Abstract-Terahertz-frequency magnetoelectric effect in Ni-doped CaBaCo 4 O 7

Shukai Yu, C. Dhanasekhar, Venimadhav Adyam, Skylar Deckoff-Jones, Michael K. L. Man, Julien Madéo, E Laine Wong, Takaaki Harada, M. Bala Murali Krishna, Keshav M. Dani, and Diyar Talbayev

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.094421

We present a study of the terahertz-frequency magnetoelectric effect in ferrimagnetic pyroelectric ${\mathrm{CaBaCo}}_4{O}_7$ and its Ni-doped variants. The terahertz absorption spectrum of these materials consists of spin excitations and low-frequency infrared-active phonons. We studied the magnetic-field-induced changes in the terahertz refractive index and absorption in magnetic fields up to 17 T. We find that the magnetic field modulates the strength of infrared-active optical phonons near 1.2 and 1.6 THz. We use the Lorentz model of the dielectric function to analyze the measured magnetic-field dependence of the refractive index and absorption. We propose that most of the magnetoelectric effect is contributed by the optical phonons near 1.6 THz and higher frequency resonances. Our experimental results can be used to construct and validate more detailed theoretical descriptions of magnetoelectricity in ${\mathrm{CaBaCo}}_{4-x}{\mathrm{Ni}}_x{O}_7$.

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Abstract-Engineering Photophenomena in Large, 3D Structures Composed of Self-Assembled van der Waals Heterostructure Flakes

1. M. Bala Murali Krishna¹, 
2. Michael K. L. Man¹, 
3. Soumya Vinod², 
4. Catherine Chin¹,
5. Takaaki Harada¹, 
6. Jaime Taha-Tijerina²,
7. Chandra Sekhar Tiwary³, 
8. Patrick Nguyen²,
9. Patricia Chang⁴, 
10. Tharangattu N. Narayanan⁵, 
11. Angel Rubio^6,7, 
12. Pulickel M. Ajayan², 
13. Saikat Talapatra^8,9 and
14. Keshav M. Dani^1,*

Article first published online: 17 AUG 2015

DOI: 10.1002/adom.201500296

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA

http://onlinelibrary.wiley.com/doi/10.1002/adom.201500296/abstract

A photocapacitive, dissipationless, optoelectronic terahertz response is observed in robust 3D van der Waals heterostructured flakes of hexagonal boron nitride and graphene. The response is fundamentally distinct from that of the parent materials and can be tuned from insulating to photocapacitive to semiconducting by varying the composition. Such hybrid structures have broad implications for tunable optoelectronic materials and potential terahertz devices.