题目：Point Contact Andreev Reflection and the Measurement of Spin Polarization - High Fields and Novel Materials

报告人：Plamen Stanislavov Stamenov

                 爱尔兰三一学院 讲师

时间：2018年4月27日下午3:30

地点：国家脉冲强磁场科学中心B206

报告摘要：

Following a very brief introduction to the research activities within the Magnetism and Spin Electronics Group at TCD, one topic of current development will be presented, as an example.

Point Contact Andreev Reflection (PCAR) is one of the few available methods for the determination of the Fermi level spin polarisation in metals and degenerate semiconductors. It has traditionally been applied at fixed (liquid He) temperatures, using pure niobium as the superconductor, and at essentially zero applied magnetic fields, all of which limit the amount of information that it can provide – i.e. do not allow for the extraction of the sign of the spin polarisation and make the assignment of the transport regime to ballistic or diffusive almost impossible.

Here a series of experiments is described, aimed at the expansion of this parameter space to higher magnetic fields and to higher temperatures. These require redesigned experimental setups and the use of higher performance superconductors. Demonstrations are described of the determination of the sign of the spin polarisation, at fields of more than 5-7 Tesla using a low-Z superconductor, as well as operations beyond 9.2 K. Doubts about the practical reliability of the PCAR technique are dispersed using systematic series of samples – the heavy rare-earths and comparisons with alternatives, such as spin-polarised field emission, photo-emission and Tedrow-Meservey tunnelling.

The specific material examples presented include 3d-metals, order-disorder transition alloys and zero-moment half-metals – Fe, FeAl and MnRuGa, alternative low-Z and high-Z superconductors – MgB2 and NbTi, and magnetic topological insulators, such as Cr- and V-doped (Bi1-xSbx)2Te3. Finally, remarks will be made towards the possibilities of using Andreev reflection in very high DC and pulsed magnetic fields.

Ref.: Phys. Rev. B, 94, 094415 (2016) doi:10.1103/PhysRevB.94.094415.K. Borisov, C.-Z. Chang, J. S. Moodera and P. Stamenov

报告人简介：

Education and academic levels acquired:

1.Graduate education at the Physics Department of the University of Sofia "St. Kliment Ohridski", Sofia, Bulgaria; academic years (1998-2002), average score 5.92, BSc in theoretical and experimental Physics awarded via a thesis defense with a perfect score of 6.00. Thesis title:Synthesis, structure and properties of some manganese perovskites.

2.Postgraduate education at the School of Physics, Trinity College, University of Dublin, Ireland; academic years (2002-2007), PhD in Physics awarded via a thesis defense where the thesis was “Accepted as it stands - no corrections”. Thesis title:Metals, Semimetals and Semiconductors for Spinelectronics. PhD degree awarded: 04/2008.

3.Research Fellow at the Magnetism and Spin Electronics Group of the School of Physics and CRANN, Trinity College, University of Dublin, Ireland, academic years (2007-2010).

4.Ussher Lecturer in Physics (Nanomagnetism) at the School of Physics and Principal Investigator with CRANN, Trinity College, University of Dublin, Ireland, academic years (2010-2012) and (2016-).

5.Starting Investigator Research Grant (SIRG) SFI Lecturer, Trinity College, University of Dublin, Ireland, academic years (2012-2016).

Prizes:

1. National Physics Competition (Smolyan, Bulgaria) 1994 - 3rd place; 2. National Physics Conference (Stara Zagora, Bulgaria) 1995 - 1st place; 3. National Physics Competition (Smolyan, Bulgaria) 1996 - 3rd place; 4. National Computer Science Competition (Stara Zagora, Bulgaria) 1996 - 6th place; 5. UNESCO, Model United Nations Conference (Płock, Poland) 1996 - Best Speaker Prize; 6. ‘Osmarisimo’ award of the municipality of Shoumen, Bulgaria – “For achievements in the area of science and culture”; 7. National Diploma No. 12 – 1998 – “For achievements in physical sciences”; 8. Extended National Physics Team 1998 - Admitted to University of Sofia without examination.

Author and co-author:Total of 67 publications, cited more than 1630 times, since 2005 (more than 1470 times excluding self-citation of all authors),hindex = 19,mindex = 1.9.

Reviewer and Referee:(More than 150 manuscripts have been reviewed.) Nature, Physical Review Letters; Physical Review B; Applied Physics Letters; Journal of Applied Physics; Review of Scientific Instruments; European Physics Letters; Journal of Magnetism and Magnetic Materials and about 14 others. Awarded with Outstanding and Exceptional Referee for the AIP 2011, by Review of Scientific Instruments.

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