Valley–spin blockade and spin resonance in carbon nanotubes

• Published in: Nature nanotechnology Vol. 7; no. 10; pp. 630 - 634
• Main Authors: Pei, Fei, Laird, Edward A., Steele, Gary A., Kouwenhoven, Leo P.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-10-2012; Nature Publishing Group
• Subjects: 639/925/357/1017; 639/925/357/73; 639/925/927/481; Carbon; Chemistry and Materials Science; Electrons; Energy; Fabrication; letter; Materials Science; Nanotechnology; Nanotechnology and Microengineering; Nanotubes, Carbon; Quantum Dots; Resonance; Silicon
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/nnano.2012.160

The manipulation and readout of spin qubits in quantum dots have been successfully achieved using Pauli blockade, which forbids transitions between spin–triplet and spin–singlet states
1
. Compared with spin qubits realized in III–V materials
2
,
3
,
4
,
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, group IV materials such as silicon and carbon are attractive for this application because of their low decoherence rates (nuclei with zero spins)
6
,
7
. However, valley degeneracies in the electronic band structure of these materials combined with Coulomb interactions reduce the energy difference between the blocked and unblocked states
8
,
9
,
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, significantly weakening the selection rules for Pauli blockade. Recent demonstrations of spin qubits in silicon devices have required strain and spatial confinement to lift the valley degeneracy
7
. In carbon nanotubes, Pauli blockade can be observed by lifting valley degeneracy through disorder
11
,
12
,
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,
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, but this makes the confinement potential difficult to control. To achieve Pauli blockade in low-disorder nanotubes, quantum dots have to be made ultrasmall
8
,
9
, which is incompatible with conventional fabrication methods. Here, we exploit the bandgap of low-disorder nanotubes to demonstrate robust Pauli blockade based on both valley and spin selection rules. We use a novel stamping technique to create a bent nanotube, in which single-electron spin resonance is detected using the blockade. Our results indicate the feasibility of valley–spin qubits in carbon nanotubes.
The bandgap of a low-disorder, bent carbon nanotube is exploited to achieve Pauli blockade and spin resonance.