coexistence and competition of superconductivity and magnetism in ho 1- x dy x ni 2 b 2 c
Post on 10-Feb-2016
52 Views
Preview:
DESCRIPTION
TRANSCRIPT
Coexistence and Competition of
Superconductivity and Magnetism in Ho1-xDyxNi2B2C
Hyeon-Jin Doh, Jae-Hyuk Choi, Heon-Jung Kim, Eun Mi Choi, H. B. Kim, B. K. Cho and Sung-Ik Lee
National Creative Research Initiative Center for Superconductivity and Department of Physics, Pohang University of Science and Technology, Poh
ang 790-784, Republic of Korea
M. Ohashi and N. MoˆriInstitute for Solid State Physics, University of Tokyo,
M. SigristTheoretische Physik, ETH-Honggerberg, 8093 Zurich, Switzerland
Pohang Superconductivity Center Page 2Typed by Hyeonjin
Contents1. Introduction and Experiments2. Theory and Model3. Results and Discussion4. Summary
B. K. Cho, P. C. Canfield, and D. C. JohnstonPhys. Rev. Lett. 77, 163-166 (1996), PRL 77(1996) Hyeonjin Doh, Manfred Sigrist, B.K. Cho, Sung-Ik Lee Phys. Rev. Lett. 83(25), 5350-5353 (1999/12/20)Jae-Hyuk Choi, Hyeonjin Doh, Eun-Mi Choi, and Sung-Ik Lee, M. Ohashi and N. Mori. Phys. Rev. B 65(2), 024520(6) (2002) Jae-Hyuk Choi, Heon-Jung Kim, H. B. Kim, Hyeon-Jin Doh, Sung-Ik Lee, and B.K. Cho. Phys. Rev. B 72(05), 054516 (2005)
Pohang Superconductivity Center Page 3Typed by Hyeonjin
1. Introduction and Experiments History
Magnetic Superconductor containing the rare-earth atoms RMo6S8, RMo6Se8, and RRh4B4 (1970s)
YPd5B3C0.3 with TC = 23 K – Multi phase
[R. Nagarajan et al., PRL 72] RNi2B2C (TC = 0 ~16.6 K ) – Single phase.
[R. J. Cava et al., Nature 367]
Pohang Superconductivity Center Page 4Typed by Hyeonjin
1. Introduction and Experiments
Special Feature of Borocarbides There exists of compounds to compare
RNi2B2C ; R = Y, Dy, Ho, Tb, Tm, Er, Lu, Gd Underline - magnetism, Red - superconductivity
TmNi2B2C - TC = 11 K, TN = 1.5 K DyNi2B2C - TC = 6 K, TN = 10 K HoNi2B2C - TC = 8 K, TN = 5 K
High quality samples can be produced in single crystal form.
Pohang Superconductivity Center Page 5Typed by Hyeonjin
Superconducting Transition Temperature and de-Gennes Factor
Pohang Superconductivity Center Page 6Typed by Hyeonjin
Motivation
Pohang Superconductivity Center Page 7Typed by Hyeonjin
Motivation
Pohang Superconductivity Center Page 8Typed by Hyeonjin
1. Introduction and Experiments
Electrical properties Layered structure. But!! It shows 3D nature. Large N(F) [ 2.4 states/eV Ni] – relatively high TC. Multiband system.
All bands contribute to the superconductivity. Most contribution comes from Ni(3d).
Magnetic properties Originated from the 4f orbitals of the rare-earth atoms. –
RKKY interaction between the local moments. Large Spin-Orbit coupling. -Strong anisotropy; Crystal Electric Field Effects.
Pohang Superconductivity Center Page 9Typed by Hyeonjin
1. Introduction and Experiments
Crystal Structure Magnetic Structure
Pohang Superconductivity Center Page 10Typed by Hyeonjin
1. Introduction and Experiments
TC suppresion by Dy dopping into HoNi2B2
C. TN scales with de Ge
nnes factor. TC does not fit with d
e Gennes scaling B. K. Cho et al. PRL
77(1996)
Pohang Superconductivity Center Page 11Typed by Hyeonjin
Strange HC2 curve
[Canfield et al., Physics Today 51]
Pohang Superconductivity Center Page 12Typed by Hyeonjin
1. Introduction and Experiments
Neutron scattering Spiral phase
J. W. Lynn et al. PRB 55(1997)
Q=(0,0,2)
Q=(0,0,2)
Q=(0,0,2)
Pohang Superconductivity Center Page 13Typed by Hyeonjin
2. Theory and Models Model for the magnetic order
The free energy from spin degree of freedom.
Here, and - Coupling between antiferromagnetic
order and the spiral order. Two orders compete each other ( ).
SPAFSPAFSPSP
AFAF
SPSPAFAFM MMMMMTMTF 224422
22)()(
)()( 0 AFAFAF TTT )()( 0 SPSPSP TTT
SPAF
SPAF
Pohang Superconductivity Center Page 14Typed by Hyeonjin
2. Theory and Models
Magnetic fluctuation Antiferromagnetic order.
Antiferromagnetic fluctuation. Mean Field Calculation by using.
The increase of the free energy due to the magnetic fluctuation.
)(3)( 222
AFAF
SPSPAFAFAFAF TTMMTM
AFAFAF MMM
2222)3)(( MMMMTF AFSPAFAFAFAFAFAFM
222222
22))(( SP
SPAF
AFSPSPSPAFSPAFSP MMMMMT
)(),( 22222222 SPSPSPSPAFAFAFAF MMMMMMMM
Pohang Superconductivity Center Page 15Typed by Hyeonjin
2. Theory and Models
Calculation of Gaussian Fluctuation.
Experiment for comparing.
F
AF
FAFAF
AFeMd
eMMdM
)(
)( 22
F
SP
FSPSP
SPedM
eMdMM
22
AF order
Spiral order
Pohang Superconductivity Center Page 16Typed by Hyeonjin
2. Theory and Models
Superconducting order Multiple bands system.
Ni(3d), B(2p)-C(2p), and R(5d) All bands contribute the
superconductivity. In ordered states, the
magnetic moments are cancelled in Ni plain.
Two order parameter. From Ni band. From the bands other than
Ni.Observation of a Pair-Breaking Field at the Ni Site in Nonsuperconducting ReNi2B2C, PRL 76, 507-510 (1996)E. Baggio-Saitovitch, Brazil
Pohang Superconductivity Center Page 17Typed by Hyeonjin
Theory and ModelsMossbauer Results
Temperature dependence of local magnetic field at the 57Fe nucleus in TbNi2B2C and HoNi2B2C
Pohang Superconductivity Center Page 18Typed by Hyeonjin
2. Theory and Models
Free energy for two superconducting orders.
A- superconducting order from Ni(3d)bands. B- superconducting order from the other bands. 1,2 - Josepsen coupling between A and A
42
2
0
22 ||
2||)(2
2 AA
AAAA
SCbtaAi
mrdF
42
2
0
22 ||
2||)(2
2 BB
BBBB
btaAim
rd
1 20 0
2 2( . ) .A B A Bi ic c A A c c
222
221 |||| ASPBAF MM
Pohang Superconductivity Center Page 19Typed by Hyeonjin
3. Results and Discussion TC suppresion
The linearized Ginzburg-Landau equation.
BASPA MTa 12
2 ))((0
ABAFB MTa 12
1 ))((0
Pohang Superconductivity Center Page 20Typed by Hyeonjin
3. Results and Discussion
HC2 curve Comparison with the
experiments[Canfield et al., Physics Today 51]
HoNi2B2CDyNi2B2C
Pohang Superconductivity Center Page 21Typed by Hyeonjin
3. Results and Discussion
Pressure Effects Transport experiments of H
o0.9Dy0.1Ni2B2C and Ho0.6Dy0.4
Ni2B2C. For TN<TC,
dTC/dp ~ -0.64 K/Pa.-0.49 K/Pa [Michor, PRB 61]
dTN/dp ~ 0.48 K/Pa.0.482 K/Pa [Michor]
For TN>TC, TC ~ almost constants.
Solid square – TC in expSolid circle – TN in expSolid line – TN in theoryDotted line – TC in theory[J.-H. Choi, PRB 65]
Pohang Superconductivity Center Page 22Typed by Hyeonjin
3. Results and Discussion
Reentrant behavior of Ho1-xDyxNi2B2C
B. K. Cho et al., PRL 77 (1996)
Schematic diagram for the resistivity data
Pohang Superconductivity Center Page 23Typed by Hyeonjin
3. Results and Discussion
Qualitative description for Lu1-xDyxNi2B2C From the DyNi2B2C
side, if we put in Lu instead of Dy, this breaks the balance which makes zero field at Ni site.
Lu acts as magnetic impurity, through Lu has no magnetic moments.
Increasing Dy reduces the magnetic fluctuation. This enhances the superconductivity.
B. K. Cho et al., PRL 77 (1996)
Pohang Superconductivity Center Page 24Typed by Hyeonjin
3. Results and Discussion
Qualitative description for Dy1-xTbxNi2B2C
Magnetic structureJ. H. Choi et al. (1999)
Pohang Superconductivity Center Page 25Typed by Hyeonjin
3. Results and Discussion
TC suppression of Dy1-xTbxNi2B2C Tb has different type of magnetic order from Dy and H
o. The magnetic field at Ni site is not zero in TbNi2B2C at
T < TN
Tb suppresses the superconductivity from Ni bands unlike Ho and Dy.
Breakdown of the de Gennes scaling of TN. Since Tb and Dy has different type of magnetic order,
they suppress each other and TN is lower than expected from the de Gennes scaling.
Pohang Superconductivity Center Page 26Typed by Hyeonjin
4. Summary RNi2B2C is multi-band system unlike the cuprate.
There are many contributions for the superconductivity.
In HoNi2B2C and DyNi2B2C, two superconducting order parameters are introduced due to the magnetism. One interacts with the antiferromagnetic order
and the other does not. Phenomenological theory describes well.
TC and TN in Ho HC2 of HoNi2B2C and DyNi2B2C. Pressure dependence. Reentrance behavior of HoNi2B2C.
Pohang Superconductivity Center Page 27Typed by Hyeonjin
4. Summary
In Lu1-xDyxNi2B2C, Lu breaks the balance of the magnetic field and generate the field at Ni site. Lu acts as a magnetic impurity in the Dy
background. In Dy1-xTbxNi2B2C, the structure of the
antiferromagnetic order is different from Ho1-xDyxNi2B2C. The antiferromagnetic order suppresses the
superconductivity from Ni bands.
top related