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