New state of matter discovered in a magnetic metamaterial

In physics as in chemistry, it is generally accepted that matter orders, like in a crystalline solid, when cooled at sufficiently low temperature. There also exist systems that remain disordered in the manner of a gas or a liquid, even at the lowest temperatures accessible experimentally. What is much more rare, if ever observed, is a state of matter that is at the same time ordered and disordered everywhere in the system.

Such a state, simultaneously liquid and solid, was observed in a magnetic metamaterial. We emphasize here that we are not considering a magnetic equivalent of a glass of water containing ice cubes, which would be, simply, a system presenting a coexistence of two phases, physically separated and out of thermodynamic equilibrium. Instead, what we mean is a magnetic equivalent of a glass of water that would be liquid and ice everywhere in the glass, at any time.

It is difficult to get a mental representation of such a system and it may be convenient to visualize it, not in real space, but in reciprocal space. Indeed, if we could achieve a diffraction pattern of such an exotic state of matter, we would observe two features simultaneously. This pattern would present very intense points in some specific regions of the reciprocal space, called Bragg peaks, associated to the existence of a periodic arrangement and reflecting the symmetry of the solid. But this diffraction pattern would also show a diffuse background signal, associated to the disorder present in the system. It is important to stress once more that these two characteristics of the diffraction pattern would be representative of a state of matter at thermodynamic equilibrium.

In collaboration with the Nanospectroscopy beamline at the ELETTRA synchrotron radiation facility and researchers at the Jean Lamour Institute in Nancy, we have fabricated a magnetic metamaterial that exhibits all the characteristics of such an exotic state of matter. The diffraction pattern we measured on that magnetic metamaterial indeed shows a coexistence of Bragg peaks and a diffuse background (see Figure), thus indicating that the system is both ordered and disordered. The challenge is then to demonstrate that this is not a coexistence of two out-of-equilibrium phases, but a state of matter that is both liquid and solid, everywhere in the lattice, at thermodynamic equilibrium...

Figure:Representation in reciprocal space of the magnetic phase observed experimentally. The diffuse background, associated to the magnetic disorder, appears in yellow. Bragg peaks are also visible in certain regions of the reciprocal space (indicated by a red circle).
Contributors
  • Institut Néel (France) : B. Canals, I.-A. Chioar, V.-D. Nguyen, N. Rougemaille
  • Institut Jean Lamour (France) : M. Hehn, D. Lacour, F. Montaigne
  • ELETTRA synchrotron radiation facility (Italy) : A. Locatelli, T. O. Menteş, B. Santos Burgos

Our related publication :

  • Fragmentation of magnetism in artificial kagome dipolar spin ice, B. Canals, I.-A. Chioar, V.-D. Nguyen, M. Hehn, D. Lacour, F. Montaigne, A. Locatelli, T. O. Menteş, B. Santos Burgos and N. Rougemaille, Nature Communications 7, 11446 (2016). [http://www.nature.com/ncomms/2016/1...]

Corresponding author  :

N. Rougemaille B. Canals

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