arXiv subjects

D. V. Khveshchenko

Publications and source records attributed to D. V. Khveshchenko.

At least 19 recordsLinked to original sources

arXiv2026

Migdal-Eliashberg and SUS-$Y^2$-SYK

This note addresses a number of subtle issues pertaining to the long-standing problem of strong phonon-like fermion-boson coupling. Among the central topics are the customary Migdal-Eliashberg approximation in the pertinent Schwinger-Dyson gap equation and its solutions. The previously gained insight is assessed by contrasting it against the various (non-)supersymmetric variants of the Yukawa-Sachdev-Ye-Kitaev model. Also, some previously discussed (pseudo-)holographic aspects of fermion pairing in such models are commented upon.

cond-mat.str-el↗

arXiv2024

(Pre-)Modern (Non-)Fermi liquids

This note addresses the problem of constructing a proper bosonized description of the collective modes in strongly interacting (non-)Fermi liquids which is specific to two spatial dimensions. Although, in a mild form, this subtlety exists in the Fermi liquid as well, the discussion focuses on the effects of long-ranged and/or retarded interactions which can completely destroy the fermionic quasiparticles. The present analysis also provides a further insight into the nature and properties of the collective bosonic modes in such systems.

cond-mat.str-el↗

arXiv2024

Strange Sounds

This note addresses the effects of long-ranged and/or retarded interactions on the bosonic collective modes in the so-called 'strange metals'. Recently, there have been conflicting reports on the very existence of such stable collective excitations and their properties. Extending a number of approaches that were previously used in the analyses of the standard Fermi liquid one finds evidence for, both, conventional and novel behaviors of the non-Fermi-liquid counterparts of the zero-, shear-, and other 'sounds'.

cond-mat.str-el↗

arXiv2023

Diagnostic Tomography of Applied Holography

The single-particle behavior in $d\geq 1$-dimensional Fermi gases with a large number $N$ of species and strong short-range $s$-wave scattering is discussed in the $2d$ 'tomographic' framework of a (pseudo)holographic correspondence with a certain $3d$ gravity of the $AdS_3$ type. However, due to the intrinsically topological nature of such a bulk theory its dynamics reduces to a purely boundary one and so, akin to its $SYK/AdS_2$ counterpart, this formal correspondence neither represents a genuine case of, nor endorses the hypothetical generalized holographic duality.

cond-mat.str-el↗

arXiv2023

IT from QUBIT or ALL from HALL?

Generalized $1+0$-dimensional Liouvillean dynamics describing deformations of the Sachdev-Ye-Kitaev (SYK) model, as well as the various $1+1$-dimensional dilaton and Horava-Lifshitz gravity theories, can all be mapped onto single-particle quantum mechanics of a non-relativistic charge propagating in a (generally, curved) $2d$ space and subject to a (generally, non-uniform) magnetic field. The latter description provides a standard playground for the phenomenon of Quantum Hall Effect (QHE), thereby elucidating the intrinsically topological nature of pertinent gravity theories and demystifying their (pseudo)holographic connection to a broad class of the SYK-like models.

hep-th↗

arXiv2023

Reckoning with the Mother of all non-Fermi liquids: alien bosonization vs predator holography

This note addresses the problem of computing fermion propagators in a broad variety of strongly correlated systems that can be mapped onto the theory of fermions coupled to an (over)damped bosonic mode. A number of the previously applied approaches and their results are reviewed, including the conventional diagrammatic resummation and eikonal technique, as well as the 'experimental' higher dimensional bosonization and generalized (i.e., 'bottom-up' or 'non-AdS/non-CFT') holographic conjecture. It appears that, by and large, those results remain either in conflict or incomplete, thereby suggesting that the ultimate solution to this ubiquitous problem is yet to be found.

cond-mat.str-el↗

arXiv2022

SYK does not Transit Gloria Mundi just yet

This note discusses examples of 0+1-dimensional Liouvillean dynamics instigated by the various deformations of the Sachdev-Ye-Kitaev (SYK) model. In reference to such deformations the main focus is on the regions of parameter space where the competing SYK couplings are of comparable strength and can not be treated as each others perturbations in the vicinity of the conformal fixed points corresponding to the pure SYK_q models with different values of $q$. Crossovers between such fixed points ('SYK transits') can be efficiently studied in the equivalent framework of single-particle quantum mechanics.

cond-mat.str-el↗

arXiv2021

Phase space holography with no strings attached

This note discusses the Wigner function representation from the standpoint of establishing a holography-like correspondence between the descriptions of a generic quantum system in the phase space ('bulk') picture versus its spacetime ('boundary') counterpart. Under certain circumstances the former might reduce to the classical dynamics of a local metric-like variable while the latter takes on the form of some bosonized collective field hydrodynamics. This generic pseudo-holographic duality neither relies on any particular symmetry of the system in question, nor does it require any connection to an underlying 'string theory', as in the various 'ad hoc' scenarios of applied holography.

cond-mat.str-el↗

arXiv2020

Die Hard Holographic Phenomenology of Cuprates

This note discusses the attempts of fitting a number of the approximate power-law dependencies observed in the cuprates into one consistent holographic or holographically inspired hydrodynamic framework. Contrary to the expectations, the goal of reproducing as many as possible of the established behaviors of the thermodynamic and transport coefficients appears to be achievable within the simplistic picture of a non-degenerate fermion fluid with quadratic dispersion. While not immediately elucidating the essential physics of the cuprates, this observation suggests a possible reason for which the previous attempts towards that goal have remained inconclusive.

cond-mat.str-el↗

arXiv2020

One SYK SET

We study the behavior of a single electron transistor (SET) represented by a dissipative tunnel junction between a pair of quantum dots described by two (possibly, different) Sachdev-Ye-Kitaev (SYK) models. A combined influence of the soft collective charge and energy modes on charge transport is discussed, alongside the competing effects of the Coulomb blockade and emergent Kondo resonances which might all conspire to result in a non-monotonic behavior of the system's conductance.

cond-mat.str-el↗

arXiv2020

Connecting the SYK dots

We study a putative (strange) metal-to-insulator transition in a granular array of the Sachdev-Ye-Kitaev (SYK) quantum dots, each occupied by a large number N>>1 of charge-carrying fermions. Extending the previous studies we complement the SYK couplings by the physically relevant Coulomb interactions and focus on the effects of charge fluctuations, evaluating the conductivity and density of states. The latter were found to demonstrate marked changes of behavior when the effective inter-site tunneling becomes comparable to the renormalized Coulomb energy, thus signifying the transition in question.

cond-mat.str-el↗

arXiv2019

True SYK or (con)sequences

Some generalizations of the Sachdev-Ye-Kitaev (SYK) model and different patterns of their reparametrization symmetry breaking are discussed. The analysis of such (pseudo)holographic systems relates their generalized one-dimensional Schwarzian dynamics to (quasi) two-dimensional Liouvillian quantum mechanics. As compared to the original SYK case, the latter might be dissipative or have discrete states in its spectrum, either of which properties alters thermodynamics and correlations while preserving the underlying $SL(2,R)$ symmetry.

hep-th↗

arXiv2018

Seeking to develop global SYK-ness

Inspired by the recent interest in the Sachdev-Ye-Kitaev (SYK) model we study a class of multi-flavored one- and two-band fermion systems with no bare dispersion. In contrast to the previous work on the SYK model that would routinely assume spatial locality, thus unequivocally arriving at the so-called 'locally-critical' scenario, we seek to attain a spatially-dispersing 'globally-SYK' behavior. To that end, a variety of the Lorentz-(non)invariant space-and/or-time dependent algebraically decaying interaction functions is considered and some of the thermodynamic and transport properties of such systems are discussed.

cond-mat.str-el↗

arXiv2018

Thickening and sickening the SYK model

We discuss higher dimensional generalizations of the 0+1-dimensional Sachdev-Ye-Kitaev (SYK) model that has recently become the focus of intensive interdisciplinary studies by, both, the condensed matter and field-theoretical communities. Unlike the previous constructions where multiple SYK copies would be coupled to each other and/or hybridized with itinerant fermions via spatially short-ranged random hopping processes, we study algebraically varying long-range (spatially and/or temporally) correlated random couplings in the general d+1 dimensions. Such pertinent topics as translationally-invariant strong-coupling solutions, emergent reparametrization symmetry, effective action for fluctuations, chaotic behavior, and diffusive transport (or a lack thereof) are all addressed. We find that the most appealing properties of the original SYK model that suggest the existence of its 1+1-dimensional holographic gravity dual do not survive the aforementioned generalizations, thus lending no additional support to the hypothetical broad (including 'non-AdS/non-CFT') holographic correspondence.

cond-mat.str-el↗

arXiv2016

Demystifying the Holographic Mystique

Thus far, in spite of many interesting developments, the overall progress towards a systematic study and classification of various 'strange' metallic states of matter has been rather limited. To that end, it was argued that a recent proliferation of the ideas of holographic correspondence originating from string theory might offer a possible way out of the stalemate. However, after almost a decade of intensive studies into the proposed extensions of the holographic conjecture to a variety of condensed matter problems, the validity of this intriguing approach remains largely unknown. This discussion aims at ascertaining its true status and elucidating the conditions under which some of its predictions may indeed be right (albeit, possibly, for a wrong reason).

cond-mat.str-el↗

arXiv2015

Viable phenomenologies of the normal state of cuprates

We revisit the problem of constructing an elusive scaling theory of the strange metal phase of the cuprates. By using the four robust experimentally established temperature dependencies as the constitutive relations we then predict the scaling behaviors of a number of other observables, all those for which the reliable data are available being in agreement with experiment. Such predictions are also contrasted against the recent proposal inspired by the holographic approach, thus allowing one to critically assess the status of the latter.

cond-mat.str-el↗

arXiv2014

Contrasting string holography to its optical namesake

We assess the prospects of using metamaterials for simulating various aspects of analogue gravity and holographic correspondence. Albeit requiring a careful engineering of the dielectric media, some hallmark features reminiscent of the hypothetical 'generalized holographic conjecture' can be detected by measuring non-local optical field correlations. The possibility of such simulated behavior might also shed light on the true origin of those apparent holography-like phenomena in the condensed matter systems with emergent effective metrics which may not, in fact, require any references to the string-theoretical holography.

cond-mat.str-el↗

arXiv2014

Taking a critical look at holographic critical matter

Despite a recent flurry of applications of the broadly defined ('non-AdS/non-CFT') holographic correspondence to a variety of condensed matter problems, the status of this intriguing, yet speculative, approach remains largely undetermined. This note exposes a number of potential inconsistencies between the previously made holographic predictions and advocates for a compelling need to systematically contrast the latter against the results of alternate, more conventional, approaches as well as experimental data. It is also proposed to extend the list of computed observables and utilize the general relations between them as a further means of bringing the formal holographic approach into a closer contact with the physical realm.

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