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|    Semiconductor lattice marries electrons     |
|    22 Mar 23 22:30:26    |
      MSGID: 1:317/3 641bd5fa       PID: hpt/lnx 1.9.0-cur 2019-01-08       TID: hpt/lnx 1.9.0-cur 2019-01-08        Semiconductor lattice marries electrons and magnetic moments                Date:        March 22, 2023        Source:        Cornell University        Summary:        A model system created by stacking a pair of monolayer        semiconductors is giving physicists a simpler way to study        confounding quantum behavior, from heavy fermions to exotic quantum        phase transitions.                      Facebook Twitter Pinterest LinkedIN Email       FULL STORY       ==========================================================================       A model system created by stacking a pair of monolayer semiconductors is       giving physicists a simpler way to study confounding quantum behavior,       from heavy fermions to exotic quantum phase transitions.                     ==========================================================================       The group's paper, "Gate-Tunable Heavy Fermions in a Moire' Kondo       Lattice," published March 15 in Nature. The lead author is postdoctoral       fellow Wenjin Zhao in the Kavli Institute at Cornell.              The project was led by Kin Fai Mak, professor of physics in the College       of Arts and Sciences, and Jie Shan, professor of applied and engineering       physics in Cornell Engineering and in A&S, the paper's co-senior       authors. Both researchers are members of the Kavli Institute; they came       to Cornell through the provost's Nanoscale Science and Microsystems       Engineering (NEXT Nano) initiative.              The team set out to address what is known as the Kondo effect, named       after Japanese theoretical physicist Jun Kondo. About six decades ago,       experimental physicists discovered that by taking a metal and substituting       even a small number of atoms with magnetic impurities, they could scatter       the material's conduction electrons and radically alter its resistivity.              That phenomenon puzzled physicists, but Kondo explained it with a model       that showed how conduction electrons can "screen" the magnetic impurities,       such that the electron spin pairs with the spin of a magnetic impurity       in opposite directions, forming a singlet.              While the Kondo impurity problem is now well understood, the Kondo lattice       problem -- one with a regular lattice of magnetic moments instead of       random magnetic impurities -- is much more complicated and continues       to stump physicists. Experimental studies of the Kondo lattice problem       usually involve intermetallic compounds of rare earth elements, but       these materials have their own limitations.              "When you move all the way down to the bottom of the Periodic Table,       you end up with something like 70 electrons in an atom," Mak said. "The       electronic structure of the material becomes so complicated. It is very       difficult to describe what's going on even without Kondo interactions."       The researchers simulated the Kondo lattice by stacking ultrathin       monolayers of two semiconductors: molybdenum ditelluride, tuned to a       Mott insulating state, and tungsten diselenide, which was doped with       itinerant conduction electrons.              These materials are much simpler than bulky intermetallic compounds,       and they are stacked with a clever twist. By rotating the layers at       a 180-degree angle, their overlap results in a moire' lattice pattern       that traps individual electrons in tiny slots, similar to eggs in an       egg carton.              This configuration avoids the complication of dozens of electrons jumbling       together in the rare earth elements. And instead of requiring chemistry       to prepare the regular array of magnetic moments in the intermetallic       compounds, the simplified Kondo lattice only needs a battery. When a       voltage is applied just right, the material is ordered into forming a       lattice of spins, and when one dials to a different voltage, the spins       are quenched, producing a continuously tunable system.              "Everything becomes much simpler and much more controllable," Mak said.              The researchers were able to continuously tune the electron mass and       density of the spins, which cannot be done in a conventional material,       and in the process they observed that the electrons dressed with the       spin lattice can become 10 to 20 times heavier than the "bare" electrons,       depending on the voltage applied.              The tunability can also induce quantum phase transitions whereby heavy       electrons turn into light electrons with, in between, the possible       emergence of a "strange" metal phase, in which electrical resistance       increases linearly with temperature. The realization of this type       of transition could be particularly useful for understanding the       high-temperature superconducting phenomenology in copper oxides.              "Our results could provide a laboratory benchmark for theorists,"       Mak said. "In condensed matter physics, theorists are trying to deal       with the complicated problem of a trillion interacting electrons. It       would be great if they don't have to worry about other complications,       such as chemistry and material science, in real materials. So they often       study these materials with a 'spherical cow' Kondo lattice model. In the       real world you cannot create a spherical cow, but in our material now       we've created one for the Kondo lattice." Co-authors include doctoral       students Bowen Shen and Zui Tao; postdoctoral researchers Kaifei Kang and       Zhongdong Han; and researchers from the National Institute for Materials       Science in Tsukuba, Japan.              The research was primarily supported by the Air Force Office of Scientific       Research, the National Science Foundation, the U.S. Department of Energy       and the Gordon and Betty Moore Foundation.               * RELATED_TOPICS        o Matter_&_Energy        # Spintronics # Materials_Science # Physics # Graphene        o Computers_&_Math        # Spintronics_Research # Computers_and_Internet #        Hacking # Encryption        * RELATED_TERMS        o Particle_physics o Quantum_number o Quantum_entanglement        o Quantum_tunnelling o Bose-Einstein_condensate o        Electron_configuration o Quantum_dot o Linus_Pauling              ==========================================================================       Story Source: Materials provided by Cornell_University. Original written       by David Nutt, courtesy of the Cornell Chronicle. Note: Content may be       edited for style and length.                     ==========================================================================       Journal Reference:        1. Wenjin Zhao, Bowen Shen, Zui Tao, Zhongdong Han, Kaifei Kang, Kenji        Watanabe, Takashi Taniguchi, Kin Fai Mak, Jie Shan. Gate-tunable        heavy fermions in a moire' Kondo lattice. Nature, 2023; DOI:        10.1038/s41586- 023-05800-7       ==========================================================================              Link to news story:       https://www.sciencedaily.com/releases/2023/03/230322140331.htm              --- up 1 year, 3 weeks, 2 days, 10 hours, 50 minutes        * Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! 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