arXiv subjects

Anthony Hegg

Publications and source records attributed to Anthony Hegg.

9 recordsLinked to original sources

arXiv2024

Manipulable compact many-body localization and absence of superfluidity in geometrically frustrated systems

Geometric frustration is known to completely damage kinetic processes of some of the orbitals (and their associated quantum coherence) as to produce flat bands in the non-interacting systems. The impact of introducing additional interaction to the system in such frustrated systems is, however, a highly controversial issue. On the one hand, numerical studies on geometrically frustrated systems of hard-core boson (equivalent to a spin-1/2 systems) typically lead to glass or solid phases containing only local many-body coherence, indicating the persistence of the damage in quantum coherence. On the other, there continues to be noticeable claims of development of superfluidity that implies kinetic flow of particles. To resolve this apparent contradiction of great significance, we present a rigorous proof showing that density-density interaction is incapable of defeating the geometric frustration to allow propagation of those immobile particles, let alone sustaining a superfluidity. Instead, the frustrated systems develop many $\textit{compact}$ many-body localized states as "many-body scars" that do not thermalize, making them good candidates for storing $\textit{robust}$ and $\textit{manipulable}$ quantum information.

cond-mat.str-el↗

arXiv2024

Universal low-temperature fluctuation of unconventional superconductors revealed: 'Smoking gun' leaves proper bosonic superfluidity the last theory standing

Low-temperature thermal fluctuations offer an essential window in characterizing the true nature of a quantum state of matter, a quintessential example being Fermi liquid theory. Here, we examine the leading thermal fluctuation of the superfluid density across numerous families ranging from relatively conventional to highly unconventional superconductors (MgB$_2$, bismuthates, doped buckyballs, heavy fermions, UTe$_2$, doped SrTiO$_3$, Chevrel clusters, intermetallics, organic superconductors, transition metal dichalcogenides, ruthenates, iron-pnictides, cuprates, and kagome metals). Amazingly, in all of them an unprecedented universal $T^3$ depletion materializes in the low-temperature superfluid density, even in the believed-to-be-conventional MgB$_2$. This reveals a new quantum superfluid state of matter and requires a necessary change of paradigm in describing modern superconductors. We demonstrate that such unorthodox yet generic behavior can be described by a strictly Galilean consistent theory of bosonic superfluidity hosting a long-lived 'true condensate'.

cond-mat.supr-con↗

arXiv2024

Showcasing the necessity of the principle of relative motion in physical statistics: Inconsistency of the `segmented Fermi surface'

The hunt for exotic properties in flowing systems is a popular and active field of study, and has recently gained renewed attention through claims such as a ``segmented Fermi surface'' in a superconducting system that hosts steady superflow of screening current driven by an external field. Apart from this excitement and the promise of hosting Majorana zero modes, claims such as this imply exotic gap-to-gapless quantum phase transitions merely through boost of inertial frames of observation, and challenge the very concept behind the principle of relative motion. Here, we first illustrate an obvious inescapable physical inconsistency of such claims concerning the flow velocity. Taking into account this basic principle from the beginning, we then demonstrate that a proper employment of physical statistics naturally reproduces the experimental observation without causing such a conceptual crisis. This example showcases the importance of strict adherence to the basic principle of relative motion in physical statistics, especially when pushing the frontiers of physics and technology.

cond-mat.supr-con↗

arXiv2021

Transport in the emergent Bose liquid: Bad metal, strange metal, and weak insulator, all in one system

Non-saturating high-temperature resistivity ("bad metal"), T-linear low-temperature resistivity ("strange metal"), and a crossover to activation-free growth of the resistivity in the low-temperature limit ("weak insulator") are among the most exotic behaviors widely observed in many strongly correlated materials for decades that defy the standard Fermi liquid description of solids. Here we investigate these puzzling behaviors by computing temperature-dependent optical conductivity of an emergent Bose liquid and find that it reproduces all the unexplained features of the experiments, including a featureless continuum and a well-known mid-infrared peak. Amazingly and with physically intuitive mechanisms, the corresponding doping- and temperature-dependent resistivity displays the bad metal and strange metal simultaneously and sometimes weak insulating behaviors as well. The unification of all these non-Fermi liquid behaviors in a single model suggests that a new quantum state of matter, namely the emergent Bose liquid, will guide the development of the next generation of solid state physics.

cond-mat.str-el↗

arXiv2021

Probing a Bose Metal via Electrons: Inescapable non-Fermi liquid scattering and pseudogap physics

Non-Fermi liquid behavior and pseudogap formation are among the most well-known examples of exotic spectral features observed in several strongly correlated materials such as the hole-doped cuprates, nickelates, iridates, ruthenates, ferropnictides, doped Mott organics, transition metal dichalcogenides, heavy fermions, d- and f- electron metals, etc. We demonstrate that these features are inevitable consequences when fermions couple to an unconventional Bose metal [1] mean field consisting of lower-dimensional coherence. Not only do we find both exotic phenomena, but also a host of other features that have been observed e.g. in the cuprates including nodal anti-nodal dichotomy and pseudogap asymmetry(symmetry) in momentum(real) space. Obtaining these exotic and heretofore mysterious phenomena via a mean field offers a simple, universal, and therefore widely applicable explanation for their ubiquitous empirical appearance. [1] A. Hegg, J. Hou, and W. Ku, Geometric frustration produces long-sought Bose metal phase of quantum matter, Proceedings of the National Academy of Sciences Nov 2021, 118 (46) e2100545118.

cond-mat.str-el↗

arXiv2021

Geometric frustration produces long-sought Bose metal phase of quantum matter

Two of the most prominent phases of bosonic matter are the superfluid with perfect flow and the insulator with no flow. A now decades-old mystery unexpectedly arose when experimental observations indicated that bosons could organize into the formation of an entirely different intervening third phase: the Bose metal with dissipative flow. The most viable theory for such a Bose metal to date invokes the use of the extrinsic property of impurity-based disorder; however, a generic intrinsic quantum Bose metal state is still lacking. We propose a universal homogeneous theory for a Bose metal in which geometric frustration confines the essential quantum coherence to a lower dimension. The result is a gapless insulator characterized by dissipative flow that vanishes in the low-energy limit. This failed insulator exemplifies a frustration-dominated regime that is only enhanced by additional scattering sources at low energy and therefore produces a Bose metal that thrives under realistic experimental conditions.

cond-mat.supr-con↗

arXiv2017

Pressure-induced melting of magnetic order and emergence of new quantum state in alpha-RuCl3

Here we report the observation of pressure-induced melting of antiferromagnetic (AFM) order and emergence of a new quantum state in the honeycomb-lattice halide alpha-RuCl3, a candidate compound in the proximity of quantum spin liquid state. Our high-pressure heat capacity measurements demonstrate that the AFM order smoothly melts away at a critical pressure (Pc) of 0.7 GPa. Intriguingly, the AFM transition temperature displays an increase upon applying pressure below the Pc, in stark contrast to usual phase diagrams, for example in pressurized parent compounds of unconventional superconductors. Furthermore, in the high-pressure phase an unusual steady of magnetoresistance is observed. These observations suggest that the high-pressure phase is in an exotic gapped quantum state which is robust against pressure up to ~140 GPa.

cond-mat.str-el↗

arXiv2015

Exact Strongly Coupled Fixed Point in $gφ^4$ Theory

We show explicitly how a strongly coupled fixed point can be constructed in scalar $gφ^4$ theory from the solutions to a non-linear eigenvalue problem. The fixed point exists only for $d< 4$, is unstable and characterized by $ν=2/d$ (correlation length exponent), $η=1/2-d/8$ (anomalous dimension). For $d=2$, these exponents reproduce to those of the Ising model which can be understood from the codimension of the critical point. At this fixed point, $φ^{2i}$ terms with $i>2$ are all irrelevant. The testable prediction of this fixed point is that the specific heat exponent vanishes. 2d critical Mott systems are well described by this new fixed point.

cond-mat.str-el↗

arXiv2013

Breakdown of self-averaging in the Bose glass

We study the square-lattice Bose-Hubbard model with bounded random on-site energies at zero temperature. Starting from a dual representation obtained from a strong-coupling expansion around the atomic limit, we employ a real-space block decimation scheme. This approach is non-perturbative in the disorder and enables us to study the renormalization-group flow of the induced random-mass distribution. In both insulating phases, the Mott insulator and the Bose glass, the average mass diverges, signaling short range superfluid correlations. The relative variance of the mass distribution distinguishes the two phases, renormalizing to zero in the Mott insulator and diverging in the Bose glass. Negative mass values in the tail of the distribution indicate the presence of rare superfluid regions in the Bose glass. The breakdown of self-averaging is evidenced by the divergent relative variance and increasingly non-Gaussian distributions. We determine an explicit phase boundary between the Mott insulator and Bose glass.

cond-mat.dis-nn↗