More Like this

1. Spin-Filtered Tunneling Device Using a Topological Insulator

   Berlioz, Jose R. (April 2021, Masters Thesis of Engineering)

   null (Ed.)

   There has been much interest in the study of topological insulators (TI) recently. Due to their unique electronic structure, these new materials have been an active area of research to discover new quantum phenomena and their application in new technologies. Unlike the electronic structure observed in traditional semiconductors, the strong spin-orbit coupling induces a band inversion in the electronic structure of TIs. One of the side effects of this band inversion is creating metallic-like surface states at the material's surface that are protected by time invariance and whose spin angular momentum is locked to the direction of the momentum of the electron. These surface states are essentially resistant to scattering events that otherwise affect other materials. Leveraging the characteristic scattering resistance, the spin-momentum locking of the surface states, and the Dirac cone structure, a spin-resonant tunneling diode using topological insulators has been investigated to implement a negative differential resistance device. Utilizing the spin texture of the surface states, an additional spin-filter can help to suppress the valley current in a negative differential resistance device. In the spin-resonant tunneling diode, the tunneling process would also benefit from having protection from conventional scattering processes due to defects and thickness or line edge roughness. This research is focused on the manufacturing of a spin-filtered tunnel diode. Using molecular beam epitaxy to grow a three-layer heterostructure, with two layers of bismuth selenide as the topological insulator separated by a thin layer of tungsten diselenide as a tunnel barrier. The alignment of the Fermi levels of the topological insulator layers and the thickness of the tunnel barrier were investigated using X-ray Photoelectron Spectroscopy. The fabrication and initial electrical measurements of the spin-filtered tunnel diode were also investigated. 

   more » « less
2. Unconventional supercurrent phase in Ising superconductor Josephson junction with atomically thin magnetic insulator

   https://doi.org/10.1038/s41467-021-25608-1  

   Idzuchi, H.; Pientka, F.; Huang, K.-F.; Harada, K.; Gül, Ö.; Shin, Y. J.; Nguyen, L. T.; Jo, N. H.; Shindo, D.; Cava, R. J.; et al (December 2021, Nature Communications)

   Abstract In two-dimensional (2D) NbSe 2 crystal, which lacks inversion symmetry, strong spin-orbit coupling aligns the spins of Cooper pairs to the orbital valleys, forming Ising Cooper pairs (ICPs). The unusual spin texture of ICPs can be further modulated by introducing magnetic exchange. Here, we report unconventional supercurrent phase in van der Waals heterostructure Josephson junctions (JJs) that couples NbSe 2 ICPs across an atomically thin magnetic insulator (MI) Cr 2 Ge 2 Te 6 . By constructing a superconducting quantum interference device (SQUID), we measure the phase of the transferred Cooper pairs in the MI JJ. We demonstrate a doubly degenerate nontrivial JJ phase ( ϕ ), formed by momentum-conserving tunneling of ICPs across magnetic domains in the barrier. The doubly degenerate ground states in MI JJs provide a two-level quantum system that can be utilized as a new dissipationless component for superconducting quantum devices. Our work boosts the study of various superconducting states with spin-orbit coupling, opening up an avenue to designing new superconducting phase-controlled quantum electronic devices. 

   more » « less
3. Interference, diffraction, and diode effects in superconducting array based on bismuth antimony telluride topological insulator

   https://doi.org/10.1038/s42005-023-01288-9  

   Song, Xiangyu; Suresh_Babu, Soorya; Bai, Yang; Golubev, Dmitry_S; Burkova, Irina; Romanov, Alexander; Ilin, Eduard; Eckstein, James_N; Bezryadin, Alexey (July 2023, Communications Physics)

   Abstract It is well-known in optics that the spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in Young’s famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator film Bi_0.8Sb_1.2Te₃. In the limit of an extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Therefore, such arrays can be used as sensitive absolute magnetic field sensors. A key finding is that the device acts as a superconducting diode, controlled by magnetic field. 

   more » « less
4. Electronic structure of topological defects in the pair density wave superconductor

   https://doi.org/10.1103/PhysRevB.110.214508  

   Rosales, Marcus; Fradkin, Eduardo (December 2024, Physical Review B)

   Pair density waves (PDWs) are a inhomogeneous superconducting states whose Cooper pairs possess a finite momentum resulting in a oscillatory gap in space, even in the absence of an external magnetic field. There is growing evidence for the existence of PDW superconducting order in many strongly correlated materials, particularly in the cuprate superconductors and in several other different types of systems. A feature of the PDW state is that inherently it has a CDW as a composite order associated with it. Here we study the structure of the electronic topological defects of the PDW, paying special attention to the half-vortex and its electronic structure that can be detected in STM experiments. We discuss tell-tale signatures of the defects in violations of inversion symmetry, in the excitation spectrum and their spectral functions in the presence of topological defects. We discuss the “Fermi surface” topology of Bogoliubov quasiparticle of the PDWphases, and we briefly discuss the role of quasiparticle interference. 

   more » « less
5. Dynamic adhesion of 2D materials to mixed-phase BiFeO 3 structural phase transitions

   https://doi.org/10.1063/5.0096686  

   Watson, Carla; Peña, Tara; Abdin, Marah; Khan, Tasneem; Wu, Stephen M. (July 2022, Journal of Applied Physics)

   Two-dimensional materials, such as transition metal dichalcogenides, have generated much interest due to their strain-sensitive electronic, optical, magnetic, superconducting, or topological properties. Harnessing control over their strain state may enable new technologies that operate by controlling these materials’ properties in devices such as straintronic transistors. Piezoelectric oxides have been proposed as one method to control such strain states on the device scale. However, there are few studies of how conformal 2D materials remain on oxide materials with respect to dynamic applications of the strain. Non-conformality may lead to non-optimal strain transfer. In this work, we explore this aspect of oxide-2D adhesion in the nanoscale switching of the substrate structural phase in thin 1T′-MoTe 2 attached to a mixed-phase thin-film BiFeO 3 (BFO), a multiferroic oxide with an electric-field induced structural phase transition that can generate mechanical strains of up to 2%. We observe that flake thickness impacts the conformality of 1T′-MoTe 2 to structural changes in BFO, but below four layers, 1T′-MoTe 2 fully conforms to the nanoscale BFO structural changes. The conformality of few-layer 1T′-MoTe 2 suggests that BFO is an excellent candidate for deterministic, nanoscale strain control for 2D materials. 

   more » « less