Mesoscale and Nanoscale Physics
Modified Low-Temperature Scanning Tunneling Microscope for Ultrafast Pump-Probe Spectroscopy
Vibhuti N. Rai, Junyoung Sim, Nils Bogdanoff et al. (+7 more)
Combining scanning tunneling microscopy (STM) with terahertz pulses (THz-STM) enables ultrafast dynamics of
phonons,
spins, and charge carriers to be probed with atomic-scale spatial and sub-picosecond temporal resolution. However, coupling THz radiation into a low-temperature STM junction presents some technical challenges as it requires optical access for
laser illumination while maintaining junction stability. Instead of designing a completely new STM head with customized optical access and optics within the ultra-high
vacuum chamber, we modified a Besocke "Beetle" style STM with minimal changes of the cryogenic radiation shields. Despite the given geometrical conditions, we achieved efficient coupling of THz and optical pulses to the STM junction while maintaining temperatures below 6 K. We designed the optical setup on a separate
laser table, starting with femtosecond
laser pulses that are used to generate THz pulses in a LiNbO$_3$
crystal. We show the obtained THz pulse shapes and determine the effective time resolution using cross-correlation measurements. We further demonstrate the stable performance of the modified STM by measuring THz-induced tunneling currents from monolayer molybdenum disulfide (MoS$_2$) grown on Au(111). The resulting current maps resolve atomic-scale contrast revealing a point defect. The measurements confirm efficient THz coupling and stable low-temperature STM operation with atomic resolution.
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All authors Vibhuti N. Rai, Junyoung Sim, Nils Bogdanoff, Sergey Trishin, Florian Faaber, Paul Wiechers, Caroline Firschke, Tobias Kampfrath, Christian Lotze, Katharina J. Franke
Soft Condensed Matter
Nucleosome simulations suggest mechanisms of electrostatically-driven mesoscale chromatin evolution
Siddhartha G. Jena
Nucleosomes are structures made up of
proteins called histones that bind and compact DNA, driving the mesoscale organization of the chromatin
polymer. Although histone
proteins have diversified over evolutionary time, their contributions to the corresponding diversification of chromatin structure are poorly understood. Here, we mine
protein databases for histones and create in silico nucleosomes for 3241 organisms spanning $>$1.5B years of
evolution. Using a combination of electrostatic calculations and coarse-grained molecular dynamics simulations, we reveal extensive biophysical diversification of the nucleosome unit. Finally, we perform coarse-grained oligonucleosomal simulations on a subset of evolutionarily and biophysically divergent nucleosomes, demonstrating dramatic differences in bulk phase behavior of chromatin. Taken together, our results suggest a paradigm in which histones may have evolved to facilitate particular types of mesoscale chromatin behavior.
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Statistical Mechanics
Channel concentration of critical quantum geometry
Qian-Rui Lee and Daw-Wei Wang
The
quantum metric quantifies the total ground-state response along a parameter direction, but does not resolve how excitations share that response. We define channel concentration (CC) as the sum of squared normalized response weights over specified excitation channels, such as momentum blocks. An exact finite-size
theorem yields thermodynamic CCs of 2/3 for the field response of the critical transverse-field Ising model and 1/3 for the half-filled XX pairing response, despite the same leading metric scaling. In finite-size approaches to the XY Lifshitz point, field and anisotropy perturbations yield different concentrations despite a common limiting
Hamiltonian with quadratic dispersion. In a
unitary 1+1-dimensional conformal field theory (CFT) on a circle, we consider a nondegenerate
vacuum in a fixed sector perturbed by one spatially integrated scalar primary. We derive complete zero-momentum energy-level response weights, including descendants. For scaling dimension $0<\Delta<3/2$, these weights determine the normalized response distribution and an exact universal concentration function. The expression reproduces the exact Ising
lattice limit 2/3 and gives approximately 0.8515 for the three-state Potts thermal field, compared with approximately 0.800 from an exponent-only approximation. Finite-size interacting calculations compare concentrations and ranked response weights over many-body energy levels. These exact
benchmarks show which response distinctions total metric scaling misses and guide comparisons with finite-size interacting spectra.
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Strongly Correlated Electrons
Staged emergence of anomalous Hall transport in a correlated uranium Weyl semimetal
Sabin Regmi, Shuxiang Zhou, Chandan K. Singh et al. (+9 more)
Understanding how electronic correlations reshape topological states remains a central challenge in
quantum materials. Here we investigate the uranium ferromagnet UPS using magnetotransport, angle-resolved photoemission spectroscopy, thermodynamic measurements, and first principles calculations. Resonant photoemission reveals narrow U-$5f$ spectral weight at the Fermi level coexisting with broad incoherent states, consistent with the itinerant/localized duality characteristic of uranium $5f$ electrons. The anomalous Hall conductivity reaches approximately $4.5\times10^{2}\,\Omega^{-1}\mathrm{cm}^{-1}$, yet does not simply follow the ordered
magnetic moment. Temperature dependent photoemission reveals relatively little change across $T_C=118$~K, followed by a pronounced redistribution of low-energy $5f$ spectral weight below approximately 90~K. First-principles calculations identify a
symmetry protected Weyl crossing with pronounced Berry
curvature and yield an intrinsic anomalous Hall conductivity of approximately $9.6\times10^{2}\,\Omega^{-1}\mathrm{cm}^{-1}$. These results demonstrate that
magnetic order, correlated electronic reconstruction, and anomalous Hall transport develop over distinct but overlapping temperature ranges, revealing how strong correlations reshape topological transport in a uranium Weyl semimetal.
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All authors Sabin Regmi, Shuxiang Zhou, Chandan K. Singh, Alexei Fedorov, Jonathan Denlinger, Zeyu Ma, Yidi Wang, Jennifer E. Hoffman, Peter M. Oppeneer, Dariusz Kaczorowski, Tomasz Durakiewicz, Krzysztof Gofryk
Materials Science
Face-to-face anneal temperature controls lattice parameter in Ta(C,N) virtual substrates for AlGaN power electronics
Noah Zahn, Julia L. Martin, Michelle A. Smeaton et al. (+3 more)
Tantalum carbide (TaC) thin film ”virtual” substrates are a highly desirable material for $\text{Al}_{0.5}\text{Ga}_{0.5}\text{N}$ vertical power electronics devices due to
lattice matching, thermal expansion matching, and metallic conductivity. However, the material has not been demonstrated to support $\text{Al}_{x}\text{Ga}_{1-x}\text{N}$ layers of variable composition $x$, limiting the range of device applications. We present a method to achieve tunable rock salt $\text{Ta}\text{C}_{x}\text{N}_{1-x}$ virtual substrates via a face-to-face annealing of TaC thin films in an $\text{N}_2$ atmosphere. The results suggest that annealing temperatures below $1600\,^{\circ}\text{C}$ promote partial uptake of nitrogen onto carbon and anion vacancy sites to form rock salt $\text{Ta(C,N)}$ with intermediate anion compositions. At temperatures $\ge 1600\,^{\circ}\text{C}$, nitrogen primarily occupies the anion sublattice and the crystalline quality and surface morphology simultaneously degrade coincident with the formation of secondary phases. This study demonstrates the growth and processing parameters necessary to make tunable
lattice constant virtual substrates for $\text{Al}_{x}\text{Ga}_{1-x}\text{N}$ from $x = 0.5\text{-}1$, enabling vertically conducting power electronic devices with reduced defect density at high Al-content.
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All authors Noah Zahn, Julia L. Martin, Michelle A. Smeaton, Renae Gannon, Henry Garland, M. Brooks Tellekamp
Statistical Mechanics · Cross-listed from hep-th
Measuring correlations using local and nonlocal quenches
Alexey G. Mikhaylenko and Andrew G. Semenov
We present a theoretical proposal for measuring correlation functions in a
quantum field system based on the use of
quantum quenches. Using the examples of massive and massless scalar field theories, we show that a short-term perturbation of the system leads to a dependence of the further
evolution of the average field on the initial state's correlation functions. Considering two types of perturbations, namely local and nonlocal quenches, we show which correlation functions can be measured in each of these cases. The proposed procedure can be applied to study non-Gaussian correlations.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Overcoming the Hong-Ou-Mandel interference limitation for the second photon from a two-photon cascade
Raphael Joos, Michal Vyvlecka, Tim Strobel et al. (+8 more)
Quantum emitters such as
semiconductor quantum dots can provide entangled
photon pairs emitting from a system of cascaded states. However, the resulting temporal correlation between the two
photons from the three-level ladder system has been shown to set a limit on the achievable two-
photon interference. In this work, we show that such limitation, for
photons emitted by the second transition, is only due to reduced temporal overlap at the interference beam splitter. We investigate this theoretically and experimentally by determining time-resolved four-
photon coincidences between two successively emitted
photon pairs. Post-emission synchronization shows the recovery of maximum interference visibility; in prospective
quantum networks this could be achieved via deterministic
quantum memories.
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All authors Raphael Joos, Michal Vyvlecka, Tim Strobel, Benjamin Breiholz, Furkan Aglarci, Ponraj Vijayan, Hans-Georg Babin, Arne Ludwig, Michael Jetter, Simone L. Portalupi, Peter Michler
Strongly Correlated Electrons
Quantum-interference-driven orbital density wave and high-temperature superconductivity in trilayer nickelates
Youichi Yamakawa and Hiroshi Kontani
Intertwined charge-density-wave (CDW) and
spin-density-wave (SDW) orders are a hallmark of high-temperature superconducting multilayer nickelates. In trilayer La4Ni3O_{10}, charge correlations develop at temperatures above the onset of long-range
spin order, and the characteristic ordering wavevectors satisfy $Q_{cdw} \approx 2Q_{sdw}$. Here, using a density-wave equation with vertex corrections, we show that
quantum interference between short-range SDW fluctuations at $q \approx Q_{sdw}$ on the outer NiO2 layers generates an inter-outer-layer bond order at $Q_{cdw} \approx 2 Q_{sdw}$. This bond order induces a pronounced inner-layer-centered orbital order, with antiphase modulations of the Ni $d_{3z^2-r^2}$ and $d_{x^2-y^2}$ occupations, producing strong orbital polarization but only weak total charge modulation. This intertwined bond-and-orbital order accounts for the layer-selective electronic reconstruction inferred from NMR/NQR and is consistent with Raman spectroscopy and scanning tunnelling microscopy measurements. The same orbital and
spin fluctuations also cooperate to stabilize $s_{\pm}$-wave superconductivity through $M_z$ mirror-parity selection rules. Our results provide a unified microscopic framework for intertwined density-wave order and high-Tc superconductivity in multilayer nickelates.
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Materials Science
Scandium diboride: a semi-metallic, lattice, thermally matched substrate for vertical AlGaN power electronics
MVS Chandrashekhar, Daniel Joel Harrison, Ahamed Raihan et al. (+22 more)
We report the properties of hexagonal (space group P6/mmm) scandium diboride ($\mathrm{ScB}_2$) single
crystals grown by a
laser diode floating zone method at growth rates of ~1mm/hr under B-rich conditions with (002) rocking curve widths $\Delta\omega$=38” approaching the quality of commercial SiC/GaN substrates.
Lattice expansion measurements reveal matching to $\mathrm{Al_{0.55}Ga_{0.45}N}$ with a coefficient of thermal expansion ~5ppm/K at typical AlGaN growth temperatures, enabling thick AlGaN layers for ultra-wide bandgap (UWBG) power electronics >1kV. We measure semi-metallic room temperature resistivity ~15$\mu\Omega$ cm, climbing to ~93$\mu\Omega$ cm at 773K with a $T^2$ dependence effectively eliminating substrate parasitic resistance, the limiting factor in exploiting the full potential of UWBG. The Debye temperature $\theta_{D,ScB_2}$ from heat capacity and
lattice expansion is ~850K well matched to $\theta_{D,ScB_2}$, but lower than the 1100K measured for Sc-rich growth conditions. We discuss Debye matching as a key substrate codesign criterion providing significant overlap in
phonon modes for heat removal and thermal matching during AlGaN growth. The competitive thermal conductivity at room temperature 53W/mK is half that from full first principles calculations, a discrepancy we attribute to the presence of Sc-vacancies generated by B-rich growth. while the resistivity is ~2x the theoretical value, indicating that both electrons and
phonons play equal role in thermal transport. The smooth ~2.5nm rms roughness surface enables advanced heat removal modalities through engineered
phonon bridges and
phonon polaritons in $\mathrm{ScB}_2$/AlGaN interfacial
heterostructures, potentially allowing ~10-100x increase in power handling over state-of-the-art GaN/SiC.
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All authors MVS Chandrashekhar, Daniel Joel Harrison, Ahamed Raihan, Astrid D. Kengne, R. Shipra, Han Xie, Tasnia Jabin, Monte Hendrix, Ethan Scott, Roshan S. Annam, Sharad Mahatara, Evan N. Crites, Allana G. Iwanicki, Luke J. Meiler, Maxime Siegler, Renae N. Gannon, Steven R Spurgeon, Ashutosh Giri, Rajeswari Kolagani, Joshua A. Burrow, Stephan Lany, Patrick Hopkins, Tyrel M. McQueen, Michael Spencer, Satya Khushwaha
Strongly Correlated Electrons
Anisotropic Surface State Band Splitting and Low Energy Flat Bands in 3d Correlated Topological Kondo Insulator Candidate FeSb$_2$
Ziling Cao, Jie Pang, Yu Xu et al. (+22 more)
FeSb$_2$ is a correlated narrow-gap
semiconductor that has often been discussed as a $3d$-electron Kondo
insulator candidate and exhibits a low-temperature resistance plateau with possible surface-dominated conduction. We carried out a systematic high-resolution
laser-based angle-resolved photoemission spectroscopy (ARPES) study of FeSb$_2$ to investigate its electronic structure. The surface states around the zone center show clear anisotropic splitting. When the temperature is lowered into the resistance plateau regime ($<6\,\mathrm{K}$), the surface states remain robust, but their photoemission peaks become much sharper and gain spectral weight. Two distinct flat-band-like features are observed at low energy. One is located at $\sim$127 meV below the Fermi level, which exists only along a specific high-
symmetry direction, while the other is located at $\sim$70 meV below the Fermi level and is present along all the measured momentum cuts around the zone center. These results provide new information to understand the renormalization effects, the resistance plateau, and the topological nature of FeSb$_2$.
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All authors Ziling Cao, Jie Pang, Yu Xu, Taimin Miao, Bo Liang, Wenpei Zhu, Neng Cai, Mingkai Xu, Jumin Shi, Yingjie Shu, Yiwen Chen, Jiachen Wang, Shenjin Zhang, Fengfeng Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Zhihai Zhu, Xintong Li, Hanqing Mao, Guodong Liu, Zuyan Xu, Youguo Shi, Lin Zhao, X. J. Zhou
Statistical Mechanics
Navier-Stokes hydrodynamics near the critical point with out-of-equilibrium modes
Md Hasanujjaman, Golam Sarwar, Mahfuzur Rahaman et al. (+2 more)
We investigate how slow out-of-
equilibrium modes (OEM), introduced to extend the regime of validity of hydrodynamics near the critical point, fundamentally reshape the power spectrum of dynamical density fluctuations. We have used the equation of motion of slow modes for the situation when the extensive nature of thermodynamics is not altered due to the introduction of OEM. We find that the extensivity condition puts an extra constraint on the coupling of OEM with the four divergence of velocity. In the absence of OEM, the dynamic structure factor exhibits three Lorentzian peaks, one at zero frequency ($\omega$), called Rayleigh peak and the other two called Brillouin peaks located symmetrically about $\omega=0$. When the system is away from the critical point the inclusion of the OEM preserves the
symmetry of the distributions but all the peaks acquire reduced widths and the Brillouin peaks adopt unequal heights. Irrespective of the value of OEM (zero or nonzero) the Brillouin peaks vanish near the critical point. The width of the Rayleigh peak substantially reduced in presence of OEM. Such reductions of the widths in presence of the OEM indicates the reduction in the decay rate of the fluctuation which leads to slowing down of decay of the fluctuations, a distinctive feature of the critical point.
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All authors Md Hasanujjaman, Golam Sarwar, Mahfuzur Rahaman, Abhijit Bhattacharyya, Jane Alam
Superconductivity
Electronic Reconstruction Towards Topological Superconductivity in FeTe
Hongtao Rong, Yang Ge, Zi-Jie Yan et al. (+13 more)
The recent discovery of intrinsic superconductivity in stoichiometric FeTe films has renewed interest in the Te-rich end member of the iron chalcogenides for studies of unconventional and topological superconductivity, yet its intrinsic electronic structure remains unresolved. In this work, we combine molecular beam epitaxy, angle-resolved photoemission spectroscopy (ARPES), electrical transport measurements, density functional theory, and embedded dynamical mean-field theory to track the electronic reconstruction of 20-unit-
cell FeTe films as Te annealing progressively removes excess interstitial Fe and drives the system from an antiferromagnetic metal to a
superconductor. We find that this
evolution is accompanied by recovered quasiparticle coherence, reduced electronic correlations, a Lifshitz transition, and a topological phase transition, yielding dxy-dominated hole and electron pockets that favor inter-pocket scattering. In addition, a shallow dxz/dyz-derived hole band located about 2 meV below the Fermi level may provide an incipient-band pairing channel, while scattering between the two electron pockets at M may offer additional pairing channels. High-resolution polarization-dependent
laser ARPES measurements further reveal a topological surface state whose circular dichroism is consistent with the expected orbital-angular-momentum texture of stoichiometric FeTe. These results establish the intrinsic low-energy electronic structure of superconducting FeTe and identify the electronic states most relevant to superconductivity. The coexistence of intrinsic superconductivity and a topological surface state establishes stoichiometric FeTe as a promising platform for exploring topological superconductivity and possible Majorana bound states.
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All authors Hongtao Rong, Yang Ge, Zi-Jie Yan, Haoran Lin, Bing Xia, Xiaoda Liu, Zihao Wang, Pu Xiao, Lok-Kan Lai, Stephen Paplini, Jiatao Song, Jiangang Yang, Peter J. Hirschfeld, Shuolong Yang, Jiabin Yu, Cui-Zu Chang
Superconductivity
Generalized conditions for odd-frequency pairing in superconducting systems
Florian Kayatz, Annica M. Black-Schaffer and Jorge Cayao
Odd-frequency superconducting pairing has been predicted to arise in many systems and is known to lead to phenomena such as paramagnetic Meissner response and long-range superconducting proximity effect. Here, we provide generalized necessary and sufficient conditions for odd-frequency pairing appearing in any superconducting system, from bulk
superconductors to superconducting hybrid structures. This generalizes an earlier first-order expression in multiband bulk
superconductors to all superconducting systems and to all orders, in both order parameter and frequency. We then apply the derived conditions to several systems, including superconducting-ferromagnet and superconducting Josephson junctions, as well as a transition metal dichalcogenide monolayer proximitized by a conventional
superconductor, where the generalized conditions are used to understand the properties of the superconducting state.
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Superconductivity
Interface engineering of spin triplet Cooper pairs for spin-valve implementation
Debashree Nayak, Abhisek Sahoo, Pratap Kumar Sahoo et al. (+1 more)
Spin singlet Cooper pairs can be converted into equal-
spin triplet pairs at a
superconductor/heavy-metal interface under suitable conditions. Under current carrying conditions, these triplet correlations can give rise to a non
equilibrium spin moment in the heavy metal through the predicted supercurrent
spin-Hall effect. Here we demonstrate that this current induced triplet
spin moment, in conjunction with the
magnetic moment of a ferromagnetic layer, can enable a
magnetic spin-valve response in Nb/Pt/Ni/Pt/Nb vertical nano-devices. The magnitude of this
spin-valve effect depends on the efficiency of singlet-triplet Cooper pair conversion at the Nb/Pt interface. In order to facilitate efficient triplet generation, we deliberately introduced interfacial roughness to introduce finite Rashba
spin-orbit coupling at the Nb/Pt interface and an out-of-plane component of
magnetic moment at the Ni interface. In contrast, no discernible
spin-valve response was observed in devices with smooth interfaces within measurement resolutions. Since the
magnetic moment of the Ni layer and the current-induced triplet
spin moment in the Pt layer are independently switchable using a
magnetic field and bias current, respectively, the
spin valve can be controlled via either parameters. These results demonstrates a novel approach to directly utilizing the
spin polarized triplet Copper pairs in superconducting spintronic applications.
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All authors Debashree Nayak, Abhisek Sahoo, Pratap Kumar Sahoo, Kartik Senapati
Materials Science
III-V antiphase boundaries are not generated by Si or Ge substrate step edges
Charles Cornet, Sreejith Pallikkara Chandrasekharan, Audrey Gilbert et al. (+7 more)
We critically review recent experimental and theoretical advances on the valence- and structure-mismatched heteroepitaxy of III-V
semiconductors on group-IV substrates. We examine key aspects including wetting behavior, atomic configurations at the hetero-interface, substrate passivation, and the stability of antiphase boundaries (APBs). By synthesizing these findings with pioneering studies, we propose a refined description of antiphase boundaries formation. Our analysis shows that hetero-interface formation is dictated by substrate terrace reconstruction, demonstrating that APBs are not generated at monoatomic step edges. This generalized III-V/IV growth framework provides new insights for the integration of III-V
semiconductors on group-IV platforms and, more broadly, for valence-mismatched heteroepitaxy.
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All authors Charles Cornet, Sreejith Pallikkara Chandrasekharan, Audrey Gilbert, Milan Silvestre, Rozenn Bernard, Pascal Turban, Gilles Patriarche, Eric Tournie, Laurent Pedesseau, Jean-Baptiste Rodriguez
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Broadband Single-Particle Absorption Circular Dichroism Reveals Chiroptical Heterogeneity in Gold Helicoids
Rohit B. Raj, Susanna Bertuletti, Jeong Hyun Han et al. (+7 more)
Quantitative measurements of absorption circular dichroism (CD) at the single-particle level are essential for understanding how individual chiral nanostructures dissipate optical energy, yet broadband absorptance measurements remain experimentally challenging. Here, we introduce a wavelength-tunable integrating-sphere microscope that determines the absorptance of individual nanoparticles under right- and left-circularly polarized illumination through direct optical energy balance, enabling broadband measurement of the absorption dissymmetry factor, gabs. Measurements of achiral gold nanospheres and strongly anisotropic gold nanorods establish the apparent absorption CD baseline and demonstrate minimal detectable linear-dichroism-to-circular-dichroism (LD-to-CD) leakage under the experimental conditions. Applying this approach to 87 chiral gold helicoids synthesized using L-glutathione (L-helicoids) and 96 synthesized using D-glutathione (D-helicoids) reveals mean particle-level gabs values of opposite sign, with a statistically significant difference between the two populations. Individual particles nevertheless exhibit pronounced heterogeneity in response sign, magnitude, spectral position, and line shape. More than one-third of the particles in each population display opposite-sign absorption CD responses relative to their population-average tendency. Correlative SEM analysis of the L-helicoid population further shows that opposite-sign responses persist among isolated particles exhibiting the characteristic projected helicoid morphology, indicating that aggregation and gross differences in projected morphology are insufficient to explain the observed heterogeneity. These results establish broadband single-particle absorption CD spectroscopy as a direct probe of absorptive chiroptical heterogeneity and reveal particle-specific responses obscured by ensemble averaging.
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All authors Rohit B. Raj, Susanna Bertuletti, Jeong Hyun Han, Sepin Cho, Debapriya Pal, Nick Feldman, Ki Tae Nam, Willem L. Noorduin, A. Femius Koenderink, Erik C. Garnett
Superconductivity · Cross-listed from quant-ph
Superconducting qubit based on altermagnets
Xue-Feng Pan, Xin-Lei Hei, Franco Nori et al. (+1 more)
Altermagnets, characterized by vanishing net magnetization and momentum-dependent
spin splitting, provide a promising platform for next-generation Josephson devices. Here, we exploit the Josephson effect in
superconductor-altermagnet-
superconductor junctions and show how to engineer prescribed current-phase relations by device design. Based on these programmable Josephson potentials utilizing altermagnetism, we propose a new class of superconducting
qubits that combine large anharmonicity with enhanced robustness against decoherence via coherent two-Cooper-pair tunneling. We show that in the $2\phi$-junction regime, this kind of
qubit is intrinsically protected against both charge and flux noise due to parity protection.
Magnetic flux can be used to precisely control the
qubit and, under appropriate bias, this architecture further suppresses charge and flux noise. Our results establish altermagnets as a versatile platform for Josephson-potential engineering and open a new route toward high-performance superconducting
qubits combining high coherence, large anharmonicity, and broad tunability.
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All authors Xue-Feng Pan, Xin-Lei Hei, Franco Nori, Peng-Bo Li
Statistical Mechanics
Optimal probing scale for current fluctuations in a Brownian gyrator
Badr Farih
A driven colloidal rotor sustains a circulating current whose fluctuations one would like to bound. Any such bound rests on how strongly the current responds to a perturbation and on how much extra dissipation that perturbation costs, so there is a well-posed question of where to push: the response per unit Onsager-Machlup cost depends on the radius at which the probe acts, and is maximised at a definite one. We answer this for the Brownian gyrator and a quadrupolar shear under a Gaussian envelope, a probe chosen so that linear response is exactly blind to it at every observation window, so that the entire signal is second order. The problem separates: the cost is radial and does not see the circulation, while the response lives in the $m=3$ angular sector, where the resolvent reduces to Kummer's equation with $b=4$ and the susceptibility is a hypergeometric function of the envelope width. Maximising the ratio gives the optimal probing radius in closed form. It is set by whichever of the system's two clocks is faster: for weak driving $r^*=1.1264\sqrt{D/\gamma}$, the thermal radius of the trap, and for strong driving $r^*=1.5563\sqrt{D/\Omega}$, the distance diffused in one radian of rotation, with the trap stiffness dropping out entirely. The crossover is at $\Omega=\gamma$. Both limits, and the prefactors, are confirmed against direct simulation.
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Quantum Gases
From harmonic to sound-like oscillations in a quantum gas confined in a gravity compensated shell trap
Matthieu Cassus, Rishabh Sharma, Maxime Pesche et al. (+4 more)
We study the center of mass oscillations of a
quantum gas in a shell shaped trap in the presence of a vertical force opposed to
gravity. The measured harmonic frequency at the bottom of the shell is compared with an analytical formula for the trap potential including corrections beyond the rotating wave approximation. When
gravity is partially compensated, a quartic correction to the harmonic motion has to be included due to the shell
curvature. As
gravity is nearly canceled, the
quantum gas occupies a large fraction of the lower hemisphere. Driving the center of mass induces internal excitations in the
quantum gas, whose time
evolution is governed by the presence of sound waves. Relaxation processes induce a strong damping of the center of mass oscillation in this limit.
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All authors Matthieu Cassus, Rishabh Sharma, Maxime Pesche, Laurent Longchambon, Thomas Badr, Romain Dubessy, Hélène Perrin
Mesoscale and Nanoscale Physics
Observation of Kondo Effect in Rhombohedral Graphene Superlattices
Xin Liao, Qing Yin, Huiwen Wang et al. (+10 more)
Kondo effect in strongly correlated systems arises from the antiferromagnetic coupling between itinerant conduction electrons and localized
magnetic moments, giving rise to a variety of exotic
quantum phenomena. Two-dimensional moiré superlattice systems provide a highly tunable platform featuring topological flat bands, where Wannier orbitals are spatially confined by the periodic moiré potential and serve as localized
magnetic moments, enabling the observable Kondo effect. Here we experimentally demonstrate Kondo interactions in hexalayer rhombohedral
graphene moiré superlattices through magneto-transport and temperature-dependent measurements. With increasing
magnetic field, the magnetoresistance exhibits an increase-decrease transition across a critical field B_c, while the Hall resistance R_xy undergoes a sign reversal near B_c. Moreover, as temperature decreases, the longitudinal resistance R_xx first increases logarithmically and then decreases following a T^2 behavior, indicating a transition to heavy
fermion liquid. These behaviors can be consistently explained by the breakdown of Kondo singlets induced by either
magnetic field or temperature, which liberates carriers previously bound to localized moments, thereby enhancing conductivity and altering the dominant carrier type. Furthermore, our results demonstrate that the Kondo interaction can be continuously tuned by both carrier density n and displacement electric field D, and suggest the emergence of a Kondo insulating state. Our findings provide deep insight into the Kondo effect in moiré engineered flat-band systems, paving the path for exploring exotic correlated
quantum phases.
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All authors Xin Liao, Qing Yin, Huiwen Wang, Jing-Wei Dong, Jun-Xi Chen, Si-Li Wu, Cai-Zhen Li, Guowei Lyu, Kenji Watanabe, Takashi Taniguchi, Wei Jiang, Yu-Gui Yao, Zhi-Min Liao
Statistical Mechanics
Lowest-known Energy Configuration of $N=100\,000$ Coulomb Charges in a Disk: Breaking the $10^{5}$ Barrier
Georgiy K. Lavrov and Eduard G. Nikonov
We report the first calculation of the lowest-known energy configuration for $N=100\,000$ classical point charges confined to a disk and interacting via the $1/r$ Coulomb potential - a system size never before achieved for the Thomson problem in a disk, more than doubling the previous record of $N=40\,886$ reported by Amore and Zarate. An adaptive defect-targeting subdomain optimization strategy yields an approximately linear growth of the wall-clock time per cycle with $N$; for $N=100\,000$ a single $24$-core CPU workstation without GPU acceleration required $\approx31$ hours. The energy $E_{\min}=7.80466624157\times10^{9}$ deviates from the standard empirical asymptotic expansion by only $2.525\times10^{-7}$. We demonstrate that this remarkable agreement provides a stringent test of the rigorous next-order asymptotic theory for Riesz interactions, while the residual deviation is consistent with an $O(N^{4/3})$ boundary-layer correction whose absence from the standard fitting basis biases the empirical $N^{3/2}$ coefficient away from its exact crystalline value, thereby tying the deviation to the two-dimensional crystallization
conjecture. Bond-orientational order analysis reveals a polycrystalline bulk threaded by radial grain boundaries, establishing a new
benchmark for two-dimensional Coulomb systems.
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Strongly Correlated Electrons
Rapidly prototyping kagome flat band physics with acoustic metamaterials
Jiatong Yang, Benjamin H. November, Yiting Huang et al. (+3 more)
Flat bands with vanishing group velocity and quenched kinetic energy provide fertile ground for correlated states and exotic phenomena such as unconventional superconductivity. Yet, engineering and characterizing flat bands in
quantum materials is time-consuming and costly, limiting the exploration of the vast design space of possible flat band systems. Acoustic metamaterials offer an accessible alternative: they can be easily simulated, cheaply fabricated, and quickly measured. Here we present a complete workflow to rapidly prototype flat band systems using acoustic metamaterials. Our design directly implements a tight-binding model using air cavities as
lattice sites connected by channels that control hopping, allowing it to generalize to diverse
lattice geometries. Using the kagome
lattice as a proof-of-concept, we demonstrate excellent agreement between tight-binding theory, finite-element simulations, and experimental measurements. We then design a family of extended kagome
lattices whose added sites cancel successively longer-range hopping, flattening the flat band. With fabrication and measurement requiring hours rather than months and a total cost orders of magnitude lower than
quantum materials, our approach enables rapid iteration through candidate
lattices, facilitating the discovery of new flat band physics in
quantum materials.
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All authors Jiatong Yang, Benjamin H. November, Yiting Huang, S. Minhal Gardezi, Harris Pirie, Jennifer E. Hoffman
Strongly Correlated Electrons
Infrared evidence for strong $C_{3}$ symmetry breaking in 1$T$-TiSe$_{2}$
Esther van Grondelle, Kai Rossnagel, Jasper van Wezel et al. (+1 more)
The interplay between
lattice and electron degrees of freedom gives rise to competing ordered states in
quantum materials, which can lead to a series of subsequent
symmetry breaking transitions. While the differences are often subtle, these phases can be distinguished by their remaining point group
symmetries. Here, we use infrared optical spectroscopy to probe
symmetry breaking at the charge density wave transition of 1$T$-TiSe$_{2}$. We uncover a previously unobserved splitting of a doubly degenerate $E_u$ optical
phonon at $T_{\mathrm{CDW}}\approx$ 190 K that constitutes direct evidence for the breaking of three-fold rotational
symmetry. Our finding rules out proposals where the CDW transition to a low temperature chiral or nematic phase takes place through an intermediary state that preserves three-fold
symmetry. The energy difference between the two former $E_{u}$ partners can only be explained by large $C_{3}$ breaking distortions of the same order of magnitude as previously observed changes in bond lengths, suggesting that $C_{3}$
symmetry breaking plays a dominant role in the CDW transition. The linewidth of the single
phonon mode above $T_{\mathrm{CDW}}$ could be consistent with a fluctuating state where three-fold
symmetry is also broken.
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All authors Esther van Grondelle, Kai Rossnagel, Jasper van Wezel, Erik van Heumen
Strongly Correlated Electrons
Raman Scattering Evidence for Fluctuating Kagome-Plane Moments in $\mathrm{B} \parallel [111]$ in Pr$_2$Zr$_2$O$_7$ pyrochlore
Yuanyuan Xu, Huiyuan Man, Nan Tang et al. (+6 more)
The exotic
magnetic properties of the pyrochlore Pr$_2$Zr$_2$O$_7$ are determined by the coupling of
spin, orbital, and
lattice degrees of freedom. Magnetism in this material originates from the non-Kramers Pr$^{3+}$ ion, and the exotic behavior has been discussed both in the framework of dipole-quadrupole properties of
magnetic moments and disorder splitting the non-Kramers doublet. We use magneto-Raman spectroscopy to probe the
crystal electric field (CEF) excitations of Pr$^{3+}$ in
magnetic fields up to 14 T applied along the [100] and [111] crystallographic directions at 2 K. For $\mathrm{B}\parallel[100]$, the field
evolution of the Raman active
crystal field modes is quantitatively described by conventional Zeeman splitting of the Pr$^{3+}$ ground state doublet, including the thermally populated upper Zeeman branch at elevated temperature. For $\mathrm{}{B}\parallel[111]$, the spectra separate into responses from the triangular and kagome sublattices, and the CEF excitations of Pr$^{3+}$ on the triangular
lattice exhibit the expected Zeeman shift consistent with full moments polarization. In contrast, the CEF excitations of Pr$^{3+}$ on the kagome
lattice do not split as expected and instead broaden strongly with increasing field. This behavior is inconsistent with a static polarized configuration and is captured phenomenologically by a motional-narrowing description in which the kagome plane moments fluctuate between Zeeman-split levels on a meV timescale. This result offers a natural explanation for the reduced magnetization observed in $\mathrm{}{B}\parallel[111]$ and provides further evidence of the dipole-quadrupole properties of
magnetic moments. It highlights Raman scattering as a sensitive probe of exotic
spin-orbital dynamics in frustrated magnets.
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All authors Yuanyuan Xu, Huiyuan Man, Nan Tang, Li Xiang, Sami Muhammad, Komalavalli Thirunavukkuarasu, Dmitry Smirnov, Satoru Nakatsuji, Natalia Drichko
Superconductivity
New theoretical model of the dynamic anomalies in HTc superconductors
J. Sosnowski
New theoretical model of the dynamic current-voltage characteristics anomalies in HTc
superconductors in slowly varying
magnetic field has been proposed. The model is based on an analysis in details of the
magnetic flux penetration into HTc superconducting slab in such case. The comparison of model with previous experimental data has been presented. Theoretical analysis resulting from a new solution of
diffusion equation is given as well as other one based on phenomenological critical state model.
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Statistical Mechanics
Random-matrix and transport frequencies in eigenstate spectral functions
Kadir Çeven, Rohit Patil, Marcos Rigol et al. (+1 more)
The fact that generic isolated many-body
quantum systems thermalize is understood using the eigenstate thermalization hypothesis (ETH). In recent years, there has been much interest in the behavior of the ETH spectral functions, which characterize the smooth dependence of the variance of the off-diagonal
matrix elements of observables on the associated energy and frequency, and whose low-frequency part contains information about the long-time dynamics. In finite systems described by the ETH, the spectral functions are expected to exhibit plateaus below a characteristic frequency $\omega^{}_{\mathrm{ETH}}$. In this regime, the statistics of the
matrix elements of observables are expected to be described by random
matrix theory. Related frequencies that have been studied in the literature are $\omega^{}_{\mathrm{SFF}}$, which controls the onset of random-
matrix behavior in the spectral form factor, and the transport frequencies $\omega^{}_{\mathrm{tr}}$, which are derived from transport coefficients. However, a direct quantitative comparison of these frequencies is lacking. Using exact diagonalization, we conduct such a comparison for the spectral functions of current operators in clean and disordered
quantum spin ladders with diffusive energy and
spin transport. We find clear evidence for the expected low-frequency plateaus in the ETH spectral functions. For the accessible system sizes, $\omega^{}_{\mathrm{SFF}}$ is consistent with the extent of the plateaus, while the transport frequencies are systematically larger and lie in the nonuniversal regime of the spectral functions. Our findings highlight the need to better understand the origin of these quantitative differences.
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All authors Kadir Çeven, Rohit Patil, Marcos Rigol, Fabian Heidrich-Meisner
Mesoscale and Nanoscale Physics
Corbino-Enhanced Supersonic Acoustic-Emission Threshold in a GaAs Two-Dimensional Electron System
A. D. Levin, A. S. Jaroshevich, Z. D. Kvon et al. (+5 more)
We report nonlinear differential-resistance measurements in a high-mobility GaAs/AlGaAs two-dimensional electron system patterned in a Corbino geometry. At zero
magnetic field, $R_{\mathrm{diff}}(I_{dc})$ exhibits a pronounced polarity-selective threshold peak on the negative-current branch, gradually suppressed by a perpendicular
magnetic field. We interpret the Corbino anomaly as a local Cherenkov-like threshold for acoustic
phonon emission, enabled by the radial current concentration $j_r(r)=I/(2\pi r)$, which drives the local electron velocity above the sound velocity in a region adjacent to the inner contact. The polarity selectivity is attributed to Peltier heating and cooling, which modify the local thermal and boundary conditions near the contact, rather than to the kinematic threshold itself. Our results identify the Corbino geometry as a sensitive platform for probing local nonequilibrium electron–
phonon processes in a high-mobility electron system within an independently established hydrodynamic-crossover regime and suggest that the inner Corbino contact can act as a geometry-defined source for supersonic acoustic emission.
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All authors A. D. Levin, A. S. Jaroshevich, Z. D. Kvon, V. A. Chitta, M. S. Aksenov, D. V. Dmitriev, A. K. Bakarov, G. M. Gusev
Mesoscale and Nanoscale Physics
The Superconducting Talbot Effect in Phased-Array Josephson Junctions
Hechen Ren and Ziying Li
We introduce the superconducting Talbot effect—a macroscopic
quantum self-imaging phenomenon occurring when proximitized Cooper pairs propagate through a ballistic two-dimensional electron gas. By configuring periodic superconducting leads into a phased-array Josephson junction with programmable phase differences, we demonstrate active steering of the resulting superconducting Talbot carpet. To overcome transport resolution limits, we design a Vernier-scale collector array that performs sub-wavelength sampling of the fractional Talbot pattern. This approach maps real-space
quantum interference with high robustness to disorder, enabling direct extraction of Fermi wavelengths across helical,
spin-degenerate, and
spin-orbit-split Fermi surfaces. Tight-binding numerical calculations on a square
lattice validate the real-space interference patterns. Our results establish a versatile framework for coherent wavefront engineering and
quantum materials diagnostics in superconducting optics.
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Quantum Gases · Cross-listed from quant-ph
Collective advantage from a minimal record in a quantum information engine
Kangqiao Liu, Jie Gu and Deyou Chen
For a single particle, a
quantum information engine can turn measurement fluctuations into transport by raising a barrier behind the particle each time its position is measured. When many particles are present, the barrier still depends on just one number, the position of the leftmost particle, so we let the demon measure that order statistic and nothing else. A demon that resolves every position instead pays a record
entropy that grows with particle number, even though the extra distinctions never change where the barrier is placed. We show that the coarser measurement supplies an energy that is bounded independently of particle number, and that this bound yields a ceiling on the record
entropy that falls as the filling increases. At the same tilt, the collective engine then delivers $44\%$ more work per recorded nat than independent single-particle engines, each with its own optimized cycle time and each running at equal or greater power per particle. Pauli blocking ends this advantage once the accessible region just above the wall fills. We also evaluate the coherence that the coarse measurement leaves behind, and the cost of placing the barrier imprecisely.
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Superconductivity
Detection of signals in presence of noise through Josephson junction switching currents
O. V. Pountougnigni, R. Yamapi, C. Tchawoua et al. (+2 more)
Josephson junctions can be employed to reveal a sinusoidal signal in presence of Gaussian noise. To mimic realistic setups, the detection is performed linearly ramping the bias current until a switch to the finite voltage occurs; the analysis of the resulting switching currents can be exploited to decide about the presence of the harmonic drive. The signal is applied in two conditions: with an unknown initial phase (incoherent strategy) and with a known initial phase (coherent strategy). In both conditions, the analysis of the efficiency of the detection, performed through the signal-to-noise ratio, as estimated by the Kumar-Carrol index, shows that the dependence upon the Josephson junction ramp rate is beneficial, especially for relatively fast speed. One can conclude that the collection of the switching currents is a robust technique, and thus it is possible to exploit the advantages of a predetermined finite time to collect the data.
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All authors O. V. Pountougnigni, R. Yamapi, C. Tchawoua, V. Pierro, G. Filatrella