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May 02

Réunion Comics 02/02/2015

* Open position next September, post-doc for working on ab initio with Michele.

* Presentation by Su Li

Présents : Michele Amato, Arnaud Bournel, Philippe Dollfus, Joseph Friedman, Jérôme Larroque, Alice Mizrahi, Mai Chung Nguyen, Jérôme Saint Martin, Su Li, Adrien Vincent, Damir Vodenicarevic.

News

Open position next September, post-doc for working on ab initio with Michele.

Hung’s paper on misoriented graphene accepted by Nanotechnology.

Topical review on thermoelectric effects in graphene of Philippe in JPCM almost accepted (problem with the 2nd reviewer but the adjudicator disagrees with him).

Edison : 3 abstracts sent. Jérôme L., Mai Chung, Hung.

A paper submitted to phononic conference in Paris by Jérôme.

A paper of Truong to Graphene 2015.

Next deadlines, IWCE in Purdue, SISPAD in Washington. See Comics website.

Next meeting, March 11, presentation by Mai Chung.

Su Li, graphene-based all-spin logic device and spin circuits model

MTJ as input/output, graphene as channel. Physics model including TMR, STT and spin transport properties of graĥene.

Spin signal depends strongly on the material parameters (contact resistance, diffusion length) as welle as on the device geometry.

Critical current for STT should be lower than breakdown current for graphene. See 3 experimental references. Revised paper submitted to APL.

Paper indicated by Damien, Proc. IEEE 103 (1), January 2015. Same idea… But problem with brekdown current…

Optimization of the all spin logic device → high speed and reduced power consumption. As a function of material parameters and geometry. Needs of long spin diffusion length, high spin injection/detection efficiency, small contact area…

Spin circuit models. From traditional ohmic law… Considering the spin splitting of electrochemical potential. Definition of the spin resistivity/resistance. Then definition of series and parallel connections of spin resistances, based on the continuity of spin current and electrochmichal potential.

Non local spin valve geometry. Su Li’s model vs. Takahashi’s model (including or not an approximation related to ferromagnet resistance), or Otani’s model Comparison to experimental results (Nature 416, 713 (2002)). Differences related to the definition of the spin result. But final results may be equivalent after appropriate normalization. Su Li’s model may be applied whatever the type of contact (transparent or tunnel).

Motivation, control of the spin resistance by an external gate voltage. By tuning graphene conductivity. Some experimental results already available…

Model of spin transport → assuming than the spin relaxation is due to Elliott-Yafet mechanism. So linear relationship between conductivity and diffusion length. And Rashba spin orbit-coupling? Slide 23. Comparison to experimental results.

Next work, calculation of the conductivity map with top gate and back gate. Thanks to Hung’s NEGF model. Then optimize the control voltage range and the gate size.

But Hung’s calculation are done assuming ballistic tranport? OK because short length device.

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