Title: Electron-doped%20Cuprates
1 Electron-doped
Cuprates
R. L. Greene
University of Maryland Center for
Superconductivity Research
Collaborators
Yoram Dagan---UMd
Amlan Biswas-------UMd/UFl Hamza
Balci---------UMd Mumtaz Qazilbash--UMd
Patrick Fournier----Sherbrooke Girsh
Blumberg----Lucent, Bell Labs
2OUTLINE
- Background on Cuprates
- phase diagram
- Normal State Properties
- evidence for a QCP under the SC dome
- pseudogap issues
- nature of the ground state
- SC state
- pairing symmetry as a function of doping
3Phase diagram of electron- and hole-doped cuprates
(La,Pr,Nd)2-xCexCuO4-y
La2-xSrxCuO4-y
4Theoretical Phase Diagrams
TMF
T? max
Quantum critical region
T
T
Pseudogap
Ordered (pseudogap)
Disordered (Fermi liquid)
Tc
x
QCP
x
5Transport evidence for a Quantum Phase Transition
and QCP
For details see Dagan et al., Cond-mat/0310475
6Résistivité
? T2
? T
YBCO J.M. Harris et al., Phys.Rev. B 46, 14293
(92).
LSCO B. Batlogg et al., J. Low Temp. Phys. 95,
23 (94).
PCCO nos travaux sur couches minces...
7Resistivity vs doping
8? ?0 AT?
x0.17
9? ?0 AT?
10ab-plane resistivity for Pr2-xCexCuO4 films with
HgtHc2
Fournier et al., PRL 81,4720 (98)
11? T2
12Hall vs H
X0.17
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17Tmin(K)
18ARPES Nd2-xCexCuO4
N.P. Armitage et al. PRL 88 257001 (2002).
19- Linear in T resistivity is expected above a 2D
AFM to paramagnetic - metal QCP. Other powers of T would be expected
at nearby - dopings because of fitting the data over a low
temperature - Fermi Liquid T2 regime and the quantum critical
regime at higher - temperature. This is exactly the behavior we
find! - The lowest temperature Hall Coefficient shows a
kink at the same - doping (within error) as the linear in T
resistivity. This is strong - confirming evidence of the QCP.
- ARPES shows a drastic change in the Fermi surface
near the - same doping.However, the ARPES doping
resolution is not as - good as our transport data.
- The doping dependence of the low energy pseudogap
( to be shown in - a few slides) is consistent with the QCP
scenerio from transport.
20Pseudogap
High Energy (100mev)----- optics, Raman,
ARPES Low Energy (5meV) --------tunneling,
Raman
21Conductivity
Y. Onose et al. PRL 87 217001 (2001).
22Break junction between PCCO (x0.15) and Ag
H0, Superconducting state
H9 T ( c-axis), Normal state
2?SC
Normal state gap (NSG)
SC gap clearly seen
- Not residual SC at interface
- Not effect of tunnel barrier
Biswas et al., PRB 64, 104519 (2001)
23Grain Boundary Tunneling
Alff et al., Nature 422, 698 (2003)
24Nature of the Ground State
25Magnetism
Kang et al., Nature 423, 522 (2003)
Antiferromagnetic Order as the Competing Ground
State in electron-doped Nd1.85Ce0.15CuO4
They find TN37K for HgtHc2
AF order different than for undoped parent NCO
Sonier et al., PRL 91, 147002 (2003)
Antiferromagnetic order in the vortex cores
of Pr1.85Ce0.15CuO4
26Violation of Wiedemann-Franz law
R.W. Hill et al. NATURE 414 711 (2001).
Pr1.85Ce0.15CuO4 Crystal
27NMR in PLCCO
Zheng et al., PRL 90, 197005 (2003)
Fermi Liquid GS
No pseudogap
28Pairing Symmetry of Superconducting State
29For n-doped cuprates
Disagreements even for optimally doped compounds
- Penetration depth
- Kokales et al., PRL 85, 3696 (2000), Prozorov et
al., PRL 85, 3700 (2000) - ARPES
- Armitage et al., PRL 86, 1126 (2001) Sato et
al., Science 291, 1517 (2001) - Tricrystal experiment
- Tsuei et al., PRL 85, 182 (2000)
- Raman scattering
- Blumberg et al., PRL 88, 107002 (2002)
- Specific heat
- Balci et al., PRB 66, 174510 (2002)
d-wave
- Penetration depth
- Alff et al., PRL 83, 2644 (1999) Kim et al.,
PRL 91, 087001 (2003) - Skinta et al., Phys. Rev. Lett. 88, 207003 (2002)
- Tunneling spectroscopy Kashiwaya et al., PRB
57, 8680 (1998) Alff et al., PRB
58, 11197 (1998).
s-wave
30To distinguish between d-wave and s-wave by
tunneling spectroscopy
s-wave
d-wave (110) direction
Blonder, Tinkham and Klapwijk (BTK) Phys. Rev. B
25, 4515 (1982)
Tanaka and Kashiwaya Phys. Rev. Lett. 74, 3451
(1995)
Z 0 ? barrierless contact between N and S Z ? 1
? tunneling limit
N
S
Barrier strength Z
31Evidence for a transition from d-wave to s-wave
pairing symmetry in Pr2xCexCuO4
32How to differentiate s- wave and d-wave
- Use the different field dependence
- of Cel in s-wave and d-wave.
- In the temp and field range of our experiment, if
- s-wave Þ CelµH
- d-wave Þ
- CelµH1/2 in the clean limit
- G. E. Volovik, Pisma Zh. ksp. Teor. Fiz. 58,
457 (1993) JETP Lett. 58, 469 (1993). - CelµH log(H) in the dirty limit
- C. Kubert and P. J. Hirschfeld, Solid State
Commun. 105, 459 (1998)
33Temperature dependence
x 0.15
- Global fitting of the form C/T??T2 gives
- ?N 6.7 0.5 mJ/mole K2 (intercept of 10 T
data) - ?(0) 1.4 0.2 mJ/mole K2 (intercept of 0 T
data)
34Comparison with different theoretical predictions
Balci et al. PRB 66, 174510 (02)
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36s-wave theory C(H) ? ?nTH/Hc2? slope
?2.52/41.3 mJ/mole KT
372D excitation in optimally doped NCCO crystal
Tc22 K
G. Blumberg et al, PRL 88, 107002 (2002)
38Raman spectra of overdoped NCCO crystal (Tc 14K)
39Isotropic gap in overdoped NCCO crystal
40d- to s-wave transition l-2(T)
J.A. Skinta et al. PRL 88 207003 (2002) PRL 88
207005 (2002).
l-2(T) T2 -gt Exp(-D/T)
41ARPES Nd2-xCexCuO4
N.P. Armitage et al. PRL 88 257001 (2002).
42Theoretical explanation of a symmetry change in
n-doped cuprates
-
43The antiferromagnetic spin fluctuations (ASF)
peaked at the wave vector Q (?,?) are
responsible for d-wave superconductivity The
interaction via ASF has the highest strength at
the so-called hot spots, the points on the Fermi
surface connected to each other by the vector Q.
the interaction via ASF is repulsive in the
singlet channel
44-
-
-
-
d-wave symmetry for hole doped
45electron-doped case at low doping
-
-
-
-
46electron-doped in the high doping regime
-
-
-
-
47Doping dependence
48SUMMARY
- QCP scenario seems to be valid in n-type
- Kink in RH and ? T1 at xc 0.165
- d- to s-wave symmetry change near xc
- Pseudogaps in n- and p-type are different
- Significance of subtle differences in n- and
p-type properties not yet clear