Track papers across labs, topics, and trends.
Search papers, labs, and topics across Lattice.
To uncover the elusive time-reversal-symmetry-breaking loop-current phase in kagome superconductor RbV$_3$Sb$_5$, the authors measured third-order nonlinear harmonic transport across varying temperatures and crystalline orientations. Below ~35 K, they observed an abrupt onset of directional anisotropy in the longitudinal cubic response alongside an emergent magnetic-field-odd transverse cubic response, strongly deviating from conventional relaxation-time scaling. Theoretical modeling reveals that these anomalous nonlinear responses are directly driven by the quantum metric quadrupole, establishing higher-order transport as a macroscopic probe of quantum geometric tensors in correlated systems.
Quantum metric quadrupoles—not just conventional Berry curvature—directly govern nonlinear electrical conduction, offering a definitive electrical readout for elusive chiral loop currents in quantum materials.
A hidden low-temperature phase with possible loop-current order has been proposed in the kagome metals AV$_3$Sb$_5$ (A=K, Rb or Cs), but its experimental signatures remain subtle and indirect. Here, we use third-order nonlinear transport to probe this hidden phase in RbV$_3$Sb$_5$. At ~35 K, the longitudinal cubic response develops a strong kink and pronounced directional anisotropy with a strong departure from common relaxation time scaling, while the transverse cubic response acquires a magnetic field-odd component at the same temperature. Their coincident onset identifies the third-harmonic response as a sensitive marker of the low-temperature electronic reconstruction with time-reversal broken symmetry. Crucially, we find that the quantum metric quadrupole contributes directly to the longitudinal third-order response. In a loop-current charge-density-wave model, its direction selective enhancement captures the observed angular reconstruction. Our work shows how higher-order nonlinear transport translates subtle changes in electronic symmetry and quantum metric into measurable electrical signatures in quantum materials that is important for studying complex electronic phases of matter.