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Trends_3D topo. insulators

Funding: We acknowledge DFG grant HA 5893/1-1 within focused spintronics program.
Associate Professor Dr. Ewelina Hankiewicz, who is a theoretical physicist, specializes in the related fields of nanoscience and spintronics. Her areas of interest include but are not limited to: topological insulators, spin-Hall and quantum spin-Hall effects, which would allow for the easy generation of spin currents, effects of disorder on physical properties of graphene (a 2D honeycomb layer of carbon), as well as, magnetization dynamics in ferromagnets and polarized electron gases.

### Research Interests

Topological                          Transport at                         Magnetization
Insulators                              the Nanoscale                         Dynamics

### News

1. We propose Coulomb interaction induced topological insulator thin film ordered states in which coherence is established spontaneously between top and bottom surfaces in magnetic fields. In particular, Quantum Hall Superfluid at total Landau-level filling factor $\nu_T=0$ is predicted to be free of edge modes, qualitatively altering its transport phenomenology (see for details arXiv:1107.2969 (2011)).

2. We report experimentally and theoretically on all electrical measurement of spin polarization for edges states of 2D topological insulator in nanostructures fabricated from HgTe quantum wells. A split gate technique allows us to combine both quantum spin Hall and metallic spin Hall transport in a single device. Therefore, the quantum spin Hall effect can be used as a spin current injector and detector for the metallic spin Hall effect, and vice versa, allowing for an all-electrical detection of spin polarization (for details see arXiv:1107.0585 (2011)).

3. We showed very recently, that a zero gap HgTe quantum well is a single valley Dirac system. Transport experiments are supported by theoretical analysis of the system including calculations of quantized Hall plateaus and minimal conductivity. A manuscript is published now online Nature Physics 7, 418-422 (2011) (doi:10.1038/nphys1914 Article).

4. We have recently calculated the weak localization corrections in Dirac Fermion material (HgTe QWs) and have found a novel symplectic to unitary transition as a function of the carrier density for a zero magnetic field (see Phys. Rev. B 84, 035444 (2011)).

5. We predicted novel transport properties of 3D topological insulators which time reversal symmetry is broken due to surface quantum Hall effect. We took into account surface and bulk states contributions. In particular, we found: linear bulk dc magnetoresistivity and a quadratic field dependence of the Hall angle, as well as shifted cyclotron resonance (see for details Phys. Rev. B 84, 035405 (2011)).

6. Our Nature physics article concerning the ballistic spin-Hall effect has been published online May 2, 2010; Nature Physics 6, 448 (2010). Some of us predicted theoretically in 2004 (E.M. Hankiewicz at al, Phys. Rev. B 70, 241301(R)) that the spin-Hall effect can be electrically induced and detected in the H-shaped structure ( see also research highlight Transport at the nanoscale above). An application of voltage in one of the legs of H-shaped structure generates a transverse spin current (spin-Hall effect) which is transformed into electric signal through the inverse spin-Hall effect. In our new Nature Physics, we show an experimental evidence for the electrical measurement of the ballistic spin-Hall effect.

7. How different spin-orbit terms influence the transport of topological insulators? Curious? See our see our recent paper: New J. Phys. 12 (2010) 065012

8. How to find the signature of topology in bulk properties of topological insulator? Curious? Check our recent paper: Phys. Rev. B 81, 241303 (2010)

9. How the quantum spin Hall state merges into quantum Hall state in magnetic fields? Curious? See Phys. Rev. Lett. 104, 166803 (2010)

10. Do electron-electron interactions modify the spin transport? Curious? Check my topical review

Contact information

Associate Professor Dr. Ewelina Hankiewicz
Institut für Theoretische Physik und Astronomie
Arbeitsgruppe Mesoskopische Physik (AMP)
Universität Würzburg
Am Hubland 97074 Würzburg, Germany

Phone: +49-931-31 84998
FAX: +49-931-318 5141
Office: Verfügungsgebäude Physik 2, V108
e-mail: eweli na.hankiewicz@phy sik.uni-wuerzburg. de