# Dresden 2006 – wissenschaftliches Programm

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# TT: Tiefe Temperaturen

## TT 6: Solids At Low Temperature: Amorphous and Tunnel Systems, Glasses, ...

### TT 6.3: Vortrag

### Montag, 27. März 2006, 11:15–11:30, HSZ 105

**Low temperature breakdown of coherent tunneling in amorphous solids by the nuclear quadrupole interaction** — •Alexander Burin^{1}, Peter Fulde^{2}, and Ilya Polishchuk^{3} — ^{1}Department of Chemistry, Tulane University, New Orleans, LA 70118, USA — ^{2}Max-Planck-Institut fur Physik Komplexer Systeme, D-01187*Dresden, Germany — ^{3}RRC Kurchatov Institute, Kurchatov Sq. 1, 123182 Moscow, Russia

We consider the effect of the internal nuclear quadrupole interaction on
quantum tunneling of complex multi-atomic two-level systems. Two distinct
regimes of strong and weak interactions are found. They depend on the
relationship between the characteristic energy of the internal interaction
λ_{∗}, which is directly proportional to the number of tunneling
atoms per tunneling system, and a bare tunneling coupling strength Δ
_{0}. When Δ_{0}>λ_{∗}, the internal interaction is
negligible and tunneling remains coherent, being defined by the strength of
Δ_{0}. When Δ_{0}<λ_{∗}, coherent tunneling breaks down
and the effective tunneling amplitude decreases by an exponentially small
overlap factor η^{∗}≪1 between the internal ground states of the
left and right well, affecting thermal and kinetic properties of tunneling systems.
The theory is applied to interpret the anomalous behavior of the resonant
dielectric susceptibility in amorphous solids for *T*≤5*mK* in terms of the
nuclear quadrupole interaction. We suggest clarifying experiments using
external magnetic fields to test the theories predictions and to shed some
light on the internal structure of tunneling systems in amorphous solids.