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PGI-1 Seminar: Dr. Cedomir Petrovic

Two-dimensional Dirac fermions and quantum transport in bulk crystals

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22.Feb.2012 14:00
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Hörsaal of Peter Grünberg Institut in Forschungszentrum Jülich (Building 04.8, Entrance E2, 2nd floor).

Brookhaven National Laboratory

Scope

Dirac fermions have attracted great interest in recent years, as seen on the examples of materials like graphene and topological insulators [1-2]. In addition, Dirac states have shown to be rather important when considering magnetotransport in some bulk crystals [3-5]. In this talk, I will discuss two dimensional Dirac fermions and quantum transport behavior in single crystals of SrMnBi2 and CaMnBi2 [6-8]. The non-zero Berry’s phase, small cyclotron resonant mass and first-principle band structure suggest the existence of the Dirac fermions in the Bi square nets. Angular dependent magnetoresistance and quantum oscillations indicate dominant two-dimensional Fermi surfaces. The in-plane transverse magnetoresistance exhibits a crossover at a critical field B* from semiclassical weak-field ~ B2 dependence to the high-field unsaturated linear magnetoresistance (~120% in 9 T at 2 K) due to the quantum limit of the Dirac fermions. Magnetic field enhances the thermopower significantly in SrMnBi2: the maximum change of thermopower is about 1600% in 9 T field and 10 K. In contrast, magnetic field suppresses the absolute value of thermopower in CaMnBi2. First principle band structure calculations show that the chemical potential in both materials is close to the Dirac-cone like points in linear bands. The magnetic field suppresses (increases) the apparent Hall carrier density of CaMnBi2 (SrMnBi2) below 50 K, so the large magnetothermopower effect is attributed to the magnetic field shift of chemical potential. The results demonstrate the existence of two dimensional Dirac fermions in different bulk crystals with Bi and Sb square nets and show that such states are highly relevant for thermoelectric properties [9]. References: [1] Rev. Mod. Phys. 81, 109 (2009) [2] Rev. Mod. Phys. 82, 3045 (2010), [3] Phys. Rev. Lett. 102, 176403 (2009) [4] Phys. Rev. Lett. 104, 137001 (2010) [5] Phys. Rev. Lett. 107, 126402 (2011) [6] Phys. Rev. B 84, 220401 (2011) [7] Phys. Rev. B 85, 041101 (2011) [8-9] unpublished.

 

 

More about Dr. Petrovic and the work of his group "Exploratory Materials Synthesis & Characterization" can be found here:
http://www.bnl.gov/cmpmsd/emsc/

Contact

Prof. Dr. Stefan Blügel
Phone: +49 2461 61-4249
Fax: +49 2461 61-2850
email: s.bluegel@fz-juelich.de

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