et aln irradiated films
Ferrando et aln irradiated and annealed
wires Wilke et al
4.1 Upper critical field of MgB4.1 Upper critical field of MgB22 : : HHc2c2(0) vs T(0) vs Tcc
irradiated
irr.+ anneal.
HHc2c2(0) vs T(0) vs Tcc/T/Tc0c0
)1)(0(02 N
dTdHc
dHdHc2c2/dT vs T/dT vs Tcc/T/Tc0c0
Comparison with A15sComparison with A15s
DOS dependence on disorderDOS dependence on disorder
)1)(0( N
Sommerfeld Sommerfeld coefficientcoefficient
Slope of HSlope of Hc2c2
02)1)(0(
dTdHN c
Tc0 (K) N(0) (states/eV cell)MgB2 39 0.71Nb3Sn 18 12Nb3Al 18.6 15V3Si 17 15
6.1 Temperature dependence of 6.1 Temperature dependence of ResistivityResistivity
0
20
40
60
80
100
120
0 50 100 150 200 250 300
Temperature (K)
ρ (µ
Ω-c
m)
0
20
40
60
80
100
120
Undamaged
3.0×1016/cm2
4.5×1016/cm2
1.3×1017/cm2
9.3×1016/cm2
7.0×1016/cm2
5.5×1016/cm2
1.3×1016/cm2
V3Si
MgB2
p (eV)
vF (cm/s)
a (Å)
satcm
ph (cm)
phsat
Nb3Sn 4 3×107 5.3 1.8
MgB2
4 4.4×107
30.93
5.9 5.4×107 0.43
av
TT p
Fsat
satideal
1 e wher1)(
1)(
12
20)()(p
ph TT
Parallel resistor model Parallel resistor model
1377115
175450260
0.780.160.06
Fisk Z, Webb G 1976 Phys. Rev. Lett. 36 1084 Gurvitch M 1981 Phys. Rev. B 24 7404
If phph ~~ satsat saturation is expected also without disorder
0 200 400 600 8000
20
40
60
T (K)
(
cm
) Mg1-xAlxB2
Resisivity does not saturate up to 1000 KSame temperature dependence Only – band conduction
6.2 Looking for saturation in MgB6.2 Looking for saturation in MgB22
I.Pallecchi et al., PRB 79, 134508 (2009)
0 50 100 150 200 250 3000.1
1
10
100
4.1x1016 cm-2
4.1x1017 cm-2
7.6x1017 cm-2
3.2x1018 cm-2
1x1019 cm-2
cor (
cm
)
T (K)
2.5x1019 cm-2
(a)
10 1000.01
0.1
1
10
1x1019 cm-2
2.5x1019 cm-2
(b)
ph (
cm
)
T (K)
T3
0)()( TTph
6.3 Temperature dependence of 6.3 Temperature dependence of phph(T)(T)
Only carriers contribute to resistivity
3)( TTph
nph TT )(
cm)
6.3 The Gurvitch plot6.3 The Gurvitch plot
0.0
0.5
1.0
1.5
2.0
P4 Two-Gap
0.0
0.5
1.0
1.5
2.0
P5 Single-Gap
0.0 0.2 0.4 0.6 0.8 1.00.0
0.5
1.0
1.5
2.0 P6 Single-Gap
t
0.0
0.5
1.0
1.5
2.0 P0
Two-Gap contribution contribution
c sc
(t)/T
Incr
easin
g irr
adia
tion
Definitive evidence of merging of the two gaps
The merging takes place at a lower temperature than the 20 K
7.1 Energy gaps in MgB7.1 Energy gaps in MgB22
7. 2 Energy gaps: comparison with A157. 2 Energy gaps: comparison with A15
The reduced gap drops systematically below the BCS value with increasing disorder
8.1 8.1 Theoretical model for the degradation Theoretical model for the degradation of Tof Tcc. .
Testardi-Matteis model: smearing of the Testardi-Matteis model: smearing of the DOSDOS
MgB2
EF
N(E
) (S
tate
s/eV
cel
l)
21
14
7.
0
30
15
0
Nb3SnTOTAL DOS
V3SiTOTAL DOS
N(E) is the density of states
S(E,) is a Lorentian function
is the relaxation rate20
22)'(1),',(
')0,'(),',(),(
p
EEEES
dEENEESEN
)N()(
)(1)()(
where
N
Sommerfeld coefficientSommerfeld coefficient vs
0.0 0.2 0.4 0.6
0.6
0.8
1.0
N3Sn
V3Si
(eV)
N()
/N(0
) -band
-bandMgB2
N(N() vs ) vs
TTcc vs vs in A15 in A15Comparison with experimentsComparison with experiments
V3Si
N(N())
0 20 40 60 80 1000
10
20
30
400.0 0.2 0.4 0.6
T c (K)
0 (cm)
(meV)
Interband +Intraband scattering
Interband scattering
8.2 A model 8.2 A model for for suppression suppression of Tof Tcc in MgB in MgB22
M.Putti et al EPL(2007)
Interband scatteringInterband scattering and two band isotropization
Interband scatteringInterband scattering and two band isotropization
Intraband scatteringIntraband scattering and smearing of the DOS
ConclusionsConclusionsThe comparison between the behavior of damaged
MgB2 and A15s has emphasized:Some similarities :
ConclusionsConclusionsThe comparison between the behavior of damaged
MgB2 and A15s has emphasized:Some similarities Some differences:
9. Conclusions9. ConclusionsThe comparison between the behavior of damaged
MgB2 and A15s has emphasized:Some similarities Some differences Some unclear issues:
HHc2c2(0) vs T(0) vs Tcc 22(0)/k(0)/kBBTTcc vs T vs TccN (1+N (1+)) Energy gapsEnergy gaps
TTcc vs vs 00//satsat~ a/l~ a/l
10.Acknowledgements10.Acknowledgements
P Manfrinetti, A Palenzona, V Ferrando, C Tarantini, P Manfrinetti, A Palenzona, V Ferrando, C Tarantini, I Pallecchi, P.Brotto, M.Tropeano E.Galleani andI Pallecchi, P.Brotto, M.Tropeano E.Galleani andC Ferdeghini at CNR-INFM-LAMIAC Ferdeghini at CNR-INFM-LAMIA
H. U. Aebersold and E. Lehmann at PSIH. U. Aebersold and E. Lehmann at PSI
R Di Capua and P Orgiani at CNR-INFM-Coherentia R Di Capua and P Orgiani at CNR-INFM-Coherentia
X X Xi at PSU X X Xi at PSU
N Newman, R Singh and R Gandikota at ASU N Newman, R Singh and R Gandikota at ASU
B Moeckly at STI B Moeckly at STI
2.1 Defect structure:2.1 Defect structure:Cell parameters vs fluenceCell parameters vs fluenceMgB2
Comparison with A15sComparison with A15s
Defects in A15 (A3B) displacements of A and B
atoms antisite defects (A in place of
B and vice versa)
Defects in MgB2
displacements of Mg and B atoms antisite defects are energetically unfavorable
Tan (°C) Ea (eV)Nb3Sn 450 1.7
750 2MgB2 200 1
400 1.5
2.2 Defect structure: Annealing 2.2 Defect structure: Annealing experimentexperiment
Wilke 2006 Phys. Rev. B 73 134512
Main similarities:Main similarities:
Linear Linear vs T vs Tc c behaviourbehaviour HHc2c2(0) vs T(0) vs Tc c reduced gap vs Treduced gap vs Tcc
Main differences:Main differences:
DOS and its dependence on disorderDOS and its dependence on disorder Two gap featureTwo gap feature
N (1+N (1+)) Energy gapsEnergy gaps
TTcc vs vs 00//satsat
