David Rench

Coherent heteroepitaxy of Bi2Se3 on GaAs (111)B

We report the heteroepitaxy of single crystal thin films of Bi2Se3 on the (111)B surface of GaAs by molecular beam epitaxy. We find that Bi2Se3 grows highly c-axis oriented, with an atomically sharp interface with the GaAs substrate. By optimizing the growth of a very thin GaAs buffer layer before growing the Bi2Se3, we demonstrate the growth of thin films with atomically flat terraces over hundreds of nanometers. Initial time-resolved Kerr rotation measurements herald opportunities for probing coherent spin dynamics at the interface between a candidate topological insulator and a large class of GaAs-based heterostructures.

Growth and characterization of hybrid insulating ferromagnet-topological insulator heterostructure devices

We report the integration of the insulating ferromagnet GdN with epitaxial films of the topological insulator Bi2Se3 and present detailed structural, magnetic, and transport characterization of the heterostructures. Fabrication of multi-channel Hall bars with bare and GdN-capped sections enable direct comparison of magnetotransport properties. We show that the presence of the magnetic overlayer results in suppression of weak anti-localization at the top surface.

Structural and magnetic characteristics of MnAs nanoclusters embedded in Be-doped GaAs

We describe a systematic study of the synthesis, microstructure and magnetization of hybrid ferromagnet-semiconductor nanomaterials comprised of MnAs nanoclusters embedded in a p-doped GaAs matrix. These samples are created during the in situ annealing of Be-doped (Ga,Mn)As heterostructures grown by molecular beam epitaxy. Transmission electron microscopy and magnetometry studies reveal two distinct classes of nanoclustered samples whose structural and magnetic properties depend on the Mn content of the initial (Ga,Mn)As layer. For Mn content in the range 5% - 7.5%, annealing creates a superparamagnetic material with a uniform distribution of small clusters (diameter around 6 nm) and with a low blocking temperature (T_B approximately 10 K). While transmission electron microscopy cannot definitively identify the composition and crystalline phase of these small clusters, our experimental data suggest that they may be comprised of either zinc-blende MnAs or Mn-rich regions of (Ga,Mn)As. At higher Mn content (> 8 %), we find that annealing results in an inhomogeneous distribution of both small clusters as well as much larger NiAs-phase MnAs clusters (diameter around 25 nm). These samples also exhibit supermagnetism, albeit with substantially larger magnetic moments and coercive fields, and blocking temperatures well above room temperature.

Ferromagnetism and spin-dependent transport in n-type Mn-doped bismuth telluride thin films

We describe a detailed study of the structural, magnetic, and magnetotransport properties of single-crystal,

Measurements of nanoscale domain wall flexing in a ferromagnetic thin film.

n

Effects of exchange bias on magnetotransport in permalloy kagome artificial spin ice

-type, Mn-doped bismuth telluride thin films grown by molecular beam epitaxy. With increasing Mn concentration, the crystal structure changes from the tetradymite structure of the

Structural, electronic, and magnetic properties of single MnAs nanoclusters in GaAs

{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}

Ultrafast ferromagnetic-paramagnetic phase transition in MnAs observed by second-harmonic generation

parent crystal at low Mn concentrations towards a BiTe phase in the (

Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically doped topological insulator

{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}{)}_{m}({\mathrm{Bi}}_{2}{)}_{n}

Ferromagnetism in Bi2Se3: Mn epitaxial layers

homologous series. Magnetization measurements reveal the onset of ferromagnetism with a Curie temperature in the range 13.8\char21{}17 K in films with