Quantum Paracrystalline Shear Resonances in Metals

Unlike classical fluids, a quantum fermi liquid can support a long-lived and propagating shear sound wave, reminiscent of the transverse sound in crystals, despite lacking any form of long-range crystalline order. This mode is expected to be present in moderately interacting metals where the quasiparticle mass is renormalised to be more than twice the bare mass, but, it is hard to excite and detect because it does not involve charge density fluctuations, in contrast to the conventional plasma mode. We propose two strategies to excite and probe this unconventional mode. One is the appearance of sharp dips in the AC conductance of narrow channels when the frequency matches the energy dispersion of the shear sound. Another is the coupling of the mode to charge fluctuations under weak magnetic fields, that could allow to excite it using near field techniques such as those employed to excite plasma modes in two-dimensional metals.