Scientists have shown that heat can flow like water—opening new avenues for cooling microchips and other components.

New Horizons in Heat Management: How Crystals Can “Reverse” Energy Flow

Scientists from the Federal Polytechnic School of Lausanne (EPFL) have theoretically demonstrated that in highly ordered and exceptionally pure crystals, heat can behave differently than usual. Instead of the familiar diffusion from hot regions to cold ones, such materials exhibit a directed flow with vortices and even reverse heat movement. Imagine wrapping your palm around a cup of hot tea – the heat begins to “freeze.” It sounds fantastical, but it does not contradict the laws of quantum mechanics.

What Are Phonons and How Are They Related to Heat?

- A phonon is a quasiparticle representing the quantum of vibrational motion of atoms in a solid.
- In an ideal crystalline lattice, phonons carry energy, i.e., heat.
- According to the second law of thermodynamics, vibrations propagate from hotter (higher-energy) atoms to cooler ones.

How Can a Reverse Heat Flow Arise?

1. Momentum Conservation – In pure crystals, phonon collisions almost do not change their direction, allowing the creation of a collective, “non‑compressible” flow.
2. Hydrodynamic Regime – Under an almost incompressible mode, the flow does not “give up” energy to resistance but forms vortices and can even return toward the heat source.
3. Negative Thermal Resistance – Heat can move from cold regions to warmer ones, creating a negative temperature gradient while the total entropy of the system still increases.

Theoretical Model and Confirmation

- Scientists developed a hydrodynamic equation by decomposing it into key elements of flow behavior.
- Numerical simulations on a two‑dimensional graphene strip confirmed the possibility of observing such an effect.
- New analytics provide a tool for quantitative description and optimization of reverse heat flow.

Why Is This Important?

What’s Next?

- The model applies not only to phonons but also to other heat carriers: electrons, excitons, etc., making it a universal tool for future technologies in nanoelectronics and energy.
- This discovery opens the way to creating “thermal pumps” at the crystalline lattice level that can effectively manage heat even in miniature devices.

Thus, EPFL’s theoretical research demonstrates that with the right structure and purity of material, one can not only transfer heat but also direct it “backwards,” opening new prospects for energy management at the micro‑ and nanoscale.