# EUROISMAR 2019

25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

## Electron Spin Relaxation Mechanisms of Atomic Hydrogen Trapped in Silsesquioxane Cages: the Role of Isotope Substitution

26 Aug 2019, 16:15
35m
Lecture Hall B (Henry Ford Building)

### Lecture Hall B

#### Henry Ford Building

Invited talk Spin physics

### Speaker

Dr George Mitrikas (Institute of Nanoscience and Nanotechnology, NCSR Demokritos)

### Description

Encapsulated atomic hydrogen in silsesquioxane cages is a promising candidate for applications in emerging technologies like spin-based quantum computing, magnetic field sensing, and atomic clock devices. Compared to endohedral fullerenes (N@C$_{60}$ or P@C$_{60}$), which are currently the most used molecular spin systems for demonstrating single-quantum gates and quantum memories, atomic hydrogen is more attractive due to its simpler electronic 1s state and the exceptionally large hyperfine coupling of about 1420 MHz. Detailed pulsed EPR studies of parameters relevant to quantum computing like electron spin-lattice ($T_1$) and phase memory ($T_M$) relaxation times are scarce and concern exclusively cages of the type Si$_8$O$_{12}$R$_8$ with R=C$_2$H$_5$ [1], R=C$_3$H$_7$ (n-propyl) [2], and R=OSi(CH$_3$)$_2$H [3]. Recently,[4] we applied dynamical decoupling methods in order to suppress nuclear spin diffusion in H@$h_{72}$Q$_8$M$_8$, the derivative with R=OSi(CH$_3$)$_3$. Herein we examine for the first time the effect of deuterium isotopic substitution on the spin relaxation properties of H@$h_{72}$Q$_8$M$_8$, by applying pulsed electron paramagnetic resonance (EPR) methods on its deuterated analogues H@$d_{72}$Q$_8$M$_8$ and D@$d_{72}$Q$_8$M$_8$. For the latter species we measure a phase memory time of 60 $\mu$s at 180 K, the largest obtained so far for this family of molecular spins. We show that selective substitution of encapsulated or peripheral hydrogen atoms with deuterium reveals high-temperature relaxation mechanisms that were previously hidden by proton nuclear spin diffusion. Unusually short $T_M$ values observed for all deuterated species even at liquid helium temperatures are discussed in terms of tunneling reorientation of methyl groups.

[1] Weiden et al, Appl. Magn. Reson. 2001, 21, 507–516.
[2] Schoenfeld et al, Phys. Status Solidi B 2006, 243, 3008–3012.
[3] G. Mitrikas, Phys. Chem. Chem. Phys., 2012, 14, 3782–3790.
[4] G. Mitrikas et al, Phys. Chem. Chem. Phys., 2014, 16, 2378–2383.

### Primary authors

Dr George Mitrikas (Institute of Nanoscience and Nanotechnology, NCSR Demokritos) Dr Raanan Carmieli (Department of Chemical Research Support, Weizmann Institute of Science)

### Presentation Materials

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