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Coherent control of single spins in silicon carbide

In short: Electron spins that can be prepared in arbitrary states are the basic elements for quantum spintronics, such as quantum computing and nanoscale sensing. Here we demonstrate that missing atoms in a silicon carbide crystal can host single spins that are accessible by optical spectroscopy, with long coherence times even at room temperature. These results expand the interest of silicon carbide into the areas of quantum processing and integrated spintronics.

Unpaired electrons at an electronic defect in solids possess an intrinsic angular momentum, often called spin. Single spins can be prepared in an arbitrary state and are basic elements for quantum spintronics, such as quantum computing and nanoscale sensing. Recently, spectacular progress in single spin manipulation and detection has been achieved for the so-called N-V defect in diamond – a complex between a nitrogen impurity and a nearby vacancy (i.e. a lattice site with missing carbon atom) – and individual phosphorous impurity in silicon. While diamond offers optically accessible quantum states at room temperature, well-developed silicon material provides a platform for electrical interfacing with other devices. However, there are disadvantages with both materials: diamond is still an immature semiconductor while an efficient optical access of the spin is lacking for silicon. Silicon carbide (SiC) can combine the strength of both systems: having deep defects acting as luminescence centres similar to the N-V centre in diamond and benefits from mature material fabrication techniques.

Fig. 1. 4H-SiC crystal structure with (a) silicon vacancies at non-equivalent lattice sites (the hexagonal (h) and quasi-cubic (k) lattice sites) and (b) divacancies which consist of neighbouring Si and C vacancies. There are four non-equivalent forms of divacancies in 4H-SiC.

For quantum spintronics it is important that the spins have long coherence times, meaning that the system should be stable with respect to the time it takes to manipulate the spins. Long spin coherent times have recently been observed for the Si vacancy (missing Si atom, see Fig. 1(a)) and divacancies (missing neighbouring Si and C atoms, see Fig. 1(b)) in SiC at room temperature, but so far only in ensembles with high defect concentrations (>1015 vacancies per cm3 ). Research teams at Linköping, Stuttgart, Chicago, Budapest, Takasaki and Beijing have successfully designed and fabricated 4H-SiC single crystal samples with the vacancies homogeneously introduced by electron irradiation (and subsequent annealing) to low concentration in the range of  1011 defects per cm3 (or a few defects in 10 µm3 ) so that single defects can be resolvable in an optical microscope and selectively detected by photoluminescence. Overcoming difficulties in control of the charge state of defects and other issues in the detection of weak light emission, the research teams have been able to manipulated and detect single spins in SiC at room temperature (for the Si vacancies) and at cryogenic temperatures (-250 oC for the divacancies) by optical detection of magnetic resonance (ODMR), showing long spin coherent times up to 1.2 milliseconds. The demonstrated ability of optically single-spin control at room temperature shows the potential applications of defects in SiC for quantum processors that could operate at ambient conditions, and paves the way for integrated spintronics.

Details of the research are described in the following two articles

Nature Materials (2014)
/doi:10.1038/NMAT4144
Authors: David J. Christle, Abram L. Falk, Paolo Andrich, Paul V. Klimov, Jawad Ul Hassan, Nguyen T. Son, Erik Janzén, Takeshi Ohshima and David D. Awschalom

Nature Materials (2014)/doi:10.1038/NMAT4145
Authors:
Matthias Widmann, Sang-Yun Lee, Torsten Rendler, Nguyen Tien Son, Helmut Fedder, Seoyoung Paik, Li-Ping Yang, Nan Zhao, Sen Yang, Ian Booker, Andrej Denisenko, Mohammad Jamali, S. Ali Momenzadeh, Ilja Gerhardt, Takeshi Ohshima, Adam Gali, Erik Janzén and Jörg Wrachtrup

For View & News, see: Nature Materials (2014)/doi:10.1038/NMAT4171 by Andrea Morello

Media attention: CS Compound Semiconductors

Contact

Nguyen Tien Son, professor
Phone: +46 (0)13 28 25 31
E-mail: son@ifm.liu.se

Funding

  • Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University.
  • Knut and Alice Wallenberg Foundation (KAW).
  • Linköping Linnaeus Initiative for Novel Functionalized Materials.

 


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Last updated: 02/24/15