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Einfluss von Kernquadrupolmomenten auf die Amplitude von Polarisationsechose in amorphen Festkörpern

Brandt, Maximilian

English Title: Influence of nuclear quadrupole moments on the amplitude of polarisation echos in amorphous solids

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Abstract

Die physikalischen Eigenschaften von amorphen Festkörpern werden unterhalb einiger Kelvin durch atomare Tunnelsysteme bestimmt. In diesem Temperaturbereich zeigen einige isolierende Multikomponentengläser magnetfeldabhängige Eigenschaften. Zur Erklärung dieser unerwarteten Magnetfeldeffekte in nominell unmagnetischen amorphen Systemen wurden in den letzten Jahren verschiedene Modelle entwickelt. Eines dieser Modelle setzt voraus, dass die Atomkerne der tunnelnden Teilchen ein elektrisches Kernquadrupolmoment besitzen. Mit dielektrischen Polarisationsechoexperimenten haben wir an amorphem Glycerin den Zerfall der Echoamplitude in Abhängigkeit des Magnetfelds untersucht. Durch partielles Deuterieren wurden gezielt Atome mit Kernquadrupolmoment und bekannter Quadrupolfrequenz in das System eingebracht. Der beobachtete Isotopeneffekt stützt die Erklärung der Magnetfeldeffekte basierend auf einem Kernquadrupolmoment. Auch die erstmals in Glycerin beobachtete Quantenschwebung im Zerfall von Zweipulsechos kann im Rahmen dieses Modells quantitativ erklärt werden.

Translation of abstract (English)

The physical properties of amorphous solids below a few Kelvin are governed by atomic tunneling systems. At temperatures below 100\,mK, it was found that the dielectric properties of several multicomponent glasses depend strongly on applied magnetic fields. This effect is indeed very surprising, since in first order the dielectric properties of non-magnetic insulating glasses should be insensitive to magnetic fields. Several models have been developed in an attempt to explain this unusual behaviour. One model includes the modifications of the tunneling process due to the nuclear electric quadrupole moment carried by the tunneling particle. We have studied the decay of the amplitude of spontaneous polarisation echoes of amorphous glycerol as a function of an applied magnetic field. Studying partially deuterated as well as natural glycerol, we have been able to investigate samples with and without quadrupole moments of a known quadrupole frequency. The experiments confirm the necessity of quadrupole moments for the magnetic field effects and give strong evidence in favour of a quadrupole based theory. Additionally, the model is able to explain the quantum-beating observed in the decay of the two-pulse-echo in deuterated glycerol.

Item Type: Dissertation
Supervisor: Enss, Dr. Christian
Date of thesis defense: 22 July 2004
Date Deposited: 03 Aug 2004 15:06
Date: 2004
Faculties / Institutes: The Faculty of Physics and Astronomy > Kirchhoff Institute for Physics
Subjects: 530 Physics
Controlled Keywords: Amorpher Festkörper, Quadrupolmoment
Uncontrolled Keywords: Tunnelsysteme , Magnetfeldeffekt , Zweipulspolarisationsechosequenztunneling systems , nuclear quadrupole moment , amorphous solid , magnetic field effect
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