arXiv subjects

Kitinan Pongsangangan

Publications and source records attributed to Kitinan Pongsangangan.

9 recordsLinked to original sources

arXiv2026

Plasmon excitations in half-filled graphene: A Comparative study between Quantum Monte Carlo and Random Phase Approximation

Transport properties of strongly correlated materials have contributions from quasiparticle excitations such as electrons and holes as well as emerging collective excitations such as plasmonic sound-like modes which are sustained by interactions. As was shown in Phys. Rev. B 106, 205127, the thermal excitation of the long-lived plasmons in graphene provides a substantial contribution to heat and momentum transport in the interaction-dominated regime. Detailed information on these excitations is therefore necessary for the quantitative understanding of hydrodynamic transport. On the other hand, dynamics of graphene plasmons is usually studied using Dirac perturbation theory, thus neglecting the effects of a finite Brillouin zone and higher-order perturbative corrections. Both these effects can be however significant for strong-interacting systems including free-standing graphene with the effective coupling constant of the order of alpha=2. In this paper, we studied the behavior of plasmons in half-filled free standing graphene using unbiased Quantum Monte Carlo calculations. We confirm the existence of well-defined resonance peaks for plasmons around the Gamma-point. Comparison with the Random-phase-approximation (RPA) calculation for the honeycomb lattice shows that RPA yields more stable plasmon modes, while QMC shows enhanced broadening due to non perturbative interaction effects. To account for this effect, we generalize the lattice RPA calculations by dressing the fermionic propagator by a constant lifetime. As a result, the plasmon frequencies are shifted towards higher energies and the spectrum is broadened, yielding a better agreement with QMC. Our findings highlight the need to account for both a finite Brillouin zone and strong interaction effects when developing theories of electronic transport in free-standing graphene.

cond-mat.mes-hall↗

arXiv2025

Kinetic equation from Landau level basis: Beyond relaxation-time approximation

The purpose of this paper is to formulate a kinetic theory describing transport properties of electrons in a uniform magnetic field of arbitrary magnitude. Exposing an electronic system to a constant magnetic field quenches its energy bands into a series of discrete energy levels, known as Landau levels. The Landau-level states, exact solutions of the Schrödinger equation in a constant background magnetic field, are natural and suitable basis to use, especially, for the investigation of strong-magnetic-field phenomena. Starting from the Keldysh formalism, we derive the quantum kinetic equation from the Landau-level basis. As an illustration, we apply the kinetic equation to calculate the electrical conductivity of a two-dimensional electron gas exposed to a perpendicular magnetic field.

cond-mat.mes-hall↗

arXiv2025

Hydrodynamics of particle-hole symmetric systems: a quantum Monte Carlo study

The emergence of hydrodynamic behavior in electronic flow within clean, particle-hole-symmetric systems at half-filling is a non-trivial problem. Navier-Stokes (NS) equations describe the momentum flow, while experimental measurements typically capture the current flow profiles. However, in particle-hole-symmetric systems, electric current and momentum flow are entirely decoupled because electrons and holes move in opposite directions with equal distribution functions. This makes it challenging to link NS equations to observed flow patterns. In this work, we demonstrate that the hydrodynamic behavior of the charge current at half filling can emerge despite the absence of momentum flow. By combining Boltzmann transport theory with numerically exact Quantum Monte Carlo simulations of clean graphene samples, we show that NS-type equations can be derived directly for the charge current, eliminating the need for any additional mechanism coupling the velocity field and charge current in explaining the experimentally observed hydrodynamic flow profiles in graphene at half-filling. We show that a new transport quantity - the current diffusion coefficient - replaces viscosity and expect this description to be valid for any particle-hole symmetric system. Our results provide new insights into the interpretation of experimental data and demonstrate how Quantum Monte Carlo calculations can serve as an alternative to experiments in transport measurements to verify the kinetic theory results.

cond-mat.mes-hall↗

arXiv2025

Bulk Hydrodynamic Transport in Weyl Semimetals

The role of collective longitudinal modes, plasmons, in bulk hydrodynamic transport in Weyl semimetals is explored. In contrast to graphene, where these modes are gapless, plasmons in Weyl semimetals are gapped. This gap, however, can be made arbitrarily small by decreasing the temperature or the chemical potential, making plasmon modes thermally accessible, both in thermodynamics and transport. In very clean Weyl semimetals near charge-neutrality where the plasmon gap is minimal, we find that they leave an imprint in the thermal conductivity and the viscosity.

cond-mat.mes-hall↗

arXiv2023

The shear viscosity of interacting graphene

One of the hallmark properties of fluids is their shear viscosity which is, among other things, responsible for parabolic flow profiles through narrow channels. In recent years, there has been a growing number of observations of said flow profiles in electronic transport measurements in a variety of material systems, most notably in graphene. In this paper, we investigate the shear viscosity of interacting graphene from a theoretical point of view. We study both a phenomenological as well as a microscopic model and find excellent agreement between the two. Our main finding is collective modes make a sizeable contribution to the viscosity that can equal or even outweigh the electronic contribution that is usually assumed dominant. We comment on how this finding carries over to systems beyond graphene and related Dirac materials.

cond-mat.str-el↗

arXiv2022

Hydrodynamics of charged two-dimensional Dirac systems II: the role of collective modes

We study the hydrodynamic properties of ultraclean interacting two-dimensional Dirac electrons with Keldysh quantum field theory. We study it from a weak-coupling and a strong-coupling perspective. We demonstrate that long-range Coulomb interactions play two independent roles: (i) they provide the inelastic and momentum-conserving scattering mechanism that leads to fast local equilibration; (ii) they facilitate the emergence of collective excitations, for instance plasmons, that contribute to transport properties on equal footing with electrons. Our approach is based on an effective field theory of the collective field coupled to electrons. Within a conserving approximation for the coupled system we derive a set of coupled quantum-kinetic equations. This builds the foundation of the derivation of the Boltzmann equations for the interacting system of electrons and plasmons. From this, we explicitly derive all the conservation laws and identify the extra contributions of energy density and pressure from the plasmons. We demonstrate that plasmons show up in thermo-electric transport properties as well as in quantities that enter the energy-momentum tensor, such as the viscosity. In a parallel paper we discuss some of the phenomenology of the corresponding hydrodynamic equations with an eye on thermo-electric transport properties.

cond-mat.str-el↗

arXiv2022

Hydrodynamics of charged two-dimensional Dirac systems I: thermo-electric transport

In this paper we study thermo-electric transport in interacting two-dimensional Dirac-type systems using a phenomenological Boltzmann approach. We consider a setup that can accommodate electrons, holes, and collective modes. In the first part of the paper we consider the electron-hole hydrodynamics, a model that is popular in the context of graphene, and its transport properties. In a second part, we propose a novel type of hydrodynamics. In that setup, the `fluid' consists of electrons, holes, and plasmons. We study its transport properties, especially the thermo-electric behavior. The results of this part can also be adapted to the study of a fluid consisting of electrons and phonons. This paper is accompanied by a technical paper in which we give a detailed derivation of the Boltzmann equations and the encoded conservation laws.

cond-mat.str-el↗

arXiv2021

Thermo-electric response in two-dimensional Dirac systems: the role of particle-hole pairs

Clean two-dimensional Dirac systems have received a lot of attention for being a prime candidate to observe hydrodynamical transport behavior in interacting electronic systems. This is mostly due to recent advances in the preparation of ultrapure samples with sufficiently strong interactions. In this paper, we investigate the role of collective modes in the thermo-electric transport properties of those systems. We find that dynamical particle-hole pairs, plasmons, make a sizeable contribution to the thermal conductivity. While the increase at the Dirac point is moderate, it becomes large towards larger doping. We suspect, that this is a generic feature of ultraclean two-dimensional electronic systems, also applicable to degenerate systems.

cond-mat.str-el↗

arXiv2021

Chiral symmetry breaking through spontaneous dimerization in kagomé metals

Due to an uprise in the variety of candidate compounds, kagome metals have recently gained significant attention. Among other features, kagome metals host Dirac cones as a key band structure feature away from half filling, and potentially yield an exceptionally large fine structure, beyond values found in other 2D Dirac materials such as graphene. We investigate the possibility of chiral symmetry breaking in kagome metals. Based on a heuristic lattice model, we determine the critical coupling strength and the ordering pattern by means of a Schwinger-Dyson mean-field analysis. As the leading instability we identify a dimerization pattern which spontaneously opens an excitation gap at the Dirac point and breaks the chiral symmetry.

cond-mat.str-el↗