arXiv subjects

Taewon Yuk

Publications and source records attributed to Taewon Yuk.

16 recordsLinked to original sources

arXiv2025

Tilted Dirac cones and their topology in Holographic Materials

We explore strongly correlated materials with tilted Dirac cone by introducing a method to realize this spectral feature within a holographic setup. Following the work by Moradpouri et al., we construct an asymptotically AdS spacetime by uplifting the vielbein of Volovik et al to tilt the flat spacetime light cone. We then couple the resulting metric to holographic fermions and compute their spectral functions, confirming the presence of a tilted Dirac cone in momentum space. We also calculate the topological number using the holographic Green's function and find that the Chern number is independent of the tilting parameter. Additionally, we show that the optical conductivity exhibits a Drude peak even at zero chemical potential, revealing nontrivial strong-coupling effects absent in field-theoretic models.

hep-th↗

arXiv2025

Topology in Holographic Mean-Field Theory at Zero and Finite Temperature

We investigate topological invariants in strongly interacting many-body systems within holographic mean-field theory (H-MFT) framework. Analytic expressions for retarded Green's functions are obtained for all possible fermionic bilinear interactions in the limit of probe background limit $\mathrm{AdS}_4$, from which we construct topological Hamiltonians. Integrating Berry curvature over the momentum domain for the gapped spectra yields well-defined and quantized Chern numbers, enabling a systematic classification of them across interaction types. These topological invariants remain robust under deformation parameters like interaction and temperature, indicating that H-MFT encodes effective single-particle-state topology near a quantum critical point in strongly correlated systems. We point out why topological number is defined in the holographic theories while it is not in the perturbative field theory.

hep-th↗

arXiv2025

Topological transition as a percolation of the Berry curvature

We first study the importance of the sign of the Berry curvature in the Euler characteristic of the two-dimensional topological material with two bands. Then we report an observation of a character of the topological transition as a percolation of the sign of the Berry curvature. The Berry curvature F has peaks at the Dirac points, enabling us to divide the Brillouin zone into two regions depending on the sign of the F: one with the same sign with a peak and the other with the opposite sign. We observed that when the Chern number is non-zero, the oppositely signed regions are localized. In contrast, in the case of a trivial topology, the oppositely signed regions are delocalized dominantly. Therefore, the oppositely signed region will percolate under the topological phase transition from non-trivial to trivial. We checked this for several models including the Haldane model, the extended Haldane model, and the QWZ model. Our observation may serve as a novel feature of the topological phase transition.

cond-mat.mes-hall↗

arXiv2025

Symmetric Tensor Coupling in Holographic Mean-Field Theory: Deformed Dirac Cones

We extend the holographic mean-field theory to rank-two symmetric tensor field as an external source coupled with fermion. We classify the roles of symmetric tensor coupling according to the effect on the spectral density: cone-angle change, squashing, and tilting of the spectral light cones. The over-tilted light cone is also achieved in a generalized prescription, which consistently retains the causality condition. Our results provide agreements between the holographic spectra with those observed in real materials, such as type-II Dirac cones and strained graphene.

hep-th↗

arXiv2025

Holographic mean field theory and Kondo lattice

We first study a non-relativistic field theory model for the Kondo lattice by introducing the Kondo condensation, whose main effect is the hybridization of the flat band of the localized electron with dispersive one of the itinerant electron. The problem here is that the resulting Kondo condensation arises only in strong coupling where the validity of the mean field theory is questionable. Therefore, we build a holographic mean field theory of the Kondo lattice with strong coupling by identifying the effect of the lattice with the fermion's spectral shape due to the coupling with the order parameter representing the symmetry breaking. For the flat band spectrum we use the mixed quantization, and for the dispersive spectrum we intoduce the second fermion in standard quantization. The coupling of the two fermions with the scalar order representing the Kondo condensation provides the hybrization of the two spectrum, reproducing the main feature of the Kondo lattice together with the fuzzy character of the spectrum of the strongly coupled system.

hep-th↗

arXiv2024

Classes of Holographic Mott Gaps

The fermion gaps are classified into order gap or Mott gap depending on the presence/absence of the order parameter. We construct the holographic model of the Mott gap using the field that is supported by the density only without introducing any order parameter. We then classify the Mott gap, depending on the shape of the gap in the density of states and whether the Fermi surface is touching the valence bond or not, into three classes: i) Symmetric gap, ii) Asymmetric gap with isolated Fermi sea. iii) Asymmetric gap with Fermi sea touching the valence band. Finally, we identify possible non-minimal gauge interactions that produce a flatband without symmetry breaking.

hep-th↗

arXiv2024

First order phase transition in the D3-D7 model from the point of view of the fermionic spectral functions

We consider the D3-D7 model and use the spectral function of a probe fermion on D7 to analyze the first order phase transition from the black-hole embedding phase to another black-hole embedding phase in the presence of the finite density and temperature. From the fermionic spectral functions, we study the temperature dependence of the decay rate, and we observe various phenomena that support the first order phase transition including jump in it at the critical temperature that corresponds to the first order phase transition.

hep-th↗

arXiv2024

Encoding the lattice in the Holography

One of the most wanted features of holography in its condensed matter physics application is to encode the structure of lattice, which is the most direct data of the material. In this paper, we propose a method to encode the lattice structure by embedding the tight binding data into the Dirac equation in the AdS bulk. We explicitly worked out the idea for the Graphene and Haldane model, and the result shows that some degrees of freedom escape the free-electron on-shell curve, and Green's function loses the pole structure completely. It implies that the electronic structure is not described by the band structure only, which is consistent with what many ARPES data tell us, and it also implies that the system is in non-fermi liquid even for the graphene, which is consistent with recent experiments for the clean graphene.

hep-th↗

arXiv2024

Mean field theory for strongly coupled systems: Holographic approach

In this paper, we develop the holographic mean field theory for strongly interacting fermion systems. We investigate various types of the symmetry-breakings and their effect on the spectral function. We found analytic expressions of fermion Green's functions in the probe-limit for all types of tensor order parameter fields. We classified the spectral shapes and singularity types from the analytic Green's function. We calculated the fermions spectral function in the full backreacted background and then compared it with the analytic results to show the reliability of analytic results in the probe limit.

hep-th↗

arXiv2024

Order parameter and spectral function in $d$-wave holographic superconductors

We consider the $d$-wave holographic superconductor model with full backreaction on the metric, addressing a missing part in the literature. We have identified the corrected order parameter by comparing the fermionic spectral function with the momentum-dependent order parameter. By numerical investigations of the fermionic spectral function in the presence of a tensor condensate, we find the Fermi arc and the gapped behavior, which closely resemble ARPES data. Moreover, we have examined the influence of the coupling constant, chemical potential, and temperature on the spectral function. We find that $d$-wave fermionic spectral function can be obtained through $p_x$ and $p_y$ condensates combined with two fermion flavors. Similarly, combining $d_{x^2-y^2}$ and $d_{xy}$ orbitals symmetry with two fermion flavors leads to a $g$-wave spectral function.

hep-th↗

arXiv2023

Fermi arc in $p$-wave holographic superconductors

We have investigated the fermionic spectral function in $p$-wave holographic superconductors. We show that the vector model with minimal coupling reveals a $p$-wave spectral function with Fermi arc. This should be contrasted with the previous investigation where $p$-wave arc was demonstrated in the presence of a tensor field. We study the momentum dependent order parameter, the $ω$-gap in the real part of the conductivity and the fermion spectral function. In addition, we juxtapose the fermionic spectral gap with the order parameter in the holographic set. We demonstrate the impact of coupling constants, temperature and chemical potential on the spectral function.

hep-th↗

arXiv2023

Flow Equation and Fermion Gap in the Holographic Superconductors

We reconsider the fermion spectral function in the presence of the Cooper pair condensation and identified the interaction type of complex scalar and fermion, which gives consistent results with the expected s-wave superconductor for the first time. We derive the matrix Riccati equation, which allows the precise calculation of the fermion spectral function. Apart from the gap structure, we studied the effect of the chemical potential and the density and compared it with the BCS theory. We found that two theories give similar results in small chemical potential but very different ones in the high-density case, which we attribute to the correlation effect.

hep-th↗

arXiv2023

Holographic Lieb lattice and gapping its Dirac band

We first point out that the Laia-Tong model realizes the Lieb lattice in the holographic setup. It generates a flat band of sharp particle spectrum together with a Dirac band of unparticle spectrum. We then construct a model which opens a gap to the Dirac band so that one can realize a well-separated flat band, which can play the role of the hydrogen atom of strongly correlated systems. We then study the phase transition between the gapped and gapless phases analytically. We also made methodological progress to find a few other quantizations and we express the Green functions in any quantization in terms of that in the standard quantization.

hep-th↗

arXiv2022

ABC-stacked multilayer graphene in holography

A flat band can be studied an infinitely strong coupling, realized in a simple system. Therefore, its holographic realization should be interesting. Laia and Tong gave a realization of the flat band over the entire momentum region by introducing a particular boundary term. Here, we give a model with a flat band over a finite region of momentum space using a bulk interaction term instead of the boundary term. We find that the spectrum of our model is precisely analogous to that of the ABC stacked multilayer graphene. In the presence of the chemical potential, the flat band is bent in our holographic model, which is very close to the band deformation due to the spin-orbit

hep-th↗

arXiv2021

The emergence of Strange metal and Topological Liquid near Quantum Critical Point in a solvable model

We discuss quantum phase transition by an exactly solvable model in the dual gravity setup. By considering the effect of the scalar condensation on the fermion spectrum near the quantum critical point(QCP), we find that there is a topologically protected fermion zero mode associated with the metal to insulator transition. We also show that the strange metal phase with T-linear resistivity emerges at high enough temperature as far as the gravity has a horizon. The phase boundaries are calculated according to the density of states, giving insights on structures of the phase diagram near the QCP.

hep-th↗

arXiv2020

Ginzberg-Landau-Wilson theory for Flat band, Fermi-arc and surface states of strongly correlated systems

We consider a holographic theory as a Ginzberg-Landau theory working for strongly interacting system near the quantum critical point: we take the bulk matter field $Φ^I(r,x)$, the dual of the fermion bilinear, as the order parameter. We calculate and classify the fermion spectral functions in the presence of such orders. Depending on the symmetry, we found spectral features like the gap, pseudo-gap, flat disk bands and the Fermi-arc connecting the two Dirac cones, which are familiar in Dirac material and Kondo lattice. Many of above features are associated with the zero modes whose presence is tied with a discrete symmetry of the interaction. The interaction induced zero modes either makes the strongly correlated system fermi-liquid like, or creates a disk-like flat band. Some of the order parameters in the bulk theory do not have an interpretation of symmetry breaking in terms of the boundary space, which opens the possibility of 'an order without symmetry breaking'.

hep-th↗