Looking to Control Quantum Effects on Demand?

The Programmable Quantum Materials Energy Frontier Research Center was founded with the goal of creating quantum effects on demand. Led by Columbia University, with partners at the University of Washington and Brookhaven National Laboratory, the Department of Energy-funded Center has spent the last four years exploring how to create and control quantum phenomena.

Such control could revolutionize computing and communications, and greatly reduce our use of energy. For example, solving the origins of superconductivity, the resistance-free flow of electrons through a material, could yield electronic devices that don’t waste energy. Controlling magnetism, which occurs when the direction that electrons are spinning lines up, can be a means of encoding information. Identifying novel sources of light can yield new photonic devices, like lasers, and computer chips, and be used in imaging instruments to increase resolution. 

The Center has focused on van der Waals materials, atom-thin layers that, when stacked and twisted into what are called moiré patterns, can produce unique quantum effects. The most famous is graphene, but the Center’s researchers also explore other effects, including novel materials made in-house. 

To date, the Center’s 19 Principal Investigators and 21 postdocs and graduate students have published 90 papers that have been cited over 5,000 times. We asked Dmitri Basov, a physics professor at Columbia who leads the Center, to pick 10 highlights, which are summarized below:

1. Matthew Yankowitz et al. Tuning superconductivity in twisted bilayer graphene. Science 2019

A few years ago, researchers discovered that graphene can act as a superconductor … if the atom-thin layers of the carbon-based material are twisted at exactly the right angle relative to one another. Hence, the moniker, “magic angle” graphene. 

In this work, the Center’s researchers reveal another way to control the phenomenon: by applying pressure. A hydrostatic squeeze let them adjust the twist angle of their graphene sheets while maintaining superconductivity. That flexibility could prove useful in engineering graphene-based electronic devices.

Read More: Unlocking Graphene’s Superconducting Powers with a Twist and a Squeeze

2. Alexander Kerelsky et al. Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature 2019

Here, the Center takes a close look at the structure of twisted layers of graphene under the lens of a powerful microscope that can image a sample atom by atom. In the images, the team explored how the number of electrons present can shift graphene from resisting electrical flow to conducting it. 

The Center also found notable similarities to a class of high-temperature superconductors called the cuprates. Understanding superconductivity in simpler graphene systems could help researchers solve the current mysteries that surround superconductivity, and figure out how to raise the temperature even higher.

Read More: Similarities in the insulating states of twisted bilayer graphene and cuprates

3. Leo McGilly et al. Visualization of moiré Superlattices Nature Nanotechnology 2020 

In this work, the Center takes another deep dive into the structure of twisted van der Waals materials, including superconductive graphene, a material called tungsten diselenide that acts as a semiconductor of electricity, and an insulating material called boron nitride that resists electrical flow. The researchers use an instrument that can image samples at room temperature at a resolution of fewer than five nanometers to compare the materials.  

4. Kyle Seyler et al. Signatures of moiré-trapped valley excitons In MoSe₂/WSe₂ heterobilayers. Nature 2019

The quantum phenomena to be found in van der Waals materials include superconductivity, insulating behavior, magnetism, and—at least in theory—light-based optical effects.

In this work, the Center finds experimental evidence of such optical effects via light emitted by quantum particles called excitons that are trapped in the moiré lattice. These excitons, which can be individually isolated, interact with light in a way that could be used to encode information and may prove useful in novel communications devices. 

Read More: It’s all in the twist: Physicists stack 2D materials at angles to trap particles on the nanoscale

5. Augusto Ghiotto et al. Quantum criticality in twisted transition metal dichalcogenides Nature 2021

As materials move from one phase to another—think water transitioning from a liquid to a gas, or a van der Waals material turning from a metal to an insulator—there is a critical point. In quantum materials, researchers want to better understand this transition point as a means to control particular properties. In this work, the Center identifies the quantum critical point that marks the metal-to-insulator transition in twisted layers of tungsten diselenide. 

Read More: With a Little Twist, Researchers Delve Into a Quantum Physics Puzzle

6. Nikhil Sivadas et al. Stacking-dependent magnetism in bilayer CrI₃. Nano Letters 2018

Magnetism is another phenomenon the Center has been exploring and attempting to exploit in different materials, including one called chromium triiodide. Bulk crystals of this material are not magnetic, but stacks of atom-thin layers are. In this work, the Center showed how stacking order can influence magnetism in chromium triiodide, a finding that could apply to other types of 2D magnets.

7. Tiancheng Song et al. Switching 2D magnetic states via pressure tuning of layer stacking. Nature Materials 2019

Force doesn’t just influence electrical conductivity. In this paper, the Center returns to chromium triiodide and shows that hydrostatic pressure can also turn magnetism on and off. Different combinations of tunable controls, including twist angle, stack order, and pressure, could help engineer magnetism into novel devices. 

8. Ipshita Datta et al. Low-loss composite photonic platform based on 2D semiconductor monolayers. Nature Photonics 2020

In optical communications applications, silicon currently reigns. However, the material consumes a lot of optical bandwidth and electrical power. Here, the Center shows how an atom-thin layer of a van der Waals material called tungsten diselenide can serve as a low-loss and low-power light phase modulator that could potentially improve silicon-based photonic devices. 

Read More: Columbia Team Discovers New Way to Control the Phase of Light Using 2D Materials

9. Sai Swaroop Sunku et al. Photonic crystals for nano-light in moiré graphene superlattices. Science 2018

Graphene isn’t just a promising material for conducting electricity. It might also prove useful as a light source for photonic devices. In this work, the Center showed how the twist angle of layers of graphene can influence the emergence of nano-light sources called plasmonic polaritons, which they can produce on demand.

 10. A. J. Sternbach et al. Programmable hyperbolic polaritons in van der Waals semiconductors. Science 2021

The ability to control light at its smallest scales will have applications in both photonic devices and high-resolution imaging systems. In this work, the Center finds evidence of hyperbolicity—here, the ability for light to pass through a structure—in layers of tungsten diselenide. This programmable property, activated by shining light on the material, lets the team transport images through the layers with superfine, nanoscale resolution. 

Read More: Switching Nanolight On and Off