By harnessing the power of high-resolution scanning tunneling microscopy (STM) techniques in the study of novel materials, our group has had fundamental breakthroughs in understanding correlated electronic states, including high-Tc cuprate superconductors, heavy fermion systems, disordered semiconductors, and topological quantum states. The kind of high-resolution spectroscopic information we obtain using these techniques, some of which have been specifically developed by our group, cannot be obtained from any other experimental methods and as such have had a significant impact on understanding novel electronic states in materials in general.
One fundamental goal of our current program is to build a body of knowledge of how correlated electron states form as electrons are cooled, be it in the pseudogap state, in cuprates, or a heavy fermion state in actinides, and to probe how they transform into other correlated states such as unconventional superconducting states. Another fundamental goal of our group is to probe topological systems, which are defined by their boundary excitations, such as Dirac-like or Majorana excitations. These excitations often occur at the boundary of materials, making STM measurements a very powerful method to study them. We have a broad program focused in this area that includes studies on both bulk-synthesized samples as well as more recent efforts with in situ fabricated MBE grown nanostructures. Our aim is to not only provide experimental indications that these excitations do occur in specific solid state settings, but to find ways in which they can be manipulated so as to demonstrate their novel properties, such as non-abelian characteristics (Majoranas).
Finally, another defining feature of our research program is developing new ways in which we can probe electronic phenomena on the atomic scale in solids with high resolution. For example, we are harnessing spin-polarized STM tunneling from magnetic tips or developing Josephson STM tunneling from superconducting tips for new high-resolution experiments on correlated and topological electronic materials.
1. S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A. Bernevig, A. Yazdani, “Observation of Majorana fermions in ferromangetic atomic chains on a superconductor,” Science 346, 6209 (2014).
2. E. H. da Silva Neto, P. Aynajian, A. Frano, R. Comin, E. Schierle, E. Weschke, A. Gyenis, J. Wen, J. Schneeloch, Z. Xu, S. Ono, G. Gu, M. Le Tacon, and A. Yazdani, “Ubiquitous interplay between charge ordering and high-temperature superconductivity in cuprates,” Science 343, 393 (2014).
3. B. B. Zhou, S. Misra, E. H. da Silva Neto, P. Aynajian, R. E. Baumbach, J. D. Thompson, E. D. Bauer, and A. Yazdani, “Visualizing nodal heavy fermion superconductivity,” Nature Physics 9, 474 (2013).
4. H. Beidenkopf, P. Roushan, J. Seo, L. Gorman, I. Drozdov, Y. S. Hor, R. J. Cava, and A. Yazdani, “Spatial fluctuations of helical Dirac fermions on the surface of topological insulators,” Nature Physics 7, 939 (2011).
5. C. V. Parker, P. Aynajian, E. H. da Silva Neto, A. Pushp, S. Ono, J. Wen, Z. Xu, G. Gu, and A.Yazdani, “ Fluctuating stripes at the onset of the pseudogap in the high-Tc superconductor Bi2Sr2CaCu2O8+x,” Nature 468, 677 (2010).
6. J. Seo, P. Roushan, H. Beidenkopf, Y. S. Hor, R. J. Cava, and A. Yazdani, “Transmission of topological surface states through surface barriers,” Nature 466, 343 (2010).
7. A. Richardella, P. Roushan, S. Mack, B. Zhou, D. Huse, D. Awschalom, and A. Yazdani, “Visualizing critical spatial correlations for electronic states near the metal-insulator transition GaMnAs,” Science 327, 665 (2010).
8. P. Roushan, J. Seo, C. V. Parker, Y.-S. Hor, D. Hsieh, D Qian, A. Richardella, M. Z. Hasan, R. J. Cava, and A. Yazdani, “Topological surface states protected from backscattering by chiral spin texture,” Nature 460, 1106 (2009).
9. A. Pushp, C. V. Parker, A. N. Pasupathy, K. K. Gomes, S. Ono, J. Wen, Z. Xu, G. Gu, and A. Yazdani, “Extending universal nodal excitations optimizes superconductivity in Bi2Sr2CaCu2O8+ d,” Science 324, 1689, (2009).
10. A. N. Pasupathy, A. Pushp, K. K. Gomes, C. V. Parker, J. Wen, Z. Xu, G. Gu, S. Ono, Y. Ando, and A. Yazdani, “Electronic origin of the inhomogeneous pairing interaction in the high-Tc superconductor Bi2Sr2CaCu2O8+d ,” Science 320, 196 (2008).