Nonperturbative behavior of the quantum phase transition to a nematic Fermi fluid

We discuss shape (Pomeranchuk) instabilities of the Fermi surface of a two-dimensional Fermi system using bosonization. We consider in detail the quantum critical behavior of the transition of a two-dimensional Fermi fluid to a nematic state which breaks spontaneously the rotational invariance of the Fermi liquid. We show that higher dimensional bosonization reproduces the quantum critical behavior expected from the Hertz-Millis analysis, and verify that this theory has dynamic critical exponent $z=3$. Going beyond this framework, we study the behavior of the fermion degrees of freedom directly, and show that at quantum criticality as well as in the quantum nematic phase (except along a set of measure zero of symmetry-dictated directions) the quasiparticles of the normal Fermi liquid are generally wiped out. Instead, they exhibit short-ranged spatial correlations that decay faster than any power law, with the law $\mid x{\mid }^{-1}\exp (-\mathrm{const}\mid x{\mid }^{1∕3})$ and we verify explicitly the vanishing of the fermion residue utilizing this expression. In contrast, the fermion autocorrelation function has the behavior $\mid t{\mid }^{-1}\exp (-\mathrm{const}\mid t{\mid }^{-2∕3})$. In this regime we also find that, at low frequency, the single-particle fermion density of states behaves as $N^{*}\left(\omega \right)=N^{*}\left(0\right)+B{\omega }^{2∕3}\ln \omega +\cdots$, where $N^{*}\left(0\right)$ is larger than the free Fermi value, $N\left(0\right)$, and $B$ is a constant. These results confirm the non-Fermi liquid nature of both the quantum critical theory and of the nematic phase.

Figure 1

The (normalized) quadrupole density spectral function ${\tilde{S}}_2^{+}(q,s)=S_2^{+}(q,s)∕N\left(0\right)$, Eqs. (2.26, 2.29) for $q\ne 0$, very close to the nematic quantum phase transition from the Fermi liquid phase, $F_2\left(0\right)\to -1^{+}$. As the QCP is approached, there is a large increase of spectral weight in the $z=3$ overdamped quadrupolar mode at very low frequency. Notice the delta function contribution of the propagating mode with $z=1$ discussed in the text. The propagating mode with $z=2$ gives a similar delta function contribution (with smaller spectral weight) to $S_2^{-}(q,s)$.

Figure 2

Bosonization’s Feynman diagram series.