7/2/2023 0 Comments Physics phenomena![]() ![]() At the same time, the new simulator is not as successful at tuning the interactions between electrons when they share the same site. The system can also reach much lower effective temperatures and assess the thermodynamic ground states of the model. While there are other quantum simulators, such as one that uses cold atom systems and an artificial lattice created by laser beams, Mak says his team’s simulator has the distinct advantage of being a “true many-particle simulator” that can easily control – or tune – particle density. The magnetic ground state of Mott insulators is also an important phenomena the researchers are continuing to study. Mott insulators are materials that should behave like metals and conduct electricity, but instead function like insulators – phenomena that physicists predicted the Hubbard model would demonstrate. ![]() So far, the researchers have used the simulator to make two significant discoveries: observing a Mott insulating state, and mapping the system’s magnetic phase diagram. What kind of magnetic phase is it? How do the magnetic phases depend on the electron density?” “We then measure the system and map out the phase diagram. “We can control the occupation of the electron at each site very precisely,” Mak said. ![]() That’s how you can get magnetism and superconductivity.”īecause electrons have a negative charge and repel each other, these ensuing interactions become increasingly complicated when there are so many of them in play – hence the need for a simplified system to understand their behavior. “But when the electrons hop around and interact, that’s very interesting. “If you don’t have this interaction, everything is actually well understood and sort of boring,” said Mak. But the electrons have enough kinetic energy that, occasionally, they can hop over the barrier and interact with neighboring electrons. ![]() These electrons are usually trapped in place by the energy barrier between the sites. The moiré superlattice looks like a series of interlocking hexagons, and in each juncture – or site – in the crosshatch pattern, the researchers place an electron. And when you put one on top of the other, you create a pattern called a moiré superlattice.” Mak said. “What we have done is take two different monolayers of this semiconductor, tungsten disulfide (WS2) and tungsten diselenide (WSe2), which have a lattice constant that is slightly different from each other. Their lab partnered with co-author Allan MacDonald, a physics professor at the University of Texas at Austin, who in 2018 theorized a Hubbard model simulator would be possible by stacking two atomic monolayers of semiconductors, the sort of materials Mak and Shan have been studying for a decade. Both researchers are members of the Kavli Institute at Cornell for Nanoscale Science, and they came to Cornell through the provost’s Nanoscale Science and Molecular Engineering (NEXT Nano) initiative. Their shared lab specializes in the physics of atomically thin quantum materials. The project is led by Kin Fai Mak, associate professor of physics in the College of Arts and Sciences and the paper’s co-senior author along with Jie Shan, professor of applied and engineering physics in the College of Engineering. The lead author is postdoctoral associate Yanhao Tang. Their paper, “ Simulation of Hubbard Model Physics in WSe2/WS2 Moiré Superlattices,” was published March 18 in Nature. The team then used this solid-state platform to map a longstanding conundrum in physics: the phase diagram of the triangular lattice Hubbard model. This simplified system enables the team to better understand the essential physics of many interacting quantum particles.Ī Cornell-led collaboration has successfully created such a simulator using ultrathin monolayers that overlap to make a moiré pattern. Cornell researchers stacked two atomic monolayers of a semiconductor – tungsten disulfide and tungsten diselenide – to create a moiré superlattice that acts as a simulator for the Hubbard model. ![]()
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