Hall Effect in Sr14−xCaxCu24O41
E. Tafra1, B. Korin-Hamzić2, M. Basletić1, A. Hamzić1, M. Dressel3, J. Akimitsu4
1. Department of Physics, Faculty of Science, University of Zagreb, Croatia
2. Institute of Physics, Zagreb, Croatia
3. 1. Physikalisches Institut, Universität Stuttgart, Germany
4. Department of Physics, Aoyama-Gakuin University, Kanagawa, Japan
outline introduction to Sr14−xCaxCu24O41
structure → anisotropydistribution of self-doped holes
results (0 ≤ x ≤ 11.5)electrical resistivity vs THall coefficient vs T
discussionestimation of effective number of carriers neff
relation to high-Tc cuprates
structure of Sr14−xCaxCu24O41
isoelectronic substitution of Sr by Ca → change in properties
b=
12.9
Å
a=11.4 Å
A14 Cu2O3 laddersCuO2 chains
cC
chains: ladders: cC=2.75 Å cL=3.9 Å
10·cC≈7·cL≈27.5 Å
cL
ladders and chains structures are incommensurable → intrinsic source of disorder
CuO2 plane
high-Tc 2D cuprates
quasi-1D behaviour: anisotropy of conductivity: c/a 10 , c/b 103 – 104
[T. Vuletić, et al., Phys. Rep. (2006)]
a
c
Sr14−xCaxCu24O41 properties superconductivity occurs for x ≥ 10 under pressure (p = 3-5
GPa) for T ≤ 12 K [Uehara et al., JPSJ (1996)] [Nagata et al., PRL (1998)]
system is intrinsically hole doped: average Cu valence = +2.25 → 6 self-doped holes per f.u.
Ca substitution → holes are transferred from the chains to the ladders
[Osafune et al., PRL (1997)] [Mizuno et al., JPSJ (1997)]
[Motoyama et al., PRB (1997)] [Kato et al., Phys. C (1996)]
precise amount of hole transfer is still under disscusion: experiments give contradictory results
Motivation for Hall effect measurements
number of holes in ladders n:
◊ NEXAFS [Nücker et al., PRB (2000)]
Δ NMR [Piskunov et al., PRB (2005)]
□ optical [Osafune et al., PRL (1998)]
XAS [Rusydi et al., PRB (2007)]
Δ
why Hall effect: long missing basic experiment holes in chains are localized [T. Vuletić, et al., Phys. Rep. (2006)]
in La2-xSrxCuO4: n = V/eRH = x, for small x [Ono et al., PRB (2007)]
resistivity vs temperature
measured in two geometries
j||a and j||c
x ≤ 9: ρ ~ exp(∆ / T)
x = 11.5 (T>80 K): dρa / dT < 0
dρc / dT > 0
change in slope: transition to CDW[Vuletić et al. PRL
(2003)]
Hall coefficient vs temperature geometry:
full symbols:
j||a, B||b empty symbols:
j||c, B||b no difference in RH
dashed lines: scaled ρa
x ≤ 9:
RH ~ exp(∆ / T)
∆ ~ 1000 K (x = 0) to
∆ ~ 100 K (x = 9) solid black line:
RH = V/4ne calculated assuming n=1 hole/f.u.
effective number of carriers
effective number of carriers (●):
neff = V/(4eRH) number of holes in ladders
n:
◊ NEXAFS [Nücker et al., PRB (2000)]
Δ NMR [Piskunov et al., PRB (2005)]
□ optical [Osafune et al., PRL (1998)]
XAS [Rusydi et al., PRB (2007)]
also neff from RH at 1GPa (○)
[Nakanishi et al., JPSJ (1998)]
Δ
our results in good agreement with NMR and NEXAFS
minor change in number of carriers is responsible for pronounced change in resistivity with x
Sr2.5Ca11.5Cu24O41 Sr2.5Ca11.5Cu24O41
dρc / dT > 0
dρa / dT < 0
dRH(T) / dT < 0
neff = 1.33 →
neff (per Cu) = 0.09
comparison with La1.92Sr0.08CuO4:
n (per Cu) = 0.08[Ando et al.,PRL 92 (2004)]
[Ando et al.,PRL 93 (2004)]
La1.92Sr0.08CuO4
dρab / dT > 0
dRH(T) / dT < 0
~ T1
~ T-1
cot(ΘH) in Sr2.5Ca11.5Cu24O41
cot(ΘH) ~ T2
common for HTC explanation of that
behavior still under
debate
Sr2.5Ca11.5Cu24O41
T > 140 K cot(ΘH) ~ T2
that behavior is not changed by the increased anisotropy
cot(ΘH)=ρab/RHB
cot(ΘH)=ρc/RHB
[Ando et al.,PRL 92 (2004)]
Conclusion Hall coefficient RH:
positive, hole-like, temperature dependent x < 11.5, RH ~ exp(∆ / T)
x = 11.5 ρc ~ T1 ;ρa ~ RH ~ T-1
cot(ΘH) ~ T2 → common for HTC → independent of anisotropy of ladder plane
effective number of carriers neff ~ 1/RH
comparison with number of holes in ladders n good agreement with NEXAFS and NMR results minor change in number of carriers → responsible for
pronounced change in resistivity with x
Hall effect in Sr14−xCaxCu24O41 two geometries:
j||a, B||b → all samples j||c, B||b → x = 0 and
11.5
particular care for temperature stabilization
three pairs of Hall contacts
better statistics self-compensation of
magnetoresistance
Sr14−xCaxCu24O41 and Bechgaard-Fabre salts
[Korin-Hamzić et al.,PRB 67 (2003)]
[Moser et al.,PRL 84 (2000)]
RH and ρ vs temperature
RH and ρ vs T for x = 0
RH(T) ~ ρ(T) no marked changes
in RH at TCDW
TCDW values in agreement with [Vuletić et al. PRL (2003)]
Sr14−xCaxCu24O41 superconductivity
occurs for x ≥ 10 under pressure (p = 3-8 GPa) for T < 12 K
[Nagata et al., J. Phys. Soc. Jpn. (1997)]
occurs by carrier doping in low-dimensional antiferromagnetic spin structure
[T. Vuletić, et al., Phys. Rep. (2006)]
distribution of doped holes Madelung potential
calculations:[Mizuno et al., J. Phys. Soc. Jpn. (1997)]
x=0: nL=0
x>0: nL>0
optical conductivity:[Osafune et al., Phys. Rev. Lett. (1998)]
x=0: nL=1
x=11: nL=2.8
NEXAFS:[Nücker et al., Phys. Rev. B. (2000)]
x=0: nL=0.8
x=12: nL=1.1
NMR:[Piskunov et al., Phys. Rev. B. (2005)]
nL(x=12)-nL(x=0)=0.42
applied pressure: nL ↑
XAS[Rusydi et al., Phys. Rev. B. (2007)]
x=0: nL=2.8
x=11: nL=4.4