Welcome to QIS Seminars!
Speaker: Prof. Chunlei Qu
https://personal.stevens.edu/~cqu5/
Abstract: Many combinatorial optimization problems such as the Max-Cut and the traveling salesman problems can be cast in terms of an Ising model. A special-purpose optical processor known as an optical Ising machine is able to solve these hard optimization problems with an optical acceleration. In this talk, I will discuss a fully connected large-scale optical Ising machine that is engineered with Fourier and nonlinear optics. The system exhibits a rich phase diagram due to the interplay of various types of spin interactions. It is also intimately related to the Hopfield neural network and thus can be used for information storage, retrieval, and machine learning. In the second part of the talk, I will discuss how to make a superfluid gyroscope with a spin-orbit-coupled Bose-Einstein condensate.
Time: 11:00am April 15 (2022)
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Speaker: Prof. Fei Xue from University of Alabama
https://www.uab.edu/cas/physics/people/faculty/fei-xue
Abstract:
Spintronics studies the interplay between electron charge and spin degrees of freedom. An archetypal application is magnetic random access memory, in which electric current switches the magnetization between two bi-stable states (representing “0” and “1”). With the rapid commercialization of these devices, research has switched to other ways to use electricity to control the magnetization. One focus has been on the spin Hall effect, in which spin-orbit coupling in a nonmagnetic metal enables spin currents flowing transverse to applied electric fields. This spin current can exert a torque and switch the magnetization, so called spin-orbit torque. Spin-orbit torque has great potential to expand the range of spintronics applications for magnetic memory and neuromorphic computing.
One property of spin-orbit torques that is important for many applications is the ability to deterministically switch magnets with perpendicular anisotropy. In this talk, I will show how hidden material properties, like crystal symmetry, can efficiently provide such behavior using two-dimensional semimetals. I will present our findings that when local site symmetry is lower than the global symmetry, electric fields can generate unconventional spin currents. Although this unconventional spin current is hidden in bulk properties, it can exert an unconventional torque in adjacent ferromagnets and switch the perpendicular magnetization.
Another forefront research area is using antiferromagnetic materials in spintronic devices. I consider the spin-orbit torque in collinear antiferromagnets with staggered magnetizations on two sublattices. Using the two-dimensional antiferromagnet CrI3 as an example, I show that current-induced staggered spin-orbit torques can switch the antiferromagnetic Neel order and drive sub-terahertz magnetic oscillations by simply changing the electric-field strength.
Time: 11:00am April 1 (2022)
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Speaker: Geo Jose (University of Oklahoma)
Abstract: The Sachdev-Ye-Kitaev (SYK) model has received a lot of attention recently. The model exhibits quantum chaos, is nearly conformally invariant, exactly solvable in the large N limit, and maps into the horizon of a black-hole. In condensed matter, this model describes matter without quasiparticles. Several dispersive extensions of the original model have been suggested, which in the strong coupling regime generically lead to a linear in temperature dc resistivity, reminiscent of the “strange metal” phase of high-temperature superconductors. I will briefly review these models and describe a semimetallic extension of the SYK model which realizes a novel type of non-Fermi liquid, in which resistivity has a sublinear scaling with temperature.
Time: Dec 3 (2021) 11:00am
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