Professor John Davis

Associate Professor

University of Alberta

Department of Physics

Title:  Superfluid Helium Electromechanics

Abstract: Liquid helium posses many properties that make it an attractive medium for studies of mechanical systems in the quantum regime, such as low mechanical and dielectric losses.  The flip side of this is to imagine using optomechanics or electromechanics to revisit the novel physics of superfluid helium, including bosonic helium-4 and fermionic helium-3.  In particular, when spatially restricted in one dimension, helium superfluids are expected to demonstrate quasi-two dimensional behavior with qualitatively different physics than in three dimensions.  By using nanofabrication techniques to both confine the helium and provide an electromechanical detection scheme, we are beginning the journey of studying such two-dimensional superfluids.

Professor John Davis

Associate Professor

University of Alberta

Department of Physics

Title:  Superfluid Helium Electromechanics

Abstract: Liquid helium posses many properties that make it an attractive medium for studies of mechanical systems in the quantum regime, such as low mechanical and dielectric losses.  The flip side of this is to imagine using optomechanics or electromechanics to revisit the novel physics of superfluid helium, including bosonic helium-4 and fermionic helium-3.  In particular, when spatially restricted in one dimension, helium superfluids are expected to demonstrate quasi-two dimensional behavior with qualitatively different physics than in three dimensions.  By using nanofabrication techniques to both confine the helium and provide an electromechanical detection scheme, we are beginning the journey of studying such two-dimensional superfluids.

Dr. Allen Scheie

Postdoctoral Research Associate

Oak Ridge National Laboratory

Neutron Scattering Division

Title: Witnessing entanglement in quantum magnets using neutron scattering

Abstract: In this talk I show how information about solid state quantum entanglement can be extracted from magnetic neutron scattering using model-independent techniques. Using the 1D spin chain KCuF3, we examine three entanglement witnesses applicable to neutron scattering: one tangle, two tangle, and Quantum Fisher Information (QFI). We find that QFI is the most experimentally robust, giving good agreement between theory and experiment over all measured temperatures, and witnessing multipartite entanglement up to 75 K. We then apply the entanglement witnesses to the 2D triangular lattice KYbSe2, showing the presence of appreciable entanglement in the low temperature phase. We then use diffuse scattering fits, heat capacity comparisons, and nonlinear spin wave fits to demonstrate that KYbSe2 is proximate to a quantum spin liquid. We thus provide a rigorous route to studying and understanding highly entangled quantum phases.

Dr. Allen Scheie

Postdoctoral Research Associate

Oak Ridge National Laboratory

Neutron Scattering Division

Title: Witnessing entanglement in quantum magnets using neutron scattering

Abstract: In this talk I show how information about solid state quantum entanglement can be extracted from magnetic neutron scattering using model-independent techniques. Using the 1D spin chain KCuF3, we examine three entanglement witnesses applicable to neutron scattering: one tangle, two tangle, and Quantum Fisher Information (QFI). We find that QFI is the most experimentally robust, giving good agreement between theory and experiment over all measured temperatures, and witnessing multipartite entanglement up to 75 K. We then apply the entanglement witnesses to the 2D triangular lattice KYbSe2, showing the presence of appreciable entanglement in the low temperature phase. We then use diffuse scattering fits, heat capacity comparisons, and nonlinear spin wave fits to demonstrate that KYbSe2 is proximate to a quantum spin liquid. We thus provide a rigorous route to studying and understanding highly entangled quantum phases.

Professor Jun Hee Lee

School of Energy and Chemical Engineering

Ulsan National Institute of Science and Technology

South Korea

Title: Ultimate-density atomic semiconductor via flat phonon bands

Abstract: Dispersion-less flat energy bands in momentum space generate localized states and are known to cause unconventional phenomena such as graphene superconductivity in electrons and individual spin flips in magnons. However flat bands in phonon were not discovered yet. For the first time, we discovered flat bands in phonon exist surprisingly in a ferroelectric HfO₂ and produce a localized motion of atoms as if their chemical bond temporarily disappears by an external voltage. With the vanishing bond, each atom can be freely displaced by the voltage for the information storage. Our discovery of the atom control directly in a solid will lead us to the design of ultimate-density memory semiconductors reaching up to ~100 TB [1]. Our theory is directly applicable to the Si-compatible HfO₂ so can be materialized in all electronic devices [2]. Just as Einstein’s theory of relativity (E=mc²) enabled us to make bombs out of atoms not out of materials, with our “Atomic Semiconductor” we will open the era of designing memories on an atomic scale rather than a materials scale and carrying a data center in the palm of your hand.

[1] “Scale-free ferroelectricity driven by flat phonon bands in HfO₂”, H.-J. Lee et al., Science 369, 1343 (2020).

[2] “A key piece of the ferroelectric hafnia”, B. Noheda et al., Science 369, 1300 (2020).

Professor Jun Hee Lee

School of Energy and Chemical Engineering

Ulsan National Institute of Science and Technology

South Korea

Title: Ultimate-density atomic semiconductor via flat phonon bands

Abstract: Dispersion-less flat energy bands in momentum space generate localized states and are known to cause unconventional phenomena such as graphene superconductivity in electrons and individual spin flips in magnons. However flat bands in phonon were not discovered yet. For the first time, we discovered flat bands in phonon exist surprisingly in a ferroelectric HfO₂ and produce a localized motion of atoms as if their chemical bond temporarily disappears by an external voltage. With the vanishing bond, each atom can be freely displaced by the voltage for the information storage. Our discovery of the atom control directly in a solid will lead us to the design of ultimate-density memory semiconductors reaching up to ~100 TB [1]. Our theory is directly applicable to the Si-compatible HfO₂ so can be materialized in all electronic devices [2]. Just as Einstein’s theory of relativity (E=mc²) enabled us to make bombs out of atoms not out of materials, with our “Atomic Semiconductor” we will open the era of designing memories on an atomic scale rather than a materials scale and carrying a data center in the palm of your hand.

[1] “Scale-free ferroelectricity driven by flat phonon bands in HfO₂”, H.-J. Lee et al., Science 369, 1343 (2020).

[2] “A key piece of the ferroelectric hafnia”, B. Noheda et al., Science 369, 1300 (2020).

Professor Dima Pesin

Associate Professor

University of Virginia

Title: Optical and transport properties of metals with nontrivial band geometry

Abstract: I will describe how the geometry of the band structure of metals manifests itself in their optical and transport properties. I particular, I will discuss optical Hall response of chiral crystals in the presence of a DC transport current – the gyrotropic Hall effect – and show that it is related to the Berry curvature dipole. The latter fact makes the gyrotropic Hall effect a diagnostic tool for topological properties of three-dimensional chiral metals. I will also talk about manifestations of band geometry is electron-electron collisions, and the ensuing anomalous Hall effect in the hydrodynamic regime.

Professor Dima Pesin

Associate Professor

University of Virginia

Title: Optical and transport properties of metals with nontrivial band geometry

Abstract: I will describe how the geometry of the band structure of metals manifests itself in their optical and transport properties. I particular, I will discuss optical Hall response of chiral crystals in the presence of a DC transport current – the gyrotropic Hall effect – and show that it is related to the Berry curvature dipole. The latter fact makes the gyrotropic Hall effect a diagnostic tool for topological properties of three-dimensional chiral metals. I will also talk about manifestations of band geometry is electron-electron collisions, and the ensuing anomalous Hall effect in the hydrodynamic regime.

Dima Pesin

Associate Professor of Physics

University of Virginia

Title: TBA

Abstract: TBA

Dima Pesin

Associate Professor of Physics

University of Virginia

Title: TBA

Abstract: TBA