epr of quasiparticles by fluctuations of cooper pairs jan stankowski institute of molecular physics,...

EPR OF QUASIPARTICLES BYFLUCTUATIONS OF COOPER PAIRS

Jan Stankowski

Institute of Molecular Physics, Polish Academy of Sciences

Kazimierz Dolny 2005

TRANSPORT PHENOMENA

Microwave Absorption (MA) was discovered in HTSC as a zero field „EPR” line

MA results from by Cooper pair breaking when fluxes penetrate through a Josephson weak links (JWL)

Dynamics of the field dependent MA implies, that flux flow, its pinning and creep by: 1o defects and 2o weak contacts give the nonresonant AC dissipation.

AIM OF THIS WORKElectron paramagnetic resonance - EPR in quasiparticles system and sharp AC anomaly in field BEPR(f) close to g0

0

VORTEX

CURRENT INDUCED VORTEX MOTION CAUSE QP FLUCTUATIONS

V ~ J x Ф

CHEMICAL DEFECTS POTENTIAL IS B INDEPENDENT

JWC POTENTIAL IS PERIODICALY B DEPENDENT

B B

= n0 + 0 = n0 = n0 + 0 = n0 + 0

U

SC

WJL

ANALYSIS OF AC ABSORPTION

Vortex motion (VM) model by Coffey and Clem

VM resistivity is due to formation of quasiparticles (QP)

In two-liquid model: n=nQP + 2nSC

DISTRIBUTION OF CPs AND NORMAL ELECTRONS (QPs)

QP

CP

MAGNETIC FIELD DEPENDENT AC ABSORPTION IN SUPERCONDUCTORS

ZERO FIELD ABSORPTION LINE FOR JWL

HTSC RESISTIVITY VS. MAGNETIC FIELD

T=80 K

T=85 K

E. Silva et al., Int. J. of Modern Physics B, 17, 922 (2003)

VORTEX MOTION HYSTERESIS LOOPS

AC ABSORPTION

DIFFERENTIALMMMA SIGNAL

VORTEX MOTION HYSTERESIS LOOP LC CIRCUIT FOR 22 MHz

Magnetic field modulation (50Hz )

U

MAGNETIC ANOMALY IN

SLIGHTLY DOPED FULLERENE

TWO PARAMAGNETIC CENTERS

ddelocalize C160

defect localized C160

AMPLITUDE I’i OF THE EPR SIGNAL IN C60:Rb

SPIN EFFECT IN TRANSPORT PHENOMENA

- EPR OF QP in VMHL

- BLOCH two coil EPR DETECTION

- EPR in MICROWAVE IMPEDANCE

sample

LC OSCILLATING CIRCUIT (22MHz)

JOSEPHSON HYSTERESIS LOOP IN LC CIRCUIT FOR 22 MHz

50Hz B field modulation

U

BLOCH NMR HEAD

Magnetic field

Generating coil

Receiving coil

15 MHz

AC INDUCTION IN BLOCH TWO COIL METHOD

YBCO signal

DPPH strong sample

NON-LINEAR VORTEX TO THE MAGNETIC FIELD

CuO2 plane

Mag

neti

c F

ield

AC DISSIPATION IN YBCO AT 21 GHz, from E. SILVA J. Low Temp. Phys. , 131, 871 (2003)

0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.800.00

0.01

0.02

0.03

0.04

0.05

Gauss H

c = 0.66658 ± 0.00644

Lorentz H

c = 0.66455 ± 0.00657

[

cm

]

H [T]

COMPUTER EXTRACTION OF THE SPIN SIGNAL FROM AC DISSIPATION

LOW FREQUENCE LIMIT g -factor close to 2

HIGH FREQUENCE

g -factor for localized state: C601- ion in fullerene

and Cu2+ - ion in YBCO

CONCLUSIONS

1. FLUX MOTION GENERATING QP LEADS TO NONRESONANT AC MAGNETIC FIELD DISSIPATION

2. EPR OF NORMAL ELECTRONS (QP) IS RELATED TO LOCALIZED SPIN STATE ON PARAMAGNETIC CENTERS gg0 SHOWING THAT CONDUCTING CARRIERS ARE STRONGLY CORRELATED ELECTRONS

Low field study of EPR and paramagnetic fluctuation can be used to study interaction between

local pairs (boson liquid) and quasiparticles (quasi Fermi liquid).

T.Domański, K.I.Wysokiński, Phys.Rev. B 66,064517-1 (2002)

COLLABORATION

R. Micnas - theory advisor UAM

IFM PANJ. Martinek - theory of nonresonant MAW. Kempiński - MMMA experimentsL. Piekara-Sady - fullerenesJ. Grembowski - low freq.exp.W. Bednarski - comuter expert

THANKS FOR ATTENTION

Institute of Molecular Physics, Polish Academy of Sciencese-mail: janstank@ifmpan.poznan.pl