College of Arts and Sciences

Continue reading… No seminar (Thanksgiving holiday)

Creating and probing new phases in quantum materials

Qiong Ma

Physics Department, Massachusetts Institute of Technology

Physics Department, Boston College

Abstract: There are two fundamental ways for us to understand nature. One way is to understand our world by breaking it into smaller and smaller building blocks. Primary examples include the discoveries of chemical elements and elementary particles. The other way is: given the same building blocks, we ask what the possible ways are for them to be organized by nature. On the level of condensed matter, even with the same chemical composition and parent lattice structure,

Continue reading… Qiong Ma (MIT)

Current Fluctuations Driven by Magnetic Resonance

Arne Brataas

Department of Physics, Norwegian University of Science and Technology

When spins in magnetic materials precess, they emit currents into the surrounding conductors. We will explain how dynamical magnets also induce current noise. The shot noise characterizes and detects magnetic resonance and new aspects of electron transport in magnetic nanostructures.

We generalize the description of current fluctuations driven by spin dynamics in three ways using scattering theory. First, our approach describes a general junction with any given electron scattering properties. Second, we consider antiferromagnets as well as ferromagnets.

Continue reading… Arne Brataas (NUST, Norway)

Spintronics: Fundamentals and recent developments

Sergio M. Rezende

Departamento de Física, Universidade Federal de Pernambuco, Recife, Brazil

Zoom Recording

Abstract.— Spintronics is the field of physics and technology that makes use of the electron spin to transport and process information. The birth of this field dates to the 1980s and was triggered by the discovery of the Giant Magnetoresistance in magnetic multilayers. In the 2000s this field gained new impulse with the discovery of several phenomena involving spin currents and ferromagnetic films, such as the spin Hall effect,

Continue reading… Sergio M. Rezende (Universidade Federal de Pernambuco, Brazil)

Which geometries can and which cannot be given to thin nematic elastomer surfaces

Hillel Aharoni

Department of Physics, Weizmann Institute of Science

Youtube video

Abstract.– Thin nematic elastomer sheets can be programmed, via the nematic director field embedded into them, to take different shapes in different environments. Recent experiments from various groups demonstrate excellent control over the director field, thus opening a door for achieving accurate and versatile designs of shape-shifting surfaces. At the crux of any effort to implement this design mechanism lies the inverse design problem —

Continue reading… Hillel Aharoni (Weizmann Institute of Science, Israel)

Optics of materials with Dirac and Weyl fermions

Alexey Belyanin

Department of Physics and Astronomy, Texas A&M University

Youtube video

Relativistic Dirac and Weyl fermions were extensively studied in quantum field theory. Recently they emerged in the non-relativistic condensed-matter setting as gapless quasiparticle states in some types of crystals. Notable examples of 2D systems include graphene and surface states in topological insulators such as Bi2Se3. Their 3D implementation is Dirac and Weyl semimetals. Most of the research has been focused on their topological properties and electron transport. However,

Continue reading… Alexey Belyanin (Texas A&M University)

Title: Harnessing Nitrogen Vacancy Centers in Diamond for Next-Generation Quantum Science and Technology

Chunhui Du, Department of Physics, University of California, San Diego

Zoom Recording

Abstract: Advanced quantum systems are integral to both scientific research and modern technology enabling a wide range of emerging applications. Nitrogen vacancy (NV) centers, optically-active atomic defects in diamond, are directly relevant in this context due to their single-spin sensitivity and functionality over a broad temperature range. Many of these advantages derive from their quantum-mechanical nature of NV centers that are endowed by excellent quantum coherence,

Continue reading… Chunhui Du (UC San Diego)

Quantum detailed balance & exact solutions of interacting driven-dissipative systems

Aashish Clerk, Pritzker School of Molecular Engineering, The University of Chicago

Zoom Recording

I’ll discuss a new approach that allows one to non-perturbatively find the steady states of driven-dissipative systems described by a Lindblad master equation.  The focus will be on driven nonlinear resonator systems, a class of system that is at the forefront of research in superconducting quantum circuits and quantum optics.    I’ll discuss new phenomena revealed by these solutions, including a new kind of generalized photon blockade effect that is effective even for extremely weak system nonlinearity,

Continue reading… Aashish Clerk (U Chicago)

Topology in Charge-Density Wave Systems

Barry Bradlyn

Physics department, the University of Illinois at Urbana-Champaign

Zoom recording

Abstract.-The recent discover of Weyl semimetals has shown that topological effects can play a significant role in the behavior of gapless systems. However, correlation effects in known Weyl semimetals did not seem to play a significant role in most materials. Here I will show that the charge density wave compound (TaSe_2)_4I is a Weyl semimetal with strong correlations due to electron-phonon coupling. I will show how the topological charge of the Weyl nodes leaves its mark on the behavior of the collective phase mode of the charge density wave,

Continue reading… Barry Bradlyn (UIUC)

Tunable correlated and topological states in twisted graphene heterostructures

Matthew Yankowitz

Department of Physics, University of Washington

Zoom Recording

Abstract.– In van der Waals heterostructures composed of two rotated graphene sheets, a moiré superlattice results in the emergence of flat electronic bands over a small range of twist angles. A variety of highly tunable correlated and topological states have recently been identified in these platforms owing to the quenched kinetic energy of charge carriers and the intrinsic Berry curvature of the flat bands. I will discuss our recent work investigating these states in three different twisted graphene platforms.

Continue reading… Matthew Yankowitz (University of Washington)

Continue reading… No seminar (faculty meeting)

Charge-spin conversion effects and magnetization switching enabled by spin-orbit coupling

Pietro Gambardella

Department of Materials, ETH Zurich, CH – 8093 Zürich, Switzerland

Zoom Recording

The coupling of spin and orbital angular momenta underlies the magnetoelectric properties of matter. Although small, the spin-orbit interaction determines the preferred orientation of the order parameter in ferromagnets and antiferromagnets as well as the possibility to excite the magnetization out of equilibrium while ensuring the conservation of angular momentum. In recent years, advances in the understanding of the nonequilibrium charge-spin conversion processes mediated by the spin-orbit interaction have opened new perspectives for controlling the static and dynamic magnetization of all classes of magnetic materials,

Continue reading… Pietro Gambardella (ETH Zürich, Switzerland)

Coherent information processing with on-chip microwave magnonics

Zoom Recording

In the race of post-CMOS computing technologies, coherent information processing with microwave circuits have demonstrated great potentials with the recent breakthrough in quantum computing, where both the quanta and the phase of the excitation states can be utilized for carrying and processing information. In this seminar, I will show that magnons—the collective excitations of exchange-coupled spins in magnetic materials—act as a new candidate for coherent information transfer and processing. Compared with other excitations, magnons exhibit special advantages: 1) their frequencies are naturally in the microwave regime and can be noninvasively tuned by an external magnetic field,

Continue reading… Yi Li (Argonne National Lab)