Chimeric states of matter: Meissner effect without superconductivity

TL;DR

The paper challenges the all-or-nothing view of symmetry breaking by showing that phases can interpolate via mixed anomalies between broken and unbroken realizations, creating chimeric states. Using an effective field theory with a 2-form symmetry and a conserved 3-form current $K^{\lambda\mu\nu}=\epsilon^{\lambda\mu\nu\rho}\partial_\rho \phi$ and its mixed anomaly with the background gauge field, it demonstrates that Meissner screening can arise in media with nonzero $d.c.$ conductivity, i.e., a Meissner effect without full superconductivity. A lattice Josephson-junction network model with an auxiliary link field $\xi_{ij}$ shows how to realize chimeric conductors or insulators by tuning the anomaly sector, yielding Ohmic response or full flux expulsion. These findings expand the phase diagram of matter and point to potential applications in magnetic shielding and contactless transport by decoupling flux expulsion from complete conductivity.

Abstract

Symmetry is central to how we classify phases of matter: solids break spatial translations, superfluids break particle-number conservation, and superconductors "break" gauge symmetry. Mixed anomalies involving higher-form symmetries, however, present a generalization of spontaneous symmetry breaking that admits a wider and more versatile set of possibilities. We introduce chimeric states of matter, in which aspects of broken and unbroken phases coexist. We find that the Meissner effect -- usually regarded as the defining hallmark of superconductivity -- can occur in media that are resistive or even insulating when probed by electric fields. We demonstrate this by constructing an effective field theory of "symmetry chimerization" and propose that Josephson junction networks could provide a laboratory realization. These results broaden the landscape of possible phases of matter, showing that physical media can mix features of symmetry-restored and symmetry-broken states in a single substrate.

Figures (3)

• Figure 1: Infinitely extending lines intersect winding planes. Left: Spherical winding plane. Sum of oriented intersections is zero ($+1$ into, $-1$ out of surface). Spherical winding planes can contract to zero without changing the intersection number. Right: Stack of infinitely extending winding planes. Total oriented intersection is non-zero but cannot change unless planes are punctured or torn. Conclusion: intersection number is topologically protected and hence conserved.
• Figure 2: The anomalous 2-form symmetry picture generalizes the notion of SSB of the $U(1)$ symmetry and yields Goldstone bosons. SSB implies mixed anomaly, but not necessarily vice versa.
• Figure 3: Top: chimeric conductors and insulators fully screen magnetic fields according to the Meissner effect. Bottom left: chimeric insulator only partially screens electric fields. Bottom right: chimeric conductor admits dissipative d.c. current.