Columbia Study Confirms Quantum Fluctuations Alter Properties of Nearby Crystals

Researchers at Columbia University have experimentally confirmed that quantum fluctuations originating from the vacuum within two-dimensional materials are capable of altering the properties of nearby crystals, a theoretical possibility pursued for decades. Led by Higgins Professor of Physics Dmitri Basov and a team of 32 collaborators across 17 institutions, the study details how placing a nanometer-sized flake of hexagonal Boron Nitride (hBN) on top of the superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br, or κ-ET, halted superconductivity—a significant proof of concept for material tuning. “It’s a holy grail we’ve been searching for decades,” said Basov, describing the long-sought confirmation. The team discovered that matching the vibrational resonance between hBN and κ-ET enabled an interaction that impedes electron flow, demonstrating a new method for manipulating material states without external driving forces.

Quantum Fluctuations Suppress Superconductivity in κ-ET Crystals

The team, a collaboration of 32 researchers from 17 institutions led by Columbia postdoctoral fellows Itai Keren, Tatiana Webb, and Shuai Zhang, achieved this by placing a nanometer-thick flake of hexagonal Boron Nitride (hBN) atop κ-(BEDT-TTF)₂Cu[N(CN)₂]Br, commonly known as κ-ET, a superconducting material. Remarkably, superconductivity within the κ-ET crystal ceased without any additional external stimuli like lasers or driving forces, a result that, while not ideal for enhancing lossless electrical flow, establishes a crucial proof of concept. “Any new knob that people can find for tuning superconductivity is significant,” said Keren. The suppression of superconductivity occurred because the quantum fluctuations within the hBN layers vibrate at a resonance frequency that precisely matches that of κ-ET, leading to an interaction that disrupts electron movement and prevents the formation of a superconducting state. Testing with superconductors possessing different resonant frequencies yielded no effect, confirming the specificity of this interaction.

This discovery stems from theoretical work by Angel Rubio from the Max Planck Institute for the Structure and Dynamics of Matter, who initially proposed the potential of quantum fluctuations, a concept Basov initially deemed “impossible, but it was so appealing, it was impossible not to try.” The impact extends beyond simply halting superconductivity; the effect was observed across almost ½ micrometer—10x the width of the hBN flake—suggesting a substantial influence. “Vacuum fluctuations are extremely small, but the effect observed is huge,” Rubio noted, highlighting the potential for persistent material modification without external force, a departure from conventional methods involving mechanical force, heat, or laser pulses. The team utilized a cryogenic magnetic force microscope to confirm these findings, proving that quantum fluctuations alone can modify material properties, and opening avenues for innovative material design.

Hexagonal Boron Nitride as a Quantum Cavity Material

Hexagonal boron nitride (hBN) is rapidly becoming a crucial material in the exploration of quantum material manipulation, moving beyond its established role as an inert spacer in industrial and experimental setups. This realization, confirmed in a new paper published in Nature, represents a significant step toward harnessing these fluctuations for material modification—a theoretical possibility now experimentally proven for the first time. A cavity, in this context, confines electromagnetic waves, and while seemingly empty, still hosts quantum fluctuations; nano-scale hBN sheets offer an exceptionally small space for these to strengthen.

The hyperbolic nature of hBN is central to this effect, amplifying internal vibrations—a phenomenon Webb described as “a remarkable effect that you can have with hyperbolic materials.” This ability to modify electronic properties without external force offers the potential for more persistent changes, opening avenues for tunable material designs, and Keren anticipates “others hunting for new combinations” of materials and cavities. “We now have a proof of concept that this is a viable way to modify the electronic properties of materials, and it’s something we could integrate into material designs,” Webb explained.

Magnetic Force Microscopy Confirms Vacuum-Mediated Interactions

While seemingly counterintuitive for those seeking to improve lossless electrical flow, this outcome serves as a crucial validation of a long-held theoretical possibility. The success of this experiment hinged on the resonant frequency of the hBN matching that of κ-ET, a detail the researchers predicted would facilitate interaction. “That was our intuition: if the vibrations match, they should interact with each other,” Keren explained, detailing how the electromagnetic environment within the κ-ET crystal changed, hindering electron movement and preventing the establishment of a superconducting state. Crucially, the team found no effect when testing hBN against a superconductor with differing resonant frequencies, solidifying the link between vibrational matching and material modification.

Hyperbolic Material Resonance Enables Material Property Tuning

The ability to manipulate material properties through resonance with quantum vacuum fluctuations promises a new era of materials engineering, moving beyond traditional methods reliant on external forces. This interaction occurs without any applied lasers or external driving forces, representing a fundamental shift in how materials can be controlled. This method offers the potential for persistent material modification, unlike previous techniques requiring continuous energy input. “If we can control these, we can tune our superconductor at will,” Keren explained, anticipating a surge in research focused on discovering new material combinations leveraging this principle.