Abstract
The understanding of phenomena falling outside the Ginzburg-Landau paradigm of phase transitions represents a key challenge in condensed matter
physics. A famous class of examples is constituted by the putative deconfined
quantum critical points between two symmetry-broken phases in layered
quantum magnets, such as pressurised SrCu2(BO3)2. Experiments find a weak
first-order transition, which simulations of relevant microscopic models can
reproduce. The origin of this behaviour has been a matter of considerable
debate for several years. In this work, we demonstrate that the nature of the
deconfined quantum critical point can be best understood in terms of a novel
dynamical mechanism, termed Nordic walking. Nordic walking denotes a
renormalisation group flow arising from a beta function that is flat over a range
of couplings. This gives rise to a logarithmic flow that is faster than the wellknown walking behaviour, associated with the annihilation and complexification of fixed points, but still significantly slower than the generic running
of couplings. The Nordic-walking mechanism can thus explain weak first-order
transitions, but may also play a role in high-energy physics, where it could
solve hierarchy problems. We analyse the Wess-Zumino-Witten field theory
pertinent to deconfined quantum critical points with a topological term in 2+1
dimensions. To this end, we construct an advanced functional renormalisation
group approach based on higher-order regulators. We thereby calculate the
beta function directly in 2+1 dimensions and provide evidence for Nordic
walking.
The Ginzburg-Landau paradigm of phase transitions is remarkable in
its seemingly universal applicability. Consequently, finding and thoroughly understanding examples that violate this paradigm is invaluable to discovering new mechanisms and their applications to
quantum condensed matter physics and beyond. A proposed
mechanism beyond Ginzburg-Landau theory that has been a matter of
intense debate
physics. A famous class of examples is constituted by the putative deconfined
quantum critical points between two symmetry-broken phases in layered
quantum magnets, such as pressurised SrCu2(BO3)2. Experiments find a weak
first-order transition, which simulations of relevant microscopic models can
reproduce. The origin of this behaviour has been a matter of considerable
debate for several years. In this work, we demonstrate that the nature of the
deconfined quantum critical point can be best understood in terms of a novel
dynamical mechanism, termed Nordic walking. Nordic walking denotes a
renormalisation group flow arising from a beta function that is flat over a range
of couplings. This gives rise to a logarithmic flow that is faster than the wellknown walking behaviour, associated with the annihilation and complexification of fixed points, but still significantly slower than the generic running
of couplings. The Nordic-walking mechanism can thus explain weak first-order
transitions, but may also play a role in high-energy physics, where it could
solve hierarchy problems. We analyse the Wess-Zumino-Witten field theory
pertinent to deconfined quantum critical points with a topological term in 2+1
dimensions. To this end, we construct an advanced functional renormalisation
group approach based on higher-order regulators. We thereby calculate the
beta function directly in 2+1 dimensions and provide evidence for Nordic
walking.
The Ginzburg-Landau paradigm of phase transitions is remarkable in
its seemingly universal applicability. Consequently, finding and thoroughly understanding examples that violate this paradigm is invaluable to discovering new mechanisms and their applications to
quantum condensed matter physics and beyond. A proposed
mechanism beyond Ginzburg-Landau theory that has been a matter of
intense debate
| Original language | English |
|---|---|
| Article number | 20 |
| Number of pages | 13 |
| Journal | Nature Communications |
| Volume | (2025) 16 |
| DOIs | |
| Publication status | Published - 2 Jan 2025 |