Strongly Correlated Electrons · Cross-listed from hep-th
Thermal Order in the Biconical Model
Michael Smolkin and Lev Yung
Thermal fluctuations are generally expected to destroy order and restore
symmetries at sufficiently high temperatures. Recently, however, a family of scalar theories in $2+1$ dimensions was shown to exhibit $\mathbb Z_2$
symmetry breaking that persists to arbitrarily high temperatures using a variety of approaches, including the $\epsilon$-expansion, the FRG, and large-$N$ techniques. Although the similarities among these theories suggest that they belong to the same universality class, this connection has not been established explicitly. In this work, we fill this gap. Using large-$N$ methods, we analytically study the biconical vector model in a range of spacetime dimensions, including $2+1$, at leading and next-to-leading order in the $1/N$ expansion. We determine the RG flow, fixed-point structure, and the CFT data of the infrared theory, reproducing and extending previous results and thereby unifying the apparently distinct constructions within a common analytic framework. We derive the effective potential, establish its stable minima at zero and finite temperature, and demonstrate spontaneous $\mathbb{Z}_2$
symmetry breaking at arbitrarily high temperatures for large finite $N$.
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Statistical Mechanics
Universal crossovers in weakly-monitored quantum critical states
Abhishek Kumar, Rushikesh A. Patil, Andreas W. W. Ludwig et al. (+1 more)
We study post-measurement ensembles of ground states of tricritical and critical 1D
quantum Ising
Hamiltonians subjected, respectively, to weak energy and
spin measurements without post-selection. These measurements act as relevant perturbations about the unmeasured critical ground states. Using finite-size renormalization group (RG) crossover analyses, we characterize their universal properties through the
entanglement effective central charge, effective Affleck-Ludwig boundary
entropy, and signatures of multifractality from moments of measurement-averaged correlation functions. In both cases, we find evidence for "measurement-dominated" or "measurement-altered" fixed points governed by the underlying Born-rule randomness. For critical Ising, we find a direct RG flow to a projective-measurement fixed point with area-law
entanglement, whereas for the tricritical Ising model, we find evidence for a weak-measurement fixed point with logarithmic
entanglement. These results clarify the RG-flow structure of weakly measured multicritical Ising ground states and show how intrinsic measurement-induced randomness can generate complex and rich universal long-distance scaling behavior in the post-measurement ensembles, accessible to controlled analytical RG and numerical finite-size RG crossover analyses.
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All authors Abhishek Kumar, Rushikesh A. Patil, Andreas W. W. Ludwig, Romain Vasseur
Materials Science
Investigation of GeSn aspect ratio trapping growth up to 8% Sn
Hryhorii Stanchu, Quang Minh Thai, Fernando M. de Oliveira et al. (+10 more)
Aspect ratio trapping (ART) growth of germanium-tin (GeSn) is a promising approach to target important objectives on the quest towards commercialization of complementary metal-
oxide-
semiconductor (CMOS)-compatible GeSn optoelectronics devices. Its local growth on patterned substrate allows for versatile device integration into photonics integrated
circuit or for stand-alone structure like focal plane array imager. Additionally, high aspect ratio from nano-sized window can terminate early threading dislocation propagation on the
oxide sidewalls, leaving subsequent growth defect-free and potentially improving the device performance. Knowledge remains missing regarding GeSn ART growth kinetics, morphology and how they evolve from thin film growth, with successful growth itself yet to be demonstrated. In this work, we report GeSn ART growth up to 8% Sn. Two configurations – self-induced Ge core/GeSn shell for Sn content between 6% and 8%, and bulk GeSn ART for Sn content below 1% – are observed. We present a comprehensive study on GeSn ART growth kinetics through different growth rounds and designs, showing a link between pyramid shape of ART island and successful Sn incorporation, as well as the role of growth selectivity and local heating.
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All authors Hryhorii Stanchu, Quang Minh Thai, Fernando M. de Oliveira, Mourad Benamara, Stephen Margiotta, Matthew Cook, Xiaoxin Wang, Jifeng Liu, Perry C. Grant, Baohua Li, Wei Du, Gregory Salamo, Shui-Qing Yu
Strongly Correlated Electrons · Cross-listed from hep-th
Size Operator and Spectral Clustering in the Two Coupled SYK Model
Juan Santos-Suárez, Martí Berenguer, Javier Mas et al. (+1 more)
At large $N$, two coupled Sachdev-Ye-Kitaev models realize an eternal traversable wormhole with a discrete spectrum. We show that at finite $N$ the spectrum organizes into clusters labeled by operator size. Low-size clusters evolve into the conformal towers and define a weak-ergodicity-breaking subspace responsible for the long-lived wormhole revival dynamics. Moreover, the competition between size energy and size
entropy provides a microscopic interpretation of the wormhole-black hole transition. These results reveal operator size as the bridge between the finite-$N$ spectrum and the emergent gravitational physics at large $N$.
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All authors Juan Santos-Suárez, Martí Berenguer, Javier Mas, Alfonso V. Ramallo
Mesoscale and Nanoscale Physics
Magnetic Skyrmion Interacting with Optical Skyrmion
Lan Bo, Jian Chen, Xichao Zhang et al. (+3 more)
Magnetic skyrmions (MSks) and optical skyrmions (OSks) embody
topology in matter and in light, respectively. Here we investigate the interaction between a single MSk and an OSk beam. Three distinct nonlinear dynamical modes are identified: rotation, skipping, and trochoidal motion. By decomposing the optical driving force into gradient, orbital-angular-momentum, and
spin-angular-momentum contributions, we clarify their respective roles of radial confinement, azimuthal drift, and precessional modulation. The skipping motion arises from the azimuthal asymmetry of the OSk beam and exhibits spatial selectivity originating from the magnetization-polarization coupling between the MSk and OSk. In three dimensions, the coupling acquires a propagation-dependent phase dominated by the differential Gouy phase, which yields $z$-asymmetric skipping trajectories. These results bridge topological particles and topological fields within a unified framework, offering helicity-selective and phase-programmable routes to optomagnonic control.
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All authors Lan Bo, Jian Chen, Xichao Zhang, Yan Zhou, Chengwei Qiu, Masahito Mochizuki
Mesoscale and Nanoscale Physics
Thermal Stability of Two-Dimensional Crystals with Extended OH Hydrogen-Bonded Chains
Alexander V. Savin
Numerical simulations of the dynamics of monolayer structures of molecules deposited on a sheet of hexagonal boron nitride (h-BN) have been performed. It is shown that molecules containing benzene rings and hydroxyl groups in their structure can form stable two-dimensional
crystals with linear chains of hydrogen bonds OH$\cdots$OH$\cdots$OH$\cdots$ Such structures are formed by the following molecules: phenol (C$_6$H$_5$OH), hydroquinone (C$_6$H$_4$(OH)$_2$), 4-phenylphenol (C$_6$H$_5$–C$_6$H$_4$OH), 4-(4-phenylphenyl)phenol (C$_6$H$_5$–C$_6$H$_4$–C$_6$H$_4$OH), paracetamol (CH$_3$C(O)NHC$_6$H$_4$OH), 4-hydroxybenzanilide (C$_6$H$_5$C(O)NHC$_6$H$_4$OH) and 4,4-dihydroxybenzanilide (C$_6$H$_4$OHC(O)NHC$_6$H$_4$OH). On the one hand, the benzene rings in these molecules ensure their strong interaction with the flat substrate; on the other hand, they do not hinder the formation of extended hydrogen-bonded chains. The monolayer structures of these molecules exhibit high thermal stability: the onset melting temperatures of their 2D
crystals are 47, 187, 127, 247, 167, 307, and 377 $^\circ$C, respectively. The simulations allow us to conclude that multilayer structures composed of h-BN sheets and molecules of hydroquinone, paracetamol, and 4-hydroxybenzanilide can be used for the development of novel
proton-exchange membranes capable of operating at elevated temperatures.
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Materials Science
Revealing Intrinsic Anisotropy of Collective Magnetic Excitations in Twinned Crystals of a Kitaev-Heisenberg Quantum Magnet
Naipeng Zhang, Nikolai Simonov, Mykhaylo Ozerov et al. (+11 more)
Quantum magnets with competing interactions often emerge from delicate balances among microscopic parameters, making it essential to disentangle intrinsic
spin dynamics from extrinsic disorder effects. Here, we introduce a
multimodal optical approach combining magneto-infrared spectroscopy with domain-resolved micro-Raman spectroscopy at high
magnetic fields to reconstruct the intrinsic
magnetic excitation spectrum of twinned
crystals of the Kitaev-Heisenberg
quantum magnet Na$_3$Co$_2$SbO$_6$. Far-infrared spectroscopy reveals multiple field-tunable
magnetic excitations, but the intrinsic response is obscured by replica features arising from twin domains. By correlating magneto-infrared and domain-resolved Raman spectra, we isolate the single-domain
magnon response and uncover a pronounced twofold in-plane
magnon anisotropy. This anisotropy far exceeds that expected from the measured in-plane g-factor anisotropy and is instead dominated by anisotropic bond-dependent exchange interactions. By unifying high-field, high-resolution and spatially selective optical probes, our work establishes a broadly applicable framework for revealing intrinsic
spin dynamics and constraining the
spin Hamiltonian in multidomain
quantum magnets.
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All authors Naipeng Zhang, Nikolai Simonov, Mykhaylo Ozerov, Sumedh Rathi, Nolan Heffner, Sara Huszar, Long Chen, Haidong Zhou, Guangxin Ni, Chaebin Kim, Martin Mourigal, Stephen M. Winter, Zhigang Jiang, Dmitry Smirnov
Materials Science
Gradient expansion approximation of the inhomogeneous electron-gas revisited: Higher-order corrections
Mario Benites, Angel Rosado and Efstratios Manousakis
In our recently published work (our Ref. 1) we revisited the gradient expansion approximation (GEA) of the interacting electron gas, and recalculated the leading-order contribution$-$with respect to the Wigner-Seitz radius $r_s$$-$to the coefficient $B_{xc}[n]$ of the square of the gradient of the electron density in the high-density and slowly varying limits. That work resolved historical controversies regarding these coefficients and demonstrated that serious misconceptions have led to incorrect constraints being imposed on popular functionals within the generalized gradient approximation (GGA). In the present paper, we extend this calculation to obtain the coefficient of the next-to-leading term, which scales as $r_s \ln(r_s)$ relative to the leading order. First, we establish a systematic framework to evaluate the integral expressions for the $b_{xc}$ coefficient of the leading term ($\sim q^2$) of the density-density response function in the long-wavelength limit ($q \to 0$)$-$a prerequisite for computing $B_{xc}[n]$. The significance of the calculation stems from the proof that the coefficient of this $r_s \ln(r_s)$ term receives no corrections from higher-order diagrammatic expressions. Consequently, our derived value serves as an exact, definitive constraint for future GGA functional development; in the high-density slowly-varying limit, any valid functional must reproduce the exact constraints established in both our previous work and the present paper.
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Statistical Mechanics · Cross-listed from quant-ph
Thermalization of open quantum systems with pseudomodes
R. Kevin Kessing, Thibaut Lacroix, Susana F. Huelga et al. (+1 more)
Pseudomode approaches allow for an exact and unapproximated description of a
quantum system interacting arbitrarily strongly with a bath. In general, a system coupled to pseudomodes will not thermalize to the system's Gibbs state: This is to be expected when the system-bath coupling is non-perturbative, but conflicts with common thermodynamic intuition when the system-bath coupling is asymptotically weak. We explore under which circumstances pseudomode models satisfy detailed balance (and subsequently thermalize to the system Gibbs state) and how specific choices of parameters can force "weak" detailed balance that is restricted to a limited frequency range. A combination of Hermitian and non-Hermitian pseudomodes that yields a flat effective-temperature profile is also considered. The results and criteria established here are relevant for the construction of pseudomode models in contexts where thermodynamic consistency is required.
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All authors R. Kevin Kessing, Thibaut Lacroix, Susana F. Huelga, Martin B. Plenio
Materials Science · Cross-listed from physics.app-ph
Reduced Dark Current in Cd0.9Zn0.1Te Detector Arrays by Aluminium Oxide Passivation
Sudarshan Singh, Luc Montpetit, Eloïse Rahier et al. (+3 more)
Contrary to the prevailing view that processing cadmium zinc telluride (CZT)
semiconductors above 150 {\deg}C leads to irreversible device degradation, here we show that Al2O3 passivation layer deposited by atomic layer deposition at 250 {\deg}C not only preserves CZT detector performance but also substantially improves it. Pixelated metal-
semiconductor (MS) and metal-
insulator-
semiconductor (MIS) CZT detectors were passivated with a thin atomic-layer-deposited Al2O3 film and characterized electrically. The passivated devices exhibited no measurable degradation, even under a high-bias operation of 1000 V. Instead, the dark current decreased by approximately a factor of five, while the interpixel leakage current was reduced by nearly one order of magnitude, from ~41 nA to ~2-3 nA at -200 V. Passivation also produced highly uniform dark-current characteristics across adjacent pixels and completely eliminated current-voltage hysteresis, indicating suppression of defect-assisted charge transport. Furthermore, no significant difference in dark current was observed between the MS and MIS detectors after passivation, suggesting that the Al2O3 layer dominates the surface electrical behavior. These results demonstrate that optimized Al2O3 passivation at 250 {\deg}C is fully compatible with high-performance CZT detector processing and provides a practical route toward lower-noise, higher-spectral-resolution X-ray imaging systems.
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All authors Sudarshan Singh, Luc Montpetit, Eloïse Rahier, Mahmoud R. M. Atalla, Sebastian Koelling, Oussama Moutanabbir
Mesoscale and Nanoscale Physics
Strain engineering of transient exciton diffusion in WSe2 monolayers at cryogenic temperatures
Roberto Rosati, Mohammed Adel Aly Nouh, Robert Schmidt et al. (+2 more)
Tungsten-based transition metal dichalcogenides exhibit dark
excitons as the energetically lowest states. These are crucial for
exciton thermalization and propagation and they dominate low-temperature photoluminescence via the emergence of pronounced
phonon sidebands. After a resonant excitation, highly mobile hot dark
excitons are formed, which quickly thermalize into an
equilibrium distribution. The application of strain modifies the
exciton energy landscape and, in particular, the relative energy separation between bright and dark
exciton states. The impact of strain on the transient photoluminescence and
diffusion of non-
equilibrium excitons has remained largely unexplored so far. In this work, we investigate the spatiotemporal
exciton dynamics in strained hBN-encapsulated WSe2 monolayers at cryogenic temperatures. We demonstrate that tensile strain abruptly increases the excess energy of hot
excitons, thereby accelerating their transient
diffusion. We trace this back to suppressed
phonon-mediated scattering from bright to dark
excitons. Furthermore, we predict a periodic modulation of the transient
exciton diffusion in the presence of a compressive strain resulting from strain-driven emission of M
phonons. The gained microscopic insights illustrate how strain can be used to engineer transient photoluminescence and
exciton diffusion in technologically promising 2D
semiconductors.
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All authors Roberto Rosati, Mohammed Adel Aly Nouh, Robert Schmidt, Rudolf Bratschitsch, Ermin Malic
Mesoscale and Nanoscale Physics
Comparison of Lindblad and circuit approaches for quantum heat transport
Bayan Karimi
We compare two popular models applicable to analyzing heat transport by thermal microwave
photons in
quantum circuits. The first model is derived from a weak-coupling Lindblad master equation, with transition rates determined by
Fermi's golden rule induced by thermal dissipation sources. The second approach employs a
circuit model, where thermal Johnson-Nyquist noise generated by dissipative elements introduces currents, and consequently Joule power, in other parts of the
circuit. This leads to a Landauer type expression of heat transport where the transmission coefficient is proportional to the transconductance in the
circuit. We find that the two models yield identical results in a linear
circuit in the weak coupling limit with an analytic expression of power in an archetypal
circuit of a cavity mediating heat between two baths. Our analysis yields a quantitative assessment of the range of validity of the weak coupling assumption in a
circuit. Due to the correspondence of the two results, we feel confident in applying the weak coupling Lindblad model also for analyzing heat transport in
quantum circuits consisting, e.g. of
qubits and/or non-linear resonators.
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Superconductivity
Superconducting dome due to the Fano-Feshbach shape resonance in artificial high-Tc superlattices
Gaetano Campi, Andrea Alimenti, Danielle Villa et al. (+7 more)
In this work we provide compelling experimental validation of the Bianconi Perali Valletta (BPV) theory predicting a superconducting dome based on a
quantum material design of Artificial High TC Superlattices (AHTS) made with a selected nanoscale
heterostructure geometry. These AHTS are SNSN superlattices of
quantum wells of period d, composed of first units, superconducting doped Mott
insulator layers with Rashba
spin orbit coupling (S) of thickness L, intercalated by second units, normal metal spacers (N). In these superlattices, grown by molecular beam epitaxy (MBE), the experimental superconducting dome is obtained by material
quantum design changing the chemical potential via the
quantum geometrical factor L/d which tunes the Fano-Feshbach shape resonance in the pair transfer between superconducting gaps in the BCS regime and different gaps in the BEC-BCS crossover. Here we present a systematic magneto-transport study of AHTS artificial superlattices across the full doping range of the superconducting dome, from the deeply underdoped to the overdoped regime, using pulsed
magnetic fields up to 72 T. By varying the L/d ratio, we tune the effective hole concentration delta=0.45(1-L/d) and map the
evolution of the resistive transitions, the upper critical
magnetic field and the Ginzburg-Landau coherence length
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All authors Gaetano Campi, Andrea Alimenti, Danielle Villa, G. Alexander Smith, Fedor F. Balakirev, Luis Balicas, Andrea Perali, Sergio Caprara, Gennady Logvenov, Antonio Bianconi1
Strongly Correlated Electrons
Optimized Tensor-Network Renormalization for Quantum Dynamics: Resolving the Spectral Function of $\mathrm{K_2Co(SeO_3)_2}$
Jiahang Hu, Runze Chi, B. Normand et al. (+2 more)
Tensor-network methods have opened a powerful route for the study of dynamical spectral functions in two-dimensional
quantum systems. However, existing approaches within the framework of infinite projected entangled-pair states construct the required renormalization tensors solely from the ground-state environment and can suffer from severe numerical instability. We identify the origin of this instability and introduce an excitation-tailored corner-transfer-
matrix renormalization-group (ET-CTMRG) method to resolve it. By incorporating excitation tensors into the renormalization procedure, the method constructs a substantially more accurate effective
Hamiltonian matrix and thereby yields reliable and well-converged excitation spectra. For Heisenberg antiferromagnets, it reduces truncation errors by orders of magnitude and for the particularly complex case of the supersolid phase in the triangular-
lattice XXZ magnet $\mathrm{K_2Co(SeO_3)_2}$, it achieves excellent quantitative agreement with inelastic
neutron-scattering measurements. ET-CTMRG therefore provides a robust framework for investigating the dynamical properties of strongly correlated
quantum systems.
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All authors Jiahang Hu, Runze Chi, B. Normand, Hai-Jun Liao, T. Xiang
Materials Science
Real-time dynamics of the two-step charge-density-wave transition in bulk 1T-TaS$_2$
Daeheon Kim, Jinseok Oh, Kahyeon Koh et al. (+4 more)
The charge-density wave (CDW) of bulk 1T-TaS2 is built from
Star-of-David (SoD) clusters tiling a sqrt{13} x sqrt{13} superlattice, and it melts through a two-step sequence accompanied by order-of-magnitude changes in resistivity. Whether these steps proceed by collapse of the SoD amplitude or by rearrangement of the SoD
lattice has remained unresolved, because the relevant dynamics occur on length and time scales beyond the reach of ab initio molecular dynamics. Here we follow the CDW transitions in real time using a machine-learning force field trained on first-principles data, giving access to 1404-atom supercells over 5 ns. The two steps are mechanistically distinct. Above 200 K, SoD clusters translate coherently by transiently dissolving and re-forming about shifted centers, a deformation-formation process that preserves the local SoD amplitude while randomizing the interlayer stacking order and nucleating domain walls. Only near 350 K does the SoD distortion itself collapse. These results provide microscopic support for the recently proposed two-step model of the CDW transition and offer a framework for interpreting light-induced hidden phases and cavity-modified transition temperatures in 1T-TaS2.
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All authors Daeheon Kim, Jinseok Oh, Kahyeon Koh, Yejun Cho, Angel Rubio, Noejung Park, Dongbin Shin
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Spread complexity as a probe in generalized and long-range Aubry-Andre-Harper models
Triyas Sapui, Tanoy Kanti Konar, Subinay Dasgupta et al. (+1 more)
We investigate the spread complexity of
quantum quenches in generalized and long-range Aubry-Andre-Harper (AAH) models, encompassing regimes with and without mobility edges. In particular, in the generalized AAH models supporting energy-dependent mobility edges, we demonstrate that the long-time averaged spread complexity exhibits nonanalytic behavior when the post-quench quasiperiodic potential crosses the mobility edge associated with the energy of the initial eigenstate, thereby accurately identifying the mobility-edge transition. Such a behavior is supported by the spreading of local density of states. We further derive analytical expressions for the moments and the corresponding Lanczos coefficients for quenches between the limits of vanishing and strong quasiperiodic potentials. The Lanczos coefficients display qualitatively distinct behavior depending on the presence of mobility edges - they exhibit an initial plateau followed by a decay with the Krylov basis index, in contrast to the nearly constant behavior of the conventional AAH model without mobility edges. For LR hopping, the coefficients decay with the Krylov basis index for quenches from the localized to the extended phase, while they coincide with the AAH results for quenches in the opposite direction.
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All authors Triyas Sapui, Tanoy Kanti Konar, Subinay Dasgupta, Aditi Sen De
Superconductivity
Florian Simon, Thomas Bernat and Annica M. Black-Schaffer
The interplay of superconductivity and the
quantum geometry of the normal state has recently been the subject of an array of studies, especially regarding the superfluid weight. In this work, we turn our
attention to the
quantum geometry of the superconducting state itself, set by the Bogoliubov-de Gennes (BdG)
Hamiltonian, which dictates the
geometric and topological properties of superconductivity. We show that under three general conditions, namely superconducting fitness, orbital uniformity of the superconducting pairing, and absence of normal-state
spin-flip terms, the BdG
quantum geometry exactly separates into a sum of the normal-state
quantum geometry and an additional pairing
quantum geometry, thereby displaying a simple composite structure. We show that this separation holds for all
spin-singlet and -triplet pairings, including nonunitary
spin-triplet pairing. We further provide explicit analytical formulas for the pairing
quantum geometry for all these cases. These results establish how superconducting pairing alone easily drives both
topology and a finite
quantum metric, thus being present even in topological trivial or flat band
superconductors, with no normal state
quantum geometry. To complement these results, we also derive the BdG
quantum geometry of a general two-orbital
spin-singlet
superconductor with non-uniform pairing and finite superconducting fitness. Here, our explicit analytical results establish a non-separable composite BdG
quantum geometry, with the normal state and pairing contributions generally intertwining, thereby producing even more possibilities for finite
quantum geometry. Our results provide design rules for creating
superconductors and superconducting hybrid structures with nontrivial
topology and finite
quantum metric and will additionally help in the experimental diagnosis of unconventional superconductivity.
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Mesoscale and Nanoscale Physics
Discrete states and ballistic interference in quantum wires approaching macroscopic lengths
Henok Weldeyesus, Taras Patlatiuk, Christian P. Scheller et al. (+4 more)
Increasing the size of a system showing
quantum effects is a difficult task limited by decoherence, a diminishing
quantum level spacing, and the effects of disorder spoiling the
quantum behavior when growing in size. Systems in 1D offer very strong confinement in the transverse directions, thus generally enhancing
quantum effects, but are notoriously sensitive to disorder. In this work, we present a system of 1D electrons exhibiting discrete
quantum levels and fully ballistic coherent
quantum interference with lengths of up to 18\,$\mu$m. Tunneling spectroscopy between two parallel
quantum wires with a central gated segment shows intricate interference patterns exhibiting several different periods in
magnetic field and density. An analysis over three different wire lengths and a comparison with single particle numerical simulations without any free parameters remarkably explains the full pattern including the observed periods. Therefore, these wires are essentially ideal 1D systems with aspect ratios approaching 1'000. In addition, at low bias, we also observe not only the Coulomb charging energies but can clearly resolve the discrete orbital and
spin states in up to 10\,$\mu$m long wires when filling 100 electrons with the center gate. This is made visible by a state-of-the-art low temperature and low noise measurement system. The
spin filling sequence is completely regular, strictly alternating
spin up and down, avoiding high
spin states, while the peak conductance is modulated in accordance with the previously discussed interference patterns. These striking results show that single particle Schrödinger
quantum mechanics such as ballistic
quantum interference and discrete
quantum states may be observed, under the right conditions, in systems of up to 18\,$\mu$m length, thus approaching macroscopic sizes.
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All authors Henok Weldeyesus, Taras Patlatiuk, Christian P. Scheller, Amir Yacoby, Loren N. Pfeiffer, Ken W. West, Dominik M. Zumbühl
Superconductivity
Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han et al. (+6 more)
The first-principles search for
superconductors is severely limited by the high cost of electron-
phonon coupling (EPC) calculations. Here we develop a low-cost, physically transparent framework that identifies strong-EPC materials directly from static orbital-based
Hamiltonians without explicit
phonon perturbation calculations. Verification using density functional perturbation theory (DFPT) for representative
superconductors shows that the framework captures semi-quantitatively the EPC scale at substantially lower computational cost. Applied to more than 36,000 compounds in the MattKeyBond database, it identifies 34 dynamically stable superconducting candidates with calculated $T_c > 10$ K after DFPT verification. These candidates reveal two distinct routes to relatively high-$T_c$ superconductivity: a metallized covalent $\sigma$-bond route that is more favorable for achieving high-$T_c$
superconductors, and a
Fermi-level density-of-states accumulation route that can enhance $T_c$ but usually to a more limited extent.
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All authors Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang
Materials Science
Magnetically tunable symmetry-enforced nodal lines producing huge anomalous Hall conductivity in altermagnetic $\alpha$-MnTe
Mathews Benny, Xujia Gong, Amar Fakhredine et al. (+17 more)
Altermagnetic $\alpha$-MnTe exhibits huge anomalous
Hall conductivity (AHC) up to room-temperature together with weak ferromagnetism arising from
spin and orbital polarizations. We clarify the origin of the large value of the AHC by identifying two sets of distinct
symmetry-enforced nodal lines in the valence bands with Mn character, located at $k_z=0$ and $k_z=\frac{\pi}{c}$, protected by mirror
symmetry $M_z$ and glide
symmetry $G_z = \{M_z\,|\,0,0,\tfrac{c}{2}\}$, respectively. Both nodal lines are energy-dependent with an approximate C$_6$
symmetry, which is reduced to an exact C$_2$
symmetry due to the presence of the Néel vector. The highest valence band exhibits a Mexican-hat dispersion, whereas the second-highest valence band exhibits an inverted Mexican-hat dispersion, with nodal lines at the crossing between the two bands. Within first-principles accuracy, we demonstrate that these nodal lines give rise to the large AHC observed experimentally and exhibit a strong interplay with the weak ferromagnetism. We further show that even a small
spin canting strongly modifies the nodal lines and the AHC, making them both magnetically tunable. By disentangling the altermagnetic and
ferromagnetic contributions to the AHC, the altermagnetic contribution dominates at small canting angles, while the
ferromagnetic contribution becomes sizeable for larger values. Using linear dichroism in angle-resolved photoemission spectroscopy, we show a signature of the nodal line at the border of the Brillouin zone.
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All authors Mathews Benny, Xujia Gong, Amar Fakhredine, Raphaël Salazar, Ashutosh S. Wadge, Juraj Krempaský, Gunther Springholz, Sarath Sasi, Mahdi Hajloui, Martin Heinrich, Dawid Wutke, Rafał Kurleto, Natalia Olszowska, Sahar Izadi Vishkayi, Asiyeh Shokri, Ján Minár, Carmine Ortix, Jeroen van den Brink, Jakub Schusser, Carmine Autieri
Materials Science
GRADAR: orientation-map-driven detection and ranking of grains for targeted two-beam electron channeling contrast imaging
Johan Ewald Westraadt
Electron channeling contrast imaging (ECCI) resolves individual dislocations in bulk samples, but only when the imaged grain is held in a two-beam diffraction condition to well under half a degree. In a polycrystal it must be re-established grain by grain, and every published workflow we are aware of chooses the grain first and solves the stage for that orientation. This paper treats the inverse problem: nominate one reflection family and a stage envelope, and determine which grains of an EBSD-mapped polycrystal can reach that family's two-beam condition, a question posed in 2019 and open since. At fixed tilt $t$, stage rotation sweeps the incident beam around a cone of half-angle $t$ in each grain's
crystal frame, and a family with Bragg angle $\theta_B$ is reachable exactly when one of its plane normals lies within $(t + \theta_B)$ of the specimen surface. On a measured 163-grain austenitic stainless steel map at 20 kV, {111} reachability rises from 38.7% at 7 deg tilt to 77.3% at 15 deg; {220} and {311} already reach 79.8% and 91.4% at 7 deg. Ranking survivors by predicted darkness alone is wrong: same-family candidates are equivalent with respect to their own band at exact Bragg incidence, and the darkest tend to lie closest to rival-band Bragg conditions. GRADAR therefore ranks darkest-clean, gating every candidate on a minimum clearance from all rivals, and returns a dial-ready stage move per selected grain. Because the beam moves only ~0.12 deg per degree of stage rotation at 7 deg tilt, an ordinary rotation stage sets the selected condition to better than 0.1 deg. The predicted sweep is checked against the AstroECP
dataset's published silicon precession series: simulated and measured traces agree at r = 0.84, and the measured intensity is dark at all 16 predicted two-beam edges. Per-grain polycrystal validation is deferred to a companion study.
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Superconductivity
Emergence of Double-Dome Superconductivity in the Pressurized Dirac Semimetal BaMg2Bi2
Qi Wang, Juefei Wu, Cuiying Pei et al. (+3 more)
Dirac semimetal BaMg2Bi2 is reported to be a unique topological material that manifests surface superconductivity that coexistswith bulk band
topology at ambient pressure. Here, we present a comprehensive investigation of high-pressure superconductingproperties in BaMg2Bi2 single
crystal. Significantly, a pressure-driven double-dome superconducting behavior was revealed, withthe superconducting transition temperature Tc approaching the maximum values of 6.67 K at 4.5 GPa and 7.22 K at 10.4 GPafor the first and second superconducting domes, respectively. The combination of high-pressure X-ray diffraction,
Hall resistivitymeasurements, and theoretical calculations demonstrates that, the first superconducting regime is closely related to the pressure-modulated Lifshitz transition, whereas the second superconducting phase emerges concurrently with a structural transition fromthe ambient-pressure P3m1 phase to a high-pressure Pnma phase.
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All authors Qi Wang, Juefei Wu, Cuiying Pei, Yi Zhao, Yiyan Wang, Yanpeng Qi
Mesoscale and Nanoscale Physics
Floquet spin-group theory for light-tailored spin splitting in collinear magnets
Tongshuai Zhu, Zixuan Li, Huaiqiang Wang et al. (+2 more)
Spin groups have emerged as a fundamental
symmetry framework for
spin-splitting antiferromagnets, including altermagnets. For periodically driven magnets, where new
spin-splitting electronic structures can emerge beyond
equilibrium, an analogous
symmetry theory is still lacking. Here, we develop a Floquet
spin-group theory for optically driven collinear magnets by combining the static
spin group of the
magnetic crystal with the dynamical
symmetry group of the light field. This theory determines the
symmetry-allowed parity, momentum dependence, and nodal structure of light-induced
spin splitting under general periodic driving. We show that odd-, even-, and mixed-parity
spin splittings can be selectively switched within the same material by tailoring the drive
symmetry, accompanied by distinct
symmetry-allowed transport responses. We further uncover higher-order $h$- and $k$-wave Floquet
spin splittings unique to three-dimensional systems. Our work extends
spin-group theory from static magnets to periodically driven systems, providing a general
symmetry principle for engineering light-controlled nonequilibrium
spin-resolved electronic structures.
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All authors Tongshuai Zhu, Zixuan Li, Huaiqiang Wang, Su-Huai Wei, Jiawei Ruan
Mesoscale and Nanoscale Physics
Second-harmonic generation in twisted double bilayer graphene: Double-resonant enhancement from moiré flat bands
Takaaki V. Joya, Takuto Kawakami and Mikito Koshino
We theoretically investigate second-harmonic generation (SHG) in twisted double
bilayer graphene (TDBG) with AB–AB and AB–BA stacking configurations using a perturbative approach based on an effective continuum
Hamiltonian. We present a systematic analysis of the SHG response as a function of twist angle, vertical bias voltage,
Fermi energy, and stacking configuration. We find that the SHG signal is strongly enhanced at small twist angles due to the emergence of moiré flat bands and the associated increase in the joint density of states. Beyond this conventional enhancement mechanism, we demonstrate that the reduced bandwidth enables a pronounced double-resonant process, in which optical transitions at both $\omega$ and $2\omega$ are simultaneously satisfied over extended regions of the moiré Brillouin zone. This mechanism leads to a substantial amplification of the SHG response, analogous to the enhancement observed in systems with discrete energy levels, but realised here in a tuneable moiré band structure. Furthermore, we show that the AB–AB and AB–BA configurations exhibit a systematic $\pi$ phase shift in the SHG response at large bias voltages, reflecting their distinct
symmetry and electronic structure. Our results identify double-resonance effects as a generic mechanism for enhancing SHG in moiré systems and provide a unified framework for understanding and controlling nonlinear optical responses in tuneable flat-band materials.
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Disordered Systems and Neural Networks
Bayesian Inference with Structured Signal: Static Replica Symmetry Breaking on the Nishimori Line in the Planted Spin Glass
Andrea Vincenzo Dell'Abate and Louise Budzynski
A common assumption in theoretical models of
Bayesian inference is that the signal has i.i.d. components. To study the effect of correlations in the signal prior, we consider a minimal model: the planted
spin glass on random regular graphs, where the signal is sampled from an Ising model with coupling $\kappa$. Depending on the phase of the prior, we find that adding structure in the signal can either help or hinder inference. In the paramagnetic regime, correlations in the signal lower the reconstruction threshold, so that weaker signal strength is sufficient for recovery. In the
ferromagnetic regime, the prior alone already enables partial recovery, and we identify the threshold above which the observations provide additional information. When the prior itself is in a replica
symmetry breaking (RSB) phase, we detect a static RSB transition in the posterior under Nishimori conditions. This provides an example where a non-separable, correlated prior leads to static RSB in a Bayes-optimal inference problem. We discuss the consequences of this glassy phase for algorithmic performance, in particular for Belief Propagation.
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Superconductivity
Superconducting ternary compounds Li-X-B (X=Mo, W) within the mild pressure range: First-principles predictions
Bangshuai Zhu, Juefei Wu, Dexi Shao et al. (+6 more)
Among the superconducting hydrides under high pressure, a number of studies concentrate on the ternary compounds to explore unique
superconductors, which are capable of reducing the stable pressure and maintain superconductivity. In this work, to verify our proposed strategy of ternary composition lines (TCLs) to explore ternary compounds, we combined the first-principles calculations and
crystal structure predictions to study the ternary compounds Li-X-B (X=Mo, W) under high pressure. After calculations along five and four TCLs in Li-W-B and Li-Mo-B, respectively, five Li-W-B compounds and four Li-Mo-B compounds were predicted. The compositions of LiWB4, Li4MoB2 and LiMo2B2 could be thermodynamically stable under high pressure, and Li2WB6 is around 0.02 eV/atom above the convex hull at 0 GPa, which has potential for synthesizing. Both of the predicted Li2WB6 P6/mmm and Li2WB4 R-3m are superconducting and their Tc are around 11 K, which are similar to the Tc of WB2 P6/mmm around 100 GPa. An anomalous increase of Tc was found in Li4MoB2 C2/m upon compression. We carried out full ternary search (FTS) to evaluate the validity of the TCLs strategy in Li-W-B system at 0 GPa. Our results are helpful for understanding the phase diagram of Li-X-B (X=Mo, W) under high pressure and the introducing of Li atoms provide candidate structures to reduce the measured stable pressure from ~100 GPa in WB2 P6/mmm to 0 GPa. Meanwhile, we preliminary validate the strategy of TCLs in structure predictions and we expect to improve this strategy in the future, shedding light on the studies of ternary compounds.
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All authors Bangshuai Zhu, Juefei Wu, Dexi Shao, Junjie Wang, Yu Han, Cuiying Pei, Qi Wang, Jian Sun, Yanpeng Qi
Superconductivity
Cryogenic focused-ion-beam microstructuring enabling quantitative $c$-axis transport measurements in Tl$_2$Ba$_2$CuO$_{6+\delta}$
Ayanesh Maiti, Carsten Putzke, Linus Holeschovsky et al. (+10 more)
Absolute transport measurements in correlated
quantum materials are often limited by disorder, inhomogeneity,
geometric uncertainty, and small
crystal size. Focused ion beam (FIB) technology offers a route to overcome many of these limitations by enabling transport devices with precisely defined geometry to be fabricated from lamellae extracted from carefully selected regions of a
crystal, but its application to cuprate
superconductors has been hindered by ion-beam-induced damage. Here we study the clean overdoped cuprate Tl2201 and show that conventional FIB processing causes thermally driven oxygen loss, while cryogenic FIB microstructuring largely suppresses this degradation and preserves the
crystal structure from the bulk to the atomic scale. Microstructured devices quantitatively reproduce established in-plane resistivity and
Hall carrier density measurements without rescaling. Applying this approach to $c$-axis transport, we obtain absolute $\rho_c(T)$ values approximately three times larger than previously reported, bringing the transport anisotropy into quantitative agreement with the known
Fermi surface geometry within an isotropic relaxation-time approximation. These results resolve a long-standing discrepancy between transport and
quantum oscillation measurements in overdoped Tl2201 and establish cryogenic FIB microstructuring as a route to reliable quantitative transport measurements in
quantum materials where disorder, inhomogeneity, geometry, or small
crystal size have previously limited experimental accuracy.
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All authors Ayanesh Maiti, Carsten Putzke, Linus Holeschovsky, Roemer D. H. Hinlopen, Chunyu Guo, Dorothee Herrmann, Seunghyun Khim, Berit H. Goodge, Andre W. Tyler, Michele S. Conroy, Andreas W. Rost, Andrew P. Mackenzie, Philip J. W. Moll
Superconductivity
Pressure-induced concurrent amorphization and superconductivity in topological material NbNiTe5
Lingxiao Zhao, Yi Zhao, Bangshuai Zhu et al. (+6 more)
We have systematically studied the structural and electronic properties of a topological material NbNiTe5 under high pressure. The
evolution of the normal state resistance shows a non-monotonic trend from 0.7 GPa to 5.1 GPa, in accordance with the second-order transition along the inter-layer direction observed in X-ray diffraction and Raman spectra. At around 10 GPa, the sample starts amorphization, which is concurrent with the emergence of superconductivity. Upon further compression, the structural disorder enhances and the superconducting transition becomes clearer, suggesting that the superconductivity is modulated by the degree of disorder in NbNiTe5 under high pressure. Within 45.7 GPa, the superconducting transition temperature (Tc) slowly rises from 0.6 K at 9.5 GPa to 1.4 K at 45.7 GPa. Our findings extend the family of transition metal chalcogenide
superconductors and shed new light on understanding superconductivity in disordered systems.
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All authors Lingxiao Zhao, Yi Zhao, Bangshuai Zhu, Qi Wang, Cuiying Pei, Juefei Wu, Jin-Ke Bao, Wen-He Jiao, Yanpeng Qi
Mesoscale and Nanoscale Physics
Optical switching of magnetic order in few-layer CrSBr
Lukas Husel, Julian Trapp, Moritz Würf et al. (+7 more)
Manipulating magnetism with light is crucial for both fundamental understanding and technological advancements of information storage devices. The layered antiferromagnet CrSBr, part of the recently emerging class of two-dimensional van der Waals magnets, offers a unique path towards optical control of magnetism via magneto-
excitons, which allow optical readout of the
spin alignment and also provide a strong absorption channel. Here, we use
exciton absorption and photoluminescence to demonstrate optical switching of the
magnetic order in bi- and trilayer CrSBr. Using a continuous-wave
laser with a power as low as a few microwatts at near-critical external
magnetic fields, we demonstrate both local and remote switching of the
magnetic configuration in extended lateral domains and further employ this mechanism to deterministically prepare the zero-field
magnetic configuration. Our results establish optical switching as a useful means of controlling magnetism in CrSBr, with potential applications in magneto-optoelectronic devices.
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All authors Lukas Husel, Julian Trapp, Moritz Würf, Anna Rupp, Tim Wedl, Kenji Watanabe, Takashi Taniguchi, Iva Plutnarova, Zdenek Sofer, Alexander Högele
Materials Science
Synthesis and structural validation of close-to-stoichiometric NiTe$_2$ single crystals
T. Tirasutt, L. H. Tjeng and A. C. Komarek
We report the synthesis of stoichiometric NiTe$_{2}$ single
crystals via chemical vapor transport together with precise structural characterization. A combined analysis using powder and single
crystal X-ray diffraction (XRD) was performed to determine
lattice parameters and structural details. High-resolution single
crystal XRD reveals no evidence of interstitial nickel, confirming a close-to-stoichiometric composition. This work establishes a reliable
benchmark for the
crystal structure of stoichiometric NiTe$_{2}$, offering a reference for future studies on its physical properties.
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