Found 26 papers in cond-mat
Date of feed: Mon, 01 Jan 2024 01:30:00 GMT

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Influence of Rhenium Concentration on Charge Doping and Defect Formation in MoS2. (arXiv:2312.17304v1 [cond-mat.mtrl-sci])
Kyle T. Munson (1), Riccardo Tori (1), Fatimah Habis (2), Lysander Huberich (3), Yu-Chuan Lin (1), Yue Yuan (4), Ke Wang (5), Bruno Schuler (3), Yuanxi Wang (2), John B. Asbury (1, 4), Joshua A. Robinson (1,4,5,6) ((1) Department of Materials Science and Engineering, The Pennsylvania State University, (2) Department of Physics, University of North Texas, (3) nanotechATsurfaces Laboratory, Empa-Swiss Federal Laboratories for Materials Science and Technology, (4) Department of Chemistry, The Pennsylvania State University, (5) Materials Research Institute, The Pennsylvania State University, (6) Department of Physics, The Pennsylvania State University)

Substitutionally doped transition metal dichalcogenides (TMDs) are the next step towards realizing TMD-based field effect transistors, sensors, and quantum photonic devices. Here, we report on the influence of Re concentration on charge doping and defect formation in MoS2 monolayers grown by metal-organic chemical vapor deposition. Re-MoS2 films can exhibit reduced sulfur-site defects; however, as the Re concentration approaches 2 atom%, there is significant clustering of Re in the MoS2. Ab Initio calculations indicate that the transition from isolated Re atoms to Re clusters increases the ionization energy of Re dopants, thereby reducing Re-doping efficacy. Using photoluminescence spectroscopy, we show that Re dopant clustering creates defect states that trap photogenerated excitons within the MoS2 lattice. These results provide insight into how the local concentration of metal dopants affect carrier density, defect formation, and exciton recombination in TMDs, which can aid the development of future TMD-based devices with improved electronic and photonic properties.


Spectral sum rules reflect topological and quantum-geometric invariants. (arXiv:2312.17318v1 [cond-mat.str-el])
Alexander Kruchkov, Shinsei Ryu

Topological invariants are fundamental characteristics reflecting global properties of quantum systems, yet their exploration has predominantly been limited to the static (DC) transport and transverse (Hall) channel. In this work, we extend the spectral sum rules for frequency-resolved electric conductivity $\sigma (\omega)$ in topological systems, and show that the sum rule for the longitudinal channel is expressed through topological and quantum-geometric invariants. We find that for dispersionless (flat) Chern bands, the rule is expressed as, $ \int_{-\infty}^{+\infty} d\omega \, \text{Re}(\sigma_{xx} + \sigma_{yy}) = C \Delta e^2$, where $C$ is the Chern number, $\Delta$ the topological gap, and $e$ the electric charge. In scenarios involving dispersive Chern bands, the rule is defined by the invariant of the quantum metric, and Luttinger invariant, $\int_{-\infty}^{+\infty} d\omega \, \text{Re}(\sigma_{xx} + \sigma_{yy}) = 2 \pi e^2 \Delta \sum_{\boldsymbol{k}} \text{Tr} \, \mathcal{G}_{ij}(\boldsymbol{k})$+(Luttinger invariant), where $\text{Tr} \, \mathcal {G}_{ij}$ is invariant of the Fubini-Study metric (defining spread of Wannier orbitals). We further discuss the physical role of topological and quantum-geometric invariants in spectral sum rules. Our approach is adaptable across varied topologies and system dimensionalities.


The Club Sandwich: Gapless Phases and Phase Transitions with Non-Invertible Symmetries. (arXiv:2312.17322v1 [hep-th])
Lakshya Bhardwaj, Lea E. Bottini, Daniel Pajer, Sakura Schafer-Nameki

We provide a generalization of the Symmetry Topological Field Theory (SymTFT) framework to characterize phase transitions and gapless phases with categorical symmetries. The central tool is the club sandwich, which extends the SymTFT setup to include an interface between two topological orders: there is a symmetry boundary, which is gapped, and a physical boundary that may be gapless, but in addition, there is also a gapped interface in the middle. The club sandwich generalizes so-called Kennedy-Tasaki (KT) transformations. Building on the results in [1, 2] on gapped phases with categorical symmetries, we construct gapless theories describing phase transitions with non-invertible symmetries by applying suitable KT transformations on known phase transitions provided by the critical Ising model and the 3-state Potts model. We also describe in detail the order parameters in these gapless theories characterizing the phase transitions, which are generally mixtures of conventional and string-type order parameters mixed together by the action of categorical symmetries. Additionally, removing the physical boundary from the club sandwiches results in club quiches, which characterize all possible gapped boundary phases with (possibly non-invertible) symmetries that can arise on the boundary of a bulk gapped phase. We also provide a mathematical characterization of gapped boundary phases with symmetries as pivotal tensor functors whose targets are pivotal multi-fusion categories.


Skyrmion and incommensurate spin dynamics in centrosymmetric Gd$_2$PdSi$_3$. (arXiv:2312.17323v1 [cond-mat.str-el])
M. Gomilšek, T. J. Hicken, M. N. Wilson, K. J. A. Franke, B. M. Huddart, A. Štefančič, S. J. R. Holt, G. Balakrishnan, D. A. Mayoh, M. T. Birch, S. H. Moody, H. Luetkens, Z. Guguchia, M. T. F. Telling, P. J. Baker, S. J. Clark, T. Lancaster

Skyrmions are particle-like vortices of magnetization with non-trivial topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions (DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd- and Eu-based skyrmion-lattice (SkL) hosts with net zero DMI, where both the dominant SkL stabilization mechanisms and ground-state magnetic properties remain controversial. In this Letter we use muon spectroscopy ($\mu$SR) to address these by investigating both static and dynamic spin properties of the most-studied centrosymmetric SkL host, Gd$_2$PdSi$_3$. We find that spin fluctuations in the non-coplanar SkL phase are highly anisotropic, implying that spin anisotropy plays a prominent role in stabilizing this phase. Intriguingly, we also observe strongly-anisotropic spin fluctuations in the ground-state (IC-1) incommensurate magnetic phase of the material, indicating that it is a complex multi-$q$ magnetic structure. On the other hand, the higher-field coplanar IC-2 phase is found to be single-$q$ with mostly isotropic spin dynamics.


Damage Rate Laws and Failure Statistics for Lumped Coupled-Field Systems via Averaging. (arXiv:2312.17350v1 [physics.app-ph])
Arjun Roy, Joseph P. Cusumano

We study the non-linear dynamics and failure statistics of a coupled-field fatigue damage evolution model. We develop a methodology to derive averaged damage evolution rate laws from such models. We show that such rate laws reduce life-cycle simulation times by orders of magnitude and permit dynamical systems analysis of long-time behavior, including failure time statistics. We use the averaged damage rate laws to study 1 DOF and 2 DOF damage evolution models. We identify parameter regimes in which the systems behave like a brittle material and show that the relative variability for failure times is high for such cases. We also use the averaged rate laws to construct damage evolution phase portraits for the 2 DOF system and use insights derived from them to understand failure time and location statistics. We show that, for brittle materials, as the relative variability in failure time increases, the variability in failure location decreases.


Topological transitions in the site-diluted Yao-Lee spin-orbital model. (arXiv:2312.17359v1 [cond-mat.str-el])
Vladislav Poliakov, Wen-Han Kao, Natalia B. Perkins

The Yao-Lee (YL) model is an example of exactly solvable spin-orbital models that are generalizations of the original Kitaev honeycomb model with extra local orbital degrees of freedom. Similar to the Kitaev model, both spin and orbital degrees of freedom are effectively represented using sets of three-flavored Majorana fermions. The YL model exhibits a quantum spin liquid ground state with gapped and immobile Z$_2$ fluxes and three-fold degenerate itinerant Majorana fermions. Our work demonstrated that by introducing different time-reversal symmetry (TRS) breaking fields one can split the degeneracy of Majorana fermions and close the gap for some of the bands, thus changing its topology. We calculated a comprehensive topological phase diagram for the YL model by considering various combinations of TRS breaking fields. This investigation revealed the emergence of distinct topological regions, each separated by nodal lines, signifying an evolution in the model's topological properties. We also investigated the impact of vacancies in the system. Our findings revealed that while vacancies modify the low-energy spectrum of the model, their presence has a limited impact on the topological properties of the model, at least for small enough concentrations.


Time-reversal symmetry breaking in the chemosensory array: asymmetric switching and dissipation-enhanced sensing. (arXiv:2312.17424v1 [physics.bio-ph])
David Hathcock, Qiwei Yu, Yuhai Tu

The Escherichia coli chemoreceptors form an extensive array that achieves cooperative and adaptive sensing of extracellular signals. The receptors control the activity of histidine kinase CheA, which drives a non-equilibrium phosphorylation-dephosphorylation reaction cycle for response regulator CheY. Recent single-cell FRET measurements revealed that kinase activity of the array spontaneously switches between active and inactive states, with asymmetric switching times that signify time-reversal symmetry breaking in the underlying dynamics. Here, we show that the asymmetric switching dynamics can be explained by a non-equilibrium lattice model, which considers both the dissipative reaction cycles of individual core units and the coupling between neighboring units. The model reveals that large dissipation and near-critical coupling are required to explain the observed switching dynamics. Microscopically, the switching time asymmetry originates from irreversible transition paths. The model shows that strong dissipation enables sensitive and rapid signaling response by relieving the speed-sensitivity trade-off, which can be tested by future single-cell experiments. Overall, our model provides a general framework for studying biological complexes composed of coupled subunits that are individually driven by dissipative cycles and the rich non-equilibrium physics within.


Understanding the magnetic interactions of the zig-zag honeycomb lattice: Application to $\alpha$-RuCl$_3$. (arXiv:2312.17433v1 [cond-mat.str-el])
E.M. Wilson, J.T. Haraldsen

This investigation covers the effects of variable exchange interactions on the spin dynamics of the zig-zag honeycomb lattice. Using a Holstein-Primakoff expansion of the Heisenberg Hamiltonian with easy-axis anisotropy, we characterize the effects of multiple nearest-neighbor and next-nearest-neighbor interactions with asymmetry within the context of a frustrated and non-frustrated zig-zag magnetic configuration. Furthermore, we compare to the known inelastic neutron scattering data for the proximate quantum spin liquid $\alpha$-RuCl$_3$, and we provide insight into the evolution of the spin dynamics, showing that the Heisenberg interaction dominates the majority of the spin excitation behavior. By analyzing the frustrated system with multiple interactions, direction-dependent Dirac nodes present themselves, and we can demonstrate that a standard Heisenberg model can accurately describe the observed magnon spectra.


Bilayer Vanadium Dioxide Thin Film with Elevated Transition Temperatures and High Resistance Switching. (arXiv:2312.17437v1 [cond-mat.mtrl-sci])
Achintya Dutta, Ashok P, Amit Verma

Despite widespread interest in the phase-change applications of vanadium dioxide (VO$_2$), the fabrication of high-quality VO$_2$ thin films with elevated transition temperatures (TIMT) and high Insulator-Metal-Transition resistance switching still remains a challenge. This study introduces a two-step atmospheric oxidation approach to fabricate bilayer VO$_{2-x}$/VO$_2$ films on a c-plane sapphire substrate. To quantify the impact of the VO$_2$ buffer layer, a single-layer VO$_2$ film of the same thickness was also fabricated. The bilayer VO$_{2-x}$/VO$_2$ films wherein the top VO$_{2-x}$ film was under-oxidized demonstrated an elevation in TIMT reaching ~97 $^\circ$C, one of the highest reported to date for VO$_2$ films and is achieved in a doping-free manner. Our results also reveal a one-order increase in resistance switching, with the optimum bilayer VO$_2$/VO$_2$ film exhibiting ~3.6 orders of switching from 25 $^\circ$C to 110 $^\circ$C, compared to the optimum single-layer VO$_2$ reference film. This is accompanied by a one-order decrease in the on-state resistance in its metallic phase. The elevation in TIMT, coupled with increased strain extracted from the XRD characterization of the bilayer film, suggests the possibility of compressive strain along the c-axis. These VO$_{2-x}$/VO$_2$ films also demonstrate a significant change in the slope of their resistance vs temperature curves contrary to the conventional smooth transition. This feature was ascribed to the rutile/monoclinic quasi-heterostructure formed due to the top VO$_{2-x}$ film having a reduced TIMT. Our findings carry significant implications for both the lucid fabrication of VO$_2$ thin film devices as well as the study of phase transitions in correlated oxides.


Electrochemical transport in Dirac nodal-line semimetals. (arXiv:2312.17439v1 [cond-mat.mes-hall])
R. Flores-Calderón, Leonardo Medel, A. Martín-Ruiz

Nodal-line semimetals are topological phases where the conduction and the valence bands cross each other along one-dimensional lines in the Brillouin zone, which are symmetry protected by either spatial symmetries or time-reversal symmetry. In particular, nodal lines protected by the combined $\mathcal{PT}$ symmetry exhibits the parity anomaly of 2D Dirac fermions. In this Letter, we study the electrochemical transport in a $\mathcal{PT}$-symmetric Dirac nodal line semimetals by using the semiclassical Boltzmann equation approach. We derive a general formula for the topological current that includes both the Berry curvature and the orbital magnetic moment. We first evaluate the electrochemical current by introducing a small $\mathcal{PT}$-breaking mass term (which could be induced by inversion-breaking uniaxial strain, pressure, or an external electric field) and apply it to the hexagonal pnictide CaAgP. The electrochemical current vanishes in the zero-mass limit. Introducing a tilting term that does not spoil $\mathcal{PT}$ symmetry that protects the nodal ring, we obtain a finite electrochemical current in the zero-mass limit, which can be regarded as a direct consequence of the parity anomaly. We show that the parity anomaly induced electrochemical transport is also present at nonzero temperatures.


Phase Boundaries, Isotope Effect and Superconductivity of Lithium Under Hydrostatic Conditions. (arXiv:2312.17498v1 [cond-mat.supr-con])
Stefano Racioppi (1), Iren Saffarian-Deemyad (2), William Holle (2), Francesco Belli (1), Richard Ferry (3), Curtis Kenney-Benson (3), Jesse Smith (3), Eva Zurek (1), Shanti Deemyad (2) ((1) 1Department of Chemistry, State University of New York at Buffalo, Buffalo, New York, USA, (2) Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah, USA, (3) High Pressure Collaborative Access Team, X-Ray Sciences Division, Argonne National Laboratory, Argonne, IL, USA)

We present theoretical and experimental studies of superconductivity and low temperature structural phase boundaries in lithium. We mapped the structural phase diagram of 6Li and 7Li under hydrostatic conditions between 5 top 55GPa and within the temperature range of 15 to 75K, observing the FCC-hR1-cI16 phase transitions. 6Li and 7Li show some differences at the structural boundaries, with a potential shift of the phase boundaries of 6Li to lower pressures. Density functional theory calculations and topological analysis of the electron density elucidates the superconducting properties and interatomic interactions within these phases of lithium.


Electron-doped magnetic Weyl semimetal LixCo3Sn2S2 by bulk-gating. (arXiv:2312.17547v1 [cond-mat.mtrl-sci])
Hideki Matsuoka, Yukako Fujishiro, Susumu Minami, Takashi Koretsune, Ryotaro Arita, Yoshinori Tokura, Yoshihiro Iwasa

Manipulating carrier density through gate effects, both in electrostatic charge storage and electrochemical intercalation mode, offers powerful control over material properties, although commonly restricted to ultra-thin films or van der Waals materials. Here we demonstrate the application of gate-driven carrier modulation in the microdevice of magnetic Weyl semimetal Co3Sn2S2, fabricated from a bulk single crystal via focused ion beam (FIB). We discovered a Li-intercalated phase LixCo3Sn2S2 featuring electron doping exceeding 5*1021 cm-3, resulting in the Fermi energy shift of 200 meV. The carrier density dependent anomalous Hall conductivity shows fair agreement with density functional theory (DFT) calculation, which also predicts intercalated Li+ ion stabilization within the anion layer while maintaining the kagome-lattice intact. This likely explains the observed rigid band behavior and constant Curie temperature, contrasting with magnetic site substitution experiments. Our findings suggest ionic gating on FIB devices broadens the scope of gate-tuning in quantum materials.


Effect of Exchange Interaction and Spin-Orbit Coupling on Spin Splitting in CdSnX (X = S, Se and Te) nanoribbons. (arXiv:2312.17562v1 [cond-mat.mtrl-sci])
Sutapa Chattopadhyay, Vikas Kashid, P. Durganandini, Anjali Kshirsagar

We have studied the topological properties of free standing Sn doped cadmium chalcogenide (CdSnX, X = S, Se and Te) nanoribbons of varying widths and three types of edges viz., distorted armchair, normal armchair and normal zigzag edges. The unsatisfied bonds of X and Sn atoms at the edges cause non-zero values of the magnetic moment. This introduces an exchange field leading to inverted band structure. The electronic band structures of distorted armchair edge nanoribbons also exhibit different types of spin splitting property for different X atoms due to the different local orbital angular momentum at specific X atomic site with the inclusion of spin orbit coupling (SOC). The gap opening at the band crossings near the Fermi level after inclusion of SOC are mainly due to SOC of Sn atom and are responsible for the electron and hole pockets making the system topologically exotic. All the distorted edge nanoribbons show metallic behaviour with non-zero magnetic moments. Amongst CdX (X = S, Se and Te) nanoribbons, systems containing S atoms exhibit Weyl-like semi-metallic behavior and not much change with width, that of Se atoms exhibit Zeeman-type spin splitting and significant change with varying width, whereas systems containing Te atoms show signature of Rashba spin splitting along with Zeeman-type spin splitting and moderate change with varying width. The armchair edge nanoribbons show wide gap semiconducting behaviour. Zeeman-type spin splitting is seen in the valence band region for systems containing S atoms and Rashba spin splitting is visible in the conduction band region for systems containing Se and Te atoms. For zigzag edge nanoribbons, no such signature of spin splitting is observed although all the nanoribbons acquire very high magnetic moments.


Utilizing the Janus MoSSe surface polarization property in complementary metal-oxide-semiconductor field effect transistor design. (arXiv:2312.17594v1 [cond-mat.mtrl-sci])
Yun-Pin Chiu, Hsin-Wen Huang, Yuh-Renn Wu

Janus transition metal dichalcogenides (JTMDs) have attracted much attention because of their outstanding electronic and optical properties. The additional out-of-plane dipole in JTMDs can form n- and p-like Ohmic contacts, and this may be used in device applications such as pin diodes and photovoltaic cells. In this study, we exploit this property to design n- and p-type metal-oxide-semiconductor field effect transistors (MOSFETs). First, we use density-functional theory calculations to study the inherent dipole field strength in the trilayer JTMD MoSSe. The intrinsic dipole of MoSSe causes band bending at both the metal/MoSSe and MoSSe/metal interfaces, resulting in electron and hole accumulation to form n- and p-type Ohmic contact regions. We incorporate this property into a 2D finite-element-based Poisson-drift-diffusion solver to perform simulations, on the basis of which we design complementary MOSFETs. Our results demonstrate that JTMDs can be used to make n- and p-MOSFETs in the same layer without the need for any extra doping.


Spin-orbit coupling tuned crossover of gaped and gapless topological phases in the chalcopyrite HgSnX 2 (X=N/P): An ab-initio investigation. (arXiv:2312.17669v1 [cond-mat.mtrl-sci])
Surasree Sadhukhan, Sudipta Kanungo

The coupling between electron orbital momentum and spin momentum, known as spin-orbit coupling (SOC), is a fundamental origin of a multitude of fascinating physical phenomena, especially it holds paramount significance in the realm of topological materials. In our work, we have predicted the topological phase in Hg-based chalcopyrite compounds using the first principles density functional theory. The initial focus was on HgSnN 2 , revealing it to be a nonmagnetic Weyl semimetal, while HgSnP 2 displayed characteristics of a strong topological insulator. What makes our work truly unique is that despite both compounds having the same SOC strength, arises from Hg, they exhibit distinct topological phases due to the distinct hybridization effect of the Hg-5d and X-p bands. This finding can address a significant factor, i.e., the effect of the band hybridization in deriving distinct topological phases, keeping the symmetry aspect intact. Our results indicate that due to the presence of band hybridization between the dominant X-np orbitals n=2 and 3 for X=N and P respectively and a minor contribution from Hg-5d, we can tune the topological phase by manipulating SOC strength, which equivalently achievable by chemical substitutions. This investigation stands as a remarkable illustration of the unique roles that hybridization plays in sculpting the topological properties of these compounds while simultaneously preserving their underlying symmetries.


Chiral anomaly induced monopole current and nonlinear circular dichroism. (arXiv:2312.17690v1 [cond-mat.str-el])
Nikolai Peshcherenko, Claudia Felser, Yang Zhang

We propose a topological probe for detecting chirality imbalance in time reversal invariant Weyl and Dirac semimetals via nonlinear Hall response. The chiral anomaly effect, occurring in parallel electric and magnetic fields, causes a energy shift between Weyl cones of different chirality, which leads to chirally asymmetric intra-node relaxation. Due to this asymmetry, nonlinear Hall currents induced by Berry curvature in different Weyl nodes do not perfectly compensate. Hence, the net current is determined by the quantized monopole charge, weighted by the transport relaxation time. We predict that the current arising from this chiral asymmetry could also be detected in nonlinear circular dichroism measurements.


Anisotropy-driven topological quantum phase transition in magnetic impurities. (arXiv:2312.17702v1 [cond-mat.str-el])
Germán G. Blesio, Luis O. Manuel, Armando A. Aligia

A few years ago, a topological quantum phase transition (TQPT) has been found in Anderson and Kondo 2-channel spin-1 impurity models that include a hard-axis anisotropy term $DS_z^2$ with $D > 0$. The most remarkable manifestation of the TQPT is a jump in the spectral density of localized electrons, at the Fermi level, from very high to very low values as $D$ is increased. If the two conduction channels are equivalent, the transition takes place at the critical anisotropy $D_c \sim 2.5\; T_K$, where $T_K$ is the Kondo temperature for $D=0$. This jump might be important to develop a molecular transistor. The jump is due to a corresponding one in the Luttinger integral, which has a topological non-trivial value $\pi/2$ for $D > D_c$. Here, we review the main results for the spectral density and highlight the significance of the theory for the interpretation of measurements conducted on magnetic atoms or molecules on metallic surfaces. In these experiments, where $D$ is held constant, the energy scale $T_K$ is manipulated by some parameters. The resulting variation gives rise to a differential conductance $dI/dV$, measured by scanning-tunneling spectroscopy, which is consistent with a TQPT at an intermediate value of $T_K$. We also show that the theory can be extended to integer spin $S>1$ and two-impurity systems. This is also probably true for half-integer spin and non-equivalent channels in some cases.


Evidence for $\pi$-shifted Cooper quartets in PbTe nanowire three-terminal Josephson junctions. (arXiv:2312.17703v1 [cond-mat.mes-hall])
Mohit Gupta, Vipin Khade, Colin Riggert, Lior Shani, Gavin Menning, Pim Lueb, Jason Jung, Régis Mélin, Erik P. A. M. Bakkers, Vlad S. Pribiag

Josephson junctions are typically characterized by a single phase difference across two superconductors. This conventional two-terminal Josephson junction can be generalized to a multi-terminal device where the Josephson energy contains terms that result from entanglement of multiple independent phase variables. It was recently proposed that such multi-terminal couplings should result in a $\pi$-shifted quartet supercurrent. We show for the first time experimental signature of this $\pi$-shifted supercurrent, by using a three-terminal Josephson junction based on selective-area-grown PbTe nanowires. We further observe conductance steps at zero magnetic field co-existent with supercurrent in both two- and three-terminal devices, indicating ballistic superconductivity in the few quantum modes regime. Superconducting transport in the few-modes regime is a necessary condition for realizing topologically protected bound states such as Majorana zero modes in one-dimensional nanowires and Weyl nodes in multi-terminal Josephson junctions.


Contrastive learning through non-equilibrium memory. (arXiv:2312.17723v1 [cond-mat.dis-nn])
Martin Falk, Adam Strupp, Benjamin Scellier, Arvind Murugan

Learning algorithms based on backpropagation have enabled transformative technological advances but alternatives based on local energy-based rules offer benefits in terms of biological plausibility and decentralized training. A broad class of such local learning rules involve \textit{contrasting} a clamped configuration with the free, spontaneous behavior of the system. However, comparisons of clamped and free configurations require explicit memory or switching between Hebbian and anti-Hebbian modes. Here, we show how a simple form of implicit non-equilibrium memory in the update dynamics of each ``synapse'' of a network naturally allows for contrastive learning. During training, free and clamped behaviors are shown in sequence over time using a sawtooth-like temporal protocol that breaks the symmetry between those two behaviors when combined with non-equilibrium update dynamics at each synapse. We show that the needed dynamics is implicit in integral feedback control, broadening the range of physical and biological systems naturally capable of contrastive learning. Finally, we show that non-equilibrium dissipation improves learning quality and determine the Landauer energy cost of contrastive learning through physical dynamics.


Phases of 2d massless QCD with qubit regularization. (arXiv:2312.17734v1 [hep-lat])
Hanqing Liu, Tanmoy Bhattacharya, Shailesh Chandrasekharan, Rajan Gupta

We investigate the possibility of reproducing the continuum physics of 2d SU(N) gauge theory coupled to a single flavor of massless Dirac fermions using qubit regularization. The continuum theory is described by N free fermions in the ultraviolet (UV) and a coset Wess-Zumino-Witten (WZW) model in the infrared (IR). In this work, we explore how well these features can be reproduced using the Kogut-Susskind Hamiltonian with a finite-dimensional link Hilbert space and a generalized Hubbard coupling. Using strong coupling expansions, we show that our model exhibits a gapped dimer phase and another phase described by a spin-chain. Furthermore, for N=2, using tensor network methods, we show that there is a second-order phase transition between these two phases. The critical theory at the transition can be understood as an SU(2)_1 WZW model, using which we determine the phase diagram of our model quantitatively. Using the confinement properties of the model we argue how the UV physics of free fermions could also emerge, but may require further modifications to our model.


Symmetry Breaking in an Extended O(2) Model. (arXiv:2312.17739v1 [hep-lat])
Leon Hostetler, Ryo Sakai, Jin Zhang, Alexei Bazavov, Yannick Meurice

Motivated by attempts to quantum simulate lattice models with continuous Abelian symmetries using discrete approximations, we study an extended-O(2) model in two dimensions that differs from the ordinary O(2) model by the addition of an explicit symmetry breaking term $-h_q\cos(q\varphi)$. Its coupling $h_q$ allows to smoothly interpolate between the O(2) model ($h_q=0$) and a $q$-state clock model ($h_q\rightarrow\infty$). In the latter case, a $q$-state clock model can also be defined for non-integer values of $q$. Thus, such a limit can also be considered as an analytic continuation of an ordinary $q$-state clock model to noninteger $q$. In previous work, we established the phase diagram of the model in the infinite coupling limit ($h_q\rightarrow\infty$). We showed that for non-integer $q$, there is a second-order phase transition at low temperature and a crossover at high temperature. In this work, we establish the phase diagram at finite values of the coupling using Monte Carlo and tensor methods. We show that for non-integer $q$, the second-order phase transition at low temperature and crossover at high temperature persist to finite coupling. For integer $q=2,3,4$, we know there is a second-order phase transition at infinite coupling (i.e. the well-known clock models). At finite coupling, we find that the critical exponents for $q=3,4$ vary with the coupling, and for $q=4$ the transition may turn into a BKT transition at small coupling. We comment on the similarities and differences of the phase diagrams with those of quantum simulators of the Abelian-Higgs model based on ladder-shaped arrays of Rydberg atoms.


Fermion-Monopole Scattering in the Standard Model. (arXiv:2312.17746v1 [hep-th])
Marieke van Beest, Philip Boyle Smith, Diego Delmastro, Rishi Mouland, David Tong

We study the scattering of fermions off 't Hooft lines in the Standard Model. A long-standing paradox suggests that the outgoing fermions necessarily carry fractional quantum numbers. In a previous paper, we resolved this paradox in the context of a number of toy models where we showed that the outgoing radiation is created by operators that are attached to a co-dimension 1 topological surface. This shifts the quantum numbers of the outgoing states associated to non-anomalous symmetries to be integer valued as required, while the quantum numbers associated to anomalous symmetries are fractional. Here we apply these ideas to the Standard Model.


Edge-selective extremal damping from topological heritage of dissipative Chern insulators. (arXiv:2304.09040v3 [cond-mat.mes-hall] UPDATED)
Suraj S. Hegde, Toni Ehmcke, Tobias Meng

One of the most important practical hallmarks of topological matter is the presence of topologically protected, exponentially localised edge states at interfaces of regions characterised by unequal topological invariants. Here, we show that even when driven far from their equilibrium ground state, Chern insulators can inherit topological edge features from their parent Hamiltonian. In particular, we show that the asymptotic long-time approach of the non-equilibrium steady state, governed by a Lindblad Master equation, can exhibit edge-selective extremal damping. This phenomenon derives from edge states of non-Hermitian extensions of the parent Chern insulator Hamiltonian. The combination of (non-Hermitian) topology and dissipation hence allows to design topologically robust, spatially localised damping patterns.


Gauge field fluctuation corrected QED3 effective action by fermionic particle-vortex duality. (arXiv:2308.06916v3 [hep-th] UPDATED)
Wei-Han Hsiao

We develop a non-perturbative framework to incorporate gauge field fluctuations into QED3 effective actions in the infrared by fermionic particle-vortex duality. The utility is demonstrated by the application to models containing N species of 2-component Dirac fermions in a couple of solvable and interpretable electromagnetic backgrounds: N = 1 or 2. For the N = 1 model, we establish a correspondence between fermion Casimir energy at finite density and the magnetic Euler-Heisenberg Lagrangian, and we further evaluate the correction to their amplitudes. This in turn predicts the amplification of charge susceptibility and the reduction of magnetic permeability. We additionally supply physical interpretations to each component of our calculation as well as alternative derivations based on energy density measurements in different characteristic lengths. For N = 2, we show that the magnetic catalysis is erased in a U(1)$\times$U(1) QED3 and therefore there is no breakdown of chiral symmetry. Some reasoning is offered based on the properties of the lowest Landau level wave functions.


Topological Quantum Computation on a Chiral Kondo Chain. (arXiv:2309.03010v3 [cond-mat.str-el] UPDATED)
Tianhao Ren, Elio J. König, Alexei M. Tsvelik

We describe the chiral Kondo chain model based on the symplectic Kondo effect and demonstrate that it has a quantum critical ground state populated by non-Abelian anyons. We show that the fusion channel of two arbitrary anyons can be detected by locally coupling the two anyons to an extra single channel of chiral current and measuring the corresponding conductance at finite frequency. Based on such measurements, we propose that the chiral Kondo chain model with symplectic symmetry can be used for implementation of measurement-only topological quantum computations, and it possesses a number of distinct features favorable for such applications. The sources and effects of errors in the proposed system are analyzed, and possible material realizations are discussed.


Universal click-chemistry approach for the DNA functionalization of nanoparticles. (arXiv:2309.15534v2 [physics.chem-ph] UPDATED)
Nicole Siegel, Hiroaki Hasebe, German Chiarelli, Denis Garoli, Hiroshi Sugimoto, Minoru Fujii, Guillermo P. Acuna, Karol Kolataj

Nanotechnology has revolutionized the fabrication of hybrid species with tailored functionalities. A milestone in this field is the DNA conjugation of nanoparticles, introduced almost 30 years ago, which typically exploits the affinity between thiol groups and metallic surfaces. Over the last decades, developments in colloidal research have enabled the synthesis of an assortment of non-metallic structures, such as high-index dielectric nanoparticles, with unique properties not previously accessible with traditional metallic nanoparticles. However, to stabilize, integrate and provide further functionality to non-metallic nanoparticles, reliable techniques for their functionalization with DNA will be crucial. Here, we combine well-established dibenzylcyclooctyne-azide click-chemistry with a simple freeze-thaw method to achieve the functionalization of silica and silicon nanoparticles, which form exceptionally stable colloids with a high DNA surface density of 0.2 molecules/nm2. Furthermore, we demonstrate that these functionalized colloids can be self-assembled into high-index dielectric optical antennas with a yield of up to 78% via the use of DNA origami. Finally, we extend this method to functionalize other important nanomaterials, including oxides, polymers, core-shell and metal nanostructures. Our results indicate that the method presented herein serves as a crucial complement to conventional thiol functionalization chemistry and thus greatly expands the toolbox of DNA-functionalized nanoparticles currently available.