Showing 1–50 of 103 results for author: Tan, T

Skyrmion Fractional Chern Insulator: An Intrinsically Multiband Route to Fractionalization in Rhombohedral Graphene

Authors: Julian May-Mann, Tixuan Tan, Patrick J. Ledwith, Zhengyan Darius Shi, Trithep Devakul

Abstract: We propose an unconventional microscopic origin for the fractional quantum anomalous Hall (FQAH) effect in rhombohedral graphene moiré superlattices: skyrmion fractionalization. We view the state at filling $ν<1$ as a metal of skyrmion vacancies, charge $+e$ objects formed by removing layer-pseudospin skyrmions from the interaction-generated skyrmion lattice Chern insulator at $ν=1$. These vacanci… ▽ More We propose an unconventional microscopic origin for the fractional quantum anomalous Hall (FQAH) effect in rhombohedral graphene moiré superlattices: skyrmion fractionalization. We view the state at filling $ν<1$ as a metal of skyrmion vacancies, charge $+e$ objects formed by removing layer-pseudospin skyrmions from the interaction-generated skyrmion lattice Chern insulator at $ν=1$. These vacancies are intrinsically multiband degrees of freedom, absent in single Chern band-projected studies. Building on a recently proposed ideal limit, we first develop an effective field theory showing that skyrmion vacancies can themselves fractionalize, thereby inducing charge fractionalization. Focusing on $ν=\frac{2}{3}$, we then construct explicit variational trial wavefunctions for the resulting skyrmion fractional Chern insulator and provide numerical evidence, together with general arguments, showing that this process is energetically favored. Our results establish a realistic route to the FQAH that does not rely on a partially filled Chern band, but instead arises from fractionalization of collective pseudospin textures. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Ab initio calculations of $^{229}$Th band-to-band internal conversion rate in $^{229}$ThO$_2$

Authors: Udeshika C. Perera, H. B. Tran Tan, H. W. T. Morgan, Eric Hudson, Daniel A. Rehn, Andrei Derevianko

Abstract: We present an ab initio calculation of the band-to-band internal-conversion rate of the $\hbarω_{\rm nuc} \approx 8.35$ eV isomeric transition in $^{229}$ThO$_2$. Because the nuclear transition energy exceeds the electronic band gap of ThO$_2$, the isomer can decay nonradiatively by resonantly promoting a valence electron into the conduction band. We formulate this process as a Brillouin-zone sum… ▽ More We present an ab initio calculation of the band-to-band internal-conversion rate of the $\hbarω_{\rm nuc} \approx 8.35$ eV isomeric transition in $^{229}$ThO$_2$. Because the nuclear transition energy exceeds the electronic band gap of ThO$_2$, the isomer can decay nonradiatively by resonantly promoting a valence electron into the conduction band. We formulate this process as a Brillouin-zone sum over vertical interband transitions weighted by local Th-centered hyperfine matrix elements, which are evaluated directly from all-electron full-potential linearized augmented-plane-wave Bloch spinors. A finite nuclear magnetization model is included to regularize the short-range hyperfine interaction and to account for the Bohr-Weisskopf effect. After applying scissor shifts to span the experimentally reported ThO$_2$ band gaps, we find calculated internal-conversion lifetimes in the range of $1-16~μ{\rm s}$. The lifetime increases strongly as the band gap approaches $ω_{\rm nuc}$ because the resonant interband phase space at the nuclear transition energy is reduced. For the larger reported ThO$_2$ gaps, the calculated lifetime is comparable to the measured conversion-electron Mössbauer lifetime [Nature 648, 300 (2025)]. Our analysis implies that choosing solid-state hosts with band-gap values slightly lower than $ω_{\rm nuc}$ can optimize solid-state nuclear clock performance with internal-conversion electron readout. △ Less

Submitted 9 July, 2026; originally announced July 2026.

Cavity-enhanced superconductivity in the two-dimensional limit of NbSe2

Authors: Hanxiang Zhang, Zexin Feng, I-Te Lu, Zhiwei Li, Songhao Guo, Qiuyu Shang, Thomas Tan, Xiaodan Lyu, Xiangming Shen, Dening Luan, Mingcheng Panmai, Kenji Watanabe, Takashi Taniguchi, Ranjan Singh, Angel Rubio, Weibo Gao

Abstract: Vacuum electromagnetic fluctuations have emerged as a means of controlling collective quantum phases without external driving. Cavity-induced modification of superconductivity has been widely predicted. What sets the size of the effect, and which microscopic channel carries it, remain open. Here we couple few-layer NbSe2 to a terahertz complementary split-ring resonator (CSRR) and show that the en… ▽ More Vacuum electromagnetic fluctuations have emerged as a means of controlling collective quantum phases without external driving. Cavity-induced modification of superconductivity has been widely predicted. What sets the size of the effect, and which microscopic channel carries it, remain open. Here we couple few-layer NbSe2 to a terahertz complementary split-ring resonator (CSRR) and show that the enhancement grows sharply on approaching the two-dimensional limit. In bilayer NbSe2 the superconducting transition temperature rises by 10%, from 3.02 K to 3.41 K, on a cavity resonant at 0.92 THz - roughly four times the shift measured in a ten-layer device at the same resonance. Within a single device the shift maps onto the simulated cavity field profile, falling from 0.39 K at the field maximum to zero outside the resonator, with the lower critical field following the same spatial ordering; because all regions are measured on one continuous flake in a single cooldown, sample-to-sample variation is excluded by construction. The frequency dependence is non-monotonic, with suppression below resonance and maximal enhancement near 0.96 THz. Quantum electrodynamical density functional theory calculations show that cavity coupling redistributes spectral weight in the Eliashberg function, weakening the total electron-phonon coupling while hardening the logarithmic average phonon frequency; competition between the two reproduces a sign change in Tc. These results identify dimensionality, local field amplitude and detuning as the control parameters of cavity-enhanced superconductivity, and point to electron-phonon reweighting as its microscopic origin. △ Less

Submitted 19 August, 2026; v1 submitted 17 June, 2026; originally announced June 2026.

Comments: 28 pages, 10 figures

Visualizing orbital magnetism in electron doped rhombohedral multilayer graphene

Authors: Owen I. Sheekey, Trevor B. Arp, Benjamin A. Foutty, Ruoxi Zhang, Tixuan Tan, Ludwig F. W. Holleis, Yi Guo, Sandesh S. Kalantre, Canxun Zhang, Mark Zakharyan, David Gong, Aidan Keough, Youngjoon Choi, Ysun Choi, Siyuan Xu, Tian Xie, Ben Hodder Alexander, Marisa Hocking, Qingrui Cao, Martin E. Huber, Takashi Taniguchi, Kenji Watanabe, Chenhao Jin, Etienne Lantagne-Hurtubise, Aaron Sharpe , et al. (2 additional authors not shown)

Abstract: Electron doped rhombohedral multilayer graphene at high displacement field features an exceptionally flat band minimum with near-ideal quantum geometry. Experiments in this regime observe the formation of a 'quarter metal,' in which the electron liquid condenses into a single spin- and valley flavor. Remarkably, recent experiments have found a zero resistance state in the same region of the densit… ▽ More Electron doped rhombohedral multilayer graphene at high displacement field features an exceptionally flat band minimum with near-ideal quantum geometry. Experiments in this regime observe the formation of a 'quarter metal,' in which the electron liquid condenses into a single spin- and valley flavor. Remarkably, recent experiments have found a zero resistance state in the same region of the density- and displacement-field-tuned parameter space, attributed to the formation of a chiral superconductor from an orbitally ferromagnetic normal state. Here, we use nanoSQUID-on-tip magnetometry to map the orbital magnetization of electron-doped rhombohedral graphene devices ranging in thickness between 3 and 15 layers. Magnetization within the quarter metal phases peaks at finite density, consistent with concentration of the Berry curvature in a finite-momentum 'ring of fire'. Correlating transport and local magnetometry data in a superconducting tetralayer sample reveals a finite orbital ferromagnetic moment, providing direct evidence of valley polarization in the superconducting ground state. We further show that widely observed stochastic switching of the resistivity in both metallic and superconducting regimes arises from a density-tuned sign change in the valley-resolved total magnetic moment. This leads to the formation of metastable magnetic domains under typical gate control sequences and can also be harnessed for electric-field controlled switching of the magnetization across the entire device. Finally, high resolution measurements of the magnetization across a superconducting transition allow us to put an upper bound on the 'condensation magnetization' of 0.1 Bohr magneton per carrier, placing a strong quantitative restriction on theoretical models for ferromagnetic superconductivity. △ Less

Submitted 4 August, 2026; v1 submitted 28 May, 2026; originally announced May 2026.

Electrically Tunable Terahertz Chirality from Quantum Geometry

Authors: Sobhan Subhra Mishra, Thomas CaiWei Tan, Faxian Xiu, Ranjan Singh

Abstract: Quantum geometry encoded in the momentum space structure of electronic wavefunctions, governs charge dynamics through Berry curvature, enabling unconventional transport and optical responses. In topological semimetals, this geometry is sampled over Fermi pockets, suggesting electrical control by Fermi surface tuning, yet such control has remained largely limited to DC transport. Here we show that… ▽ More Quantum geometry encoded in the momentum space structure of electronic wavefunctions, governs charge dynamics through Berry curvature, enabling unconventional transport and optical responses. In topological semimetals, this geometry is sampled over Fermi pockets, suggesting electrical control by Fermi surface tuning, yet such control has remained largely limited to DC transport. Here we show that electrostatic gating of the 3D Dirac semimetal Cd3As2 reshapes Fermi pockets surrounding photoinduced Floquet Weyl nodes, enabling electrical control of terahertz (THz) emission chirality. Gate tuning selectively modulates the Berry curvature driven linearly polarized THz component by up to 60% and 49% at positive and negative bias, respectively, while the orthogonal linearly polarized photon-drag component remains unchanged. With the two orthogonal fields intrinsically phase-locked at \sfracπ{2} by the excitation geometry, the selective gate-tuned amplitude control enables the polarization tuning across the Poincaré sphere, achieving near-circular polarization (χ\approx-42°) at +10 V. These results establish Fermi surface tuning as a general route to programmable quantum geometric control of chiral terahertz emission. △ Less

Submitted 29 April, 2026; originally announced April 2026.

Logarithmic growth of operator entanglement in a clean non-integrable circuit

Authors: Mao Tian Tan, Tomaž Prosen

Abstract: We study a so-called semi-ergodic brickwork dual-unitary circuits where, in the infinite volume limit, the two-point correlation functions of single-site operators exhibit ergodic behavior along one light ray and non-ergodic behavior along the other light ray. Here, however, we study intermediate and long-time dynamics of a system in a finite, large volume. Under such dynamics, the Heisenberg evol… ▽ More We study a so-called semi-ergodic brickwork dual-unitary circuits where, in the infinite volume limit, the two-point correlation functions of single-site operators exhibit ergodic behavior along one light ray and non-ergodic behavior along the other light ray. Here, however, we study intermediate and long-time dynamics of a system in a finite, large volume. Under such dynamics, the Heisenberg evolution of a single traceless single-site operator lies within a restricted subspace, and this time evolution can be mapped to a simpler problem of a single qutrit scattering with a bunch of qubits sequentially. Despite the model being non-integrable and free from any quenched disorder, the operator entanglement grows at most logarithmic in time, contrary to prior expectations. The auto-correlation function can be written in terms of a sum of products of $SO(3)$ matrices, allowing for a random matrix prediction for the auto-correlation function at late times. The operator size distribution also becomes bimodal at certain times, displaying intermediate behavior between chaotic and free systems. △ Less

Submitted 19 March, 2026; originally announced March 2026.

Journal ref: Phys. Rev. B 113, 224316 (2026)

Three phases of odd robotic active matter

Authors: Fan Bo, Shiqi Liu, Zenghong He, Wyatt Joyce, Gregor Leech, Kiet Tran, Keilan Ramirez, Nicholas Boechler, Nicholas Gravish, Hongbo Zhao, Tzer Han Tan

Abstract: Nonreciprocal interactions in active matter are known to generate exotic mechanical behaviors such as odd elasticity and odd viscosity. However, these phenomena have largely been studied in isolation, raising a fundamental question: Is there a single system that embodies these distinct regimes of odd matter and can transition between phases, establishing a unified phase diagram for nonreciprocal a… ▽ More Nonreciprocal interactions in active matter are known to generate exotic mechanical behaviors such as odd elasticity and odd viscosity. However, these phenomena have largely been studied in isolation, raising a fundamental question: Is there a single system that embodies these distinct regimes of odd matter and can transition between phases, establishing a unified phase diagram for nonreciprocal active matter? To address this, we introduce a tunable robotic active matter platform, the Magnetomechanically Augmented Spinning roBotic (MASBot) collective, in which particle-level control of chirality, activity, and pairwise interactions enables access to distinct phases of odd matter. By continuously increasing repulsive forces relative to attractive and transverse forces, we experimentally map a transition from an odd elastic crystal to an odd viscous liquid, and then to a chiral active gas. We find that this latter phase forms a non-space-filling, nonreciprocal active gas stabilized by long-range hydrodynamic attractive forces, whose statistical signatures are consistent with those of a two-dimensional self-gravitating point vortex gas. Within these phases, adjusting spinning frequency and introducing spatially patterned activity allows us to fine-tune odd mechanical responses and tailor power spectra. Further polar and rotational symmetry breaking at the particle scale leads to novel emergent states such as phase separation and collective translation. Together, our system provides a fundamental experimental testbed for nonequilibrium physics and establishes a blueprint for treating robotic swarms as programmable states of matter, enabling functions that range from resilient structures to adaptive swarm reconfiguration. △ Less

Submitted 10 March, 2026; originally announced March 2026.

Relaxation Process During Complex Time Evolution In Two-Dimensional Integrable and Chaotic CFTs

Authors: Chen Bai, Weibo Mao, Masahiro Nozaki, Mao Tian Tan, Xueda Wen

Abstract: We investigate the complex time evolution of a vacuum state with the insertion of a local primary operator in two-dimensional conformal field theories (2d CFTs). This complex time evolution can be considered as a composite process constructed from Lorentzian time evolution and a Euclidean evolution induced by a post-selected measurement. Our main finding is that in the spatially-compact system, th… ▽ More We investigate the complex time evolution of a vacuum state with the insertion of a local primary operator in two-dimensional conformal field theories (2d CFTs). This complex time evolution can be considered as a composite process constructed from Lorentzian time evolution and a Euclidean evolution induced by a post-selected measurement. Our main finding is that in the spatially-compact system, this complex time evolution drives the state of the subsystems to those of the primary state with the same conformal dimensions of the inserted operator. Contrary to the compact system, the subsystems of the spatially non-compact system evolve to states that depend on the non-unitary process during a certain time regime. In holographic systems with a compact spatial direction, this process induced by a heavy local operator can correspond to the relaxation from a black hole with an inhomogeneous horizon to that with a uniform one, while in the ones with a non-compact spatial direction, it can correspond to the relaxation to that with a horizon depending on the non-unitary process. △ Less

Submitted 14 January, 2026; originally announced January 2026.

Comments: 29 pages+appendices, 8 figures

Report number: RIKEN-iTHEMS-Report-26

Generative Multi-Objective Bayesian Optimization with Scalable Batch Evaluations for Sample-Efficient De Novo Molecular Design

Authors: Madhav R. Muthyala, Farshud Sorourifar, Tianhong Tan, You Peng, Joel A. Paulson

Abstract: Designing molecules that must satisfy multiple, often conflicting objectives is a central challenge in molecular discovery. The enormous size of chemical space and the cost of high-fidelity simulations have driven the development of machine learning-guided strategies for accelerating design with limited data. Among these, Bayesian optimization (BO) offers a principled framework for sample-efficien… ▽ More Designing molecules that must satisfy multiple, often conflicting objectives is a central challenge in molecular discovery. The enormous size of chemical space and the cost of high-fidelity simulations have driven the development of machine learning-guided strategies for accelerating design with limited data. Among these, Bayesian optimization (BO) offers a principled framework for sample-efficient search, while generative models provide a mechanism to propose novel, diverse candidates beyond fixed libraries. However, existing methods that couple the two often rely on continuous latent spaces, which introduces both architectural entanglement and scalability challenges. This work introduces an alternative, modular "generate-then-optimize" framework for de novo multi-objective molecular design/discovery. At each iteration, a generative model is used to construct a large, diverse pool of candidate molecules, after which a novel acquisition function, qPMHI (multi-point Probability of Maximum Hypervolume Improvement), is used to optimally select a batch of candidates most likely to induce the largest Pareto front expansion. The key insight is that qPMHI decomposes additively, enabling exact, scalable batch selection via only simple ranking of probabilities that can be easily estimated with Monte Carlo sampling. We benchmark the framework against state-of-the-art latent-space and discrete molecular optimization methods, demonstrating significant improvements across synthetic benchmarks and application-driven tasks. Specifically, in a case study related to sustainable energy storage, we show that our approach quickly uncovers novel, diverse, and high-performing organic (quinone-based) cathode materials for aqueous redox flow battery applications. △ Less

Submitted 19 December, 2025; originally announced December 2025.

The ideal limit of rhombohedral graphene: Interaction-induced layer-skyrmion lattices and their collective excitations

Authors: Tixuan Tan, Patrick J. Ledwith, Trithep Devakul

Abstract: We introduce an ideal limit of rhombohedral graphene multilayers. In this limit, we show analytically how short-range repulsion stabilizes a layer-pseudospin skyrmion lattice, which generates an effective magnetic field and gives rise to a Chern band. This establishes the real-space origin of interaction-driven topology in moiré rhombohedral graphene. The resulting interaction-induced skyrmion lat… ▽ More We introduce an ideal limit of rhombohedral graphene multilayers. In this limit, we show analytically how short-range repulsion stabilizes a layer-pseudospin skyrmion lattice, which generates an effective magnetic field and gives rise to a Chern band. This establishes the real-space origin of interaction-driven topology in moiré rhombohedral graphene. The resulting interaction-induced skyrmion lattice is physically analogous to magnetic skyrmion crystals and hosts a hierarchy of collective excitations naturally described within the framework of skyrmion-lattice dynamics. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Spatially Structured Entanglement from Nonequilibrium Thermal Pure States

Authors: Chen Bai, Mao Tian Tan, Bastien Lapierre, Shinsei Ryu

Abstract: We study quantum quench dynamics in (1+1)-dimensional critical systems, starting from thermal pure states called crosscap states, and evolving them under spatially inhomogeneous Hamiltonians. The spatial inhomogeneity is introduced through a deformation of the Hamiltonian, expressed as linear combinations of the generators of the $SL^{(q)}(2,\mathbb{R})$ subalgebra of the Virasoro algebra. We anal… ▽ More We study quantum quench dynamics in (1+1)-dimensional critical systems, starting from thermal pure states called crosscap states, and evolving them under spatially inhomogeneous Hamiltonians. The spatial inhomogeneity is introduced through a deformation of the Hamiltonian, expressed as linear combinations of the generators of the $SL^{(q)}(2,\mathbb{R})$ subalgebra of the Virasoro algebra. We analyze the free massless Dirac fermion theory and holographic conformal field theory as prototypical examples of integrable and non-integrable dynamics. Consistent with general expectations, "Möbius-type" deformations lead to thermalization in the non-integrable case, and to periodic revivals in the integrable one. In contrast, "sine-square-type" and "displacement-type" deformations prevent both thermalization and scrambling, instead producing late-time, graph-like entanglement patterns. These patterns emerge from the interplay between the deformed Hamiltonian and the crosscap initial state and appear to be universal: they are determined solely by the deformation profile while remaining largely insensitive to microscopic details. Finally, we perform a holographic calculation in three-dimensional gravity using AdS$_3$/CFT$_2$, which reproduces the main features of our (1+1)-dimensional study. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Comments: 27+26 pages (single column), 14 figures

Journal ref: Phys. Rev. B 113, 064311 (2026)

Nonvolatile Switching of Magnetism via Gate-Induced Sliding in Tetralayer Graphene

Authors: Daniel Brandon, Tixuan Tan, Yiwen Ai, Peter Golemis, Akshat Gandhi, Lujin Min, Kenji Watanabe, Takashi Taniguchi, Trithep Devakul, Kenji Yasuda

Abstract: Interlayer sliding degrees of freedom often determine the physical properties of two-dimensional (2D) materials. In graphene, for instance, the metastable rhombohedral stacking arrangement hosts correlated and topological electronic phases, which are absent in conventional Bernal stacking. Here, we demonstrate a sliding-induced first-order structural phase transition between Bernal and rhombohedra… ▽ More Interlayer sliding degrees of freedom often determine the physical properties of two-dimensional (2D) materials. In graphene, for instance, the metastable rhombohedral stacking arrangement hosts correlated and topological electronic phases, which are absent in conventional Bernal stacking. Here, we demonstrate a sliding-induced first-order structural phase transition between Bernal and rhombohedral tetralayer graphene driven by gate voltages. Through transport measurement, we observe bistable switching between a Bernal-dominant state and a rhombohedral-Bernal mixed state across a wide space of the gate-voltage phase diagram. The structural phase transition results in nonvolatile switching between a paramagnet and a ferromagnet accompanied by the anomalous Hall effect. The sign reversal of the anomalous Hall effect under opposite displacement fields suggests that it may originate from domain boundaries between the Bernal and rhombohedral regions. Our discovery paves the way for on-demand toggling of quantum phases based on the sliding phase transition of 2D materials and offers a playground to explore unconventional physics at the stacking domain boundaries. △ Less

Submitted 30 September, 2025; originally announced October 2025.

Interference-caged quantum many-body scars: the Fock space topological localization and interference zeros

Authors: Tao-Lin Tan, Yi-Ping Huang

Abstract: We propose a general mechanism for realizing athermal finite-energy-density eigenstates -- termed interference-caged quantum many-body scars (ICQMBS) -- which originate from exact many-body destructive interference on the Fock space graph. These eigenstates are strictly localized to specific subsets of vertices, analogous to compact localized states in flat-band systems. Central to our framework i… ▽ More We propose a general mechanism for realizing athermal finite-energy-density eigenstates -- termed interference-caged quantum many-body scars (ICQMBS) -- which originate from exact many-body destructive interference on the Fock space graph. These eigenstates are strictly localized to specific subsets of vertices, analogous to compact localized states in flat-band systems. Central to our framework is a connection between interference zeros and graph automorphisms, which classify vertices according to the graph's local topology. This connection enables the construction of a new class of topological ICQMBS, whose robustness arises from the local topology of the Fock space graph rather than from conventional conservation laws or dynamical constraints. We demonstrate the effectiveness of this framework by developing a graph-theory-based search algorithm, which identifies ICQMBS in both a one-dimensional spin-1 XY model and two-dimensional quantum link models across distinct gauge sectors. In particular, we discover the proposed topological ICQMBS in the two-dimensional quantum link model and provide an intuitive explanation for previously observed order-by-disorder phenomena in Hilbert space. Our results reveal an unexpected synergy between graph theory, flat-band physics, and quantum many-body dynamics, offering new insights into the structure and stability of nonthermal eigenstates. △ Less

Submitted 10 April, 2025; originally announced April 2025.

Comments: 51 pages, 23 figures

A spinless crystal for a high-performance solid-state $^{229}$Th nuclear clock

Authors: Harry W. T. Morgan, James E. S. Terhune, Ricky Elwell, Hoang Bao Tran Tan, Udeshika C. Perera, Andrei Derevianko, Eric R. Hudson, Anastassia N. Alexandrova

Abstract: Solid-state $^{229}$Th nuclear clocks require a host material whose band gap is larger than the 8.4 eV nuclear transition energy. As such, excitation of the $^{229}$Th nuclear state has so far only been demonstrated in metal fluorides, specifically CaF$_2$, LiSrAlF$_6$, and ThF$_4$, where the large electronegativity of the halogen leads to sufficient band gaps. However, it is expected that the nuc… ▽ More Solid-state $^{229}$Th nuclear clocks require a host material whose band gap is larger than the 8.4 eV nuclear transition energy. As such, excitation of the $^{229}$Th nuclear state has so far only been demonstrated in metal fluorides, specifically CaF$_2$, LiSrAlF$_6$, and ThF$_4$, where the large electronegativity of the halogen leads to sufficient band gaps. However, it is expected that the nuclear magnetic moment of the fluorine gives rise to a leading order broadening mechanism that limits the clock stability. Here, we use concepts of molecular design to identify a polyatomic anion, SO$_4^{2-}$, that is both nuclear spin free and of sufficient electron affinity to result in a high band gap metal sulfate system. Using state-of-the-art calculations, we find that the band gap of Th(SO$_4$)$_2$ is approximately 9 eV, large enough for direct laser excitation of $^{229}$Th. Low concentrations of $^{229}$Th in the otherwise spinless $^{232}$Th(SO$_4$)$_2$ crystal mitigate $^{229}$Th-$^{229}$Th interactions. Furthermore, the introduction of $^{229}$Th does not modify the material band gap nor introduce electronic states associated with nuclear quenching. By removing one of the primary sources of nuclear line broadening in the crystal, the nuclear magnetic dipole-dipole interaction, a nuclear clock with instability as low as $σ= 4.6\times10^{-23}/\sqrtτ$, where $τ$ is the averaging time, may be realized. This is roughly six orders of magnitude lower than previously thought possible. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 7 pages of main text and references, 3 pages of supporting information. 2 figures

Electrically tunable Floquet Weyl photon emission from Dirac semimetal Cd3As2

Authors: Sobhan Subhra Mishra, Thomas CaiWei Tan, Manoj Gupta, Faxian Xiu, Ranjan Singh

Abstract: The ability to optically engineer the Dirac band and electrically control the Fermi level in two-dimensional (2D) Dirac systems, such as graphene, has significantly advanced quantum technologies. However, similar tunability has remained elusive in three-dimensional Dirac systems. In this work, we demonstrate both optical and electrical tunability of the band structure in the 3D Dirac semimetal Cd3… ▽ More The ability to optically engineer the Dirac band and electrically control the Fermi level in two-dimensional (2D) Dirac systems, such as graphene, has significantly advanced quantum technologies. However, similar tunability has remained elusive in three-dimensional Dirac systems. In this work, we demonstrate both optical and electrical tunability of the band structure in the 3D Dirac semimetal Cd3As2. Photoexcitation with circularly polarized light breaks time-reversal symmetry, lifting the degeneracy at Dirac points to transform the material into a Floquet Weyl semimetal with chiral Weyl nodes. This transition induces nonzero Berry curvature, giving rise to helicity-dependent transverse anomalous photocurrents, detectable through terahertz emission at normal incidence. Furthermore, applying an external electric field displaces the Fermi level away from the Dirac point, enlarging the Dirac cone projection leading to a reduced density of states of Fermi arcs. As a result, we achieve precise electrical control over Floquet band engineering, resulting in a large modulation of THz emission. Moreover, at oblique incidence, the circular photon-drag effect induces helicity-dependent longitudinal photocurrents. Simultaneous generation and manipulation of both longitudinal and transverse photocurrents enable precise control of the helicity of emitted THz pulses. These results pave the way for electric field-controlled Floquet Weyl THz sources, offering significant potential for applications in quantum computing and low-power electronics. △ Less

Submitted 27 January, 2025; originally announced January 2025.

Comments: 26 pages, 4 figures, 4 supplementary figures

A high optical access cryogenic system for Rydberg atom arrays with a 3000-second trap lifetime

Authors: Zhenpu Zhang, Ting-Wei Hsu, Ting You Tan, Daniel H. Slichter, Adam M. Kaufman, Matteo Marinelli, Cindy A. Regal

Abstract: We present an optical tweezer array of $^{87}$Rb atoms housed in an cryogenic environment that successfully combines a 4 K cryopumping surface, a <50 K cold box surrounding the atoms, and a room-temperature high-numerical-aperture objective lens. We demonstrate a 3000 s atom trap lifetime, which enables us to optimize and measure losses at the $10^{-4}$ level that arise during imaging and cooling,… ▽ More We present an optical tweezer array of $^{87}$Rb atoms housed in an cryogenic environment that successfully combines a 4 K cryopumping surface, a <50 K cold box surrounding the atoms, and a room-temperature high-numerical-aperture objective lens. We demonstrate a 3000 s atom trap lifetime, which enables us to optimize and measure losses at the $10^{-4}$ level that arise during imaging and cooling, which are important to array rearrangement. We perform both ground-state qubit manipulation with an integrated microwave antenna and two-photon coherent Rydberg control, with the local electric field tuned to zero via integrated electrodes. We anticipate that the reduced blackbody radiation at the atoms from the cryogenic environment, combined with future electrical shielding, should decrease the rate of undesired transitions to nearby strongly-interacting Rydberg states, which cause many-body loss and impede Rydberg gates. This low-vibration, high-optical-access cryogenic platform can be used with a wide range of optically trapped atomic or molecular species for applications in quantum computing, simulation, and metrology. △ Less

Submitted 8 July, 2025; v1 submitted 12 December, 2024; originally announced December 2024.

Comments: 20 pages, 10 figures

Journal ref: PRX Quantum 6 (2025) 020337

Fractional Chern mosaic in supermoiré graphene

Authors: Yves H. Kwan, Tixuan Tan, Trithep Devakul

Abstract: We propose the realization of a fractional Chern mosaic: a state characterized by a spatially varying topological order. This state is enabled by a separation of length scales that emerges when three graphene sheets are sequentially rotated by a small twist angle. The resulting structure features not only conventional moiré lattices, but also a much larger supermoiré lattice. We demonstrate that a… ▽ More We propose the realization of a fractional Chern mosaic: a state characterized by a spatially varying topological order. This state is enabled by a separation of length scales that emerges when three graphene sheets are sequentially rotated by a small twist angle. The resulting structure features not only conventional moiré lattices, but also a much larger supermoiré lattice. We demonstrate that a fractional Chern mosaic arises when electron correlations induce fractionalization locally on the moiré scale, while the pattern of fractionalization varies at the supermoiré scale. △ Less

Submitted 13 November, 2024; originally announced November 2024.

Comments: 5+11 pages

Wavefunction approach to the fractional anomalous Hall crystal

Authors: Tixuan Tan, Julian May-Mann, Trithep Devakul

Abstract: We propose fractional anomalous Hall crystals (FAHCs) as possible ground states of strongly interacting electrons in parent bands with Berry curvature. FAHCs are exotic states of matter that spontaneously break continuous translation symmetry to form a fractional Chern insulator. We construct a unified family of variational wavefunctions that describe FAHCs and their competing states in the presen… ▽ More We propose fractional anomalous Hall crystals (FAHCs) as possible ground states of strongly interacting electrons in parent bands with Berry curvature. FAHCs are exotic states of matter that spontaneously break continuous translation symmetry to form a fractional Chern insulator. We construct a unified family of variational wavefunctions that describe FAHCs and their competing states in the presence of uniform parent Berry curvature. We calculate their variational energy with Coulomb interactions semi-analytically in the thermodynamic limit. Our analysis reveals that FAHCs can be energetically favorable over both Wigner crystals and integer anomalous Hall crystals for sufficiently strong interactions or flat dispersion. △ Less

Submitted 10 September, 2024; originally announced September 2024.

Importance of electron-phonon coupling near the electron-liquid to Wigner-crystal transition in two-dimensional atomically thin materials

Authors: Tixuan Tan, Vladimir Calvera, Steven A. Kivelson

Abstract: We study the effect of electron-phonon coupling on the location of the Fermi Liquid to Wigner Crystal transition in the two-dimensional electron gas realized in various material platforms. Based on dimensional estimates of the relevant parameters, we conclude that (as conventionally assumed) phonons are negligible in traditional semiconductor quantum well systems, but likely play a significant rol… ▽ More We study the effect of electron-phonon coupling on the location of the Fermi Liquid to Wigner Crystal transition in the two-dimensional electron gas realized in various material platforms. Based on dimensional estimates of the relevant parameters, we conclude that (as conventionally assumed) phonons are negligible in traditional semiconductor quantum well systems, but likely play a significant role in various recently synthesized atomically thin two-dimensional materials. △ Less

Submitted 5 August, 2024; originally announced August 2024.

Comments: 4 + 4 pages, 2 figures

Journal ref: Phys. Rev. B 110, L241104 (2024)

Magnetic and nematic order of Bose-Fermi mixtures in moiré superlattices of 2D semiconductors

Authors: Feng-Ren Fan, Tixuan Tan, Chengxin Xiao, Wang Yao

Abstract: We investigate the magnetic orders in a mixture of Boson (exciton) and Fermion (electron or hole) trapped in transition-metal dichalcogenides moiré superlattices. A sizable antiferromagnetic exchange interaction is found between a carrier and an interlayer exciton trapped at different high symmetry points of the moiré supercell. This interaction at a distance much shorter than the carrier-carrier… ▽ More We investigate the magnetic orders in a mixture of Boson (exciton) and Fermion (electron or hole) trapped in transition-metal dichalcogenides moiré superlattices. A sizable antiferromagnetic exchange interaction is found between a carrier and an interlayer exciton trapped at different high symmetry points of the moiré supercell. This interaction at a distance much shorter than the carrier-carrier separation dominates the magnetic order in the Bose-Fermi mixture, where the carrier sublattice develops ferromagnetism opposite to that in the exciton sublattice. We demonstrate the possibility of increasing the Curie temperature of moiré carriers through electrical tuning of the exciton density in the ground state. In a trilayer moiré system with a p-n-p type band alignment, the exciton-carrier interplay can establish a layered antiferromagnetism for holes confined in the two outer layers. We further reveal a spontaneous nematic order in the Bose-Fermi mixture, arising from the interference between the Coulomb interaction and p-wave interlayer tunneling dictated by the stacking registry. △ Less

Submitted 3 April, 2025; v1 submitted 15 July, 2024; originally announced July 2024.

Comments: 6 pages, 4 figures

Journal ref: Physical Review B 111 (2025) 155109

Fractional quantum anomalous Hall effect in a singular flat band

Authors: Wenqi Yang, Dawei Zhai, Tixuan Tan, Feng-Ren Fan, Zuzhang Lin, Wang Yao

Abstract: In the search of fractional quantum anomalous Hall (FQAH) effect, the conventional wisdom is to start from a flat Chern band isolated from the rest of the Hilbert space by band gaps, so that many-body interaction can be projected to a landscape that mimics a Landau level. Singular flat bands (SFB), which share protected touching points with other dispersive bands, represent another type of flat la… ▽ More In the search of fractional quantum anomalous Hall (FQAH) effect, the conventional wisdom is to start from a flat Chern band isolated from the rest of the Hilbert space by band gaps, so that many-body interaction can be projected to a landscape that mimics a Landau level. Singular flat bands (SFB), which share protected touching points with other dispersive bands, represent another type of flat landscapes differing from Landau levels and Chern bands in topological and geometric properties. Here we report the finding of FQAH phases in a SFB, which emerges in the bipartite limit of the nearest-neighbor tight-binding model of twisted bilayer MoTe$_2$. At 1/3 and 2/3 filling of the SFB, FQAH effects are demonstrated using density matrix renormalisation group calculations with all bands, as well as exact diagonalization calculations with the two touching bands. Gapping the band touching can turn the SFB into a nearly flat Chern band, but counter-intuitively this suppresses the FQAH effect, as the gap opening introduces strong inhomogeneity to the quantum geometry. An optical scheme to realize such SFB for cold atoms is provided. Our findings uncover a new arena for the exploration of fractional quantum Hall physics beyond the Landau level and Chern insulator paradigms. △ Less

Submitted 12 May, 2025; v1 submitted 2 May, 2024; originally announced May 2024.

Journal ref: Phys. Rev. Lett. 134, 196501 (2025)

Local operator quench induced by two-dimensional inhomogeneous and homogeneous CFT Hamiltonians

Authors: Weibo Mao, Masahiro Nozaki, Kotaro Tamaoka, Mao Tian Tan

Abstract: We explore non-equilibrium processes in two-dimensional conformal field theories (2d CFTs) due to the growth of operators induced by inhomogeneous and homogeneous Hamiltonians by investigating the time dependence of the partition function, energy density, and entanglement entropy. The non-equilibrium processes considered in this paper are constructed out of the Lorentzian and Euclidean time evolut… ▽ More We explore non-equilibrium processes in two-dimensional conformal field theories (2d CFTs) due to the growth of operators induced by inhomogeneous and homogeneous Hamiltonians by investigating the time dependence of the partition function, energy density, and entanglement entropy. The non-equilibrium processes considered in this paper are constructed out of the Lorentzian and Euclidean time evolution governed by different Hamiltonians. We explore the effect of the time ordering on entanglement dynamics so that we find that in a free boson CFT and RCFTs, this time ordering does not affect the entanglement entropy, while in the holographic CFTs, it does. Our main finding is that in the holographic CFTs, the non-unitary time evolution induced by the inhomogeneous Hamiltonian can retain the initial state information longer than in the unitary time evolution. △ Less

Submitted 2 April, 2024; v1 submitted 23 March, 2024; originally announced March 2024.

Comments: 37 pages+appendices, 6 figures. v2: references added

Report number: RIKEN-iTHEMS-Report-24

Journal ref: JHEP 07 (2024) 200

Parent Berry curvature and the ideal anomalous Hall crystal

Authors: Tixuan Tan, Trithep Devakul

Abstract: We study a model of electrons moving in a parent band of uniform Berry curvature. At sufficiently high parent Berry curvature, we show that strong repulsive interactions generically lead to the formation of an anomalous Hall crystal: a topological state with spontaneously broken continuous translation symmetry. Our results are established via a mapping to a problem of Wigner crystallization in a r… ▽ More We study a model of electrons moving in a parent band of uniform Berry curvature. At sufficiently high parent Berry curvature, we show that strong repulsive interactions generically lead to the formation of an anomalous Hall crystal: a topological state with spontaneously broken continuous translation symmetry. Our results are established via a mapping to a problem of Wigner crystallization in a regular 2D electron gas. Interestingly, we find that a periodic electrostatic potential induces a competing state with opposite Chern number. Our theory offers a unified perspective for understanding several aspects of the recently observed integer and fractional quantum anomalous Hall effects in rhombohedral multilayer graphene and provides a recipe for engineering new topological states. △ Less

Submitted 8 July, 2024; v1 submitted 6 March, 2024; originally announced March 2024.

Designing topology and fractionalization in narrow gap semiconductor films via electrostatic engineering

Authors: Tixuan Tan, Aidan P. Reddy, Liang Fu, Trithep Devakul

Abstract: We show that topological flat minibands can be engineered in a class of narrow gap semiconductor films using only an external electrostatic superlattice potential. We demonstrate that, for realistic material parameters, these bands are capable of hosting correlated topological phases such as integer and fractional quantum anomalous Hall states and composite Fermi liquid phases at zero magnetic fie… ▽ More We show that topological flat minibands can be engineered in a class of narrow gap semiconductor films using only an external electrostatic superlattice potential. We demonstrate that, for realistic material parameters, these bands are capable of hosting correlated topological phases such as integer and fractional quantum anomalous Hall states and composite Fermi liquid phases at zero magnetic field. Our results provide a path towards the realization of fractionalized topological states in a broad range of materials. △ Less

Submitted 10 January, 2025; v1 submitted 5 February, 2024; originally announced February 2024.

Biphenylene Nanoribbon as Promising Electrocatalyst for Hydrogen Evolution

Authors: Radha N Somaiya, Zicong Marvin Wong, Brahmananda Chakraborty, Teck Leong Tan, Aftab Alam

Abstract: Designing efficient, metal free, and in-expensive catalyst for electrochemical hydrogen evolution reaction (HER) is crucial for large scale clean and green energy production. Recently synthesized 1D Biphenylene nanoribbons (BPRs) display few exciting properties originating from the unique co-existence of 4, 6 and 8 coordinated carbon rings. Here, we present a first principles calculation of the el… ▽ More Designing efficient, metal free, and in-expensive catalyst for electrochemical hydrogen evolution reaction (HER) is crucial for large scale clean and green energy production. Recently synthesized 1D Biphenylene nanoribbons (BPRs) display few exciting properties originating from the unique co-existence of 4, 6 and 8 coordinated carbon rings. Here, we present a first principles calculation of the electronic structure and electrocatalytic activity of various sized N-BPRs (N indicates the width). The electrocatalytic performance is evaluated based on several descriptors including electronic property, carrier mobility, Gibbs free energy ($Δ$G$_{HER}$), exchange current density etc. The electronic properties are crucially sensitive to the width (N) of BPRs transiting it from semiconducting to metallic nature at N=18. The p$_z$ orbitals of C-atoms from the central tetragonal rings are mainly responsible for the decrease in band gap with increasing width. The room temperature electron mobility is found to be as high as $\sim6.3\times$10$^4$ cm$^2$V$^{-1}$s$^{-1}$, while hole mobility is relatively lower in magnitude. Gibbs free energy also depends sensitively on the width of BPRs as evident from the p-band center analysis. We propose 15-BPR as the most promising candidate for electrocatalytic activity with extremely small overpotential ($\approx$0.005 V) and a high exchange current density, much better than the state-of-the-art Pt(111). A close inspection of the elementary reactions of HER (Volmer, Heyrovsky and Tafel) confirms Volmer-Tafel mechanism to be most dominant on 15-BPR with Tafel as the rate-determining step with a barrier of 0.56 eV. The present study provides a deeper insight into the excellent HER catalytic activity of a newly synthesized BPR which is inexpensive and is expected to hasten experimental validation towards H$_2$ production. △ Less

Submitted 1 January, 2024; originally announced January 2024.

Comments: 10 pages, 5 figures, 2 Tables, and Supporting Information (total 8-pages with 7 figures)

Inhomogeneous quenches as state preparation in two-dimensional conformal field theories

Authors: Masahiro Nozaki, Kotaro Tamaoka, Mao Tian Tan

Abstract: The non-equilibrium process where the system does not evolve to the featureless state is one of the new central objects in the non-equilibrium phenomena. In this paper, starting from the short-range entangled state in the two-dimensional conformal field theories ($2$d CFTs), the boundary state with a regularization, we evolve the system with the inhomogeneous Hamiltonians called Möbius/SSD ones. R… ▽ More The non-equilibrium process where the system does not evolve to the featureless state is one of the new central objects in the non-equilibrium phenomena. In this paper, starting from the short-range entangled state in the two-dimensional conformal field theories ($2$d CFTs), the boundary state with a regularization, we evolve the system with the inhomogeneous Hamiltonians called Möbius/SSD ones. Regardless of the details of CFTs considered in this paper, during the Möbius evolution, the entanglement entropy exhibits the periodic motion called quantum revival. During SSD time evolution, except for some subsystems, in the large time regime, entanglement entropy and mutual information are approximated by those for the vacuum state. We argue the time regime for the subsystem to cool down to vacuum one is $t_1 \gg \mathcal{O}(L\sqrt{l_A})$, where $t_1$, $L$, and $l_A$ are time, system, and subsystem sizes. This finding suggests the inhomogeneous quench induced by the SSD Hamiltonian may be used as the preparation for the approximately-vacuum state. We propose the gravity dual of the systems considered in this paper, furthermore, and generalize it. In addition to them, we discuss the relation between the inhomogenous quenches and continuous multi-scale entanglement renormalization ansatz (cMERA). △ Less

Submitted 30 October, 2023; originally announced October 2023.

Comments: 32+4 pages, 11 figures

Report number: RIKEN-iTHEMS-Report-23

Journal ref: Phys.Rev.D 109 (2024) 12, 126014

Bridging two quantum quench problems -- local joining quantum quench and Möbius quench -- and their holographic dual descriptions

Authors: Jonah Kudler-Flam, Masahiro Nozaki, Tokiro Numasawa, Shinsei Ryu, Mao Tian Tan

Abstract: We establish an equivalence between two different quantum quench problems, the joining local quantum quench and the Möbius quench, in the context of $(1+1)$-dimensional conformal field theory (CFT). Here, in the former, two initially decoupled systems (CFTs) on finite intervals are joined at $t=0$. In the latter, we consider the system that is initially prepared in the ground state of the regular… ▽ More We establish an equivalence between two different quantum quench problems, the joining local quantum quench and the Möbius quench, in the context of $(1+1)$-dimensional conformal field theory (CFT). Here, in the former, two initially decoupled systems (CFTs) on finite intervals are joined at $t=0$. In the latter, we consider the system that is initially prepared in the ground state of the regular homogeneous Hamiltonian on a finite interval and, after $t=0$, let it time-evolve by the so-called Möbius Hamiltonian that is spatially inhomogeneous. The equivalence allows us to relate the time-dependent physical observables in one of these problems to those in the other. As an application of the equivalence, we construct a holographic dual of the Möbius quench from that of the local quantum quench. The holographic geometry involves an end-of-the-world brane whose profile exhibits non-trivial dynamics. △ Less

Submitted 8 September, 2023; originally announced September 2023.

Comments: 13 pages, 9 figures

Magnetic-field periodic quantum Sondheimer oscillations in thin-film graphite

Authors: Toshihiro Taen, Andhika Kiswandhi, Toshihito Osada

Abstract: Materials with the mesoscopic scales have provided an excellent platform for quantum-mechanical studies. Among them, the periodic oscillations of the electrical resistivity against the direct and the inverse of the magnetic fields, such as the Aharonov-Bohm effect and the Shubnikov-de Haas effect, manifest the interference of the wavefunction relevant to the electron motion perpendicular to the ma… ▽ More Materials with the mesoscopic scales have provided an excellent platform for quantum-mechanical studies. Among them, the periodic oscillations of the electrical resistivity against the direct and the inverse of the magnetic fields, such as the Aharonov-Bohm effect and the Shubnikov-de Haas effect, manifest the interference of the wavefunction relevant to the electron motion perpendicular to the magnetic field. In contrast, the electron motion along the magnetic field also leads to the magnetic-field periodicity, which is the so-called Sondheimer effect. However, the Sondheimer effect has been understood only in the framework of the semiclassical picture, and thereby its interpretation at the quasiquantum limit was not clear. Here, we show that thin-film graphite exhibits clear sinusoidal oscillations with a period of about 1-3 T over a wide range of the magnetic fields (from around 10 T to 30 T), where conventional quantum oscillations are absent. In addition, the sample with a designed step in the middle for eliminating the stacking disorder effect verifies that the period of the oscillations is inversely proportional to the thickness, which supports the emergence of the Sondheimer oscillations in the quasiquantum limit. These findings suggest that the Sondheimer oscillations can be reinterpreted as inter-Landau-level resonances even at the field range where the semiclassical picture fails. Our results expand the quantum oscillation family, and pave the way for the exploration of the out-of-plane wavefunction motion. △ Less

Submitted 28 July, 2023; originally announced July 2023.

Comments: 17 pages, 5 figures

Electrostatic moiré potential from twisted-hBN layers

Authors: Dong Seob Kim, Roy C. Dominguez, Rigo Mayorga-Luna, Dingyi Ye, Jacob Embley, Tixuan Tan, Yue Ni, Zhida Liu, Mitchell Ford, Frank Y. Gao, Saba Arash, Kenji Watanabe, Takashi Taniguchi, Suenne Kim, Chih-Kang Shih, Keji Lai, Wang Yao, Li Yang, Xiaoqin Li, Yoichi Miyahara

Abstract: Moiré superlattices formed by vertically stacking van der Waals layers host a rich variety of correlated electronic phases and function as novel photonic materials. The moiré potential of the superlattice, however, is fixed by the interlayer coupling of the stacked functional layers (e.g. graphene) and dependent on carrier types (e.g. electrons or holes) and valleys (e.g. Γ vs. K). In contrast, tw… ▽ More Moiré superlattices formed by vertically stacking van der Waals layers host a rich variety of correlated electronic phases and function as novel photonic materials. The moiré potential of the superlattice, however, is fixed by the interlayer coupling of the stacked functional layers (e.g. graphene) and dependent on carrier types (e.g. electrons or holes) and valleys (e.g. Γ vs. K). In contrast, twisted hexagonal boron nitride (hBN) layers are predicted to impose a periodic electrostatic potential that may be used to engineer the properties of an adjacent functional thin layer. Here, we show that this potential is described by a simple theory of electric polarization originating from the interfacial charge redistribution, validated by its dependence on supercell sizes and distance from the twisted interfaces. We demonstrate that the potential depth and profile can be further controlled by assembling a double moiré structure. When the twist angles are similar at the two interfaces, the potential is deepened by adding the potential from the two twisted interfaces, reaching ~ 400 meV. When the twist angles are dissimilar at the two interfaces, multi-level polarization states are observed. As an example of controlling a functional layer, we demonstrate how the electrostatic potential from a twisted hBN substrate impedes exciton diffusion in a semiconductor monolayer. These findings suggest exciting opportunities for engineering properties of an adjacent functional layer using the surface potential of a twisted hBN substrate. △ Less

Submitted 13 June, 2023; originally announced June 2023.

Scrambling and Recovery of Quantum Information in Inhomogeneous Quenches in Two-dimensional Conformal Field Theories

Authors: Kanato Goto, Masahiro Nozaki, Shinsei Ryu, Kotaro Tamaoka, Mao Tian Tan

Abstract: We study various quantum quench processes induced by the Möbius/sine-square deformation of the Hamiltonian in two-dimensional conformal field theories starting from the thermofield double state in the two copies of the Hilbert space. These quantum quenches, some of which are directly related to the operator entanglement of the time-evolution operators, allow us to study scrambling and recovery of… ▽ More We study various quantum quench processes induced by the Möbius/sine-square deformation of the Hamiltonian in two-dimensional conformal field theories starting from the thermofield double state in the two copies of the Hilbert space. These quantum quenches, some of which are directly related to the operator entanglement of the time-evolution operators, allow us to study scrambling and recovery of quantum information. In particular, under the SSD time-evolution, we show from the time-dependence of mutual information that the Bell pairs, initially shared by the subsystems of the two Hilbert spaces, may revive even after the mutual information for small subsystems is completely destroyed by quantum information scrambling dynamics. This mutual information is robust against the strong scrambling dynamics. As a consequence, the steady state has a non-local correlation shared not by any of two parties but by three parties. In the holographic dual description, a wormhole connecting the two Hilbert spaces may non-linearly grow with time during the quantum quenches. We also propose effective pictures that describe the dynamics of mutual information during the time-evolution by inhomogeneous Hamiltonians. △ Less

Submitted 15 February, 2023; originally announced February 2023.

Comments: 36+26 pages, 23 figures

Report number: RIKEN-iTHEMS-Report-23

Journal ref: Phys. Rev. Research 6, 023001 (2024)

Entanglement Dynamics of the Non-Unitary Holographic Channel

Authors: Kanato Goto, Masahiro Nozaki, Kotaro Tamaoka, Mao Tian Tan

Abstract: We study the dynamical properties of a strongly scrambling quantum circuit involving a projective measurement on a finite-sized region by studying the operator entanglement entropy and mutual information (OEE and BOMI) of the dual operator state that corresponds to this quantum circuit. The time-dependence of the OEE exhibits a new dynamical behavior of operator entanglement, namely an additional… ▽ More We study the dynamical properties of a strongly scrambling quantum circuit involving a projective measurement on a finite-sized region by studying the operator entanglement entropy and mutual information (OEE and BOMI) of the dual operator state that corresponds to this quantum circuit. The time-dependence of the OEE exhibits a new dynamical behavior of operator entanglement, namely an additional fractional coefficient that accompanies the linear time growth of the OEE. For a holographic system, this is equivalent to an additional fractional coefficient that modifies the linear growth rate of the wormhole volume. The time-dependence of the BOMI shows that the projective measurement may destroy the non-local correlations in this dual state. We also propose a gravity dual as well as a line-tension picture, which is an effective model, that describe this strongly scrambling quantum circuit. △ Less

Submitted 7 November, 2022; originally announced November 2022.

Comments: 30 pages + appendices, 12 figures

Report number: RIKEN-iTHEMS-Report-22

Quantized thermoelectric Hall plateau in the quantum limit of graphite as a nodal line semimetal

Authors: Andhika Kiswandhi, Tomotaka Ochi, Toshihiro Taen, Mitsuyuki Sato, Kazuhito Uchida, Toshihito Osada

Abstract: We performed thermoelectric Hall conductivity $α_{xy}$ measurements on single-crystal graphite in the quantum limit up to 13 T. Both electrical and thermoelectric transport measurements were performed on the same crystal to extract pure $α_{xy}$, avoiding any sample quality dependence. The $α_{xy}$ converges to a plateau in the quantum limit with a linear dependence on temperature. This behavior i… ▽ More We performed thermoelectric Hall conductivity $α_{xy}$ measurements on single-crystal graphite in the quantum limit up to 13 T. Both electrical and thermoelectric transport measurements were performed on the same crystal to extract pure $α_{xy}$, avoiding any sample quality dependence. The $α_{xy}$ converges to a plateau in the quantum limit with a linear dependence on temperature. This behavior is analogous to the quantized thermoelectric Hall effect (QTHE) observed in three-dimensional Dirac/Weyl nodal-point semimetals, and experimentally confirms a theoretical proposal on the QTHE in semimetals with nodal lines as in graphite. △ Less

Submitted 5 May, 2023; v1 submitted 4 November, 2022; originally announced November 2022.

Comments: 6 pages, 4 figures, with supplemental information (5 pages, 4 figures)

Journal ref: Phys. Rev. B 107, 195106 (2023)

High-temperature self-energy corrections to x-ray absorption spectra

Authors: Tun S. Tan, J. J. Kas, S. B. Trickey, J. J. Rehr

Abstract: Effects of finite-temperature quasiparticle self-energy corrections to x-ray absorption spectra are investigated within the finite-temperature quasiparticle local density GW approximation up to temperatures $T$ of order the Fermi temperature. To facilitate the calculations, we parametrize the quasiparticle self-energy using low-order polynomial fits. We show that temperature-driven decrease in the… ▽ More Effects of finite-temperature quasiparticle self-energy corrections to x-ray absorption spectra are investigated within the finite-temperature quasiparticle local density GW approximation up to temperatures $T$ of order the Fermi temperature. To facilitate the calculations, we parametrize the quasiparticle self-energy using low-order polynomial fits. We show that temperature-driven decrease in the electron lifetime substantially broadens the spectra in the near-edge region with increasing $T$. However, the quasiparticle shift is most strongly modified near the onset of plasmon excitations. △ Less

Submitted 12 August, 2022; v1 submitted 3 August, 2022; originally announced August 2022.

Some Problems in Density Functional Theory

Authors: Jeffrey Wrighton, Angel Albavera-Mata, Hector Francisco Rodriguez, Tun S. Tan, Antonio C. Cancio, J. W. Dufty, S. B. Trickey

Abstract: Though calculations based on density functional theory (DFT) are used remarkably widely in chemistry, physics, materials science, and biomolecular research and though the modern form of DFT has been studied for almost 60 years, some mathematical problems remain. For context, we provide an outline of the basic structure of DFT, then pose several questions regarding both its time-independent and tim… ▽ More Though calculations based on density functional theory (DFT) are used remarkably widely in chemistry, physics, materials science, and biomolecular research and though the modern form of DFT has been studied for almost 60 years, some mathematical problems remain. For context, we provide an outline of the basic structure of DFT, then pose several questions regarding both its time-independent and time-dependent forms. Progress on any of these would aid in development of better approximate functionals and in interpretation. △ Less

Submitted 20 January, 2023; v1 submitted 30 June, 2022; originally announced July 2022.

Topological Defects in Floquet Circuits

Authors: Mao Tian Tan, Yifan Wang, Aditi Mitra

Abstract: We introduce a Floquet circuit describing the driven Ising chain with topological defects. The corresponding gates include a defect that flips spins as well as the duality defect that explicitly implements the Kramers-Wannier duality transformation. The Floquet unitary evolution operator commutes with such defects, but the duality defect is not unitary, as it projects out half the states. We give… ▽ More We introduce a Floquet circuit describing the driven Ising chain with topological defects. The corresponding gates include a defect that flips spins as well as the duality defect that explicitly implements the Kramers-Wannier duality transformation. The Floquet unitary evolution operator commutes with such defects, but the duality defect is not unitary, as it projects out half the states. We give two applications of these defects. One is to analyze the return amplitudes in the presence of "space-like" defects stretching around the system. We verify explicitly that the return amplitudes are in agreement with the fusion rules of the defects. The second application is to study unitary evolution in the presence of "time-like" defects that implement anti-periodic and duality-twisted boundary conditions. We show that a single unpaired localized Majorana zero mode appears in the latter case. We explicitly construct this operator, which acts as a symmetry of this Floquet circuit. We also present analytic expressions for the entanglement entropy after a single time step for a system of a few sites, for all of the above defect configurations. △ Less

Submitted 19 March, 2024; v1 submitted 13 June, 2022; originally announced June 2022.

Comments: 54 pages, LaTeX; typos corrected

Journal ref: SciPost Phys. 16, 075 (2024)

Nonlinear co-generation of graphene plasmons for optoelectronic logic operations

Authors: Y. Li, N. An, Z. Lu, Y. Wang, B. Chang, T. Tan, X. Guo, X. Xu, J. He, H. Xia, Z. Wu, Y. Su, Y. Liu, Y. Rao, G. Soavi, B. Yao

Abstract: Surface plasmons in graphene provide a compelling strategy for advanced photonic technologies thanks to their tight confinement, fast response and tunability. Recent advances in the field of all optical generation of graphene plasmons in planar waveguides offer a promising method for high speed signal processing in nanoscale integrated optoelectronic devices. Here, we use two counter propagating f… ▽ More Surface plasmons in graphene provide a compelling strategy for advanced photonic technologies thanks to their tight confinement, fast response and tunability. Recent advances in the field of all optical generation of graphene plasmons in planar waveguides offer a promising method for high speed signal processing in nanoscale integrated optoelectronic devices. Here, we use two counter propagating frequency combs with temporally synchronized pulses to demonstrate deterministic all optical generation and electrical control of multiple plasmon polaritons, excited via difference frequency generation (DFG). Electrical tuning of a hybrid graphene fibre device offers a precise control over the DFG phase matching, leading to tunable responses of the graphene plasmons at different frequencies across a broadband (0 - 50 THz) and provides a powerful tool for high speed logic operations. Our results offer insights for plasmonics on hybrid photonic devices based on layered materials and pave the way to high speed integrated optoelectronic computing circuits. △ Less

Submitted 7 June, 2022; originally announced June 2022.

Journal ref: Nat. Commun. 13, 3138 (2022)

Magneto-optical trap of a Group III atom

Authors: Xianquan Yu, Jinchao Mo, Tiangao Lu, Ting You Tan, Travis L. Nicholson

Abstract: We realize the first magneto-optical trap of an atom in main group III of the Periodic Table. Our atom of choice (indium) does not have a transition out of its ground state suitable for laser cooling; therefore, laser cooling is performed on the $\lvert 5P_{3/2},F=6 \rangle \rightarrow \lvert 5D_{5/2},F=7 \rangle$ transition, where $\lvert 5P_{3/2},F=6 \rangle$ is a long-lived metastable state. Op… ▽ More We realize the first magneto-optical trap of an atom in main group III of the Periodic Table. Our atom of choice (indium) does not have a transition out of its ground state suitable for laser cooling; therefore, laser cooling is performed on the $\lvert 5P_{3/2},F=6 \rangle \rightarrow \lvert 5D_{5/2},F=7 \rangle$ transition, where $\lvert 5P_{3/2},F=6 \rangle$ is a long-lived metastable state. Optimization of our trap parameters results in atoms numbers as large as $5\times10^8$ atoms with temperatures of order 1 mK. Additionally, through trap decay measurements, we infer a one-body trap lifetime of 12.3 s. This lifetime is consistent with background gas collisions and indicates that our repumpers have closed all leakage pathways. We also infer a two-body loss rate of $1.6\times 10^{-11}\ \mathrm{cm^3/s}$, which is comparable to those measured in alkali atoms. The techniques demonstrated in this work can be straightforwardly applied to other group III atoms, and our results pave the way for realizing quantum degenerate gases of these particles. △ Less

Submitted 7 June, 2022; v1 submitted 15 April, 2022; originally announced April 2022.

Comments: Main text: 6 pages, 4 figures. Supplemental material: 4 pages, 1 figure. Final published version. Published as PRA Letter, Editors' Suggestion, Physics Feature

Journal ref: Physical Review A 105, L061101 (2022)

Weak localization on moiré superlattice in twisted double bilayer graphene

Authors: Masaki Kashiwagi, Toshihiro Taen, Kazuhito Uchida, Kenji Watanabe, Takashi Taniguchi, Toshihito Osada

Abstract: Moiré superlattice created by twist stacking has multiple physical properties. These physical properties depend on the twist angle, hence investigation of the twist angle dependency is important for the deep understanding of physical phenomena in moiré superlattice. In this work, negative magnetoresistance owing to weak localization (WL) was investigated in twisted double bilayer graphene (TDBG) a… ▽ More Moiré superlattice created by twist stacking has multiple physical properties. These physical properties depend on the twist angle, hence investigation of the twist angle dependency is important for the deep understanding of physical phenomena in moiré superlattice. In this work, negative magnetoresistance owing to weak localization (WL) was investigated in twisted double bilayer graphene (TDBG) as a function of the twist angle. The ratio of the intervalley scattering time to the intravalley scattering time, estimated using the WL formula for bilayer graphene, tended to decrease as the twist angle increased. This feature is qualitatively explained by the enhancement of intervalley scattering due to the reduction of the intervalley distance in the moiré Brillouin zone (BZ) of the TDBG. This indicates that WL in the TDBG occurs for the moiré superlattice with the reconstructed BZ. △ Less

Submitted 16 June, 2022; v1 submitted 10 March, 2022; originally announced March 2022.

Comments: 3 figures

Journal ref: Jpn. J. Appl. Phys. 61, 100907/1-5 (2022)

Thermoelectric Hall Effect at High-Magnetic-Field Quantum Limit in Graphite as a Nodal-Line Semimetal

Authors: Toshihito Osada, Tomotaka Ochi, Toshihiro Taen

Abstract: The high-magnetic-field thermoelectric effect in nodal-line semimetals with straight nodal lines was investigated. Three-dimensional (3D) Dirac/Weyl semimetals exhibit constant thermoelectric Hall conductivity at the high-magnetic-field quantum limit, resulting in a boundless linear increase of Seebeck coefficient. This is known as the quantized thermoelectric Hall effect (QTHE), and is expected t… ▽ More The high-magnetic-field thermoelectric effect in nodal-line semimetals with straight nodal lines was investigated. Three-dimensional (3D) Dirac/Weyl semimetals exhibit constant thermoelectric Hall conductivity at the high-magnetic-field quantum limit, resulting in a boundless linear increase of Seebeck coefficient. This is known as the quantized thermoelectric Hall effect (QTHE), and is expected to lead to high-performance thermoelectricity at low temperatures. Here, in addition to Dirac/Weyl semimetals, we demonstrated that 3D semimetals with straight nodal lines can also exhibit the QTHE under high magnetic fields. As a candidate material for experimental validation, we discussed the thermoelectric properties of bulk graphite. Furthermore, we investigated the dimensional crossover of thermoelectricity to two-dimensional behavior in thin-film graphite. △ Less

Submitted 22 February, 2022; originally announced February 2022.

Comments: 14 pages, 3 figures

Journal ref: J. Phys. Soc. Jpn. 91, No.6, 063701/1-4 (2022)

Anomalous Bloch oscillation and electrical switching of edge magnetization in bilayer graphene nanoribbon

Authors: Tixuan Tan, Fengren Fan, Ci Li, Wang Yao

Abstract: Graphene features topological edge bands that connect the pair of Dirac points through either sectors of the 1D Brillouin zone depending on edge configurations (zigzag or bearded). Because of their flat dispersion, spontaneous edge magnetisation can arise from Coulomb interaction in graphene nanoribbons, which has caught remarkable interest. We find an anomalous Bloch oscillation in such edge band… ▽ More Graphene features topological edge bands that connect the pair of Dirac points through either sectors of the 1D Brillouin zone depending on edge configurations (zigzag or bearded). Because of their flat dispersion, spontaneous edge magnetisation can arise from Coulomb interaction in graphene nanoribbons, which has caught remarkable interest. We find an anomalous Bloch oscillation in such edge bands, in which the flat dispersion freezes electron motion along the field direction, while the topological connection of the bands through the bulk leads to electron oscillation in the transverse direction between edges of different configurations on opposite sides/layers of a bilayer ribbon. Our Hubbard-model mean-field calculation shows that this phenomenon can be exploited for electrical switching of edge magnetisation configurations. △ Less

Submitted 16 February, 2022; originally announced February 2022.

Comments: 7 pages, 4 figures

Journal ref: Phys. Rev. B 106, 045405 (2022)

Zeeman slowing of a Group III atom

Authors: Xianquan Yu, Jinchao Mo, Tiangao Lu, Ting You Tan, Travis L. Nicholson

Abstract: We realize the first Zeeman slower of an atom in the Main Group III of the periodic table, otherwise known as the "triel elements". Despite that our atom of choice (namely indium) does not have a ground state cycling transition suitable for laser cooling, slowing is achieved by driving the transition $\lvert 5P_{3/2},F=6 \rangle \rightarrow \lvert 5D_{5/2},F=7 \rangle$, where the lower-energy stat… ▽ More We realize the first Zeeman slower of an atom in the Main Group III of the periodic table, otherwise known as the "triel elements". Despite that our atom of choice (namely indium) does not have a ground state cycling transition suitable for laser cooling, slowing is achieved by driving the transition $\lvert 5P_{3/2},F=6 \rangle \rightarrow \lvert 5D_{5/2},F=7 \rangle$, where the lower-energy state is metastable. Using a slower based on permanent magnets in a transverse-field configuration, we observe a bright slowed atomic beam at our design goal velocity of 70 m/s. The techniques presented here can straightforwardly extend to other triel atoms such as thallium, aluminum, and gallium. Furthermore, this work opens the possibility of cooling Group III atoms to ultracold temperatures. △ Less

Submitted 28 March, 2022; v1 submitted 12 January, 2022; originally announced January 2022.

Comments: 8 pages, 9 figures. Final published version

Journal ref: Physical Review Research 4, 013238 (2022)

Non-Equilibrating a Black Hole with Inhomogeneous Quantum Quench

Authors: Kanato Goto, Masahiro Nozaki, Shinsei Ryu, Kotaro Tamaoka, Mao Tian Tan

Abstract: We study quantum quench processes in (1+1)-dimensional conformal field theory (CFT) in which the initial thermal equilibrium (Gibbs) state is time-evolved by spatially inhomogeneous Hamiltonians, the so-called Möbius and sine-square-deformed (SSD) Hamiltonians. We found that, when the quench is induced by the SSD Hamiltonian, almost all the degrees of freedom are asymptotically gathered at a singl… ▽ More We study quantum quench processes in (1+1)-dimensional conformal field theory (CFT) in which the initial thermal equilibrium (Gibbs) state is time-evolved by spatially inhomogeneous Hamiltonians, the so-called Möbius and sine-square-deformed (SSD) Hamiltonians. We found that, when the quench is induced by the SSD Hamiltonian, almost all the degrees of freedom are asymptotically gathered at a single point, resulting in a point-like excitation. This excitation, which we dub black hole-like excitation, carries as much information as the total thermal entropy. In contrast, other parts of the system approach the low-entropy (low-temperature) state at late times. For the quench by the Möbius Hamiltonian, we instead found an eternal periodic oscillation of physical quantities such as von Neumann entropy for subsystems. When the CFT admits a holographic dual description, the SSD quench induces a time-dependent, inhomogeneous deformation of the bulk black hole horizon, which, at late enough times, ``touches'' the boundary. Our quench setups can be used as a way to create low-temperature states, and, also, simulate the formation and evaporation processes of black holes. △ Less

Submitted 31 March, 2025; v1 submitted 28 December, 2021; originally announced December 2021.

Comments: 10+21 pages, 19 figures. We have largely revised the manuscript. In particular, we changed the quasiparticle picture to a better one

Report number: RIKEN-iTHEMS-Report-21

Information Scrambling Versus Quantum Revival Through the Lens of Operator Entanglement

Authors: Kanato Goto, Ali Mollabashi, Masahiro Nozaki, Kotaro Tamaoka, Mao Tian Tan

Abstract: In this paper, we look for signatures of quantum revivals in two-dimensional conformal field theories (2d CFTs) on a spatially compact manifold by using operator entanglement. It is believed that thermalization does not occur on spatially compact manifolds as the quantum state returns to its initial state which is a phenomenon known as quantum revival. We find that in CFTs such as the free fermion… ▽ More In this paper, we look for signatures of quantum revivals in two-dimensional conformal field theories (2d CFTs) on a spatially compact manifold by using operator entanglement. It is believed that thermalization does not occur on spatially compact manifolds as the quantum state returns to its initial state which is a phenomenon known as quantum revival. We find that in CFTs such as the free fermion CFT, the operator mutual information exhibits quantum revival in accordance with the relativistic propagation of quasiparticles while in holographic CFTs, the operator mutual information does not exhibit this revival and the quasiparticle picture breaks down. Furthermore, by computing the tripartite operator mutual information, we find that the information scrambling ability of holographic CFTs can be weakened by the finite size effect. We propose a modification of an effective model known as the line tension picture to explain the entanglement dynamics due to the strong scrambling effect and find a close relationship between this model and the wormhole (Einstein-Rosen Bridge) in the holographic bulk dual. △ Less

Submitted 1 December, 2021; originally announced December 2021.

Report number: RIKEN-iTHEMS-Report-21

Journal ref: J. High Energ. Phys. 2022, 100 (2022)

Edge state in AB-stacked bilayer graphene and its correspondence with SSH ladder

Authors: Tixuan Tan, Ci Li, Wang Yao

Abstract: We study edge states in AB-stacked bilayer graphene (BLG) ribbon where the Chern number of the corresponding two-dimensional (2D) bulk Hamiltonian is zero. The existence and topological features of edge states when two layers ended with the same or different edge terminations (zigzag, bearded, armchair) are discussed. The edge states (non-dispersive bands near the Fermi level) are states localized… ▽ More We study edge states in AB-stacked bilayer graphene (BLG) ribbon where the Chern number of the corresponding two-dimensional (2D) bulk Hamiltonian is zero. The existence and topological features of edge states when two layers ended with the same or different edge terminations (zigzag, bearded, armchair) are discussed. The edge states (non-dispersive bands near the Fermi level) are states localized at the edge of graphene nanoribbon that only exists in certain range of momentum $k_y$. Their existence near the Fermi level are protected by the chiral symmetry with topology well described by coupled Su-Schrieffer-Heeger (SSH) chains model, i.e., SSH ladder, based on the bulk-edge correspondence of one-dimensional (1D) systems. These zero-energy edge states can exist in the whole $k_y$ region when two layers have zigzag and bearded edges, respectively. Winding number calculation shows a topological phase transition between two distinct non-trivial topological phases when crossing the Dirac points. Interestingly, we find the stacking configuration of BLG ribbon is important since they can lead to unexpected edge states without protection from the chiral symmetry both near the Fermi level in armchair-armchair case and in the gap within bulk bands that are away from Fermi level in the general case. The influence of interlayer next nearest neighbor (NNN) interaction and interlayer bias are also discussed to fit the realistic graphene materials, which suggest the robust topological features of edge states in BLG systems. △ Less

Submitted 2 December, 2021; v1 submitted 17 September, 2021; originally announced September 2021.

Comments: 11 pages, 10 figures

Geometric influence on the net magnetic moment in LaCoO$_3$ thin films

Authors: T. Joshi, D. P. Belanger, Y. T. Tan, W. Wen, D. Lederman

Abstract: The different magnetic behaviors of LaCoO$_3$ films grown on LaAlO$_3$ and SrTiO$_3$ are related to the Co-O-Co bond angles and the constraints imposed on the Co-O bond lengths by the substrate geometries. Long-range magnetic order occurs below T ~ 90 K when the Co-O-Co bond angle is greater than 163 degrees, consistent with the behavior of bulk and nanoparticles forms of LaCoO$_3$. A LaAlO$_3$ su… ▽ More The different magnetic behaviors of LaCoO$_3$ films grown on LaAlO$_3$ and SrTiO$_3$ are related to the Co-O-Co bond angles and the constraints imposed on the Co-O bond lengths by the substrate geometries. Long-range magnetic order occurs below T ~ 90 K when the Co-O-Co bond angle is greater than 163 degrees, consistent with the behavior of bulk and nanoparticles forms of LaCoO$_3$. A LaAlO$_3$ substrate prevents magnetic long-range order at low temperatures near the film-substrate interface and collinear antiferromagnetic sublattices away from the interface. At low temperatures, the antiferromagnetically ordered sublattices are non-collinear in films grown on SrTiO$_3$ substrates, leading to a significant net moment. △ Less

Submitted 18 August, 2021; originally announced August 2021.

Comments: 28 pages, 8 figures, 6 supplementary figures

MSC Class: J.2

Scale-dependent irreversibility in living matter

Authors: Tzer Han Tan, Garrett A. Watson, Yu-Chen Chao, Junang Li, Todd R. Gingrich, Jordan M. Horowitz, Nikta Fakhri

Abstract: A defining feature of living matter is the ability to harness energy to self-organize multiscale structures whose functions are facilitated by irreversible nonequilibrium dynamics. While progress has been made in elucidating the underlying principles, what remains unclear is the role that thermodynamics plays in shaping these structures and their ensuing functions. Here, we unravel how a fundament… ▽ More A defining feature of living matter is the ability to harness energy to self-organize multiscale structures whose functions are facilitated by irreversible nonequilibrium dynamics. While progress has been made in elucidating the underlying principles, what remains unclear is the role that thermodynamics plays in shaping these structures and their ensuing functions. Here, we unravel how a fundamental thermodynamic connection between the physical energy dissipation sustaining a nonequilibrium system and a measure of statistical irreversibility (arrow of time), can provide quantitative insight into the mechanisms of nonequilibrium activity across scales. Specifically, we introduce a multiscale irreversibility metric and demonstrate how it can be used to extract model-independent estimates of dissipative timescales. Using this metric, we measure the dissipation timescale of a multiscale cellular structure - the actomyosin cortex - and further observe that the irreversibility metric maintains a monotonic relationship with the underlying biological nonequilibrium activity. Additionally, the irreversibility metric can detect shifts in the dissipative timescales when we induce spatiotemporal patterns of biochemical signaling proteins upstream of actomyosin activation. Our experimental measurements are complemented by a theoretical analysis of a generic class of nonequilibrium dynamics, elucidating how dissipative timescales manifest in multiscale irreversibility. △ Less

Submitted 12 July, 2021; originally announced July 2021.

Advanced calculations of x-ray spectroscopies with FEFF10 and Corvus

Authors: J. J. Kas, F. D. Vila, J. J. Rehr, C. D. Pemmaraju, T. S. Tan

Abstract: The real-space Green's function code FEFF has been extensively developed and used for calculations of x-ray and related spectra, including x-ray absorption (XAS), x-ray emission (XES), inelastic x-ray scattering, and electron energy loss spectra (EELS). The code is particularly useful for the analysis and interpretation of the XAS fine-structure (EXAFS) and the near-edge structure (XANES) in mater… ▽ More The real-space Green's function code FEFF has been extensively developed and used for calculations of x-ray and related spectra, including x-ray absorption (XAS), x-ray emission (XES), inelastic x-ray scattering, and electron energy loss spectra (EELS). The code is particularly useful for the analysis and interpretation of the XAS fine-structure (EXAFS) and the near-edge structure (XANES) in materials throughout the periodic table. Nevertheless, many applications, such as non-equilibrium systems, and the analysis of ultra-fast pump-probe experiments, require extensions of the code including finite-temperature and auxiliary calculations of structure and vibrational properties. To enable these extensions, we have developed in tandem, a new version FEFF10, and new FEFF based workflows for the Corvus workflow manager, which allow users to easily augment the capabilities of FEFF10 via auxiliary codes. This coupling facilitates simplified input and automated calculations of spectra based on advanced theoretical techniques. The approach is illustrated with examples of high temperature behavior, vibrational properties, many-body excitations in XAS, super-heavy materials, and fits of calculated spectra to experiment. △ Less

Submitted 24 June, 2021; originally announced June 2021.

Comments: 9 pages, 9 figures. Submitted to Journal of Synchrotron Radiation

Odd dynamics of living chiral crystals

Authors: Tzer Han Tan, Alexander Mietke, Junang Li, Yuchao Chen, Hugh Higinbotham, Peter J. Foster, Shreyas Gokhale, Jörn Dunkel, Nikta Fakhri

Abstract: Active crystals are highly ordered structures that emerge from the self-organization of motile objects, and have been widely studied in synthetic and bacterial active matter. Whether collective crystallization phenomena can occur in groups of autonomously developing multicellular organisms is currently unknown. Here, we show that swimming starfish embryos spontaneously assemble into chiral crystal… ▽ More Active crystals are highly ordered structures that emerge from the self-organization of motile objects, and have been widely studied in synthetic and bacterial active matter. Whether collective crystallization phenomena can occur in groups of autonomously developing multicellular organisms is currently unknown. Here, we show that swimming starfish embryos spontaneously assemble into chiral crystals that span thousands of spinning organisms and persist for tens of hours. Combining experiments, theory, and simulations, we demonstrate that the formation, dynamics, and dissolution of these living crystals are controlled by the hydrodynamic properties and natural development of embryos. Remarkably, living chiral crystals exhibit self-sustained chiral oscillations as well as various unconventional deformation response behaviors recently predicted for odd elastic materials. Our results provide direct experimental evidence for how nonreciprocal interactions between autonomous multicellular components may facilitate novel nonequilibrium phases of chiral active matter. △ Less

Submitted 3 March, 2022; v1 submitted 16 May, 2021; originally announced May 2021.

Comments: Main: 13 pages, 4 figures / Supplement: 47 pages, 18 figures / Fixed figure compatibility and references, Corrected affiliations

Microstructural and compositional design principles for Mo-V-Nb-Ti-Zr multi-principal element alloys: a high-throughput first-principles study

Authors: Zhidong Leong, Upadrasta Ramamurty, Teck Leong Tan

Abstract: Due to the vast compositional space of multi-principal element alloys (MPEAs), the rational design of MPEAs for optimized microstructures is difficult. Therefore, a high-throughput first-principles study of Mo-V-Nb-Ti-Zr, a refractory MPEA, was conducted to gain insights into the underlying microstructures. Using Monte-Carlo simulations powered by cluster expansion, we uncover the principles gover… ▽ More Due to the vast compositional space of multi-principal element alloys (MPEAs), the rational design of MPEAs for optimized microstructures is difficult. Therefore, a high-throughput first-principles study of Mo-V-Nb-Ti-Zr, a refractory MPEA, was conducted to gain insights into the underlying microstructures. Using Monte-Carlo simulations powered by cluster expansion, we uncover the principles governing the MPEA's microstructures across a large compositional space that includes non-equiatomic compositions and encompasses the constituent binaries, ternaries, and quaternaries. In the spirit of Hume-Rothery rules for complete solid solubility, we present a quantitative expression for predicting solid solution formation from the composition. Within a consistent framework, our results reproduce the microstructural observations (solid solution vs. segregation) from numerous experiments and provide microstructural predictions for unexplored regions in the compositional space. Our work illuminates the MPEA's microstructures in terms of the separation and clustering tendencies of the elements, presenting a set of simple but powerful design principles for future experiments to rationally design MPEAs with the desired microstructures for superior mechanical properties. △ Less

Submitted 4 May, 2021; originally announced May 2021.

Comments: 13 pages, 10 figures. Accepted by Acta Materialia

Journal ref: Acta Materialia 213 (2021) 116958

Electrically Tunable Four-Wave-Mixing in Graphene Heterogeneous Fiber for Individual Gas Molecule Detection

Authors: Ning An, Teng Tan, Zheng Peng, Chenye Qin, Zhongye Yuan, Lei Bi, Changrui Liao, Yiping Wang, Yunjiang Rao, Giancarlo Soavi, Baicheng Yao

Abstract: Detection of individual molecules is the ultimate goal of any chemical sensor. In the case of gas detection, such resolution has been achieved in advanced nanoscale electronic solid-state sensors, but it has not been possible so far in integrated photonic devices, where the weak light-molecule interaction is typically hidden by noise. Here, we demonstrate a scheme to generate ultrasensitive down-c… ▽ More Detection of individual molecules is the ultimate goal of any chemical sensor. In the case of gas detection, such resolution has been achieved in advanced nanoscale electronic solid-state sensors, but it has not been possible so far in integrated photonic devices, where the weak light-molecule interaction is typically hidden by noise. Here, we demonstrate a scheme to generate ultrasensitive down-conversion four-wave-mixing (FWM) in a graphene bipolar-junction-transistor heterogeneous D-shaped fiber. In the communication band, the FWM conversion efficiency can change steeply when the graphene Fermi level approaches 0.4 eV. In this condition, we exploit our unique two-step optoelectronic heterodyne detection scheme, and we achieve real-time individual gas molecule detection in vacuum. Such combination of graphene strong nonlinearities, electrical tunability, and all-fiber integration paves the way toward the design of versatile high-performance graphene photonic devices. △ Less

Submitted 8 April, 2021; originally announced April 2021.

Journal ref: Nano Letters 20 (2020) 6473-6480