Quantum Materials for Classical Computing

Session 2A: 10:00 AM – 12:00 PM Pacific Time on Friday, August 21.

Sinéad Griffin*, Archana Raja

The ever-increasing demand for more efficient computing – driven by the emergence of the Internet of Things (IoT) — threatens to hamper future progress across technology, science and energy.  Integrative progress across academia and industry propelled reduction in transistor density, cost and energy consumption for decades (Moore’s Law). However, this is now approaching a standstill; transformative solutions hinge on finding new materials and phenomena for the next-generation of classical computing. To reach higher density and concurrently lower power solutions, these new hardware components will inevitably be driven by spin, charge, orbital and lattice order and their resulting emergent properties, i.e. quantum materials. This symposium will look at the most promising new ideas in the field of quantum materials for replacing and augmenting existing semiconductor components, and discuss future prospects for the interplay between fundamental research and device applications through materials co-design.

Symposium Schedule:

Symposium Abstracts:

10:00 AM

Liberating a hidden antiferroelectric phase with interfacial electrostatic engineering

Prof. Julia Mundy
Physics, Harvard University
Coauthors: Bastien Grosso¹, Darrell Schlom², Dan Ferenc Segedin^3,4, Zhe Wang², Yu-Tsen Shao², Cheng Dai⁵, Berit Goodge², Quintin Meier¹, Christopher Nelson⁶, Bhagwati Prasad⁴, Fei Xue⁵, Lena Kourkoutis², Long-Qing Chen⁵, William Ratcliff⁷, Nicola Spaldin¹, Ramamoorthy Ramesh⁴, Colin Heikes^7
1ETH Zurich; ²Cornell; ³Harvard; ⁴UC Berkeley; ⁵Penn State; ⁶ORNL; ⁷NIST

Antiferroelectric materials have seen a resurgence of interest due to proposed applications in a number of energy efficient technologies ranging from energy storage to solid-state cooling. Unfortunately, relatively few families of antiferroelectric materials have been identified to date and most involve lead, precluding many proposed applications. Here, we propose a new design strategy for the construction of lead-free antiferroelectric materials using interfacial electrostatic engineering. We begin with a ferroelectric material with one of the highest known bulk polarizations, BiFeO₃. By confining atomically-precise thin layers of BiFeO₃ in a dielectric matrix, we show that a metastable antiferroelectric structure can be induced. We use picoscale electron microscopy imaging and scanning diffraction measurements to probe the structure and electric fields in this new phase. Application of an applied electric field reversibly switches between this new phase and a ferroelectric state. In addition, we can engineer coexistence of the ferroelectric and antiferroelectric states by tuning the dielectric layer, leading to an antiferroelectric phase with a stored energy density comparable to that of the best lead-based materials. The use of electrostatic confinement provides a new pathway for the design of engineered antiferroelectric materials with large and potentially coupled responses.

10:28 AM

Tuning the Mott transition to achieve near adiabatic switching in transition metal oxides

Prof. Carlos Paz de Araújo
Electrical and Computer Engineering, University of Colorado at Colorado Springs // Symetrix Corporation

Controlled doping of carbon in transition metal oxides has allowed a systematic study of Mott switching in post-CMOS devices down to the 45 nm scale. The devices have a robust switching characteristic and show a preference towards p‑type oxides and Mottness in terms of switching by rapid electron injection. A presentation of data across different oxides and the physical model of the devices is presented. Applications for nonvolatile memories and synapses in non-von Neumann computing are also discussed. cancelled

10:40 AM

Models and experimental status of amorphous topological insulators

Dr. Adolfo Grushin
Néel Institute, CNRS // Physics, University of California at Berkeley

Amorphous solids remain outside of the classification and systematic discovery of new topological materials. This is because current models and experiments in topological matter are interpreted based on symmetry, such as lattice periodicity. Extending topological properties to amorphous topological matter can be a route to significantly increase the number of new topological materials, and a route towards easily scalable topological devices. In this talk I will discuss a possible way to extend the notion of symmetry indicators, which are labels of topology, for a class of amorphous topological models we introduced, that we call topological Weaire-Thorpe models. These indicators could be the basis for a classification scheme. Lastly, I will discuss how experiments in amorphous Bi₂Se₃, in particular transport and photoemission data, are consistent with the presence of topological Dirac surface states.

11:08 AM

Electric-field control of spins in magnetically-doped ferroelectrics

Dr. Katherine Inzani
Molecular Foundry and Materials Sciences Divisions, Berkeley Lab
Coauthors: Weichaun Huang¹, Junjie Liu², Evan Sheridan³, Valentin V. Laguta⁴, Ruchira Chatterjee³, Sujit Das¹, Nima Leclerc³, Arzhang Ardavan², Ramamoorthy Ramesh^1,3, Sinead M. Griffin^3
1UC Berkeley; ²Oxford; ³Berkeley Lab; ⁴Czech Academy of Sciences

The novel functionalities offered by multiferroic materials have inspired devices for beyond Moore’s Law classical computing. In addition, the control mechanism of electric-field over spins in magnetoelectric materials has been proposed for use in defect-based quantum computing. We present a proof-of-principle theoretical and experimental study of the spin oxide qubit (SOQ) concept. Using known ferroelectric perovskite oxides doped with magnetic ions, we demonstrate the manipulation of spins by electric-field and the possibility to tailor spin control by the atomic environment. First principles modeling indicates the atomic scale effects of lattice modification on qubit switching parameters by way of strain and defect complexes, in excellent agreement with electron paramagnetic resonance observations. We further look to the choice of host lattice and alternate low-symmetry ferroelectric phases to influence the orbital environment and polarization switching pathways. This work is an example of how a quantum effect developed for the next-generation of classical computing is stimulating research towards computing with quantum advantage.

11:20 AM

Probing the Dynamics of Topologically Protected Charged Ferroelectric Domain Walls with the Electron Beam

Dr. Michele Conroy
Physics, University of Limerick // Analog Devices

Dynamic charged ferroelectric domain walls (CDWs) overturn the classical idea that our electronic circuits need to consist of fixed components of hardware. With their own unique electronic properties and exotic functional behaviours all confined to their nanoscale width, DWs represent a completely new 2D material phase. This is an area of research at its very early stages with endless possible applications. However, to harness the true potential of CDWs there is a great deal of the fundamental physics yet to uncover. As the region of interest (CDW) is atomically thin and dynamic, it is essential for the physical characterisation to be at this scale spatially and time resolved. This presentation will focus on using the applied electric field (Ef) of the scanning transmission electron microscope (STEM) probe to move DWs between charged and neutral states. Thus investigating their dynamics while imaging at the sub-atomic scale and quantifying changes in unit cell polarisation. As the applied Ef of an electron probe can be controlled in terms of dose, probe size, direction and speed a diverse set of experiments is possible. The results presented here required the resolution allowed by aberration corrected STEM due to the 2D nature of the CDWs, reinforcing the idea that advancements in STEM techniques are essential for the progress of ferroelectric CDW nanoelectronics.

11:48 AM

Emergent properties of confined, quasi-1-dimensional transition metal chalcogenides

Scott Stonemeyer
Physics, University of California at Berkeley
Coauthors: Thang Pham¹, Sehoon Oh², Alex Zettl², Peter Ercius³, Marvin L. Cohen³, Chengyu Song^3
1MIT; ²UC Berkeley; ³Berkeley Lab

Confining intrinsically low-dimensional materials, such as van der Waals (vdW) bonded quasi-two-dimensional compounds (exemplified by graphite, hexagonal boron nitride, and transition metal dichalcogenides) and quasi-one-dimensional vdW compounds (exemplified by transition-metal trichalcogenides (TMT)), down to “atomic thinness” can result in various degrees of additional size quantization which greatly influences their electrical, optical, magnetic, thermal, and mechanical properties. However, the instability of quasi-1-D vdW materials at “atomic thinness” has hindered the progress of isolating and studying their properties. Here, we report advancements in the synthesis and structural characterization of TMT and related structures within the hollow cores of multiwall carbon nanotubes (MWCNT). The MWCNT sheath simultaneously confines the chains, prevents oxidation in air environments, and facilitates characterization via scanning transmission electron microscopy. Together with complementary density functional theory calculations, we have found several emergent phenomena in these confined structures. NbSe₃ reveals static and dynamic structural torsional waves, HfTe₃ undergoes a trigonal prismatic rocking distortion concomitant with a metal-insulator transition, and Hf₂Te₉, a heretofore unknown vdW-bonded segmented linear chain, shows an emergence of topologically nontrivial spin-polarized states. These initial studies lay the groundwork necessary to study material systems at their fundamental limits and highlights the emergent properties waiting to be uncovered.