## Bosonization and the Shear Sound of Metals and The Non-linear Hall Effect in Time-Reversal-Invariant Materials

**Speaker:**Inti Sodemann, Max Planck Institute for the Physics of Complex Systems

**When:**October 23, 2019 (Wed), 03:30PM to 04:30PM (add to my calendar)

**Location:**SCI 328

**Hosted by:**Claudio Chamon

*This event is part of the Condensed Matter Theory Seminar Series. *

In the first part of the talk, we will review the bosonization approach to Fermi liquids in above one dimension and use it to study a sharp change in the excitation spectrum of fermi liquids that occurs beyond a critical interaction strength whereby an unconventional collective mode exits the particle-hole continuum. This mode is a collective shear wave that features purely transverse current oscillations, in analogy to the transverse sound of crystals. We will argue that the shear sound might be “hiding`' in several metals and describe experimental strategies to probe it, including the appearance of sharp conductivity dips in ultra-clean narrow channels and its coupling to charge-fluctuations under weak magnetic fields.

In the second part, we will describe a correction to Newton’s second law when electrons move in Bloch bands without inversion symmetry, whereby, their acceleration acquires a term proportional to the square of the electric field and orthogonal to it. This "non-linear Hall acceleration" gives rise to a "non-linear Hall effect" in time reversal invariant materials that is controlled by a quantum geometric tensor called the "Berry curvature dipole”. We will also discuss a remarkable "quantum rectification sum rule” according to which the frequency integrated rectification conductivity is entirely controlled by the Berry geometry and is independent of the band energies.