Engineering topics

Balakrishnan, Purnima P.

Publications and source records attributed to Balakrishnan, Purnima P..

3 records

DOE OSTI2024

Interface-induced superconductivity in magnetic topological insulators

The interface between two different materials can show unexpected quantum phenomena. Here, in this study, we used molecular beam epitaxy to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic topological insulator (TI) and an antiferromagnetic iron chalcogenide (FeTe). We observed emergent interface-induced superconductivity in these heterostructures and demonstrated the co-occurrence of superconductivity, ferromagnetism, and topological band structure in the magnetic TI layer—the three essential ingredients of chiral topological superconductivity (TSC). The unusual coexistence of ferromagnetism and superconductivity is accompanied by a high upper critical magnetic field that exceeds the Pauli paramagnetic limit for conventional superconductors at low temperatures. These magnetic TI/FeTe heterostructures with robust superconductivity and atomically sharp interfaces provide an ideal wafer-scale platform for the exploration of chiral TSC and Majorana physics.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Exchange-Biased Quantum Anomalous Hall Effect

The quantum anomalous Hall (QAH) effect is characterized by a dissipationless chiral edge state with a quantized Hall resistance at zero magnetic field. Manipulating the QAH state is of great importance in both the understanding of topological quantum physics and the implementation of dissipationless electronics. Here, the QAH effect is realized in the magnetic topological insulator Cr-doped (Bi,Sb) 2 Te 3 (CBST) grown on an uncompensated antiferromagnetic insulator Al-doped Cr 2 O 3 . Through polarized neutron reflectometry (PNR), a strong exchange coupling is found between CBST and Al-Cr 2 O 3 surface spins fixing interfacial magnetic moments perpendicular to the film plane. Further, the interfacial coupling results in an exchange-biased QAH effect. This study further demonstrates that the magnitude and sign of the exchange bias can be effectively controlled using a field training process to set the magnetization of the Al-Cr 2 O 3 layer. It demonstrates the use of the exchange bias effect to effectively manipulate the QAH state, opening new possibilities in QAH-based spintronics.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Large Spin-Orbit-Torque Efficiency and Room-Temperature Magnetization Switching in Sr Ir O 3 / Co-Fe-B Heterostructures

Spin-orbit-torque (SOT) switching is a potentially energy-efficient mechanism by which electrical current can control magnetization. We demonstrate room-temperature SOT switching in nanometer-thick Co⁢Fe⁢B/Sr⁢Ir⁢O 3 bilayers despite the amorphous nature of CoFeB and the interface. This behavior is attributed to the large spin Hall angle in Sr⁢Ir⁢O 3 as well as high spin transmission at the interface that contribute to the SOT efficiency ξ SOT . Our bilayers exhibit large ξ SOT of up to 1.4 and effective spin Hall conductivity of 0.9 ×10 5 (ℏ/2e)Ω –1 ⁢m –1 . In our bilayers, we observe unidirectional magnetoresistance and current-induced magnetization switching with a low critical current density of 1.38 ×10 10 A/m 2 at room temperature. Finally, our results are promising for heterostructures combining technologically relevant CoFeB with high spin-orbit-coupling oxides.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗