Yafis Barlas

Assistant Professor of Physics

University of Nevada, Reno

Title: Correlated and Topological Phases in flat bands of two-dimensional crystals

Abstract: Due to their vanishing density of states and gapless semi-metallic behavior at charge neutrality, honeycomb lattice two-dimensional (2D) crystals are ideal candidates to host topological states. Even more interesting are twisted or strained 2D crystals, as the electron dispersion in these systems can be weakly dispersing, (i.e exhibit a small bandwidth) or completely flat. In these situations, the interplay of topology and correlation driven phases in flat bands of 2D crystals can result in emergent topological order.  Similarly, at high magnetic fields, multi-layer graphene and twisted bilayer graphene exhibit topological bands and various correlated states. In this talk, I will discuss a new class of interacting and non-interacting symmetry protected topological phases stabilized by mirror symmetry in 2D Dirac semi-metals. This quantum parity Hall state, exhibits two one-dimensional counter-propagating metallic edge states, distinguished by even or odd parity under the system’s mirror reflection symmetry.​ I will also discuss some of our results in twisted 2D crystals at high magnetic fields.

Yafis Barlas

Assistant Professor of Physics

University of Nevada, Reno

Title: Correlated and Topological Phases in flat bands of two-dimensional crystals

Abstract: Due to their vanishing density of states and gapless semi-metallic behavior at charge neutrality, honeycomb lattice two-dimensional (2D) crystals are ideal candidates to host topological states. Even more interesting are twisted or strained 2D crystals, as the electron dispersion in these systems can be weakly dispersing, (i.e exhibit a small bandwidth) or completely flat. In these situations, the interplay of topology and correlation driven phases in flat bands of 2D crystals can result in emergent topological order.  Similarly, at high magnetic fields, multi-layer graphene and twisted bilayer graphene exhibit topological bands and various correlated states. In this talk, I will discuss a new class of interacting and non-interacting symmetry protected topological phases stabilized by mirror symmetry in 2D Dirac semi-metals. This quantum parity Hall state, exhibits two one-dimensional counter-propagating metallic edge states, distinguished by even or odd parity under the system’s mirror reflection symmetry.​ I will also discuss some of our results in twisted 2D crystals at high magnetic fields.

Professor Mark Novotny

Mississippi State University

Department of Physics and Astronomy

Title: Generalization of Bloch’s Theorem for Tight-binding Models:Quantum Dragon Nanomaterials and Nanodevices

Abstract: Bloch’s Theorem arguably has the largest economic impact of any condensed matter theorem.  Bloch’s Theorem can only be used for translationally invariant systems, and together with the tight-binding model gives band structures and hence devices such as transistors and optoelectronics.  For tight-binding models, a generalization of Bloch’s Theorem for some strongly disordered (non-translationally invariant) systems is stated and proved.  The theorem generalization leads to predictions of novel electrical properties for some nanomaterials and nanodevices with strong disorder, whimsically called quantum dragons [1].  A number of different predictions of quantum dragon materials and devices [2] will be presented.  Furthermore, conjectures and testing of scaling for materials that are ‘close to quantum dragons’ are given [3].  For example, a perfect quantum wire is one in which impinging electrons from an appropriate incoming lead have probability unity of propagating through the device to the end of an outgoing lead, T(E)=1, for all electron energies E that propagate through the leads. Some quantum dragons are predicted to be perfect quantum wires (see the device in the figure below [3]), while others may make a unique FET (Field Effect Transistor) or quantum sensor or spintronics nanodevice. 

[1] M.A. Novotny, Energy-independent total quantum transmission of electrons through nanodevices with correlated disorder, Phys. Rev. B 90, 165103 (2014).

[2] G. Inkoom and M. Novotny, Quantum dragon solutions for electron transport through nanostructures based on rectangular graphs, J. Physics Commun. 11, 115019 (2018). 

[3] M.A. Novotny and T. Novotný, Order amidst Disorder in 2D+3D Quantum Dragon Composite Nanodevices with varying Breadth, J. Phys: Conf. Ser. 1740, 012002 (2021).

Professor Mark Novotny

Mississippi State University

Department of Physics and Astronomy

Title: Generalization of Bloch’s Theorem for Tight-binding Models:Quantum Dragon Nanomaterials and Nanodevices

Abstract: Bloch’s Theorem arguably has the largest economic impact of any condensed matter theorem.  Bloch’s Theorem can only be used for translationally invariant systems, and together with the tight-binding model gives band structures and hence devices such as transistors and optoelectronics.  For tight-binding models, a generalization of Bloch’s Theorem for some strongly disordered (non-translationally invariant) systems is stated and proved.  The theorem generalization leads to predictions of novel electrical properties for some nanomaterials and nanodevices with strong disorder, whimsically called quantum dragons [1].  A number of different predictions of quantum dragon materials and devices [2] will be presented.  Furthermore, conjectures and testing of scaling for materials that are ‘close to quantum dragons’ are given [3].  For example, a perfect quantum wire is one in which impinging electrons from an appropriate incoming lead have probability unity of propagating through the device to the end of an outgoing lead, T(E)=1, for all electron energies E that propagate through the leads. Some quantum dragons are predicted to be perfect quantum wires (see the device in the figure below [3]), while others may make a unique FET (Field Effect Transistor) or quantum sensor or spintronics nanodevice. 

[1] M.A. Novotny, Energy-independent total quantum transmission of electrons through nanodevices with correlated disorder, Phys. Rev. B 90, 165103 (2014).

[2] G. Inkoom and M. Novotny, Quantum dragon solutions for electron transport through nanostructures based on rectangular graphs, J. Physics Commun. 11, 115019 (2018). 

[3] M.A. Novotny and T. Novotný, Order amidst Disorder in 2D+3D Quantum Dragon Composite Nanodevices with varying Breadth, J. Phys: Conf. Ser. 1740, 012002 (2021).

Professor Hiro Nakamura

Department of Physics

University of Arkansas

Host: Seo

Title: Complex geometrical phases in quantum materials probed by transport

Abstract: Recent advances in condensed matter physics brought the phase part of wavefunction in the forefront, as exemplified by the Berry phase in graphene. However, experimentally probing complex phases in a momentum space is not easy. In this talk, we present how advanced transport techniques such as quantum interference and planer Hall effect could shed light on higher-order and/or anisotropic quantum phases in solids. We show recent application of these techniques to three-dimensional (3D) topological antiperovskites, which points to a unique spin/pseudospin texture in this material [1,2]. Preliminary results from a 2D material with distinct spin texture (few-layer WSe₂) also showcase an impact of different anisotropy of such phase patterns.

1. H. Nakamura et al., Nature Comm. 11, 1161 (2020).

2. D. Huang, H. Nakamura, and H. Takagi, arXiv:2101.05512 (2021)

Professor Hiro Nakamura

Department of Physics

University of Arkansas

Host: Seo

Title: Complex geometrical phases in quantum materials probed by transport

Abstract: Recent advances in condensed matter physics brought the phase part of wavefunction in the forefront, as exemplified by the Berry phase in graphene. However, experimentally probing complex phases in a momentum space is not easy. In this talk, we present how advanced transport techniques such as quantum interference and planer Hall effect could shed light on higher-order and/or anisotropic quantum phases in solids. We show recent application of these techniques to three-dimensional (3D) topological antiperovskites, which points to a unique spin/pseudospin texture in this material [1,2]. Preliminary results from a 2D material with distinct spin texture (few-layer WSe₂) also showcase an impact of different anisotropy of such phase patterns.

1. H. Nakamura et al., Nature Comm. 11, 1161 (2020).

2. D. Huang, H. Nakamura, and H. Takagi, arXiv:2101.05512 (2021)

Prof. Yashar Komijani

Department of Physics

University of Cincinnati

Host: Gannon/Kaul

Title: Critical charge fluctuations and superconductivity in magnetic environments

Abstract:

Quantum electronic matter has long been understood in terms of two limiting behaviors of electrons: one of delocalized metallic states, and the other of localized magnetic states. Heavy fermions are miniature high-Tc superconductors whose small energy scales provide the possibility of tuning the ground state between these two limits and enable accessing the strange metallic behavior which develops at the brink of localization. I will discuss the attempts [1,2] to map out the phase diagram of heavy-fermions using dynamical large-N method and the Schwinger boson representation of the spins. I will then highlight the recent observation of quantum critical point and strange metal behavior in the stoichiometric ferromagnetic heavy-fermion CeRh6Ge4 [3]. This is surprising as the abrupt change in the patterns of entanglement and the Fermi surface that usually accompanies singular charge fluctuations are absent in a ferromagnet. I will argue that the innocuous easy-plane magnetic anisotropy that is present in this system, produces triplet resonating valence bond (tRVB) states, which lead to a highly entangled ordered phase, similar to a magnetically-frustrated anti-ferromagnet. Doping such a tRVB host provides a route towards realizing triplet superconductivity in a magnetic environment [4].

References: [1] Y. Komijani, P. Coleman, PRL 120, 157206 (2018); ibid 122, 217001 (2019).

[2] J. Wang, Y.-Y. Chang, C.-Y. Mou, S. Kirchner, C.-H. Chung, PRB 102, 115133 (2019).

[3] B. Shen, Y. Zhang, Y. Komijani, M. Nicklas, R. Borth, A. Wang, Y. Chen, Z. Nie, R. Li, X. Lu, H. Lee, M. Smidman, F. Steglich, P. Coleman, H. Yuan, Nature 579, 51 (2020).

[4] P. Coleman, Y. Komijani, E. König, PRL 125, 077001 (2020).

Prof. Yashar Komijani

Department of Physics

University of Cincinnati

Host: Gannon/Kaul

Title: Critical charge fluctuations and superconductivity in magnetic environments

Abstract:

Quantum electronic matter has long been understood in terms of two limiting behaviors of electrons: one of delocalized metallic states, and the other of localized magnetic states. Heavy fermions are miniature high-Tc superconductors whose small energy scales provide the possibility of tuning the ground state between these two limits and enable accessing the strange metallic behavior which develops at the brink of localization. I will discuss the attempts [1,2] to map out the phase diagram of heavy-fermions using dynamical large-N method and the Schwinger boson representation of the spins. I will then highlight the recent observation of quantum critical point and strange metal behavior in the stoichiometric ferromagnetic heavy-fermion CeRh6Ge4 [3]. This is surprising as the abrupt change in the patterns of entanglement and the Fermi surface that usually accompanies singular charge fluctuations are absent in a ferromagnet. I will argue that the innocuous easy-plane magnetic anisotropy that is present in this system, produces triplet resonating valence bond (tRVB) states, which lead to a highly entangled ordered phase, similar to a magnetically-frustrated anti-ferromagnet. Doping such a tRVB host provides a route towards realizing triplet superconductivity in a magnetic environment [4].

References: [1] Y. Komijani, P. Coleman, PRL 120, 157206 (2018); ibid 122, 217001 (2019).

[2] J. Wang, Y.-Y. Chang, C.-Y. Mou, S. Kirchner, C.-H. Chung, PRB 102, 115133 (2019).

[3] B. Shen, Y. Zhang, Y. Komijani, M. Nicklas, R. Borth, A. Wang, Y. Chen, Z. Nie, R. Li, X. Lu, H. Lee, M. Smidman, F. Steglich, P. Coleman, H. Yuan, Nature 579, 51 (2020).

[4] P. Coleman, Y. Komijani, E. König, PRL 125, 077001 (2020).

Prof. Kate Ross

Department of Physics

Colorado State University

Host: Kaul

Title: Microscopics of Quantum Annealing in the Disordered Dipolar Ising Ferromagnet LiHoxY1-xF4

Prof. Kate Ross

Department of Physics

Colorado State University

Host: Kaul

Title: Microscopics of Quantum Annealing in the Disordered Dipolar Ising Ferromagnet LiHoxY1-xF4