arXiv subjects

Alexander Kazantsev

Publications and source records attributed to Alexander Kazantsev.

5 recordsLinked to original sources

arXiv2026

Non-Fermi-liquid behaviour of electrons coupled to gauge phonons

We identify overdamped gauge phonons as a new microscopic route to non-Fermi-liquid behaviour in Dirac materials. These phonons couple to electronic currents rather than densities, thereby realising a lattice analogue of transverse gauge-field mechanisms without requiring proximity to a quantum critical point. By computing the electronic self-energy with a phonon propagator dressed by electron-phonon interactions, we show that the low-energy behaviour is controlled by the orbital susceptibility chi and a dimensionless damping parameter alpha. In the overdamped regime, alpha >> 1, quasiparticles display strong deviations from Fermi-liquid theory. For chi > 0, Fermi-liquid behaviour persists only in a parametrically narrow infrared window before crossing over to non-Fermi-liquid scaling. For chi < 0, the Fermi-liquid regime is replaced by marginal-Fermi-liquid behaviour at the lowest energies, followed by a crossover to non-Fermi-liquid scaling. These results establish strain-induced gauge phonons as a promising source of anomalous metallic behaviour in systems such as twisted bilayer graphene.

cond-mat.str-el↗

arXiv2025

Non-conservation of the valley density and its implications for the observation of the valley Hall effect

We show that the conservation of the valley density in multivalley insulators is broken in an unexpected way by the electric field that drives the valley Hall effect. This implies that time-reversal-invariant fully gapped insulators, in which no bulk or edge state crosses the Fermi level, can support a valley Hall current in the bulk and yet show no valley density accumulation at the edges. Thus, the valley Hall effect cannot be observed in such systems. If the system is not fully gapped then valley density accumulation at the edges is possible. The accumulation has no contribution from undergap states and can be expressed as a Fermi surface average, for which we derive an explicit formula. We demonstrate the theory by calculating the valley density accumulations in an archetypical valley-Hall insulator: a gapped graphene nanoribbon. Surprisingly, we discover that a net valley density polarization is dynamically generated for certain edge terminations.

cond-mat.mes-hall↗

arXiv2024

Nonconserved Density Accumulations in Orbital Hall Transport: Insights from Linear Response Theory

We present a linear response theory for stationary density accumulations in anomalous transport phenomena, such as the orbital Hall effect, where the transported density is odd under time reversal and the underlying charge is not conserved. Our framework applies to both metals and insulators, topologically trivial or nontrivial, and distinguishes between contributions from bulk and edge states, as well as undergap and dissipative currents. In time-reversal invariant systems, we prove a microscopic reciprocity theorem showing that only dissipative currents at the Fermi level contribute to density accumulation, while undergap currents do not. In contrast, in non-time-reversal invariant systems, non-dissipative density accumulations, such as magnetoelectric polarization, can appear in both the bulk and edges. Importantly, we find that the net density accumulation does not always vanish, pointing to a global non-conservation that implies the existence of a non-vanishing integrated ``net torque'' in addition to a ``distributed torque'', which has zero spatial average. We show that the distributed torque can be absorbed in the divergence of a redefined current that satisfies Onsager reciprocity, while the net torque must be explicitly accounted for. Finally, we apply our theory to two-dimensional models with edge terminations.

cond-mat.mes-hall↗

arXiv2022

On the origin of Abrikosov's quantum linear magnetoresistance

Compensated semimetals with Weyl spectra are predicted to exhibit unsaturated linear growth of their resistivity in quantizing magnetic fields. This so-called quantum linear magnetoresistance was introduced by Abrikosov, but approximations used in the theory remained poorly specified, often causing a confusion about experimental situations in which the analysis is applicable. Here we derive Abrikosov's exact result using an alternative formalism based on diffusion of cyclotron orbits in a random potential. We show that both Weyl spectrum and a disorder smooth on the scale of the magnetic length are essential conditions for the validity of the theory, and the linear magnetoresistance appears in the extreme quantum limit where only the zeroth Landau level is half filled. It is the interplay between the relativistic-like nature of Weyl fermions and the classical dynamics of their cyclotron centers, which leads to the linear magnetoresistance. We also derive an analogous result in two dimensions, which has been missing in the literature and is relevant for numerous graphene-based systems.

cond-mat.mes-hall↗

arXiv2020

Two-loop renormalization of the matter superfields and finiteness of ${\cal N}=1$ supersymmetric gauge theories regularized by higher derivatives

The two-loop anomalous dimension of the chiral matter superfields is calculated for a general ${\cal N}=1$ supersymmetric gauge theory regularized by higher covariant derivatives. We obtain both the anomalous dimension defined in terms of the bare couplings, and the one defined in terms of the renormalized couplings for an arbitrary renormalization prescription. For the one-loop finite theories we find a simple relation between the higher derivative regulators under which the anomalous dimension defined in terms of the bare couplings vanishes in the considered approximation. In this case the one-loop finite theory is also two-loop finite in the HD+MSL scheme. Using the assumption that with the higher covariant derivative regularization the NSVZ equation is satisfied for RGFs defined in terms of the bare couplings, we construct the expression for the three-loop $β$-function. Again, the result is written both for the $β$-function defined in terms of the bare couplings and for the one defined in terms of the renormalized couplings for an arbitrary renormalization prescription.

hep-th↗